Posted online October 15, 2003
Effects of FD141 and its analogs on the germination and morphology of selected plant pathogenic fungi. M. ABRIL (1), K. J. Curry (1), and D. E. Wedge (2). (1) Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, MS 39406-5018; (2) USDA-ARS, Natural Products Utilization Research Unit, University, MS 38677. Publication no. P-2004-0001-SOA.
A USDA experimental natural product fungicide referred to as FD141, and seven of its chemical analogs plus seven commercially available fungicides were evaluated for their ability to inhibit fungal germination. Botrytis cinerea, Colletotrichum acutatum, C. fragariae, C. gloeosporioides, Phomopsis obscurans, and P. viticola were used for this purpose. FD141 and the commercially available fungicides were effective germination inhibitors, while most FD141 analogs were less effective. However, one of the experimental analogs, FD142, caused anomalous development in germ tubes of three of the six fungi.
Effects of pre-till herbicide and cover crop residue on early leaf spot epidemics of peanut. E. G. CANTONWINE and A. K. Culbreath. Univ. of Georgia, Dept. of Plant Pathology, Tifton, GA 31793. Publication no. P-2004-0002-SOA.
Epidemics of early leaf spot (Cercospora arachidicola) of peanut (Arachis hypogaea) are less severe under strip-tillage than conventional tillage in rotated fields. An experiment was conducted to assess the effects of pre-till herbicide and cover crop residue (CCR) typical of strip-till systems, on disease development in the cv. Georgia Green. Treatments consisted of strip or conventional tillage, a pre-till herbicide (glyphosate or paraquat) or no herbicide, with or without CCR. No fungicides were applied during the experiment. Leaf spot intensity was assessed weekly using the Florida 1-10 scale or by counting leaf spots from 10 branches per plot. Pre-till herbicides did not affect epidemics. The rate of epidemic development was similar for all treatments, but leaf spot counts and disease ratings were significantly lower (P < 0.05) in strip-tilled plots and conventionally tilled plots with CCR than in conventionally tilled plots without CCR. Strip-tillage without CCR did not significantly enhance epidemics. Based on first year results, CCR has a greater role than pre-till herbicide in the suppression of leaf spot by strip-tillage.
Dinamica poblacional y manejo de nematodos, en guayabo (Psidium guajava), en Calvillo, Aguascalientes, Mexico. M. CEPEDA-S (1), E. González-G (2), J. López (3), G. Gallegos-M (1), y F. D. Hernández-C (1). (1) Univ. Autónoma Agraria Antonio Narro, Depto. de Parasitología, Buenavista, Saltillo, Coahuila, México C.P. 25315; (2) Campo Exp. de Pabellón INIFAP-CEPAB, Pabellòn de Arteaga, AGS, México C.P. 20660; (3) Valent de México, S.A. de C.V, Zapopan, Jalisco, México. Publication no. P-2004-0003-SOA.
Con el objeto de conocer la dinámica poblacional y la actividad del DiTera DF (Myrothecium verrucaria), se instaló un diseño de bloques al azar, con 4 tratamientos y 4 repeticiones T1, DiTera DF (4 kg/ha.), T2, DiTera DF (1.6 kg/ha), T3, Carbofuran 5G (40 kg/ha), T4, Testigo, se realizaron 6 aplicaciones en T1 y T2, y en T3 solo una aplicación, se efectuaron 17 muestreos de suelo de cada unidad experimental, de Junio 2001 a Noviembre de 2002, los resultados indican la presencia de Dorylaimus spp., Rhabditis spp., Aphelenchus spp., Aphelenchoides spp., y Meloidogyne incognita; DiTera a 4 kg/ha, redujo la población de los cinco géneros.
Evaluacion de la efectividad biologica del nematicida Ditera DF (Myrothecium verrucaria), en nemátodos asociados al guayabo (Psidium guajava), en Calvillo, Aguascalientes, México. M. CEPEDA-S (1), E. González-G (2), J. López (3), G. Gallegos-M (1), y F. D. Hernández-C (1). (1) Univ. Autónoma Agraria Antonio Narro, Depto. de Parasitología, Buenavista, Saltillo, Coahuila, México C.P. 25315; (2) Campo Experimental de Pabellón-INIFAP-CEPAB, Pabellón de Arteaga, AGS, México C.P. 20660; (3) Valent de México, S.A. de C.V, Zapopan, Jalisco, México. Publication no. P-2004-0004-SOA.
Con el objeto de evaluar el DiTera DF, se estableció un diseño de bloques al azar con 5 tratamientos y 5 repeticiones; T-1, DiTera DF 10.5 Kg/Ha; T-2, DiTera DF 7.0 Kg/Ha; T-3, DiTera DF 3.5 Kg/Ha; T-4, Carbofuran 200 gr/ árbol y T-5, Testigo, se realizaron 7 aplicaciones en los tratamientos de DiTera y solo una aplicación de Carbofuran, se realizò un muestreo inicial y final, para conocer las población de nematodos, así como el descascaramiento de los frutales en tallo, ramas gruesas y ramas delgadas; El DiTera DF a 10.5 Kg/Ha, resultó ser el mejor, al reducir la población de los géneros, Meloidogyne incognita, Pratylenchus spp. y Dorylaimus spp., en suelo y raíz del frutal, así como el presentar menor descascaramiento en tallo, ramas gruesas y ramas delgadas.
