Link to home

2010 Northeastern Division Meeting Abstracts

October 27-29, 2010 - Northampton, Massachusetts

Major plant-parasitic nematodes in the northeast region and challenges they pose to agricultural plant managers
G. ABAWI (1)
(1) Dept. of Plant Pathology & Plant-Microbe Biology, NYSAES, Cornell University, Geneva, NY

Large and diverse nematode communities occur in most agricultural soils and play a significant role in soil ecological processes. Soil inhabiting nematodes are generally characterized into functional trophic groups, which include the herbivores (plant parasites), fungivores, bacterivores, omnivores and predators. Relative abundance of these groups has been used as an indicator of soil health. However, several widely distributed genera of plant-parasitic nematodes have been documented to directly and/or indirectly cause significant agronomic crop losses throughout the northeast. At large population densities, plant-parasitic nematodes can directly reduce crop growth and marketable yield. In addition, several are also known to predispose plants and/or interact with other pathogens, pests, and soil organisms to cause plant diseases of complex etiology. Root-knot (primarily Meloidogyne hapla), lesion (principally Pratylenchus penetrans), dagger (Xiphinema americanum and X. revise), cyst (PCN, Heterodera rostochiensis; SBCN, H. schachtii; CCN, H. trifolii; TCN, H. tabacum), bulb and stem (Ditylenchus dipsaci), and foliar (Aphelenchoides spp.) nematodes are the primary nematode pathogens that require effective management in the northeast. Although management practices continue to emphasis the use of chemical nematicides, significant progress has been made on the use of alternative management options including bio-fumigant cover crops, crop rotations, resistant crop varieties, antagonistic organisms and bio-based IPM strategies. Important diseases caused by plant-parasitic nematodes in the northeast and their management options will be illustrated and discussed during the presentation.

Effect of silicon amendment on the enhancement of soybean resistance to Phakopsora pachyrhizi
G. ARSENAULT-LABRECQUE (1), J. Montpetit (1), W. Rémus-Borel (1), R. R. Bélanger (1)
(1) Université Laval, Québec, QC, CANADA

Soybean rust caused by Phakopsora pachyrizi is a major threat to soybean production throughout the world. Silicon (Si) could represent an alternative solution to repeated fungicide applications because of its reported prophylactic role against many plant pathogens and in particular biotrophic fungi. However, little is known about the potential effects of Si on soybean because the plant’s ability to absorb Si is poorly defined. Our objectives were 1) to evaluate and quantify the deposition of Si in shoots of soybean plants (cv. Williams 82) fed with various Si concentrations, 2) to determine if there exists a differential ability to accumulate Si among soybean cultivars of various origins and 3) to evaluate if the absorption and subsequent accumulation of Si could enhance the resistance of soybean plants to P. pachyrizi. Scanning electron microscopy and X-ray microanalysis mapping were used to determine Si deposition in soybean leaves of plants treated with 0, 0.4 or 1.7 mM Si and rust severity was assessed daily. The experiment with cv. Williams 82 revealed no significant differences in the plant’s Si content regardless of the Si concentration in the solution. This translated into no effect of the treatment on rust incidence. These results support the concept that no benefits are conferred to a plant that can not absorb Si beyond background levels. On the other hand, cv. Hikmok displayed a significantly higher Si concentration in planta than all others when fed with Si. Interestingly, the same cultivar displayed the highest resistance to P. pachyrizi under Si treatment. This resistance appeared to be mediated in part by a hypersensitive response based on the occurrence of lesions typical of this reaction. Our results suggest a potential role for Si as part of an integrated approach to control soybean rust.

Assessment of butternut health throughout New England and New York
D. R. BERGDAHL (1), J. A. Bergdahl (1)
(1) Plant Technologies, LLC., Charlotte, VT, U.S.A.

The butternut canker fungus (Sirococcus clavigignenti-juglandacearum) (SCJ), believed an exotic pathogen, has had serious biological, ecological, and economic impacts on butternut (Juglans cinerea) throughout eastern North America. Butternut is a rare species in this region but when found is often associated with early European farms and sites with a history of Native American use. Since limited information was available on the health status of butternut, this study assessed incidence, severity, and mortality of 2034 trees in New England (NE) and New York (NY) (2006–2009). SCJ infection levels were about 95+% for butternut in northern NE and NY but somewhat lower in Southern NE (MA, CT, & RI) based on observations of the main stem and root flare areas. However, it is very likely that small twig and branch infections occurred high in the crowns and could not be seen. All trees were assigned a crown class (dominant, co-dominant, intermediate, or suppressed) and then given a health class rating ranging from 1 (relatively healthy) to 4 (dead). Dominant and co-dominant trees had the highest health class ratings (1 & 2) and lowest levels of mortality, whereas the reverse was true for intermediate and suppressed trees. Current butternut mortality levels in ME, NH, NY, & VT were 28.1, 27.3, 24.5, & 29.5 percent, respectively. In MA, CT, and RI, mortality levels were 15.7, 5.0, & 5.9%, respectively. Virtually no nut production was observed during this study, and seedling and sapling regeneration was woefully lacking and when found, it was usually infected with SCJ. Also, it was apparent that SCJ is not the only pathogenic organism associated with declining trees but is probably the most important. Opportunistic leaf, stem, & root diseases were observed but their relative impact on butternut health remains unknown. Funding: USDA FS FHM and Plant Technologies.

Antagonistic activity of two strains of Pseudomonas against Helminthosporium solani, the causal agent of potato silver scurf
A. BOJANOWSKI (1), B. Mimee (1), R. J. Tweddell (1)
(1) Centre de recherche en horticulture, Université Laval, Québec, QC, CANADA

Silver scurf, caused by the fungus Helminthosporium solani Durieu and Mont., is a surface-blemishing disease spoiling the appearance of potato tubers. The disease has emerged as an economically important disease in the last twenty years. This is mainly due to the appearance of H. solani strains resistant to thiabendazole. As a result, many efforts have been put forth to develop effective biocontrol alternatives to thiabendazole application. Recently, two strains (94-19 and E-30) of Pseudomonas, isolated from suppressive soils, showed strong antifungal activity against H. solani. The aim of this work was to further investigate the antagonistic interactions between H. solani and these bacteria. A bioassay was first designed to monitor the activity of bacterial extracts against H. solani. The effect of the medium on the production of antifungal compounds by the bacteria was then evaluated in vitro. Strain 94-19 produced antifungal metabolite(s) against H. solani in all liquid media tested while strain E-30 produced antifungal metabolite(s) only when co-cultivated with living fungal cells, particularly H. solani cells. Although the antifungal compounds involved in the antagonistic interactions were not determined, the presence in strain 94-19 of genes for the synthesis of pyrrolnitrin, pyoluteorin and 2,4-diacetylphloroglucinol suggests that these compounds are involved. These genes were not detected in strain E-30. The results presented in this study open the way to new avenues of investigation towards achieving biological control of potato silver scurf.

