Posted online March 5, 2002
Turfgrass diseases caused by Pythium spp. are important to the golf industry in the southeastern U. S. Reports of Pythium-incited diseases affecting hybrid bermudagrass (Cynodon dactylon × transvaalensis), overseeded with Poa trivialis, are on the rise in Alabama. The overall goal of this research was to examine the population dynamics and diversity of Pythium spp. over a one year period on overseeded bernudagrass putting greens. Three golf greens on each of five golf courses in central Alabama were identified for sampling. Each golf green was divided into four quadrants and sampled on a monthly basis for twelve months beginning December 2000. Environmental data, including air and soil temperature, soil moisture, relative humidity and soil pH were also collected. Seventeen soil cores (2.5 cm deep, 8 mm diam.) were removed from each quadrant, and dilution plated onto a Pythium selective agar medium. Colonies of Pythium were enumerated and populations compared to environmental data. An inverse relationship was observed between the number of colony forming units and air and soil temperature. A direct correlation also existed between soil pH and total colony forming units.
Mississippi Soybean Management by Application of Research and Technology (SMART) program. M. A. BLAINE (1), J. G. Thomas (2), W. F. Moore (3), J. L. Hamer (4), M. C. Wardlaw (5), and B. D. Ward (5). (1) Dept. Plant and Soil Sciences; (2) Dept. Agricultural and Biological Engineering; (3) Extension Plant Pathologist emeritus and SMART program manager; (4) Retired Extension Entomologist and SMART program manager; (5) Program Assistant, Mississippi State University, Mississippi State, MS 39762. Publication no. P-2002-0002-SOA.
The SMART program demonstrates to producers the impact of timely management can have on improving the profitability of soybean production. This program, sponsored by the Mississippi Soybean Promotion Board, is a cooperative effort between soybean producers, Mississippi State University, the Mississippi Soybean Association, private industry and agricultural consultants to provide soybean producers with the opportunity to observe the benefits of implementing existing and new research based technologies. Recommended practices are designed to address specific in-field production concerns and identify profit limiting factors. SMART is a total program approach from fall tillage to harvest and recommendations are based on known historical and profit limiting factors determined by frequent producer contact and in-field scouting. Two hundred and fifteen fields have been involved with SMART during the past ten years. Program fields are enrolled for a two year period. The number one goal of SMART to increase statewide soybean yields and profits. The state average yield (1992-2000) is 1780 kg/ha. The overall average for SMART fields during the same time is 2835.4kg/ha. The average yield is 3312.5 kg/ha for irrigated fields and 2244.7 kg/ha for non-irrigated fields.
Stratego™: A new trifloxystrobin-based fungicide for control of rice diseases. J. R. BLOOMBERG, A. Hopkins, K. Vodrazka, and R. Rudolph. Bayer Corp., Kansas City, MO 64120-0013. Publication no. P-2002-0003-SOA.
STRATEGO™ is a new broad-spectrum fungicide product from Bayer Agriculture Division formulated as an emulsifiable concentrate containing 250 g ai/liter. STRATEGO™ is currently registered for use on peanuts and wheat. Registration for use on rice and other crops is pending with the U.S. EPA. Data from more than 30 trials indicate excellent commercial potential for STRATEGO™ in control of sheath blight Rhizoctonia solani and rice blast Pyricularia grisea. STRATEGO™ also controls several secondary diseases including brown leaf spot Bipolaris oryzae, narrow brown leaf spot Cercospora oryzae, leaf smut Entyloma oryzae, leaf blast Pyricularia grisea and kernel smut Tilletia barclayana, syn. Neovossia horrida. STRATEGO™ will also provide suppression of false smut Ustilaginoidea virens. Data currently supports the use of STRATEGO™ for broad-spectrum disease control compared to commercial standards. STRATEGO™ will be recommended at a dosage of 256 to 292 g ai/ha (14 to 16 oz product/A).
Effect of silicon (Si) on the components of resistance in St. Augustinegrass to gray leaf spot in Florida. M. O. BRECHT (1), L. E. Datnoff (2), T. A. Kucharek (1), and R. T. Nagata (2). (1) Dept. Plant Pathology, University of Florida, Gainesville, FL 32611; (2) Everglades Research and Education Center, Belle Glade, FL 33430. Publication no. P-2002-0004-SOA.
Six rates (0, 0.5, 1, 2, 5, 10 Mton/ha) of calcium silicate slag (20% Si) were evaluated in a greenhouse in relation to resistance to gray leaf spot (Magnaporthe grisea) in the St. Augustinegrass cultivars Floratam and FX10. Components of resistance evaluated were incubation period, latent period, lesion number, lesion size, percent disease, and spore number per lesion. Lesions in FX10 did not produce spores in any treatment. Silicon treatments had no significant effect (P = 0.05) on the incubation period or latent period in either cultivar nor spore number per lesion in Floratam. Lesion number was significantly reduced when compared to the control by all Si rates in Floratam and 5 and 10 Mton/ha rates in FX10. Percent disease was significantly lowered compared to the control in Floratam with 1, 2, 5, 10 Mton/ha rates and 0.5, 1, 5 10 rates in FX10. Lesion size was not reduced by silicon in Floratam, but was reduced when compared to the control with the 10 Mton/ha rate in FX10.
Potential toxicity of chlorine and hydrogen dioxides on herbaceous and woody ornamental crops. W. E. COPES (1), G. A. Chastagner (2), and R. L. Hummel (2). (1) Small Fruit Research Station USDA-ARS, Poplarville, MS 39470; (2) Research and Extension Center, Washington State University, Puyallup, WA 98371. Publication no. P-2002-0005-SOA.