Temperature effect on sporulation of Botryosphaeria dothidea, B. obtusa, and B. rhodina. W. E. COPES (1) and F. F. Hendrix, Jr. (2). (1) Small Fruit Research Station, USDA-ARS, Poplarville, MS 39470; (2) Dept. of Plant Pathology, University of Georgia, Athens, GA 30602. Publication no. P-2004-0005-SOA.
Botryosphaeria spp. were grown on autoclaved apple and peach stems with constant moisture at 6, 12, 18, 24, and 30°C to determine the effect of temperature on sporulation. Conidia per pycnidium were counted weekly from 4 to 10 wks after inoculation. Number of conidia per pycnidium of B. dothidea and B. obtusa had a quadratic response to temperature with maximum sporulation at 24°C and 18°C, respectively. For B. dothidea and B. obtusa, percent conidia with a septum or dark pigmentation was not affected by temperature and pycnidia were erumpent through the bark typical of their habit in nature. Number of conidia per pycnidium of B. rhodina was significant; however, sporulation was not different between 12, 24, and 30°C and between 6, 18, 24, and 30°C, so a distinct pattern of significance was not present. In contrast, percent B. rhodina conidia with dark pigmentation and a septum had a quadratic response due to temperature with a maximum at 24°C. Mycelia and pycnidia of B. rhodina grew on top of the bark atypical of their habit in nature. While all three species produced conidia from 6 to 30°C, greatest numbers of conidia or conidia with dark pigmentation, which would affect duration conidia remain viable, occurred at 18 to 24°C.
Efficacy of fungicides on tobacco blackshank. A. S. CSINOS. Department of Plant Pathology, University of Georgia, CPES, Tifton, GA 31794. Publication no. P-2004-0006-SOA.
Blackshank incited by Phytophthora parasitica var. nicotianae is managed by the use of resistant cultivars, cultural practices and chemicals. A shift from race 0 to race 1 of the pathogen has increased in the past few years with introduction of new cultivars with resistance to race 0. Ridomil Gold 4E (mefenoxam), Ultra Flourish 2E (mefenoxam) and FAC 321 2E (metalaxyl) were evaluated at equivalent rates of active ingredient using multiple applications at preplant, at plant, first cultivation or at last cultivation in a field infested with both race 0 and 1 of the pathogen. All treatments significantly increased yield of tobacco and reduced disease as compared to the control. No difference was detected among products when used at equivalent rates of active ingredient. Vigor ratings of FAC 321 2E were the lowest while Ultra Flourish 2E had the highest vigor. Plant heights of FAC 321 were the lowest while plots treated with Ridomil Gold 4E were the tallest. Both races of the pathogen were controlled by all of the products. Producers will rely more chemicals to manage this disease as the pathogen shifts to race 1.
Integration of Bacillus-Rhizobium inoculants and tillage to manage dry bean and soybean root rot. C. ESTEVEZ DE JENSEN, J. Kurle, and J. Percich. University of Minnesota, Dept. of Plant Pathology, St. Paul, MN 55108. Publication no. P-2004-0007-SOA.
Field studies were conducted in north central Minnesota to integrate management strategies to limit the effects of root rot and soil physical factors that affect dry bean and soybean yields. Disruption by moldboard tillage of the soil impedance layer (> 2,000 Kpa at 15 cm soil depth) reduced disease severity (DS; 1 = no disease 9 = dead plant) from 4.4 to 3.8 (chisel vs. moldboard tillage) in dry bean. In soybean DS was reduced by 12%. Inoculation of dry bean with Bacillus subtilis MBI600 plus Rhizobium tropici UMR 1899 reduced DS from 4.7 to 3.5 (uninoculated vs. inoculated). In soybeans inoculation with Bradyrhizobium japonicum RCR 3437 plus B. subtilis MBI600 decreased DS from 3.9 to 3.1 (uninoculated vs. inoculated). In dry bean plots population of Fusarium solani differed between chisel and moldboard at 0-7 cm depth, but not at 7-15 cm depth. In soybean plots no differences were found. Dry bean yields in moldboard were 21% greater than in chisel tilled plots (869 vs.1,050 Kg ha(^–1) respectively). Dry bean yields were unaffected by inoculation. Soybean yields were increased by 105% with inoculation (1,569 vs. 3,221 Kg ha(^–1)) and by 10% when moldboard was compared to chisel tilled plots (2,509 vs. 2,282 Kg ha(^–1)). Integration of tillage and inoculation may be beneficial in the control of bean and soybean root rot.
Additive effect of soil bulk density and Fusarium solani on dry bean and soybean root rot. C. ESTEVEZ DE JENSEN (1), D. Wang (2), J. Kurle (1), and J. Percich (1). (1) Dept. Plant Pathology; (2) Dept. Soil Water & Climate, University of Minnesota, St. Paul, MN 55108. Publication no. P-2004-0008-SOA.