Armillaria species distribution and site relationships in Pinus and Tsuga-dominated forests in Massachusetts
N. J. BRAZEE (1), R. L. Wick (1)
(1) Department of Plant, Soil, and Insect Sciences, University of Massachusetts, Amherst, MA

The distribution of Armillaria species was investigated across 32 plots at eight sites within four conifer-dominated forest types (eastern hemlock, pitch pine, eastern white pine, and eastern white pine – oak). In total, 320 isolates were collected from 19 host tree species, with 207/320 (65%) isolations coming from the three primary conifers. To date, 280 isolates have been identified to species using a PCR-RFLP protocol that targets variation within the IGS-1 and IGS-2 regions of the rDNA cluster. All six northeastern Armillaria species (A. calvescens, A. gallica, A. gemina, A. mellea, A. sinapina, and A. solidipes) have been encountered in this study. Overall, A. solidipes (syn. A. ostoyae) was the most abundant species encountered, making up 161/280 isolates. While this species prefers conifers, it was found on hardwoods 39 times (24%). In contrast, Armillaria species typically associated with hardwoods were frequently encountered on conifers. Armillaria mellea (sensu stricto) was collected a total of 26 times from eastern white pine and pitch pine, and A. gallica was found a total of 27 times on eastern hemlock, pitch pine, and white pine. Armillaria species incidence was significantly different by forest type, as pitch pine forests had a higher incidence of A. solidipes (70/80; p < 0.001), and eastern hemlock forests had a greater incidence of A. gallica (32/80; p < 0.001), compared to expected values. Incidence of A. solidipes was significantly different by soil type, with a greater incidence on excessively drained, sandy soils (p = 0.006). Occurrence by crown class was also significant, with a greater number of infected pitch pine (p = 0.001) and white pine (p < 0.001) occupying the intermediate and suppressed crown classes. The results illustrate how assumptions of Armillaria species incidence by host can be erroneous in eastern forests where hardwoods and conifers are mixed.

Effect of microbial communities in recycled irrigation water on the development of three Pythium species
M. L. BURGOS-GARAY (1), G. W. Moorman (1)
(1) The Pennsylvania State University

A concern in commercial greenhouse production is the harboring of Pythium species in recycled irrigation water and spread to susceptible crops. Pythium species are among the most damaging pathogens in horticulture causing damping-off, root rots, and stem rots. Despite frequent attempts to recover Pythium from recycled water, success in isolation is sporadic. The main objective is to determine if microbial communities recovered from recycled irrigation water from commercial greenhouses have a deleterious effect on the growth, reproduction, and survival of three pathogenic species, Pythium aphanidermatum, P. irregulare, and P. cryptoirregulare. The identification of bacteria exhibiting in vitro inhibition in the development of Pythium may be useful information that can be implemented as alternative strategy to control disease cause by Pythium because such organisms could be grown and added to irrigation systems. Microscopic observations of the interaction between microorganisms in recycled irrigation water and Pythium species indicate a deleterious effect on Pythium development with decreased numbers of zoospores released and suppressed formation of sporangia. These results suggest that microbial communities residing in recycled irrigation water may play a role in the suppression of Pythium.

Dispersal, infection and resistance factors affecting biological control of Canada thistle by Puccinia punctiformis
S. A. CONAWAY (1), K. Shea (2), D. K. Berner (3), P. A. Backman (1)
(1) Dept. of Plant Pathology, Pennsylvania State University, University Park, PA; (2) Dept. of Biology, Pennsylvania State University, University Park, PA; (3) Foreign Disease-Weed Science Research Unit, USDA, ARS, Ft. Detrick, MD

The noxious weed Canada thistle, Cirsium arvense, causes extensive problems in pasture, landscapes and naturalized areas. Controlling Canada thistle with conventional management tactics is difficult due to the plant’s robust root system, aggressive growth and wind-dispersed seeds. The rust pathogen Puccinia punctiformis is a promising biological control agent that reduces Canada thistle infestations through fatal, systemic infections. Establishing severe, self-sustaining epidemics of P. punctiformis in Canada thistle requires a thorough understanding of the biology of both pathogen and host. To better understand the conditions under which epidemics can develop, we performed a series of experiments to evaluate dispersal characteristics of the various P. punctiformis spore types. Dispersal gradients were measured by releasing spores in windy field conditions and capturing spores at varying distances from the source. Terminal velocities of spores were also compared in a particle settling tower. By all measure, aerial movement of the two major types of P. punctiformis spores is significantly different. It is hypothesized that Canada thistle plants can have genetic resistance to some P. punctiformis lines. To investigated this possibility, we also compared resistance of thistle genotypes across Pennsylvania, which showed differential responses. Finally, to assess optimum timing and host tissue infection court, we evaluated the effects of season and placement of inoculum.

A disease of New Guinea impatiens (Impatiens hawkeri W. Bull) caused by Pythium cryptoirregulare
M. L. DAUGHTREY (1), J. Komorowska-Jedrys (1), M. Tobiasz (1), G. W. Moorman (2)
(1) Cornell University, Riverhead, NY, U.S.A.; (2) The Pennsylvania State University, University Park, PA, U.S.A.

Root rot diseases caused by various species of Pythium are common in container-grown flower crops produced in greenhouses in the northeastern United States. Diagnosis of the causal agent using morphological traits of the isolate is not precise in the case of Pythium irregulare because there are at least four cryptic species within the P. irregulare complex. One of those, P. cryptoirregulare, is commonly found in greenhouses along with P. irregulare sensu stricto. A Pythium species has been consistently associated with New Guinea impatiens showing stunting, wilting and black vascular discoloration of stem and roots in NY since the 1980s. Isolates from discolored roots or stems of nine New Guinea impatiens clinic samples from 2003–2009 were identified as P. irregulare using morphological characteristics. Subsequent identification using ITS sequence data indicated that the DNA of all isolates matched that of P. cryptoirregulare. Potted New Guinea impatiens plants that were lightly wounded and inoculated at the base with an 8 mm diameter plug from a corn meal agar culture of any of four P. cryptoirregulare isolates showed stunted root systems and some root rot three weeks later. The oomycete was recovered on corn meal agar from 80–100 percent of root samples and 20–100 percent of stems of inoculated plants, but not from five control plants treated with plain agar plugs. The identity of the recovered pathogen was confirmed as P. cryptoirregulare by ITS sequencing.