In a first step to developing spray strategies, chlorine dioxide (ClO(2)), at 0, 5, 50, 100, and 1,000 ppm, and hydrogen dioxide (H(2)O(2), Zerotol), at 0, 900, 2,700, 5,400, and 10,200 ppm, were sprayed 5 times at 3 day intervals on 8 bedding plant and 9 shrub species. Toxicity symptoms were rated using Horsfall-Barrett categories, with marketability being reduced if >5% surface area was affected. ClO(2) caused >5% damage on no plants at 5, and 20 ppm; on poppy after 4 sprays at 50 ppm; on pansy after 3 sprays, on azalea, mountain laurel, and poppy after 4 sprays, and on a fern after 5 sprays at 100 ppm ClO(2); and on all plants, including coleus, evolvulus, galium, English ivy, juniper, lilac, rhododendron and St. Johns-wort at 1,000 ppm. H(2)O(2) caused >5% damage on coleus after 4 sprays at 900 ppm, on rhododendron leaves and candytuft flowers after 5 sprays at 2,700 ppm; and on the same plants in fewer sprays at higher rates. Rates of ClO(2) and H(2)O(2) that should control pathogen propagules did not damage most plants tested.
Effect of spray initiation timing on control of early leaf spot of peanut with chlorothalonil, tebuconazole, and pyraclostrobin. A. K. CULBREATH and T. B. Brenneman. Coastal Plain Expt. Stn., Tifton, GA 31793-0748. Publication no. P-2002-0006-SOA.
Field studies were conducted at Plains and Tifton, GA in 2001 to compare chlorothalonil (CHL), 1.3 kg/ha; pyraclostrobin (PYR), 0.22 kg ha; and tebuconazole (TEB), 0.22 kg/ha; at 6 spray initiation dates for control of early leaf spot (Cercospora arachidicola) of peanut (Arachis hypogaea). Fungicides were applied on a 14-day schedule for a maximum of 7 sprays. Final Florida 1-10 scale (1 = no disease, 10 = killed by leaf spot) ratings were 8.9 for the control, 4.5, 5.9, 6.5, 7.3, 7.7 and 8.6 for CHL; 2.4, 3.1, 2.8, 4.6, 6.9, and 8.1 for PYR; and 4.5, 4.5, 5.8, 6.7, 7.3, and 7.8 for TEB for 30, 44, 58, 72, 86, and 100 days after planting (DAP) initiation dates, respectively (LSD = 0.8). Yields were 2419 kg/ha for the control, 3533, 3431, 3793, 2854, 2707, and 2452 kg/ha for CHL; 3439, 4134, 3885, 3520, 3032, and 2755 kg/ha for PYR; and 3683, 3301, 3280, 3049, 2679 and 2679 kg/ha for TEB for the 30, 44, 58, 72, 86, and 100 DAP initiation dates, respectively (LSD = 403). Results show the curative activity of both PYR and TEB, and indicate that PYR can provide control of early leaf spot superior to CHL or TEB applied two weeks before.
Alternatives to benomyl for management of Cercospora leaf spot of turnip greens. J. P. DAMICONE (1), B. A. Kahn (2), and M. A. Trent (1). (1) Dept. Ento. & Plant Path.; (2) Dept. Hort. & L.A., Okla. St. Univ., Stillwater, OK 74078. Publication no. P-2002-0007-SOA.
Leafy brassicas are grown for processing in Oklahoma where Cercospora leaf spot is a significant disease that reduces quality. Fungicides and a plant defense activator with potential for replacing benomyl were evaluated at various application regimes for control of Cercospora leaf spot on turnip greens. Up to 4 applications were made on 7-day intervals beginning at the 5-6 leaf stage. Disease severity, defined as the percentage of leaf area with symptoms, was estimated 7 days after the last application. Benomyl (0.28 kg/ha) provided from 70% to over 90% reduction in disease severity depending on spray timing (P < 0.05). Reductions in disease severity for azoxystrobin (0.17 kg/ha) and tebuconazole (0.19 kg/ha) were similar to benomyl. Acibenzolar-s-methyl (35 g/ha), copper sulfate (2.5 kg/ha), and copper hydroxide (1.73 kg/ha) were less effective than benomyl and did not consistently reduce disease severity. Copper fungicides were often phytotoxic. Depending upon timing, as few as one application of benomyl and tebuconazole, and two applications of azoxysptrobin provided optimum disease control.
Effects of mulch and irrigation on center rot of onion. R. GITAITIS (1), J. C. Diaz-Perez (2), R. Walcott (3), and H. Sanders (1). (1) Univ. Georgia, Tifton; GA; (2) Dept. Horticulture, Tifton, GA; (3) Univ. Georgia, Athens, GA. Publication no. P-2002-0008-SOA.
Onions (Allium cepa) grown on black plastic, wheat straw, or bare ground either with drip or overhead irrigation were rated for center rot, caused by Pantoea ananatis. In 2000 and 2001, there was no significant effect of type of irrigation on center rot incidence or severity. In both years, center rot development was delayed by 7-14 days in onions grown on straw mulch or bare ground compared to those grown on black plastic. Similarly, center rot was delayed 7-10 days in onions grown on straw mulch compared to bare ground in 2000 but not 2001. However, in both years, onions on straw mulch had the lowest yields and lowest percentage of jumbo-grade bulbs. Approximately 80% and 50% of the bulbs from plants with symptoms at harvest had internal rots in 2000 and 2001, respectively. In contrast, 20% and 1% of the bulbs from plants with no foliar symptoms at harvest had internal rot in 2000 and 2001, respectively.
Association of Pantoea ananatis with tobacco thrips, Frankliniella fusca. R. GITAITIS (1), L. Wells (1), H. Sanders (1), D. Riley (2), and R. Walcott (3). (1) Univ. Georgia, Tifton; (2) Dept. Entomology, Tifton; (3) Univ. Georgia, Athens, GA. Publication no. P-2002-0009-SOA.
Pantoea ananatis, which causes center rot of onion, was isolated from 5% of the tobacco thrips, Frankliniella fusca, collected from onion fields. Thrips were surface-sterilized in 10% sodium hypochlorite and immersion in 70% ethanol. After rinsing in sterile PBS (phosphate-buffered saline), thrips were placed in PBS and crushed. Aliquants were plated onto King’s medium B. Suspect bacteria were identified by physiological and morphological characteristics, gas-chromatography of fatty acids, rot of onion slices in vitro, and PCR. Amplicons were produced by the amplification of ITS DNA (internal transcribed spacer region) with the primers Pan ITS1 and EC5. The bacterium also was isolated from tobacco thrips feeding on peanut foliage. Populations of P. ananatis recovered from leaf discs were two-to-three orders of magnitude greater from peanut leaves after thrips feeding than from thrips-free leaves.