The combined influence of bulk density (BD) and inoculation with Fusarium solani f. sp. phaseoli on soybean and dry bean growth and development was evaluated under greenhouse conditions. Field soil, obtained from the surface (0-15 cm) of a Verndale sandy loam, was pasteurized, air dried and brought to 20% gravimetric water content. Treatments consisted of soil packed to BD: 1.3, 1.6, and 1.7 g/cc, and a compacted layer (1.7 g/cc) located in the middle section of the pot. Half of the pots were inoculated with F. solani and the remaining were pathogen free. Dry bean ‘Montcalm’ and soybean ‘Jim’ were sown separately. Disease severity (DS) (scale 1-9, 9 is most severe) in dry bean grown in soil infested with F. solani increased (4.4, 6.9, and 7.5) as soil BD increased (1.3, 1.6, 1.7 g/cc respectively). The presence of a compacted layer also increased DS (5.4). BD also increased DS in soybean. Dry bean and soybean biomass in F. solani infested soil were reduced as BD was increased from 1.3 to 1.7 g/cc. In pathogen free soil, BD decreased both dry bean and soybean biomass, but the reduction was less than in the infected soil. Less water uptake occurred in plants with root rot than those growing in pathogen free soil. The detrimental effect of high soil BD and F. solani were additive.
Mechanical transmission has contributed to the spread of bacterial wilt on tobacco. B. A. FORTNUM and D. A. Kluepfel. Dept. Plant Pathology and Physiology, Clemson University, Clemson, SC 29634-0377. Publication no. P-2004-0009-SOA.
Bacterial wilt, caused by Ralstonia solanacearum, is an extremely damaging disease of flue cured tobacco. Bacterial wilt incidence in South Carolina, expressed as the % of fields with bacterial wilt, has increased from 0.2% in 1981 to 33% in 2001. Consolidation of tobacco allotments from 24,000 in 1981 to less than 4,000 in 2001 has resulted in larger farming units, and increased mechanization in flower and leaf removal. The role of mechanical flower and leaf removal in the spread of bacterial wilt was evaluated in randomized complete block factorial experiments in large-scale on-farm trials. Main blocks were method of flower or leaf removal (hand vs. mechanical) and subplots were tobacco variety (K 326 vs. K 346). Mechanical flower or leaf removal spread R. solanacearum from infected plants to healthy plants (P = 0.001). Host resistance (K346) did not reduce the spread of the disease through mechanical topping when compared to the susceptible control (K 326, P = 0.05). Surveys of farm equipment (2000, 2001) detected pathogenic isolates of R. solanacearum on 60% of sampled tobacco harvesters (defoliators), and stalk cutters. The role of mechanization on the observed epidemics of bacterial wilt in the southeastern USA will be discussed.
Reduction of Phytophthora capsici populations in Florida by soil solarization in autumn. R. D. FRENCH-MONAR (1), J. B. Jones (1), and P. D. Roberts (2). (1) Plant Pathology Dept., Univ. of Florida-IFAS, Gainesville, FL 32611; (2) Plant Pathology Dept., Univ. of Florida-IFAS, Southwest Florida Res. & Ed. Ctr., Immokalee, FL 34142. Publication no. P-2004-0010-SOA.
Field studies were conducted during autumn 2002 in southwest Florida to evaluate the effects of soil solarization on inoculum of Phytophthora capsici. Treatments included soil solarization and a non-solarized plastic mulch control. Microwaved soil, infested with oospores and mycelia grown in wheat seed, was placed in acrylic membrane envelopes and buried 15 cm in each of six repetitions per treatment. Six envelopes per treatment were sampled at 0, 5, and 13 weeks after solarization. Using soil dilution plating (SDP), P. capsici was not detected at all in the solarization samples, but was detected in 100, 0, and 33% of the control samples for weeks 0, 5, and 13, respectively. However, using a modified SDP technique (MSDP) in which a layer of clarified V8 juice agar amended with antibiotics was added to each SDP plate 4 days after plating with observations after an additional 4 days, P. capsici was detected in 100, 83, and 100% of control samples and in 100, 83, and 83% of solarization samples in weeks 0, 5, and 13, respectively. Although inoculum was detected equally in both treatments with MSDP, inoculum populations in the solarization samples were on average 140, 45, and 840% lower than that of the control samples for weeks 0, 5, and 13, respectively. Autumn solarization may be a useful practice for managing populations of P. capsici in soil.
Carrot rot by two fungi in the state of Mexico, Mexico. L. FUCIKOVSKY. Instituto de Fitosanidad, Colegio de Postgraduados, Montecillo-Texcoco, Edo. de México, C.P. 56230, México. Publication no. P-2004-0011-SOA.
The city of Tenango in the Toluca valley is one of the important areas of carrot production and close to Mexico City market with a population of about 20 million. The valley is situated at 2,600 m above sea level, where the sowing time is in late summer and fall and the vegetable is harvested during the winter. The carrots are washed in bins, placed into bags of 20-30 kg and sold for 20-30 pesos to private consumers or wholesalers. The carrots are used as a vegetable or for sweet juice extraction. Two bags as representative samples from eight were bought and analyzed. About half of the contents were rotted after few days when stored at 18-20°C, mainly by a massive attack of Geotrichum sp., alone and in combination with Rhizopus sp. Contamination with the fungi occurred in the field or in the bins during handling. Some bacteria were present, but no soft rot erwinias were detected. Geotrichum was inoculated onto carrots, and soft rot was produced under high humidity. Geotrichum isolates have been implicated by others in serious human respiratory conditions. This is a second report of a soft rot produced by Geotrichum on carrots in the state of Mexico and prevention measures should be taken in the future.