Use of Biochar to increase mycorrhizal colonization and suppress Fusarium crown rot of asparagus in replant soils
W. H. ELMER (1)
(1) The Connecticut Agricultural Experiment Station

Biochar (BC) is charcoal created by low temperature pyrolysis of biomass and offers new technology that sequesters and reduces atmospheric CO2. As a soil amendment, BC improves the soil structure and fertility, increases water-holding-capacity, and absorbs biological and synthetic toxins. Asparagus secretes auto-inhibitory allelochemicals (AC) that inhibit mycorrhizal associations (VAM) and increases susceptibility to crown rot caused by Fusarium oxysporum f. sp. asparagi and F. proliferatum. Fusarium-infested soil that contained old asparagus roots was amended with BC at 0, 0.3, 1.5, or 3 biochar (w/w) and then planted with 2-mo. old susceptible asparagus plants. After 12 weeks, the percentage of diseased roots declined, and VAM colonization and plant weights increased with BC rate. In another study, three rates of AC (ferulic, coumaric, and caffeic acid) were drenched into soil amended with a 0, 1.5, or 3% BC and planted. The addition of BC at both rates negated the damage caused by the AC and increased VAM. In a third study, dried, ground Fusarium-infested asparagus roots were added to soilless potting mix (12 g/liter) with and without biochar (3% w/w) and then planted with asparagus plants. The addition of the roots increased diseased roots from 5% (control) to 45%, but the inclusion of biochar reduced this value to 25%. The data support the contention that biochar can be useful in restoring old asparagus fields back to productive use.

How the dynamics of plant disease epidemics depend on the timing of inoculum production
(1) The Connecticut Agricultural Experiment Station

The effect of latent period, infectious period and the temporal shape of the sporulation/reproduction curve on the course of the ensuing plant disease epidemic is examined using numerical simulation of disease development. The mean time between mother lesion initiation and daughter lesion production (mean generation time) together with Vanderplank’s multiplication factor dominate the initial disease increase (exponential growth phase). Variation in the pathogen population about the mean generation time tends to shorten the effective generation time because lesions produced “early” tend to dominate the epidemic after a few generations. For most plant-pathogen systems the actual shape of the sporulation curve is relatively unimportant and, after a few generations, the effective shape of the reproductive curve approaches a normal distribution. For some cases there is a long drawn out tail (positive skewness) of the reproductive curve due to “late” produced lesions which do not have time in a growing season to initiate multiple generations. The net effect of this is to reduce the effective inoculum multiplication factor with each successive generation.

Characterization of Pythium species causing Pythium blight of snap bean and other crops in the eastern U.S.
L. HARRISON (3), D. Langston (2), C. A. Wyenandt (1), S. Rideout (3)
(1) Rutgers University, Bridgeton, NJ, U.S.A.; (2) University of Georgia, Tifton, GA, U.S.A.; (3) Virginia Tech, Painter, VA, U.S.A.

New Jersey, Georgia, and the Eastern Shore of Virginia (ESV) are important snap bean (Phaseolus vulgaris L.) growing regions. Profitable yields are threatened on an annual basis by Pythium blight, one of the most severe snap bean diseases in the U.S. Although the disease is well documented, the species of Pythium causing this disease on snap bean and other crops have not been well characterized. Knowing this information is important for determining proper management strategies. From 2008 to 2010, isolates were collected from the previously mentioned growing areas from different hosts, including snap bean, other legumes, cucurbits and solanaceous crops to establish the causal agent(s) of Pythium blight. Isolates were collected from soil by baiting and from plant tissue showing water-soaking and/or white, cottony growth. For each isolate, pathogenicity on snaps bean was verified and the isolate was characterized by morphology and sequence analysis of the rDNA-internal transcribed spacer (ITS) regions. All ESV isolates were identified as Pythium aphanidermatum, with the exception of one P. myriotylum and four P. ultimum isolates. Both P. aphanidermatum and P. ultimum were recovered from New Jersey crops. P. aphanidermatum and P. ultimum were also isolated from symptomatic plants in Georgia, as well as multiple isolates of P. deliense. Due to the similarity of the ITS sequences of P. deliense and P. aphanidermatum, identification of P. deliense isolates was confirmed by PCR assays using P. deliense-specific primers from 5.8S rDNA. To our knowledge, this is the first time P. deliense has been reported in Georgia, and the first report on common bean (Phaseolus vulgaris L.) and squash (Cucurbita pepo L.). This research verifies that multiple Pythium species are responsible for Pythium blight symptoms on snap beans and other crops.

The effect of spring and summer topdressing on anthracnose severity of annual bluegrass putting green turf
J. W. HEMPFLING (1), B. B. Clarke (1), J. A. Murphy (1)
(1) Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ, U.S.A.

Anthracnose is a destructive disease of annual bluegrass [ABG; Poa annua L. f. reptans (Hausskn) T. Koyama] turf caused by Colletotrichum cereale Manns. The increased frequency and severity of this disease on putting greens over the last fifteen years has been attributed, in part, to stress-inducing management practices. Previous research has indicated that sand topdressing of ABG turf during the summer can reduce anthracnose severity but the effect of topdressing in the spring on this disease has not been examined. A field study was initiated in North Brunswick, NJ to evaluate the effect of spring topdressing (0, 1.2 and 2.4 L m–2 applied as two split-applications on 20 April and 4 May 2009, and 14 and 28 April 2010) as well as the potential for this factor to interact with the effects of summer topdressing (0, 0.075, 0.15, 0.30 and 0.6 L m–2 every 14-d from 1 June to 24 August 2009, and 24 May to mid-August 2010) on anthracnose severity. The trial used a 3 × 5 factorial arranged as a RCBD with four replications and was conducted on ABG maintained at 3.2 mm on a Nixon sandy loam. Disease severity reached 10% on all treatments by early-August 2009 and mid-May 2010. Both spring and summer topdressing significantly reduced disease severity compared to no topdressing. Spring topdressing at 2.4 L m–2 was more effective at suppressing disease than 1.2 L m–2. Generally, a summer topdressing rate of 0.30 L m–2 every 14-d was required to reduce disease severity. The summer topdressing effect was more consistent than the spring topdressing effect in 2009, whereas spring topdressing was more consistent in 2010. Spring and summer topdressing can be used by turf managers as part of an IPM program to reduce anthracnose on ABG putting greens.