Potential applications of PGPR treated cotton transplants N. W. GREER, K. S. McLean, and J. W. Kloepper. Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849. Publication no. P-2002-0010-SOA.
Field tests in Alabama were conducted to assess cotton transplants with and without plant growth-promoting rhizobacteria (PGPR) with the objective of extending the northern range of the cotton producing area. Transplants were prepared using PayMaster 1218 BG/RR cotton seed grown in styrofoam trays with an individual cavity size of 3.2 × 3.2 cm. A commercial preparation, BioYield™, which contains Bacillus subtilis strain GBO3 and B. amyloliquefaciens strain IN937a was added into the soil-less medium prior to planting in some treatments. Three and 4 week old seedlings were manually transplanted into 2 fields. Stand counts, mapping data, and harvest data were collected. Seedling emergence and survival were not reduced by any biological, transplant, or fungicide treatment as compared to the control. At 74 days after planting (DAP) the number of bolls was greater for the transplant treatments with and without BioYield™ than the direct seeded treatments. At 90 DAP the number of bolls was greater on the PGPR-treated transplants than the non-treated transplants and the direct seeded treatments. Data indicate that cotton transplants matured earlier than direct seeding and that the addition of PGPR in the transplant system further enhanced maturity. These results indicate that transplanted cotton has the potential for an earlier harvest.
Identification of maize chromosome regions associated with silk antibiotic compounds, husk coverage, and aflatoxin formation. B. GUO (1), Ana Butrón (1), Neil W. Widstrom (1), David M. Wilson (2), Maurice E. Snook (2), and Robert E. Lynch (1). (1) USDA-ARS, Tifton, GA 31793; (2) Dept. of Plant Pathology, University of Georgia, Tifton, GA 31793. Publication no. P-2002-0011-SOA.
The effect of husk tightness and coverage, subsequently has an important influence on aflatoxin contamination, especially as it relates to prevention of entry by insects into the ears of southern grown hybrids. Maysin and related compounds, such as apimaysin, 3'-methoxymaysin, and chlorogenic acid, have been determined to be important antibiotic compounds against corn earworm, but, to be effective under field conditions, silk antibiotics should be accompanied by a good husk coverage. Evaluation of genotypes inoculated with Aspergillus flavus and infested with corn earworm revealed that corn earworm injury and aflatoxin contamination of maize grain are consistently correlated when ear-feeding insects and A. flavus spores are abundant in the environment. Genetic mapping of the cross GT-A1 × GT119 (inbreds differing for resistance traits) was conducted and DNA genotyping was performed on 250 F2 plants using 112 RFLP probes and 6 restriction enzymes. Phenotypic trait measurements were made on F2:3 families in a replicated experiment in 1999 and 2000. A major QTL for maysin was identified on chromosome 1S, and QTLs for husk tightness were located on chromosomes 4L and 7S. The recombination of progenies with chromosome region 1S from GT-A1 and 2L from GT119 gave the lowest aflatoxin concentrations.
A modified Nash and Snyder's medium for isolating Fusarium solani f. sp. glycines from soybean roots. R. Y. HASHMI, M. E. Schmidt, and J. S. Russin. Dept. Plant, Soil & Gen. Ag., Southern Illinois Univ., Carbondale, IL 62901-4415. Publication no. P-2002-0012-SOA.
Modified Nash & Snyder medium (SNA) is used to isolate Fusarium solani f. sp. glycines (FSG) from soybean roots. Modifications include C and N sources and antibiotic type and quantity. We compared three modifications of SNA for quantifying FSG root colonization in inbred lines grown in field and greenhouse. No medium by line interaction occurred in either arena. We also examined ability of media to recover FSG from field grown soybean. Media differed in number of colonies isolated and colony growth rate, morphology, and pigmentation. Morphology/pigment types were: 1) medium, flat, white appressed with blue center, bluish pigmentation in medium; 2) medium, flat, white with maroon center, purple pigmentation in medium; 3) small, flat, white with bluish-green concentric rings, bluish green pigmentation in medium; 4) large cottony, white with greenish-blue pigmentation on margins; and 5) medium, cottony, white, bluish pigmentation in medium. Types differed in foliar symptoms incited, with mean scores of 35, 16, 10, 5, and 3, respectively, on a 0-100 scale.
Weed hosts of Phomopsis longicolla in Arkansas soybean fields. E. W. JACKSON, M. Cordell, and P. Fenn. Dept. Plant Pathology, University of Arkansas, Fayetteville, AR 72701. Publication no. P-2002-0013-SOA.
P. longicolla is a major cause of seed infection and decay in southern soybean production. Several weeds reported to be hosts of this pathogen may serve as reservoirs of inoculum for infection of soybean. The 12 major weeds that impact Arkansas soybean production were grown in a greenhouse and inoculated with 10(^5) spores/ml and given 48 hr of dew. After 3 days, leaf pieces were surface disinfested and plated on acidified PDA. The pathogen was recovered from all 12 weeds; the greatest recoveries from pitted and entire-leaf morning glory. Pycnidia formed on leaf samples of all species incubated in moist chambers containing glyphosate-soaked paper. A July survey of morning glory, large crabgrass, common cocklebur and hemp sesbania plants in soybean fields revealed varying levels of latent P. longicolla infection in leaves and stems of all species. P. longicolla can infect and reproduce on several important weeds, but whether dissemination of inoculum from dying weeds to soybean occurs in the field needs to be demonstrated. Weed control strategies may affect the level of Phomopsis seed infection in soybeans.
Increase in populations of Rhizoctonia solani and wirestem of collard after a velvetbean cover crop. A. P. KEINATH (1) and H. F. Harrison (2). (1) Coastal REC, Clemson University, Charleston, SC 29414; (2) USDA, ARS, US Vegetable Lab., Charleston, SC 29414. Publication no. P-2002-0014-SOA.