Influence of soybean cyst nematode on sudden death syndrome development in field microplots. S. L. GIAMMARIA, C. B. Boger, and J. C. Rupe. Department of Plant Pathology, University of Arkansas, Fayetteville, AR 72701. Publication no. P-2004-0012-SOA.
The soybean cyst nematode (SCN), has often been associated with soybean sudden death syndrome (SDS) in the field. Co-inoculations with SCN and the SDS pathogen, Fusarium solani f. sp. glycines, have resulted in more rapid and severe disease development. To determine the effect of cultivar resistance to one or both of these pathogens, a microplot study was conducted in 2002. Four cultivars - Pioneer 9594, resistant to SDS and susceptible to SCN, Asgrow 5603, resistant to SCN and susceptible to SDS, Hartwig, resistant to both pathogens, and Essex, susceptible to both pathogens - were inoculated with either the fungus, the nematode, both, or not inoculated. Disease was rated twice a week after flowering. SDS was highest for Essex followed by Pioneer 9594 and then Asgrow 5603. With each of these cultivars, SDS was greater in the co-inoculated plots than the plots inoculated with just the fungus irrespective of the cultivar’s reaction to SCN. Although SCN increased SDS in all cultivars except Hartwig, in which no disease developed in any treatment, the relative rankings between the cultivars did not change.
Bacterial leaf blight and bulb rot of onion in Peru caused by Pantoea agglomerans and P. ananatis. R. D. GITAITIS (1), F. H. Sanders (1), R. R. Walcott (1), and D. Burrell (2). (1) Dept. of Plant Path., Univ. of Georgia, Tifton, GA 31793; (2) Vidalia Labs Int., Inc., Collins, GA 30421. Publication no. P-2004-0013-SOA.
A large number of sweet onions (Allium cepa L.) in Peru had blighted leaves in the field and unacceptable bulbs during grading in 2002-03. Bacteria isolated from infected tissues were gram-neg., yellow-pigmented and rod-shaped, and utilized glucose in an oxidative and fermentative manner. Fatty acid analysis, substrate utilization patterns, indole and nitrate reductase reactions, and PCR tests identified strains as Pantoea agglomerans and P. ananatis. Isolates of both species were pathogenic when inoculated onto onion seedlings, cvs. Pegasus and Sweet Vidalia. Most P. agglomerans strains from Peru fermented lactose in litmus milk and produced acid in peptone. Most P. agglomerans strains from Ga. were proteolytic in litmus milk and produced alkaline reactions in peptone. All P. ananatis strains were proteolytic in litmus milk. P. ananatis strains from Ga. and Peru produced acid and alkaline reactions, respectively, in peptone. Production of acid in peptone raises concern about validity of reports of positive utilization of certain sugars in some strains when the Hugh-Leifson method is used.
Suppression of peanut leaf spot with tillage practices, resistant genotypes and reduced fungicide regimes. S. K. GREMILLION (1), A. K. Culbreath (1), J. W. Todd (1), and R. Pittman (2). (1) The University of Georgia, Coastal Plain Expt. Stn., Tifton, GA 31793; (2) USDA-ARS, Georgia Expt. Stn., Griffin, GA 30223. Publication no. P-2004-0014-SOA.
A field experiment was conducted in 2002 to determine the effects of tillage practices, new breeding lines and fungicide regimes on early leaf spot (Cercospora arachidicola) and late leaf spot (Cercosporidium personatum) of peanut (Arachis hypogaea). Fungicide regimes were as follows: 1) nontreated control; 2) tebuconazole, 0.126 kg ai/ha, (TEB) at first appearance of leaf spot; 3) TEB at first appearance of leaf spot + 2 wk later; 4) TEB at first appearance of leaf spot + 2 wk later + 4 wk later; and 5) TEB applied at 2 wk intervals full season beginning 40 days after planting. Cultivars MDR-98, C-99R, Ga. Green, and Bayo Grande, and breeding lines RP-01, RP-08, RP-14, and RP- 20, developed from crosses of MDR-98 and Bayo Grande, were planted in strip and conventional tilled soils. Ga. Green had more severe leaf spot than the other genotypes. Leaf spot was less severe in strip-tilled plots. All fungicide spray regimes reduced incidence of leaf spot compared to non-sprayed plots. Best control was in plots sprayed on the 14-day schedule for all genotypes.
Performance of Quintec 2SC and Gavel 75DF fungicides in the Southern USA. R. A. HAYGOOD, J. E. Eger, V. B. Langston, and R. M. Huckaba. Dow AgroSciences LLC, 9330 Zionsville Rd., Indianapolis, IN 46268. Publication no. P-2004-0015-SOA.
Quintec 2 SC fungicide (quinoxyfen) is a new product for control of powdery mildew on grapes, strawberries, vegetables and other crops. Field trials demonstrated effective and consistent performance of Quintec. This protectant fungicide, which offers a new mode of action, leads to new options for mildew control and fungicide resistance management. Gavel 75DF (a premix formulation of zoxamide and Dithane Brand mancozeb in a 1:8 ratio, respectively) is a new product for control of early and late blight on potato and tomato and downy mildew on cucurbits. Zoxamide is a new active ingredient with activity against oomycete species. Studies were conducted to evaluate the performance of Gavel versus other commercially available fungicides against late blight of potato and tomato caused by Phytophthora infestans and downy mildew on cucurbits (Pseudoperonospora cubensis). Results indicated that Gavel at 1.5 lb ai/A applied on a 7 to 10 day schedule provided effective control of these diseases. Both products are registered in Europe and Gavel was recently registered in the USA. Quintec registration in the USA is pending.