Management and etiology of grape sour rot in the Niagara region
C. HUBER (2), W. McFadden-Smith (3), D. Inglis (1)
(1) Director, Cool Climate Oenology and Viticulture Institute, Brock University, St Catharines, ON, CANADA; (2) MSc Candidate, Brock University, St Catharines, ON, CANADA; (3) Tender Fruit and Grape Specialist, OMAFRA, Vineland, ON, CANADA

In 2008, due to sour rot, 20% of early grape varieties were rejected at wineries, leading to 1.5 million dollars in losses. Sour rot develops after veraison, and is defined by microbial digestion of berry tissues leading to the production of acetic acid and ethyl acetate, giving the rotten berries a characteristic odor. Increased volatile acidity in the juice pressed from rotten berries is unfavorable in wine production, especially as it is associated with spoilage organisms. Wineries routinely add potassium metabisulphite (KMS) to the surface of fruit in bins and to grape juice to kill spoilage organisms. Growers would benefit if KMS is also effective as a fruiting-zone spray to limit spoilage during berry ripening. To determine the efficacy of KMS sprays, KMS was applied at differing rates and schedules to test plots in 2009 and 2010. The microflora of clusters was sampled before and after treatment. Due to cold weather in 2009, very little sour rot developed in research plots or commercial vineyards. A variety of yeasts and bacteria were isolated from the surface of healthy clusters and identified using the sequencing of standard rDNA regions. Comparing data to an unsprayed check plot, KMS appeared to limit the proportion of yeasts in the population. However, in in vitro pathogenicity assays involving the inoculation of seedless table grapes, none of the isolates displayed the capacity to cause the symptoms of sour rot. Preliminary isolations from diseased berries were performed and one isolate, identified as Hanseniaspora uvarum, caused some of the characteristic symptoms of sour rot in injured seedless table grapes. Data for the 2010 KMS trials is pending. Treatments will be assessed for disease severity, and through an enzymatic assay for acetic acid content of the fresh juice. Isolations from diseased berries will continue from samples taken across the region.

The effects of fungicides on yields and deoxynivalenol levels on spring barley in Maine
S. B. JOHNSON (1), D. H. Lambert (1)
(1) University of Maine

Fusarium head blight of barley is an important cereal disease responsible for significant loss in disease-conducive years. Fusarium graminearum (teleomorph: Gibberella zeae) is considered the primary Fusarium head blight pathogen in North America. Shrunken kernels and accumulation of mycotoxins (primarily deoxynivalenol or DON) are responsible for yield loss and economic loss. Barley spot blotch caused by Cochliobolus sativus) is also responsible for yield loss and economic loss. This study examined the effects of Prosaro (Prothioconazole + Tebuconazole), Stratego (Propiconazole + Trifloxystrobin), and Headline (Pyraclostrobin) on spring barley yields, DON levels, and barley spot blotch levels. Levels of DON, levels of Fusarium-infected seed, seed germination, and bushel weight were not affected by fungicide treatment. All applied fungicides controlled barley spot blotch. Prosaro and Stratego applied at Feekes 8 or 10.5 did provide a statistically improved yield and an economic return compared to the untreated control. Headline did not statistically improve yield or provide an economic return compared to the untreated control.

New broad spectrum and safer fungicides for brown patch and dollar spot diseases of turf grass, powdery mildew of pumpkin and Septoria leaf spot of tomato
N. I. KHAN (1), J. A. Trogolo (1), M. Babadoost (2)
(1) Agion Technologies Inc., Wakefield, MA, U.S.A.; (2) University of Illinois, Urbana, Champaign, IL, U.S.A.

Agion Technologies Inc. is developing highly effective fungicides/bactericides with levels of mixed metals up to 1,000 times lower than the early fungicides. Agion’s formulations may function as a stand alone biocide or most valuable as a powerful synergist with conventional fungicide thereby reducing the use levels and their environmental impact, and has potential to show efficacy against the resistant strains. Agion formulations Agion-A, Agion-B, Agion-C and Agion-D significantly reduced disease severity over control in both Dollar Spot and Brown Patch field trials at Ohio State University (P = 0.05). There was no significant difference between these four formulations and the standard fungicide, Daconil (P = 0.05). These formulations showed excellent efficacy in field trials conducted this year in Illinois against Septoria Leaf Spot of Tomato and Powdery Mildew of Pumpkins, where these formulations reduced significant disease severity over control (P = 0.05) and showed no significant difference in disease reduction over control compared to standard fungicides, Quadris and Bravo (P = 0.05). These results indicate that the Agion formulations have potential to be included in the IPM programs against several diseases in variety of different crops. Trials on other field crop, vegetables and fruit tree diseases are scheduled in upcoming seasons in 2011.

White pine needle diseases in eastern Canada
G. LAFLAMME (1), C. Côté (1), L. Innes (2)
(1) Canadian Forest Service, Québec, QC, CANADA; (2) Ministère des Ressources Naturelles et de la Faune, Québec, QC CANADA

In 2009, yellowing of white pine (Pinus strobus) needles was reported from several regions in three Canadian provinces: New Brunswick, Quebec and Ontario. A similar problem was seen also in eastern United States. Several causal agents were presented as hypotheses: drought, pollution as well as several needle diseases. In the spring and summer of 2010, samples of white pine needles were collected in areas where symptoms had been seen the previous year. Sampling was done by the three provincial agencies. In addition, one white pine was sampled every month from September 2009 to August 2010 in Quebec City. At least six fungal species were observed or isolated from these needles. A few were parasites, some were endophytic fungi and were mostly obtained from diseased needles collected in June and some were secondary fungi like Hendersonnia pinicola. The most common pathogen found was Canavirgella banfieldii which is very similar to Lophophacidium dooksii. The yellowing of the current year needles is visible from late July, early August. The discoloration affects only the distal portion of the needles and not all of the needles in a fascicule are infected. Also, the lower section of trees seems to be more diseased than the top. Some white pines seem to be resistant to this disease. The teleomorph of C. bandfieldii appears on previous year needles in early summer. A second pathogen, Mycosphaerella dearnessii, has also been observed in June on previous year needles: the entire infected needle turns yellow and red bands are visible near the infection point. These needles drop a couple of weeks following their change of color. Both pathogens were often collected on the same tree. All these fungi are being sequenced and the results should clarify the synonymy of some fungal species and their classification at the family level.

Early season potyvirus epiphytotic affects cigar wrapper tobacco in Massachusetts and Connecticut
J. A. LAMONDIA (1), C. R. Vossbrinck (2), F. J. Ferrandino (2)
(1) The Connecticut Agricultural Experiment Station Valley Laboratory, Windsor, CT; (2) The Connecticut Agricultural Experiment Station, New Haven, CT