Legume cover crops may increase soilborne pathogens and root diseases in subsequent vegetable crops. In 2000 and 2001, six plots were planted to velvetbean as a summer cover crop and three were left fallow. Velvetbean was disced in three plots; in the remaining three plots it was killed with herbicide and left in place as a cover crop mulch. Collard was transplanted in October of both years. Wirestem caused by R. solani was observed in these studies both years. Populations of R. solani were estimated by wet-sieving soil and culturing organic debris on ethanol-KNO(3) medium. Cover crop mulch increased populations of R. solani compared with fallow (P < 0.01) both years. Recovery of R. solani was greater in the disced plots than in the fallow plots in 2000 but not in 2001. Wirestem incidence was always greater in cover crop mulch than in the other two treatments (P < 0.01 in 2000 and P < 0.05 in 2001). If velvetbean is used as a cover crop, it should be disced into the soil before transplanting collard to reduce the risk of wirestem.
Assessment of fungicides to reduce seedling disease of cotton in Georgia. R. C. KEMERAIT (1), K. W. Seebold (1), R. G. McDaniel (2), D. G. Spaid (3), and W. J. Parks (4). (1) Dept. of Plant Pathology, University of Georgia, Tifton, GA, 31793; (2) Coop. Extension Service, Waynesboro, GA; (3) Coop. Extension Service, Elberton, GA; (4) Coop. Extension Service, Rome, GA. Publication no. P-2002-0015-SOA.
Seedling diseases of cotton caused by Rhizoctonia solani and Pythium spp. are occasionally serious problems in Georgia and cost growers an estimated $9 million in 2000. In 2001, trials were established at four sites to assess fungicides at planting to reduce disease and increase yields. Seed was planted under conditions that would favor disease. Treatments were commercially treated seed with and without Prevail (carboxin + metalaxyl + PCNB) at 12 ounces per 100 pounds of seed or Terraclor Super X 18.8 G (etridiazole + PCNB) at 5.5 pounds in-furrow per acre. Terraclor 15 G (PCNB) at 5 pounds in-furrow per acre was included in two trials. In three trials, at least one treatment increased stand count and reduced the skip index compared to seed alone. Where plots were harvested, yields were not different despite improved stands. Use of fungicides at planting can reduce seedling disease; however research is needed to optimize economic returns.
The occurrence and fungicidal control of peanut rust in central Florida. T. A. KUCHAREK and C. R. Semer. Plant Pathology Dept., University of Florida, Gainesville, FL 32611. Publication no. P-2002-0016-SOA.
Peanut rust, caused by Puccinia arachidis, first occurred between August 13 to 17 from 1998 to 2001 at sites where fungicides for leaf spot control were being evaluated in the central Florida area. Each test was a RCBD with four replications and each treatment received six fungicide sprays in 468 L ha(^-1) of water at 207 kPa with a single SS 8008 nozzle over the center of the row. The cultivar Florunner was used in 1998 and Georgia Green was used in 1999 and 2001. Both were compared in 2000. The standard fungicide treatment was six sprays of chlorothalonil (CH). In five other treatments, CH was applied in the first and sixth sprays with the four mid-season sprays consisting of alternations of azoxystrobin (AZ) and tebuconazole (TEB) at two different rates, a tank mix of AZ with TEB at reduced rates, TEB applied at the full rate, or a tank mix of TEB with mancozeb at reduced rates. At the end of the season, the number of leaflets with rust was reduced by all fungicide treatments in 1998, 1999, and 2001 (P = 0.05). In 2000, the number of leaflets with rust was greatest in unsprayed Florunner compared to all other treatments including unsprayed Georgia Green (P = 0.05).
Field response of selected mid-south soybean varieties to the reniform nematode. G. W. LAWRENCE (1), K. S. McLean (2), H. K. Lee (1), and A. T. Kelly (1). (1) Dept. Entomology and Plant Pathology, Mississippi State University, Mississippi State, MS 39762; (2) Dept. Entomology and Plant Pathology, Auburn University, Auburn, AL 36849. Publication no. P-2002-0017-SOA.
Thirty-four mid-south soybean varieties in maturity groups (MG) III through V were evaluated for their yield response to the reniform nematode (Rotylenchulus reniformis). Included in the study were four MG III, fifteen MG IV, and fifteen MG V varieties. The test was conducted in a field located at Inverness, Mississippi that was naturally infested with the reniform nematode. Each variety was planted with and without the nematicide aldicard (0.59 kg a.i./ha) An average population density of 8,975 nematodes/500 cm(^3) across all varieties was recovered at planting. Soybean yields in MG III ranged from 46.0 to 50.1 kg/ha with DeltaKing DKxTJ193RR and Delta and Pine Land’s 3964 RR and 3961 RR. In MG I V yields ranged from50.9 to 64.3 kg/ha with DeltaKing 5661 RR and Delta and Pine Land DPLxTJ193 RR. Maturity group V yields ranged from 53.62 to 74.7kg/ha with DeltaKing 5688 RR and Delta and Pine Land 5989. The addition of Temik 15G improved soybean yields ranging from 10.6 to 14.3 kg/ha in MG III, 1.5 to 19.3 kg/ha in MG IV and 5.1 to 25.2 kg/ha. in MG V.
Evaluation of rhizobacteria to control Tomato spotted wilt in tobacco. N. MARTINEZ-OCHOA, B. Mandal, and A. S. Csinos. Dept. of Plant Pathology, University of Georgia - CPES, Tifton, GA 31793. Publication no. P-2002-0018-SOA.
Plant Growth-Promoting Rhizobacteria (PGPR) have been reported to induce systemic resistance against several plant pathogens, including tobacco viruses such as Tobacco mosaic virus (TMV) and Tobacco necrosis virus (TNV). Foliar sprays with the plant activator acibenzolar-S-methyl (Actigard) have been shown to reduce symptoms caused by Tomato spotted wilt virus (TSWV). The purpose of this study was to evaluate applications of six PGPR strains for the management of TSWV in tobacco under greenhouse conditions. Thirty days after seedlings were transplanted into float trays each bacterial suspension was applied as a soil drench. Control treatments consisted of a water only drench and a foliar spray with Actigard. Plants were mechanically inoculated with TSWV one week later. Evaluation of disease progress was conducted afterward to monitor the number and relative size of the lesions and seedlings were tested for systemic infection by enzyme-linked immunosorbent assay (ELISA) using a commercially available kit. Differences in TSWV infection compared to the nonbacterized virus-only and Actigard controls will be discussed.