Effect of delayed applications of chlorothalonil, tebuconazole, and pyraclostrobin on peanut early leaf spot. M. T. HEATH, A. K. Culbreath, and T. B. Brenneman. Dept. Plant Pathology, University of Georgia, Coastal Plain Expt. Station, P.O. Box 748, Tifton, GA 31793-0748. Publication no. P-2004-0016-SOA.
Field tests were conducted in Tifton and Plains, GA in 2001 and 2002 to compare the effects of three fungicides applied with varying spray initiation delays on early leaf spot (Cercospora arachidicola) of peanut (Arachis hypogaea). Application regimes included spray initiation dates of ca. 30, 45, 60, 75, 90, and 105 days after planting with three fungicides, pyraclostrobin (168 g a.i./ha), chlorothalonil (1.26 kg a.i./ha), tebuconazole (227 g a.i./ha) and a nontreated control. Full season treatments received seven applications. Leaf spot was rated using the Florida 1-10 scale. In both years and locations, pyraclostrobin provided better control of early leaf spot than the other fungicides when initial applications were the same. Control provided by pyraclostrobin sprays initiated 75 days after planting in 2001 and 90 days after planting in 2002 was as good as that of chlorothalonil or tebuconazole sprays initiated 30 days after planting. Differences in leaf spot control appear to be due to curative activity of pyraclostrobin.
The Texas citrus budwood certification program. C. J. KAHLKE and J. V. da Graça. Texas A&M University-Kingsville Citrus Center, Weslaco, TX 78596. Publication no. P-2004-0017-SOA.
A program to produce virus-free citrus in TX began in 1993, mainly in response to the threat of citrus tristeza virus (CTV) & its efficient vector, the brown citrus aphid (BrCA). CTV has destroyed millions of trees on sour orange (SO) rootstock in other citrus growing areas. Over 95% of commercial citrus grown in TX is on SO rootstock, & CTV is present at approximately a 1% infection rate, with no obvious disease symptoms. The arrival of the BrCA in TX is imminent. The major CTV-tolerant rootstocks are susceptible to other diseases, many of which are present in TX. Therefore, it is best to establish a virus-free program. Virus-free trees are produced through shoot-tip grafting, while virus-free status is ensured through biological and laboratory tests. Virus-free trees are mass propagated & made available to growers after horticultural evaluation for trueness to type & fruit quality. Currently, we have enough virus-tested budwood of the major commercial cultivars, & varying quantities of budwood of numerous virus-free non-commercial cultivars imported from CA. As sufficient budwood of many cultivars is now available, & horticultural evaluation has been done, the Texas Department of Agriculture will soon exercise the authority to make mandatory the use of certified virus-tested sources for the propagation of citrus in TX.
Association of Fusarium moniliforme with hardlock of cotton in the southeastern United States. J. J. MAROIS (1) and D. L. Wright (2). (1) Dept. Plant Pathology; (2) Dept. Agronomy, N. Florida Res. and Ed. Ctr., Univ. of Florida, Quincy, FL 32351. Publication no. P-2004-0018-SOA.
Hardlock is a severe disease of cotton in the Coastal Plains of the southeastern United States. It is most severe when high temperatures and high humidity occur during the growing season. Symptoms include hollow seed, discolored fiber, and fiber that does not fluff out from the bolls after opening, making it difficult or impossible to harvest with mechanical pickers. A series of isolations in 1999 and 2000 indicated that Fusarium moniliforme was associated with the symptoms. Inoculation of flowers during bloom increased disease in 2001 and 2002. Applications of thiophanate-methyl (dimethyl[1,2-phenylene)-bis(iminocarbonothioyl)] bis[carbamate]) reduced disease from 62% to 35% and increased yield of cotton lint from 716 to 1366 kg/ha. In 2002, temperature and relative humidity during 700 to 1900 on the day of bloom was correlated with disease incidence (percent disease = 0.67862 + temperature*0.08444 + relative humidity*0.01404, P < 0.005, r = 0.935, n = 7).
Efficacy of fungicides for Rhizoctonia root rot control on Catharanthus roseus (Vinca). A. D. MARTINEZ-ESPINOZA, D. S. Mueller, and J. W. Buck. Dept. of Plant Pathology, University of Georgia, Griffin, GA 30223. Publication no. P-2004-0019-SOA.