In late June 2009, stunted shade and broadleaf cigar wrapper tobacco (Nicotiana tabacum L.) plants in Massachusetts were observed with veinbanding, mosaic, and leaf mottling symptoms consistent with potyvirus infection. Plants tested positive for potyvirus, Potato virus Y (PVY), Tobacco etch virus and Tobacco vein mottling virus using independent ELISA tests (Agdia, Inc.). Two primers were designed to amplify a 400 nucleotide region between nucleotides 8200 to 8600 of PVY. RNA from symptomatic plants was used in a standard rtPCR reaction and amplified PCR product was sequenced to confirm PVY infection. Early symptom development and severity was greatest for tobacco adjacent to or near potato crops. Approximately 1200 hectares of potatoes (Solanum tuberosum) were present in the affected area in Massachusetts and volunteer potato plants were found in high incidence in fields rotated from potato in 2008 to broadleaf tobacco in 2009. Growers indicated that volunteer tubers survived overwinter and emerged in large numbers in both 2008 and 2009. Minimum soil temperatures recorded 20 cm deep in Windsor CT were –4.7 C in 2007, and only –1.85 C in 2008 and 2009. Critical temperatures required for potato tuber death are reported to be –2.8 C. Potato can serve as a virus reservoir, and volunteer tuber survival in two consecutive years likely increased early season virus incidence in 2010. Many species of aphids transmit these viruses in a nonpersistent manner. Affected tobacco was unmarketable as cigar wrapper and destroyed in the field. Crop insurance claims on losses were evaluated by adjusters and considered multiple causes, (e. g. 75% due to virus and 25% for excess precipitation). Over 255 hectares (nearly 20%) of shade and broadleaf tobacco production in Massachusetts and Connecticut were destroyed as a result of potyvirus infection at an estimated crop loss in excess of $10,000,000.

Efficacy of control methods on black rot caused by Xanthomonas campestris pv. campestris in greenhouse transplant production
H. W. LANGE (1)
(1) Cornell University, NYSAES, Geneva, NY, U.S.A.

Black rot caused by the bacterium Xanthomonas campestris pv. campestris (Xcc) is often a serious disease in New York State crucifer fields. This pathogen is seed borne and even rigorous seed testing can not guarantee every seed is free of bacteria. In greenhouse transplant operations conditions are ideal for the spread of Xcc with dense plant populations and overhead watering. Asymptomatic transplants can initiate field infections which are very difficult to control. We are investigating the efficacy of chemical and biological products that can be used to reduce the spread of Xcc in the greenhouse. Both a leaf wash (to determine CFU/g tissue) and real-time PCR were used to quantify pathogen numbers in asymptomatic seedlings. This comparison allowed us to identify treatments that were effective at suppressing Xcc in an environment favoring disease spread. Additionally, the role of plant age at time of control product application was studied to identify the most effective time to control black rot development in seedlings.

Ustilago maydis as a model system for the study of a glycolipid gene cluster in the biocontrol agent Pseudozyma flocculosa
F. LEFEBVRE (1), B. Teichmann (1), C. Labbé (1), R. R. Bélanger (1)
(1) Centre de recherche en horticulture, Université Laval, Québec, QC, CANADA

Pseudozyma flocculosa, an anamorph fungus member of the Ustilaginales, is an effective biocontrol agent (BCA) against several members of the Erysiphales. Its mode of action is still unclear but evidence suggests that flocculosin, a rare glycolipid released by the fungus, may be involved in the collapse of powdery mildew colonies. Interestingly, this molecule is quite similar to ustilagic acid, an antimicrobial metabolite produced by the model fungus Ustilago maydis. Following the sequencing of P. flocculosa genome, we found that both flocculosin and ustilagic acid were under the control of a conserved gene cluster. Because P. flocculosa is not amenable to homologous recombination, we sought to use wild-type and mutant strains of U. maydis to carry out complementation studies in order to determine the role of flocculosin-specific genes. For each P. flocculosa gene complemented into the corresponding putative U. maydis mutant strain, overexpression of the gene restored the wild type phenotype as assessed through the structural analysis of ustilagic acid molecules produced by the U. maydis strains. Furthermore, fat3, a gene coding for an acetyl-transferase specific to P. flocculosa, and assumed to account for an extra acetyl group in flocculosin was overexpressed in the U. maydis wild type strain FB1. We were thus able to make U. maydis produce a flocculosin-like molecule, i.e. with two acetyl groups instead of one, a structure never observed before in this fungus. Our results show that the U. maydis model system is well suited for the study of homologous proteins in P. flocculosa. With the imminent completion of the BCA genome assembly, one can thus expect that its annotation will be greatly facilitated by its close phylogenetic relationship with U. maydis and that these comparative analyses will shed new light on what triggers fungi to be pathogen or beneficial.

Anthracnose of Miscanthus sinensis caused by Colletotrichum graminicola
Y. LI (1), M. Windham (3), R. Trigiano (3), A. Windham (4), J. Spiers (2)
(1) Connecticut Agricultural Experiment Station, New Haven, CT; (2) USDA/ARS, Poplarville, MS; (3) University of Tennessee, Knoxville, TN; (4) University of Tennessee, Nashville, TN

Miscanthus sinensis Anders (Zebra grass, Maiden grass, Ulalia grass or Chinese silver grass) is an important ornamental grass species with yellow or gold strips on green leaves. Diseased leaves with anthracnose symptoms were collected from nurseries and landscapes in North Carolina and Tennessee in the fall of 2008. Typical leaf symptoms were fusiform, red-brown lesions with black acervuli formed in the light gray tissues. Fungal isolates from lesions were grown on half-strength potato dextrose agar at room temperature with a 12 h photoperiod. The fungal colonies were characterized by black conidiomata formed in ring on white vegetative mycelia. Setae were dark brown with three to five septa. Conidia were sickle-shaped with a range of 22.5 to 32.7 µm long and 3.1 to 5.6 µm wide. The average size of appressoria was 9.7 × 6.5 µm. These morphological characteristics are consistent with the description of Colletotrichum graminicola (Cesati) G.W. Wilson. Pathogenicity of the isolates was tested by spraying conidia suspension (105 spores/ml) on adaxial surface of detached zebra grass leaf segments using a mini sprayer. Inoculated leaf segments were incubated on two layers of paper towels in a transparent plastic box at room temperature with 12 h photoperiod. Symptoms, observed 10 days after inoculation, were initially characterized by necrotic spots, and then expanded as fusiform red-brown lesions with acervuli formed in the center of lesions. The fungus isolated from infected leaves and showed the same morphological characteristics of the isolates previously inoculated. To our knowledge, this is the first report of C. graminicola infecting zebra grasses in North Carolina and Tennessee.

Can bacteriophage be used to control bacterial spot of peach?
R. E. MARRA (1)
(1) Dept of Plant Pathology & Ecology, Connecticut Agricultural Experiment Station, New Haven, CT, U.S.A.