Reduction of caladium diseases by fungicide application as a tuber soak or soil spray. R. J. MCGOVERN, T. A. Davis, D. S. Myers, and T. E. Seijo. Univ. of Florida, Gulf Coast REC, Bradenton, FL 34203. Publication no. P-2002-0019-SOA.
Following hot water treatment, tubers of caladium ‘Florida Cardinal’ were soaked for 16 h at ambient temperature in (rate/100 gal): water alone, 3336 WP (24 oz), Spectro 90 WDG (24 oz), Armicarb 300 (4.2 lb), Heritage (4, 8, or 16 oz +/- Induce at 0.06% v/v), Hurricane (1.5 oz) or Compass (4 oz). Hurricane was also tested as an at-plant soil spray (1.5 oz; 1500 gal/A). Seed pieces were planted on 19 May 2000 at a commercial farm in West Central Florida. The experiment used a randomized complete block design with six replications consisting of 3 ft.-wide and 18 ft.-long raised beds previously fumigated with methyl bromide and covered with plastic mulch. Tubers were harvested on 8 March 2001. Plant emergence on 29 June was significantly increased by tuber soaks in Spectro 90 WDG and application of Hurricane at-planting. Spectro 90 WDG also increased the number of marketable tubers. Preplant soaks in Spectro 90 WDG or Heritage at 8 oz without Induce, and preplant or at-planting use of Hurricane significantly increased total tuber weight per plot. Both Hurricane treatments significantly reduced the severity of tuber rot (% internal discoloration).
Effects of selected fungicides on soybean disease incidence and seed quality. K. S. MCLEAN (1), G. W. Lawrence (2), and L. Carter (1). (1) Dept. Entomology & Plant Pathology, Auburn University, Auburn, AL 36849; (2) Dept. Entomology & Plant Pathology, Mississippi State University, Mississippi State, MS 39762. Publication no. P-2002-0020-SOA.
Selected fungicides were evaluated on “Carver” soybeans as seed treatments, in-furrow and foliar sprays to determine the effects on yield, disease incidence and seed quality. The fungicides Azoxystrobin and Benomyl were applied as in-furrow sprays at planting or as foliar sprays at R3 and R5 growth stages. Carboxin + Thiram and Metalaxyl were applied as seed treatments. Emergence was reduced by the Azoxystrobin applied in-furrow at planting as compared to the Carboxin + Thiram seed treatments. Stem canker incidence was low however more diseased plants were observed in the Carboxin + Thiram seed treatments compared to the Azoxystrobin treatments. Yields ranged from 25.78 to 24.71 bushels per acre. Fifty three percent to 61% of the soybean seed harvested were colonized by fungi. Phomopsis longicolla was isolated significantly more frequently from the harvested seed of the Azoxystrobin foliar treatments than the Benomyl foliar treatments and the control. Cercospora kikuchii colonized significantly fewer seed in all the foliar fungicide treatments compared to the control. Azoxystrobin applied as a foliar spray significantly reduced the presence of Alternaria alternata on soybean seed.
Citrus trizteza virus incidence and diversity in Hawaii as detected by molecular and serological assays. M. J. Melzer and J. S. HU. Dept. Plant and Environmental Protection Sciences, University of Hawaii, Honolulu, HI 96822. Publication no. P-2002-0021-SOA.
Citrus tristeza virus (CTV), the causal agent of decline and stem-pitting in citrus, has been present in Hawaii for decades where it is vectored by the brown citrus aphid. In this study, the incidence and diversity of CTV in Hawaii was examined. Samples collected on Kauai (8 sites, 91 trees), Oahu (13, 86), Maui (10, 87), and Hawaii (15, 129) underwent RT-PCR for the CTV coat protein gene as well as tissue blot immunoassays (TBIA) using four CTV antibodies. Trees testing positive for either the RT-PCR or TBIA underwent further RT-PCR using strain-specific primers for strains T3, T30, T36, and VT. The incidence of CTV on Kauai, Oahu, Maui, and Hawaii was 59, 87, 63, and 83% respectively, with an overall incidence of 74% (291/392). RT-PCR using strain-specific primers revealed that most samples harbored multiple strains including those similar to T3, T30, T36, and VT, with VT-like strains being the most prevalent. Their distribution, however, was not uniform throughout the islands. Several samples harbored strains that could not be characterized using the strain-specific primers.
The effects of tillage practices and reduced fungicide inputs on leaf spot disease progress on three peanut cultivars. W. S. MONFORT, A. K. Culbreath, and T. B. Brenneman. Coastal Plain Expt. Stn., Tifton, GA 31793. Publication no. P-2002-0022-SOA.
Field experiments were conducted in 2000 and 2001 on Georgia Green, MDR-98 and C-99R peanut (Arachis hypogaea) cultivars to determine the effects of tillage practices and reduced fungicide inputs on early leaf spot (Cercospora arachidicola) disease progress. Fungicide treatments (Trts) were: 1) no fungicide; 2) chlorothalonil (CHL) 1.26 kg/ha; 3) tebuconazole 0.23 kg/ha (sprays 3-6) and CHL 1.26 kg/ha (all other sprays); 4) azoxystrobin 0.33 kg/ha (sprays 3 and 5) and CHL 1.26 kg/ha (all other sprays), at 14-d intervals (7 sprays). Trts 5-7 used the same fungicides as Trts 2-4, at 21-d intervals (4 sprays). AUDPC values were lower in strip-till than in conventional tillage. AUDPC values for Trts 1-7 were 381, 255, 239, 228, 311, 260, and 247 in 2001 (LSD = 21) and 328, 131, 111, 119, 212, 163, and 150 in 2000 (LSD = 20), respectively, for conventional-till plots and 297, 190, 177, 186, 231, 197, and 185 in 2001 (LSD = 27) and 238, 97, 98, 95, 144, 120, and 106 in 2000 (LSD = 22), respectively, for strip-till for Georgia Green. AUDPC values were lower for C-99R and MDR-98, but followed similar trends for treatments and tillage.
First report of Sudden Death Syndrome on soybeans on Delmarva. R. P. MULROONEY and N. F. Gregory. Plant and Soil Sciences Dept., University of Delaware, Newark, DE 19717. Publication no. P-2002-0023-SOA.