Root rots of ornamental plants are important plant disease problems in landscapes and nurseries. Rhizoctonia solani is commonly associated with reduced growth, poor flower onset and quality, and plant death. Several fungicides to control Rhizoctonia root rot in vinca were evaluated. Fludioxonil (Medallion), mefenoxam (Subdue Maxx), azoxystrobin (Heritage), mefenoxam + azoxystrobin (Subdue Maxx + Heritage), fludioxonil + mefenoxam (Hurricane), and etridiazole + thiophanate methyl (Banrot) were applied at varying rates. Vinca seedlings were drenched with fungicides and three days later transplanted to inoculated potting mix (2% v/v R. solani in V8 vermiculite). After three weeks, each plant was rated for the presence of disease using a scale of 1 to 4 (1=healthy, 4=dead). Except for one formulation, fungicide mixtures performed better than single fungicides. Hurricane treatment resulted in significantly lower root rot incidence, higher fresh weight and better plant quality, followed by Subdue Maxx + Heritage. Heritage provided root rot control at the highest rate tested, but phenologic parameters were slightly reduced when compared to Hurricane. Medallion, Banrot, and Subdue Maxx had a root rot average of 1.3, 1.8, and 3.1, respectively.
Crown and root necrosis: a new type of symptom caused by Tomato spotted wilt virus in flue-cured tobacco. N. MARTINEZ-OCHOA, A. S. Csinos, and J. H. Brock. Dept. of Plant Pathology, Univ. of Georgia, Tifton, GA 31793. Publication no. P-2004-0020-SOA.
Spotted wilt caused by Tomato spotted wilt virus (TSWV) was the most damaging disease in tobacco during 2002 in Georgia. Soon after the tobacco crop was transplanted into the field in early spring, numerous samples of 30-45 day-old plants with marked crown and root necrosis and few lateral roots attached to the tap root were sent to our disease clinic. Upon closer examination, crown and root vascular tissues were also extensively necrotic. There were few signs of typical TSWV leaf spots, and some leaves showed yellowing at the tips. All tissues (roots, crown, stem, leaves) from each sample were tested separately for TSWV by ELISA using commercial antisera. All tissues in all samples tested positive for TSWV. Crown and root necrotic tissues were surface-sterilized and plated on potato dextrose agar as well. Approximately 30% of the samples tested positive for Rhizoctonia solani. We hypothesized that TSWV severely weakened the plants and R. solani was able to colonize these tissues as a secondary pathogen. Because the newly described symptoms have not been reported from other states, their significance is not known at this time.
Effects of storage time, temperature, and age of sphacelia on viability of Claviceps africana conidia. N. MONTES (1), T. Isakeit (1), L. K. Prom (2), and G. Odvody (3). (1) Texas A&M University, College Station, TX 77843; (2) USDA-ARS, College Station, TX 77845; (3) TAES, Corpus Christi, TX 78406. Publication no. P-2004-0021-SOA.
Conidia of Claviceps africana (cause of sorghum ergot), originating from sphacelia of different ages, were assessed for survival at different storage temperatures. Intact sphacelia were collected 0, 1, 2 and 3 weeks after symptom appearance and were stored in petri dishes with silica gel at 0, 7, 14 and 21°C. Surface and interior conidia were tested monthly for viability by plating onto water agar. After one month at 21°C, viability of surface conidia from all ages of sphacelia had declined from 46% to 7%. Surface conidia stored at 0 and 7°C had no loss of viability after one month, but their viability declined to 6% after 6 months. Conidia from the interior of sphacelia stored at 0 and 7°C had 10-13% viability after 6 months. Initially, viability of surface conidia from 0 and 1-week-old sphacelia was 60%, compared with 30% for 3-week-old sphacelia, but viability of conidia from all sphacelial ages declined to 2-5% after 6 months. Conidia from inside sphacelia of all ages had a higher level (5-10%) of viability after 6 months.
Fenamidone for the control of diseases of vegetables and potato. G. H. MUSSON, J. R. Bloomberg, R. Kaiser, and R. Schwehr. Bayer CropScience, Research Triangle Park, NC 27709. Publication no. P-2004-0022-SOA.
Fenamidone is a novel fungicide derived from imidazolinone chemistry. It provides a high level of control of oomycete diseases such as downy mildews (Bremia, Peronospora, Plasmopara, and Pseudoperonospora spp.) and Pythium and Phytophthora spp. in a broad range of crops. Fenamidone penetrates tissues to provide anti-sporulant, translaminar, and curative activity. It also displays good protectant activity against Alternaria spp., Mycosphaerella spp., and to a lesser degree powdery mildews and rusts. Fenamidone in combinations and as a straight product is currently under development in over 50 countries throughout the world. First labeled uses in the U.S. are expected to be on lettuce, potato, tomato, bulb vegetables, and cucurbits. Vegetable and potato trials were conducted across the U.S. in 2002. Efficacy results from these trials will be presented.
JAU 6476 for the control of foliar and soil-borne diseases in peanuts. G. H. MUSSON, J. R. Bloomberg, R. A. Myers, and M. R. Schwarz. Bayer CropScience, Research Triangle Park, NC 27709. Publication no. P-2004-0023-SOA.
JAU 6476 (tested under the code AMS 21619) is a novel broad-spectrum fungicide belonging to the new chemical class triazolinthiones, discovered and developed worldwide by Bayer CropScience. The common name for this molecule is prothioconazole. JAU 6476 is a systemic sterol biosynthesis inhibitor showing excellent efficacy against a broad range of diseases in a variety of crops. In peanuts, JAU 6476 provides activity against most major foliar and soil-borne diseases including; early and late leaf spot (Cercospora arachidocola and Cercosporidium personatum), white mold (Sclerotium rolfsii), web blotch (Phoma arachidicola), limb rot (Rhizoctonia solani), and rust (Puccinia arachidis). Multiyear trial results indicate that JAU 6476 provides outstanding disease control along with excellent crop safety and higher yields. Efficacy data will be presented.