Bacterial spot of stone fruit, caused by the bacterium Xanthomonas arboricola pv. pruni (Xap), is an important disease of peach and nectarine in the northeastern U.S. Resistant cultivars have been marginally successfully. Control options are limited to copper compounds and antibiotics, which are problematic due to phytotoxicity and resistance. We are interested in determining if a naturally occurring bacterial virus (“phage”) can be used to protect plants from infection. Twenty-three Xap strains and 43 phage strains were isolated from 19 orchards in Connecticut, New York, and Massachusetts in 2009. An absence of genetic variability was demonstrated in both collections by infecting all bacterial strains with all phage strains; all bacterial strains were equally susceptible to all phage strains, and all phage strains were equally virulent to all bacterial strains. Three bacterial strains were then infected with ten viral strains. Surviving, putatively lysogenic, strains were isolated from resulting plaques. Each of the 30 lysogenic strains was then tested for susceptibility to all 43 phage strains, and the experiment repeated. Non-lysogenic (lytic) strains were used as positive controls. Because each lysogenic strain was resistant to all 43 phage strains, we concluded that all 43 phage strains were functionally, and therefore genetically, equivalent. This absence of phage diversity may pose problems for long-term sustainability as a bio-control, given that under laboratory conditions lysogeny occurs readily in this system.

Evaluation of combined effect of compost amendments and fumigation on strawberry verticillium wilt
A. MARTIN-LAPIERRE (1), B. Mimee (1), R. J. Tweddell (1)
(1) Centre de recherche en horticulture, Université Laval, Québec, QC, CANADA

Strawberry (Fragaria × ananassa) is a valuable crop frequently affected by verticillium wilt caused by the fungus Verticillium dahliae Kleb. The disease causes wilting of mature leaves and can lead to plant death. Currently, pre-plant soil fumigation with costly chemicals is commonly used to control the disease. These chemicals, harmful for health and the environment, display variable efficiency and often lead to a negative shift in the biological equilibrium of the soil. Previous studies have shown that compost amendments may enhance plant growth and reduce symptoms of various diseases including verticillium wilt. In this context, the objective of this study was to assess the capacity of two composts and three fumigants to control strawberry verticillium wilt. To achieve this objective, V. dahliae naturally-infected field plots were fumigated with Vapam®, chloropicrin or Telone® C-17 or not (control) and subsequently planted with strawberry (cvs. Seascape and Orléans). Then, the plots were amended with either bovine manure compost or marine residue compost at a rate of 40 t/ha or not (control). The results showed no significant difference in wilting incidence between fumigated and control plots and revealed a negative impact of fumigation on fruit yield in plots not amended with compost. On the other hand, compost amendments reduced the incidence of the disease and increased fruit yield in most of the treatments. The control of the disease apparently provided by the composts could in part be explained by the presence of beneficial microorganisms. This is supported by the isolation from the tested composts of several bacteria known for their antagonistic activity against plant pathogens.

Sensitivity of the cucurbit powdery mildew pathogen to fungicides prone to resistance development
M. T. MCGRATH (1), K. L. Rivara (1), L. K. Hunsberger (1)
(1) Department of Plant Pathology and Plant-Microbe Biology, Cornell University, LIHREC, Riverhead, NY, U.S.A.

Podosphaera xanthii has a high potential to develop resistance to mobile fungicides with targeted activity, which are essential for effectively managing cucurbit powdery mildew. In 2009, 46 pathogen isolates were collected predominantly near the end of the cropping season from fungicide-treated pumpkin in commercial and research fields on Long Island, NY. Their sensitivity to fungicides at risk for resistance was determined using a cotyledon leaf disk assay. It was not feasible to test all isolates for all fungicides at all concentrations. Proportion of the isolates tested that were resistant (able to grow on at least half of the treated disks) was 100% for 50 ppm thiophanate-methyl (FRAC Group 1 fungicide), 94% for 50 ppm trifloxystrobin (Group 11), 29% for 20 ppm myclobutanil (Group 3), 13% for 40 ppm myclobutanil, 44% for 50 ppm boscalid (Group 7), 10% for 500 ppm boscalid, and 23% for 10 ppm quinoxyfen (Group 13). Resistance to FRAC Group 1 and 11 fungicides is qualitative; therefore, isolates resistant to the dose tested would not be controlled by the fungicide applied to a crop (practical or field resistance). Resistance to Group 1 and 11 fungicides was extremely high. Resistance to the other FRAC groups is quantitative, thus a range of concentrations was tested and assay sensitivity needs to be compared to field application dose and efficacy to identify an assay dose corresponding to practical resistance. Isolates resistant to 500 ppm boscalid would exhibit field resistance because this dose is in the range of an application dose. Interestingly, 2 of 3 isolates resistant to 500 ppm boscalid that were tested at 40 ppm myclobutanil and 10 ppm quinoxyfen were found to also be resistant to these unrelated chemistries. Correlated resistance could challenge control.

Effectiveness for cucurbit powdery mildew of fungicides prone to resistance development
M. T. MCGRATH (1), L. K. Hunsberger (1)
(1) Department of Plant Pathology and Plant-Microbe Biology, Cornell University, LIHREC, Riverhead, NY, U.S.A.

Fungicides able to move from their deposition point are essential for managing powdery mildew effectively in cucurbit crops, especially large-leafed types like pumpkin due to the difficulty of delivering spray material directly to the lower surface where the pathogen (Podosphaera xanthii) develops best; however, mobile fungicides are at risk for resistance development due to their single-site mode of action. A replicated field experiment was conducted with pumpkin in 2010 to examine efficacy of the primary mobile fungicide chemistries being used commercially for this disease. Efficacy of each fungicide applied at the highest label rate was compared to efficacy at lower rates and/or efficacy in previous years. Lack of consistent control could be an indication of resistance. Degree of control achieved on upper and lower leaf surfaces based on AUDPC values was 94% and 95%, respectively, for Quintec (active ingredient quinoxyfen; FRAC Group 13) at high label rate, 84% and 50%* for Procure (triflumizole; Group 3) at middle label rate, 94% and 69% for Procure at high label rate, 75%* and 31%* for Pristine (boscalid and pyraclostrobin; Groups 7 and 11) at low label rate, and 68% and 50%* for Pristine at high label rate (*AUDPC value not significantly different from non-treated control). Efficacy of Quintec and Procure was similar in 2009 and 2010. Pristine at high rate was more effective in 2009 than 2010: 98% and 80% control on upper and lower leaf surfaces, respectively, in 2009. Resistance could account for detected deviations in efficacy for Procure and especially for Pristine. Strains of the pathogen resistant to Group 11 fungicides have been common in recent years while resistance to Group 7 chemistry is a newer development.