Since its discovery in Arkansas in 1971 Sudden death syndrome (SDS) of soybean has been reported from nine additional states. The farthest east it had been found is Kentucky and Ohio. During the 2000 growing season, which was the wettest and coolest in recent memory, symptoms resembling SDS were seen in two fields in Sussex County, Delaware, and one field in nearby Somerset County, Maryland. Two of the three fields also had a history of soybean cyst nematode (SCN) infestation. Plant samples from these fields were inspected for symptoms of disease, and isolations were made from the taproots and secondary roots of the infected plants. Slow growing, blue pigment producing Fusarium solani was isolated from all the roots. Koch's postulates were completed and the pathogen identified as Fusarium solani f. sp. glycines. This discovery would make this the first report of SDS specifically on Delmarva as well as the east coast.
Leachates from the mycelia of maitake, oyster, and reishi mushrooms inhibit growth of bacteria in the laboratory. R. P. PACUMBABA, C. A. Beyl, R. O. Pacumbaba, Jr., and Y. Wang. Department of Plant and Soil Science, Alabama A&M University, Normal, AL 35762. Publication no. P-2002-0024-SOA.
Concentrated leachates obtained from mycelia of Grifola frondosa (GF, maitake), Pleurotus ostreatus (PO, oyster), and Ganoderma lucidum (GL, reishi) mushrooms (autoclaved and nonautoclaved) inhibited the growth of plant bacterial pathogens, viz., Pseudomonas syringae pv. glycinea, P. syringae pv. tabaci, Xanthomonas campestris pv. glycines, X. campestris pv. campestris, Erwinia amylovora, Ralstonia (Pseudomonas) solanacearum, and Curtobacterium flaccumfaciens pv. flaccumfaciens in the laboratory. It also suppressed the growth of human bacterial pathogens including Bacillus cereus, Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and Staphylococcus aureus. This suggested that these leachates have antibiotic properties and are heat stable. The antibiotics produced by these fungi could be use as an alternative to methyl bromide for control of soil-borne plant bacterial pathogens. The mushrooms isolates (GF, PO, and GL) produced mycelia growth with cottony texture covering the whole surface of Petri dishes containing YVMBSA medium within 20 days. Mycelial growth of these fungi completely covered the hardwood sawdust in plastic culture containers P4928 amended with YVMBS broth within 35 to 45 days. Basidiocarp initials and basidiocarps of PO and GL were induced in the culture containers.
Effects of cover crop, tillage system, and soil-applied fungicide on cotton seedling disease epidemics. G. B. PADGETT and W. Rea. Northeast Research Station, LSU Agricultural Center, Winnsboro, LA 71295. Publication no. P-2002-0025-SOA.
Increased implementation of reduced tillage practices and cover crops has generated concern about their impact on cotton seedling diseases. Experiments, initiated in 2000, monitored seedling disease epidemics in selected cover crop, tillage, and fungicide systems for cotton production. Treatments included combinations of wheat or native winter vegetation in conventional or no-tillage systems with or without an in-furrow fungicide. Plant density, maturity, and yield data were recorded and populations of Rhizoctonia spp. were quantified. Plant densities were greater in conventional tillage systems compared to no-till systems; however, this did affect yield. In-furrow fungicides improved plant densities above non-treated cotton, but yield was not affected. Highest yields were observed in systems using no-tillage practices and a wheat cover crop. Rhizoctonia spp. varied among treatments. While cotton yields were maximized in no-tillage systems with a wheat cover crop, lower plant densities compared to conventional systems could be correlated to higher pathogen populations.
Mycoflora associated with cotton boll rot in Alabama. A. J. PALMATEER (1), K. S. McLean (1), E. van Santen (2), and G. Morgan-Jones (1). (1) Dept. Entomology and Plant Pathology; (2) Dept. Agronomy and Soils, Auburn University, Auburn, AL 36849. Publication no. P-2002-0026-SOA.
A mycoflora study was conducted in order to identify the fungi found in association with specific parts of upland cotton (Gossypium hirsutum L.) and to observe the relationship between the age of the crop, growth stage, and the incidence of selected fungi including important boll rot pathogens. Cotton fields throughout Alabama were sequentially sampled at seedling, first bloom, full bloom, and plant maturity. Roots, petioles, leaves, and bolls were surface-sterilized and placed on acidified potato dextrose agar and incubated at 25EC. There was a total of 36 species of fungi recovered known to cause either cotton boll rot or fiber deterioration. The number of fungal species isolated increased as the season progressed and was highest at maturity. The principal taxa recovered from all sampling dates were (Fusarium oxysporum), F. solani), and (Rhizopus stolonifer). The multivariate canonical discriminant analysis technique was able to separate growth stage × location combinations. The loadings for the 1st canonical variate, which separated the seedling from later stages of development, were dominated by (Fusarium) spp. and (Pythium) spp. The 2nd variate separated vegetative post-seedling stages from the boll stage. As expected, loadings for this variate were highest for boll rot causing fungi.
Modeling temporal progress of southern stem rot epidemics in peanut. S. L. RIDEOUT (1), T. B. Brenneman (1), and K. L. Stevenson (2). (1) Dept. Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton, GA, 31793; (2) Dept. Plant Pathology, University of Georgia, Athens, GA 30602. Publication no. P-2002-0027-SOA.
During 1999, 2000, and 2001, peanut plants were periodically and destructively sampled from set row lengths at four locations per year. Southern stem rot epidemic development was assessed as the frequency of infected plants, plants exhibiting pod infection, and plants showing visible signs or symptoms of the pathogen, Sclerotium rolfsii. Five different models were used to fit the disease progress data: linear, exponential, monomolecular, logistic, and Gompertz. For each year, growth curve model performance was similar across all four locations. The monomolecular model provided the best fit for frequency of infected plants in 1999 (0.66 < R(^2) < 0.83) and 2000 (0.65 < R(^2) < 0.72). However, in 2001, the Gompertz model provided the best fit (0.76 < R(^2) < 0.82). The Gompertz model best described the increase in pod infections over time in all three years (0.75 < R(^2) < 0.78 in 1999, 0.62 < R(^2) < 0.75 in 2000, and 0.49 < R(^2) < 0.58 in 2001). In 1999 and 2000, the monomolecular model provided the best description of the increase in frequency of plants with signs or symptoms of S. rolfsii (0.61 < R(^2) < 0.81 and 0.43 < R(^2) < 0.66, respectively). In 2001, the frequency of plants showing signs and symptoms of the pathogen was best fit by the Gompertz model (0.63 < R(^2) < 0.74).