A novel screening technique to identify resistance to soybean sudden death syndrome. S. S. NAVI and X. B. Yang. Plant Pathology Department, Iowa State University, Ames, IA 50011. Publication no. P-2004-0024-SOA.
Sudden death syndrome (SDS) is a major soybean disease in the US. Available greenhouse techniques to identify resistance to Fusarium solani f. sp. glycines are inconsistent. We report here an effective technique for SDS resistance. Our technique involves obtaining sprouted seeds, spore suspension preparation, dip inoculation, transplanting, and evaluation. A spore suspensions was prepared by adding 20 ml distilled water to a PDA culture and disloding spores with a camel brush. Seeds germinated in paper towels were transferred @10/sterile plate. The seeds were spray-inoculated with the suspension (10(^5) conidia/ml) until dipped. 30 min later the excess inoculum was drained and the plates were incubated for 2 h at 75°F. Later, seeds at 5/pot were transplanted. The pots were placed in trays and incubated in greenhouse at 85°F in natural light. Moisture was maintained by watering trays 24 h after transplanting. Inoculated plants shown typical interveinal necrosis 15-20 d after planting, and were evaluated 10 d later for incidence and severity of SDS. Incidence reached 90% with 60-100% severity. This simple and rapid technique produced consistent results over repetitions and seasons. The study also indicated an early infection at the seed germination stage and <25 d to show symptoms.
The impact of Quadris and Headline on disease epidemics and soybean development and yield. G. B. PADGETT and W. Rea. Macon Ridge Research Station, LSU AgCenter, Winnsboro, LA 71295. Publication no. P-2004-0025-SOA.
Each year diseases adversely affect soybean profitability. In 2002, 3.5 million bushels (15% loss) were lost to diseases in Louisiana. Cercospora blight and pod diseases accounted for 40% of this loss. In an effort to manage these diseases, Quadris and Headline were evaluated for disease control, as well as their effect on soybean development. The fungicides were applied at several rates and application timings to maturity group (MG) IV and V soybean. Disease incidence was lower in soybean treated with a fungicide than in non-sprayed soybean. The majority of Headline treatments performed better than same treatment of Quadris. In general, R5 (pod elongation) applications performed better than R3 (pod initiation) applications in MG IV soybean, and performed similarly in MG V soybean. Senescence was delayed by fungicides regardless of maturity group. Seed quality was improved by late season or sequential applications of Quadris and all applications of Headline, but this did not increase yields over the non-sprayed in most fungicide treatments. Fungicides reduced disease and improved seed quality, but did not improve yield.
Diagnosis, characterization and dynamics of turfgrass diseases in the commercial and homeowner setting in Georgia in 2002. M. PEARCE, A. D. Martinez-Espinoza, and L. Burpee. Dept. of Plant Pathology, University of Georgia, Griffin, GA 30223. Publication no. P-2004-0026-SOA.
The turfgrass production and management industries in Georgia are rapidly growing in number and types of services. There are 1.6 million acres of turf in Georgia with a maintenance value of $1.56 billion. Based on disease clinic samples, turfgrass accounted for 706 out of 2413 samples submitted. Commercial turfgrass samples totaled 431 and homeowner samples totaled 275. Most turf samples were received in June, July, and August representing 26%, 33%, and 29% of the total respectively. Pathogens diagnosed and isolated included Rhizoctonia spp., Curvularia spp., Colletotrichum graminicola, Gaeumannomyces spp., and Pythium spp. Curvularia and Collectotrichum were observed more often on Centipedegrass and Zoyiagrass throughout Georgia and Rhizoctonia was diagnosed more on Bermudagrass and Zoysiagrass in Central Georgia. Gaeumannomyces was found primarily in southern and coastal Georgia on St. Augustinegrass and Centipedegrass. Pythium spp. were particularly aggressive on highly maintained turfgrass from golf courses and sod farms. Pythium spp. accounted for 64% of bentgrass disease and 40% of total commercial turfgrass disease. Pythium spp. were significantly lower in homeowner samples with only 12% diagnosed. The results indicate a pathogen disparity between commercial turfgrass and home lawns.
Ultrastructural and cytochemical aspects of silicon-mediated rice blast resistance. F. Á. RODRIGUES (1), N. Benhamou (2), L. E. Datnoff (3), J. B. Jones (1), and R. R. Bélanger (2). (1) Univ. of Florida-IFAS, Plant Pathology Dept., Gainesville, FL 32611; (2) Dépt. de Phytologie, Université Laval, Québec, Canada G1K 7P4; (3) Univ. of Florida-IFAS, Everglades Res. & Ed. Ctr., Belle Glade, FL 33430. Publication no. P-2004-0027-SOA.