The sensitivity of Colletrichum cereale to in vitro exposure with Velista™ (penthiopyrad)
(1) University of Rhode Island

The fungicide Velista™ (penthiopyrad) is a new active ingredient in the carboximide/SDHI class of fungicides being registered by DuPont Professional Products for use on golf courses and intensively managed turf. This fungicide has previously demonstrated activity against anthracnose (Colletotrichum cereale) in experimental field trials. In order to determine how well it controlled the pathogen in a controlled environment, in vitro petri dish assays were undertaken to examine it’s efficacy compared to 8 other commercially available turfgrass fungicides. Penthiopyrad was tested on 27 C. cereale isolates collected from the Northeast United States between 1993 and 1995 and 23 isolates collected from the same region in 2007. When compared to azoxystrobin, chlorothalonil, fludioxinil, fosetyl-Al, iprodione, polyoxin-D, thiophanate-methyl and triadimefon, penthiopyrad produced the lowest mean log transformed EC50 values of any chemical examined; 0.31 µL/ml and 0.19 µL/ml, from the two respective isolate collections. Of the other fungicides tested, only polyoxin-D even produced an EC50 below 4.0 µL/ml and only for the 1993–1995 isolate collection. In addition to its activity against C. cereale, penthiopyrad has performed extremely well in field trials against dollar spot (Sclerotinia homoeocarpa) and brown patch (Rhizoctonia solani) and may provide an effective, broad spectrum fungicide for simultaneous use on a wide array of turfgrass pathogens.

Characterization of Phytophthora infestans isolates from potato/tomato in 2010
K. MYERS (1), I. Small (1), S. Jensen (1), P. Zuluaga (1), S. Guha Roy (1), W. Fry (1)
(1) Department of Plant Pathology, Cornell University, 334 Plant Science, Ithaca, NY, U.S.A.

Late blight in New York and apparently also in the Northeast was much less a problem in 2010 than in 2009. Nonetheless, our lab received more than 70 samples originating from: Connecticut, Kentucky, Louisiana, Maine, Maryland, Massachusetts, New Hampshire, New York, Pennsylvania, and Wisconsin. In New York, we received samples from (Broome Chenango, Erie, Genesee, Livingston, Madison, Niagara, Suffolk, Tioga, Tompkins, Washington, Wayne, and Yates Counties). Samples were also received from Ontario, Canada. Characterization of confirmed Phytophthora infestans isolates was based upon, the protein profile, mating type, DNA genotype, resistance to metalaxyl/mefenoxam and pathogenicity of the isolate. The majority of samples were obtained from tomatoes and our preliminary results suggest that most of these belonged to the US22 clonal lineage – the new tomato strain that was epidemic in the Northeast in 2009. US22 has been largely sensitive to metalaxyl/mefenoxam and appears to be somewhat more aggressive on tomato compared to potato. From our samples, the only occurrence this year of US22 on potatoes was from a site in which the potatoes were adjacent to tomatoes that were infected with US22. US8 was also detected, but only on potatoes -- in Yates and Wayne Counties in New York, and in Ontario, Canada. US8 is very aggressive on potatoes, does very little to most tomato cultivars and is resistant to mefenoxam. We also found a few (at least three) “rare” and as yet uncharacterized genotypes of Phytophthora infestans. Two of these were from tomato, and one from potato.

Post-harvest foliar urea sprays as an effective sanitation practice for reducing ascospore production by Venturia inaequalis
R. NORTON (1), C. A. Smith (1), W. E. MacHardy (1), W. G. Lord (1)
(1) University of New Hampshire

Apples are an important crop in the Northeast and apple scab, caused by Venturia inaequalis, is the most important disease of apples. Apple scab is typically managed by applying frequent applications of chemical fungicides in the spring to prevent infection by ascospores, the only significant source of primary inoculum. We examined the use of post-harvest foliar urea sprays to reduce the production of ascospores by V. inaequalis. Single and split applications of 5% urea were sprayed by hand onto naturally-infected ‘Cortland’ leaves in the autumn of 2007, 2008 and 2009. Urea applications were made immediately after harvest, at the start of leaf fall and at 95% leaf fall to determine the most effective time of application to reduce ascospore production. Single 5% urea applications were compared to two 2.5% and three 1.6% split applications to determine if multiple applications were more effective than a single 5% application. In 2008 and 2009, an additional treatment of two 5% applications was added. The same urea treatments were applied with an air blast sprayer to ‘Marshal Mac’ trees in 2007, 2008 and 2009 to determine the effects of the above treatments on winter injury, fruit set and foliar nitrogen content. Our results indicate that all our urea treatments significantly reduced ascospore production while having no adverse effects on winter injury, fruit set and foliar nitrogen content.

Detection of propiconazole field resistant Sclerotinia homoeocarpa isolates
J. T. POPKO (1), K. Campbell-Nelson (1), C. Ok (1), G. Jung (1)
(1) University of Massachusetts-Amherst

Dollar spot (Sclerotinia homoeocarpa) is a major turfgrass disease requiring multiple fungicide applications to maintain acceptable turf quality each year. The demethylation inhibitor fungicide class (DMI) is frequently used and resistance to S. homoeocarpa has been confirmed. The objective of this study was to determine the in vitro propiconazole (DMI) sensitivity of field resistant isolates of S. homoeocarpa. Isolates were sampled from five locations (HGC, HRCC, JTRF, SMCC, and WBGC) before propiconazole treatment (0.44 kg a.i. ha–1) and seven days after treatment (DAT). Propiconazole sensitivity was determined by calculating the relative mycelium growth (RMG) percentage of all isolates on potato dextrose agar amended with 0.1, 0.3, 0.5, and 1.0 ug a.i. ml–1 of propiconazole. Isolates sampled from active or newly infected S. homoeocarpa infection centers seven days after propiconazole treatment were considered field resistant isolates since propiconazole is labeled for a minimum of 14 days control. Field resistant isolates were sampled from the WBGC, SMCC, HGC and HRCC sites, but not from JTRF (lack of infection 7-DAT). Ninety five percent of field resistant isolates ranged from 50–100% RMG on 0.1 ug a.i. ml–1 and 99% of field resistant isolates were capable of growth on 1.0 ug a.i. ml–1. Relative mycelium growth ranged from 0–40% on 0.1 ug a.i. ml–1 for all isolates sampled from JTRF and no growth was observed on 1.0 ug a.i. ml–1. Results indicate that S. homoeocarpa isolates with RMG values above 50% on 0.1 ug a.i. ml–1 of propiconazole or growth on 1.0 ug a.i. ml–1 of propiconazole are capable of causing infection seven days after application in the field. This qualitative sensitivity assay may be useful for DMI resistance monitoring of S. homoeocarpa populations.