Evaluation of in-line injected materials as alternatives to fumigation with methyl bromide. K. W. SEEBOLD (1), A. S. Csinos (1), and R. F. Davis (2). (1) Dept. Plant Pathology, University of Georgia, Tifton GA, 31793; (2) USDA-ARS, Tifton, GA. Publication no. P-2002-0028-SOA.
Injection of pesticides through irrigation tape is a promising means of delivery for methyl bromide (CH(3)Br) alternatives. Emulsifiable formulations of 1,3-dichloropropene plus 35 pct. chloropicrin (1,3-DC) were applied prior to transplanting of cucumber to plastic-mulched beds at 20.5 and 35 gallons per acre (GPA) by injection through irrigation tape to evaluate their efficacy against soilborne pathogens and nematodes. Other treatments included metam sodium injected at 37.5 GPA simultaneously with 1,3-DC (20.5 GPA) or 3 days afterward. Soil populations of Pythium spp. prior to transplanting were reduced 10-fold or more by all treatments, and all treatments were equal to CH(3)Br. Greatest suppression of Fusarium spp. in soil was seen with CH(3)Br, 1,3-DC at 35 GPA, or 1,3-DC plus metam sodium. Nematode injury at season’s end was least with 1,3-DC (alone at 20.5 or 35 GPA, or with metam sodium) and CH(3)Br. No phytotoxicity was observed. Injection of 1,3-DC plus metam sodium via irrigation tape may an effective alternative to fumigation with CH(3)Br for suppression of soilborne pathogens.
Introduction of trifloxystrobin (Gem®), a new strobilurin fungicide for use in citrus from Bayer Corporation. M. A. TOAPANTA (1), R. F. Morris (2), and W. D. Scott (3). (1) Bayer Corporation, Gainesville, FL 32607; (2) Bayer Corporation, Lakeland, FL 33809; (3) Bayer Corporation, Kansas City, MO 64120. Publication no. P-2002-0029-SOA.
Trifloxystrobin is a strobilurin fungicide currently registered on several crops in the United States under the trade names Flint® and Stratego®. Gem is the trade name for a 25 DF formulation of trifloxystrobin with pending registrations for use in citrus, rice, sugar beet and potato. When applied in a preventative spray program at rates of 70-140 g/h active ingredient, trifloxystrobin provides efficacy against the key citrus diseases, Mycosphaerella citri, greasy spot; Elsinoe fawcettii, scab; and Diaporthe citri, melanose. This activity is generally greater than or equal to fungicides currently available. In addition, tryfloxistrobin suppresses Alternaria alternata, alternaria; and Colletotrichum acutatum, post bloom fruit drop. Applications of trifloxystrobin have shown no adverse crop effects applied alone or in combination with any tested tank mix partners. Official registration is expected by March 2002.
Components of resistance to clonal lineages of Magnaporthe grisea in tall fescue cultivars. L. P. TREDWAY, K. L. Stevenson, and L. L. Burpee. Dept. Plant Pathology, University of Georgia, Athens, GA 30602. Publication no. P-2002-0030-SOA.
The components of resistance in tall fescue to Magnaporthe grisea, the causal agent of gray leaf spot, were measured in growth chamber experiments. Cultivars ranging in resistance to M. grisea were selected: Kentucky 31 (K31, susceptible), Rebel III (R3, moderately susceptible), Coronado (CO, resistant), and Coyote (CY, resistant). Plants were inoculated with M. grisea isolates representing the five clonal lineages associated with tall fescue in Georgia. Compared to K31 and R3, CY and CO exhibited longer incubation and latent periods, reduced rate of disease progress, and lower final disease incidence. Incidence of foliar blighting, rate of lesion expansion, and final lesion length were similar in CO, CY, and R3, but significantly less than in K31. Lineages of M. grisea differed significantly in virulence, but no relationship between virulence and frequency in field populations was evident. No significant interactions among cultivar and isolate were detected for any resistance component. The resistance in CY and CO is effective against all lineages of M. grisea identified in Georgia tall fescue populations to date.
Response of soybean sudden death syndrome to tillage and soybean variety. C. M. VICK, J. P. Bond, and J. S. Russin. Dept. of Plant, Soil, and General Agriculture, Southern Illinois University, Carbondale, IL 62901-4415. Publication no. P-2002-0031-SOA.
Fusarium solani f. sp. glycines causes sudden death syndrome(SDS) of soybean. Previous research conducted at Southern Illinois University found that SDS was less severe in areas that were subsoiled than in those that were no tilled. The objective of this experiment was to determine the influence of tillage on various soybean varieties with regard to SDS symptom expression. Plots were established in 2000 and 2001 and consisted of strips of conventional tillage, subsoiling, and no till. Each strip contained 32 varieties of various maturity groups that were rated as either susceptible or resistant to SDS. In 2001, subsoiling reduced SDS foliar ratings by half when compared to either no-till or conventional-tillage. In 2001, both subsoiled and conventional-tillage reduced foliar ratings similarly when compared to no-till. Limited treatment by variety interactions were detected in 2001 for the most susceptible varieties.
Effect of bermudagrass cultivar on spiral nematode (Helicotylenchus spp.) populations. N. R. WALKER (1) and D. L. Martin (2). (1) Dept. Entomology and Plant Pathology; (2) Dept. of Horticulture and Landscape Arch., Oklahoma State University, Stillwater, OK 74078. Publication no. P-2002-0032-SOA.