Evaluation of Juglans cinerea trees putatively resistant to butternut canker (Sirococcus clavigignenti- juglandacearum): A new project supported by the Canadian Interdepartmental Recovery Fund
D. RIOUX (4), P. DesRochers (4), N. Nadeau-Thibodeau (4), K. Klimaszewska (4), A. Branchaud (2), B. Roberge (6), R. Werbiski (3), M. Durand (5), L. Bernier (1)
(1) Département des sciences du bois et de la forêt, Université Laval, Québec, QC, CANADA; (2) Environment Canada, Montreal, QC, CANADA; (3) National Defence, St-Jean-sur-Richelieu, QC, CANADA; (4) Natural Resources Canada, Laurentian Forestry Centre, Quebec, QC, CANADA; (5) Odanak Council, Odanak, QC, CANADA; (6) Parks Canada Agency, Québec, QC, CANADA

Sirococcus clavigignenti-juglandacearum is considered the major pest of butternut and is threatening its survival over its native range, which extends from New Brunswick to Georgia and west to Minnesota and Arkansas. In Canada, butternut was listed as endangered under the Species at Risk Act in 2005. A project aimed at identifying, propagating and testing trees putatively resistant to butternut canker is being funded by the Interdepartmental Recovery Fund (Environment Canada). As butternut is shade intolerant, another goal is to release some trees in order to improve their vigour and, hopefully, their resistance to butternut canker. To date, 146 putatively resistant trees have been located on seven sites in the province of Quebec. These trees had to have at least 50% of live crown and canker-free stems or more than 70% of live crown with less than 25% of the combined circumference of the bole and root flares affected by cankers. Compared with a survey conducted from 2006 to 2008, current damage appears more severe on these sites. As butternut seeds are able to disseminate the pathogen, efforts will be made to vegetatively propagate the selected trees. Twigs from these butternuts will be collected and assays will be carried out to obtain plantlets from axillary bud cultures. In case of failure, the literature indicates that propagation is also possible using cutting, grafting or somatic embryogenesis techniques. Once the vegetative material is obtained, resistance tests will be conducted in a greenhouse by inoculating the stem with conidia. Material coming from susceptible trees will serve as control. Should resistant trees be found, they will be propagated and, thereafter, some material will be confronted again to the pathogen to improve its resistance while other material will be used to restore some sites, thus giving back to this valued species the status it entirely deserves.

Non-target effects of glyphosate on apples
D. A. ROSENBERGER (2), C. B. Watkins (1), J. F. Nock (1), M. R. Miranda Sazo (5), C. J. Kahlke (4), M. J. Fargione (3)
(1) Department of Horticulture, Cornell University, Ithaca, NY; (2) Department of Plant Pathology and Plant Microbe Biology, Cornell University, Highland, NY; (3) Hudson Valley Fruit Program, Cornell Cooperative Extension, Highland, NY; (4) Lake Ontario Fruit Program, Cornell Cooperative Extension, Lockport, NY; (5) Lake Ontario Fruit Program, Cornell Cooperative Extension, Newark, NY

Since 2004, apple trees in scattered orchards in southeastern New York have developed trunk cankers extending upward from the soil line. Cankers on ‘Macoun’ trees, the most severely affected cultivar, caused tree decline and death. Orientation of cankers suggested herbicide sprays were a contributing factor. Glyphosate had been used in all affected orchards. However, Macoun trunks sprayed with glyphosate in 2007 as part of a replicated trial did not develop cankers, so etiology of basal trunk cankers remains uncertain. In another trial, ‘Empire’ fruit from trees exposed to simulated glyphosate spray drift during summer of 2009 developed more internal browning, a physiological disorder, after eight months of controlled atmosphere storage than fruit from control trees. Four mature trees on each of three farms were exposed to glyphosate by applying Roundup PowerMax® at a concentration of 0.26 ml/L to one or several lower limbs on each tree. The number of limbs or shoots treated was determined by the need to collect 25 fruit from the sprayed limbs at harvest, but the canopy area exposed to glyphosate never exceeded 30% of leaf area on lower scaffold limbs. Fruit samples were harvested in early October from both treated limbs and from untreated upper limbs of both sprayed trees and unsprayed control trees. Samples were stored for eight months at 2.2°C with carbon dioxide and oxygen held at 2%. They were then held at 20°C for 7 days before they were evaluated for internal browning. Incidence of internal browning for fruit from glyphosate-exposed trees from the three farms was 22, 61, and 133% greater than for fruit from control trees. Browning was more severe in fruit from the tops of treated trees than in fruit directly sprayed with glyphosate. Thus, glyphosate exposure may affect the incidence and severity of internal browning in stored apples.

Aerial dispersal of Phytophthora infestans as a component of a Late Blight Decision Support System
I. SMALL (1), L. Joseph (1), H. Mayton (1), W. Fry (1)
(1) Cornell University, Ithaca, NY, U.S.A.

A late-blight dispersal-risk algorithm capable of determining favorability of weather conditions for sporulation, dispersal and survival of spores, and subsequent infection of host tissue has been developed. The influence of weather conditions on these processes was obtained from published and unpublished data. The algorithm uses temperature, relative humidity, wind speed and direction, as well as solar radiation. Historic (observed) data as well as forecast data are used. For each potential risk period independent indices are calculated for sporulation, dispersal and survival of sporangia, as well as for subsequent infection of target host tissue. Proximity of the target to an inoculum source (if present) may be utilized in the risk index at the discretion of the user. These indices are then integrated to provide an overall risk index. Because the algorithm uses future weather as well as historical weather, it enables users to take precautionary measures. Preliminary experiments suggest that forecast “high risk” periods could be used to enhance the efficiency of disease management practices. The Decision Support System is structured to enable the communication of “inoculation alerts” to users.

Colonization of Peronospora belbahrii by the basidiomycetous yeast, Pseudozyma
R. L. WICK (2), N. J. Brazee (2), H. C. Wick (1)
(1) Tufts University, Medford, MA, U.S.A.; (2) University of Massachusetts, Amherst, MA, U.S.A.

Downy mildew of basil, caused by Peronospora belbahrii was first reported in the United States in 2007. During 2008 and 2009 downy mildew of basil was in epidemic proportions from Florida to Massachusetts resulting in losses up to 100 percent in both greenhouses and in the field. A specimen of downy mildew received from Georgia had conspicuous mycelial growth covering the sporangiophores and sporangia. Isolations from the growth yielded a yeast. When the yeast was inoculated to downy mildew on basil leaves, a mycelial colony developed over the downy mildew. Sequence analyses were conducted on three isolates of the unknown yeast. PCR amplification of the ITS-1, 5.8S, and ITS-2 region was performed using universal primers ITS6 and ITS4. In addition, a roughly 0.9 kb amplicon was produced from the 5′ end of the nuclear large subunit (nLSU) using universal primers LROR and LR5. The sequences of the three isolates were identical from both regions. BLAST analyses of the sequences revealed a 99% similarity to Pseudozyma aphidis. Nutritional utilization and morphology of the isolates were also consistent with the genus Pseudozyma aphidis. Of 13 morphologically similar yeasts inoculated to basil downy mildew, some did not colonize and several showed vigorous growth over the sporangia. Observations of basil downy mildew from CT and MA in 2010 indicated that filamentous yeast commonly occurs on Peronospora belbahrii. An investigation of the yeast/downy mildew relationship, and a survey for more vigorous yeast isolates are underway.