The effect of bermudagrass (Cynodon dactylon; C. dactylon X C. transvaalensis) cultivar on spiral nematode (Helicotylenchus spp.) populations was evaluated. Field plots (2.4 m × 2.4 m) containing twenty-seven seeded or vegetative bermudagrass cultivars were established in the fall of 1997. Plots were arranged in a randomized complete block design with three replications. To determine nematode populations, soil samples were collected from each plot in the fall of 2000 and 2001. Nematodes were extracted from 100 cm(^3) of soil by sieving and centrifugal floatation. Plant parasitic nematodes were identified to genus, and total populations of each were determined. For both years, Mini-Verde, CN-29, Tifway, Tifgreen, and Tifsport bermudagrass plots contained low Helicotylenchus populations. Nematode populations were highest for plots containing Blackjack, Jackpot, Shangri La, J-540, Cardinal, and OKS95-1 cultivars. These results indicate that certain bermudagrass cultivars may suppress Helicotylenchus populations.
Efficacy of the nematophagous fungus ARF18 in suppressing Rotylenchulus reniformis on cotton. K. N. WANG and R. D. Riggs. Dept. Plant Pathology, University of Arkansas, Fayetteville, AR 72701. Publication no. P-2002-0033-SOA.
A strain of nematophagous fungus ARF18 was isolated from eggs of Rotylenchulus reniformis. Its effects on R. reniformis were studied in both in vitro and greenhouse tests. Soil infested with homogenized ARF18 mycelia was used in the greenhouse experiment and that consisted of four treatments and a check without ARF18. ARF18 significantly decreased both the mean number of eggs from roots and the mean total number of eggs and juveniles in the soil treated with 0.3 g mycelia per 100 g soil. The mean numbers of eggs from roots were decreased significantly at 0.1 g or 0.05 g mycelia per 100 g soil, but not at the rate of 0.01 g mycelia per 100 g soil. Regression analysis indicted that as the amount of ARF18 in the soil increases, the rate of hatching of R. reniformis eggs in the soil decreases. In the in vitro test, 75% of eggs of R. reniformis were parasitized.
Response of soybean Sudden Death Syndrome to deep tillage practices. Z. W. WEBER, S. K. Chong, J. P. Bond, and J. S. Russin. Dept. Plant, Soil, and General Agriculture, Southern Illinois University, Carbondale, IL 62901-4415. Publication no. P-2002-0034-SOA.
Soybean Sudden Death Syndrome (SDS), caused by Fusarium solani f. sp. glycines (FSG), is the second most important soybean disease in Illinois. It is most severe in high yielding environments and can be exacerbated by soil compaction and poor drainage. A field in Jackson County, IL with a history of severe SDS received the following treatments: 1) subsoiled (40 cm deep) in 1999 only (Single-Till); 2) subsoiled in 1999 and 2001 (Double-Till); 3) chisel plowed (25 cm deep) in 2001 (Chisel); and 4) No-tilled (No-Till). Measured variables were: soil moisture, temperature, bulk density, and porosity; initial and final populations of soybean cyst nematode; root colonization by FSG; and severity of SDS foliar symptoms. Soil moisture was higher in the No-Till and Single-Till plots. Likewise, foliar disease severity was higher in the No-Till treatment than any other treatment and higher in the Single-Till treatment than in the Double-Till or Chisel treatments. As a result, yield was higher in Chisel and Double-Till treatments than in the Single-Till and No-Till treatments.
Fungicide sensitivity and resistance profiles for Botrytis cinerea isolates from Louisiana strawberry farms. D. E. WEDGE (1), P. F. Pace (2), J. E. Boudreaux (3), K. J. Curry (4), and B. J. Smith (5). (1) USDA-ARS, Natural Products Utilization Research Unit, The National Center for Natural Products Research, University of Mississippi, University, MS 38677; (2) AgroStat, University, MS; (3) Horticulture Dept., Louisiana State University, Baton Rouge, LA; (4) Dept. Biological Sciences, University of Southern Mississippi, Hattiesburg, MS; (5) USDA-ARS Small Fruit Research Station, Poplarville, MS. Publication no. P-2002-0035-SOA.
Botrytis fruit rot (gray mold) is one of the most destructive diseases of strawberry. Fungicidal sprays have been widely used for the control of the fungal pathogen, Botrytis cinerea, but B. cinerea has become resistant to many antifungal compounds. Few fungicides are now available for effective control of Botrytis fruit rot. New approaches for control of B. cinerea are necessary as the effectiveness and availability of commercial fungicides decrease. Eleven B. cinerea isolates from Louisiana were evaluated in a dose-response format for sensitivity to benomyl, azoxystrobin, captan, chlorothalonil, cyprodinil, dodine, fosetyl-Al, iprodione, metalaxyl, thiabendazole, thiram, vinclozolin, butrizol, kresoxim-methyl, fenhexamid, and thiophanate-methyl. Six isolates were determined to be benzimidazole resistant, two isolates showed intermediate sensitivity, and three isolates were sensitive. Five isolates were rated resistant, one isolate intermediate, and five isolates sensitive to dicarboximide. Butrizol, cyprodinil, fenhexamid, kresoxim-methyl, and azoxystrobin provided nearly 100% growth inhibition of all 11 B. cinerea isolates at 30.0 microM. These fungicides should be considered for future disease control of Botrytis fruit rot of strawberry.
Chlorothalonil concentration in putting green soil and its in vitro effect on Arthrobotrys oligospora. J. E. WOODWARD, N. R. Walker, and J. W. Dillwith. Dept. Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078. Publication no. P-2002-0036-SOA.
Plant parasitic nematodes are common and damaging pests in golf course putting greens. The nematophagous fungus, Arthrobotrys oligospora is a potential management tool for nematodes in putting greens. However, fungicides are extensively used for the management of plant pathogenic fungi in putting greens and might have an adverse affect on the use of nematophagous fungi to manage nematodes. Four applications of chlorothalonil were made at 14 d intervals to field plots. Soil samples were collected 10 and 40 d after the first application. Chlorothalonil was quantified from soil using a gas chromatograph equipped with a mass spectrometer detector. Soil concentrations of chlorothalonil did not exceed 1.0 ppm. The tolerance of A. oligospora to the fungicide chlorothalonil was evaluated in vitro. Growth of A. oligospora ceased at chlorothalonil concentrations above 10 ppm. Results indicate that the use of chlorothalonil to manage fungal diseases may not interfere with the use of A. oligospora to manage nematodes in golf course putting greens.
Get ALL the Latest Updates for CHANGING LANDSCAPES OF PLANT PATHOLOGY. Follow APS!