Although application of silicon (Si) is known to reduce rice blast, the probable hypothesis underlying this phenomenon has been confined to that of a mechanical barrier resulting from Si polymerization in planta. We provide the first cytological evidence that Si-mediated resistance to rice blast correlates with specific leaf cell reaction that interfered with the development of Magnaporthe grisea. Accumulation of amorphous material was a typical feature of cell reaction to infection by M. grisea in samples from plants with Si which resulted in a reduced fungal colonization. In samples from plants without Si, the fungus grew actively and colonized all leaf tissues. Cytochemical labeling of chitin revealed no difference in the pattern of chitin localization over fungal cell walls in samples from plants with or without Si at 96 h after inoculation, which indicates limited production of chitinases by the rice plant. The presence of empty fungal hyphae, surrounded or trapped in amorphous material, in samples from plants with Si suggests that phenolic-like compounds or phytoalexin(s) played a role in rice defense response against infection by M. grisea. This finding brings new insights into the complex role played by Si in the nature of the rice blast resistance.
Effect of fungicide seed treatment on soybean establishment. M. L. ROSSO, C. Boger, G. Bates, C. Rothrock, T. Kirkpatrick, and J. Rupe. Dept. Plant Pathology, University of Arkansas, Fayetteville, AR 72701. Publication no. P-2004-0028-SOA.
Seedling diseases caused by Pythium spp. and other pathogens can significantly reduce soybean stands and seedling vigor. To determine the effects of cultivar resistance to Pythium spp., fungicide seed treatment, soil saturation, and seed vigor on stand establishment, tests were planted on three dates at five locations in Arkansas. Stilletto (metalaxyl, thiram and carboxin), a broad-spectrum fungicide, was the most effective fungicide across location and planting dates. Metalaxyl was more effective with the cultivar Hutcheson (Pythium-susceptible) than Archer (Pythium-resistant). Root discoloration was lower on Archer than Hutcheson for 8 of 32 tests evaluated for root disease symptoms. Other fungicides effective against Rhizoctonia solani and Fusarium spp. were occasionally effective. Soil saturation at emergence reduced stands, but fungicide seed treatment did not fully restore stands, suggesting the role of abiotic factors in stand loss. Low seed quality reduced stands. In some cases, fungicide seed treatments were effective in low, but not high, quality seed lots.
Influence of seeding rate and row pattern on peanut microclimate. L. E. SCONYERS (1), T. B. Brenneman (1), K. L. Stevenson (2), and B. G. Mullinix (3). Plant Path., University of Georgia, (1) Tifton, GA 31793; (2) Athens, GA 30602; (3) Exptl. Statistics, Tifton, GA 31793. Publication no. P-2004-0029-SOA.
The influence of peanut Arachis hypogaea seeding rate (6.2 - 22.6 seed/m) and row spacing (twin vs single) on microclimate was evaluated for 3 years in conventional field plots. All analyses included a covariance adjustment for ambient air temperature and relative humidity (RH). There were no significant (P < 0.05) differences in temperature or RH among seeding rates of 6.2 - 22.6 seed/m or between row patterns. The effect of seeding rate on microclimate in two cultivars with different growth habits was also evaluated in microplots. There were small but significant quadratic and cubic seed spacing effects on temperature for ‘Georgia Browne’ and ‘MDR-98’, respectively. There were no significant differences in microclimate between these cultivars, although there were differences in canopy architecture and main stem height (‘MDR-98’ being 3 cm taller than ‘Georgia Browne’). The increased severity of stem rot Sclerotium rolfsii observed with higher seeding rates and in MDR-98 is not primarily due to differences in microclimate.
Fungicide performance against strobilurin-resistant populations of Didymella bryoniae on watermelon. K. W. SEEBOLD (1), D. B. Langston (1), and K. L. Stevenson (2). University of Georgia, Dept. of Plant Pathology, (1) Tifton, GA 31793; (2) Athens, GA 30602. Publication no. P-2004-0030-SOA.
Resistance to strobilurin fungicides in populations of Didymella bryoniae, causal agent of gummy stem blight, is widespread in Georgia and has resulted in a number of recent disease control failures. Two experiments were conducted in the spring and summer of 2002 to evaluate the efficacy of strobilurin fungicides alone, tank-mixed with chlorothalonil (CH), or alternated with chlorothalonil, or a pre-mix of cyprodinil plus fludioxonil (Switch) against strobilurin-resistant populations of the pathogen on watermelon. Applications were made on a 7-day schedule using a backpack sprayer. In both experiments, disease severity (evaluated as the area beneath the disease progress curve) in plots treated with strobilurins alone did not differ from the untreated control. Azoxystrobin (0.9 L/ha) alternated with 2.3 L/ha of CH was not effective against gummy stem blight, but the two materials tank-mixed reduced disease severity by 60%. Chlorothalonil alone (2.3 L/ha) performed similary to the azoxystrobin-CH tank mix. No differences in disease severity were found for either CH alternated with Switch (0.99 kg/ha), three applications of CH followed by two applications of Switch, or CH alone. Strobilurins should be tank-mixed with CH if used in disease management programs where strobilurin resistance is prevalent.
University of Florida’s plant medicine program. A. J. SILAGYI and R. J. McGovern. Univ. Florida, Plant Medicine Program, Gainesville, FL 32611. Publication no. P-2004-0031-SOA.
The University of Florida has taken a bold step in teaching crop health management with the creation of the Plant Medicine Program leading to a Doctorate in Plant Medicine (D.P.M.). This innovative program offers students an extensive multidisciplinary approach to solving the challenges of crop production. Extensive coursework in the Plant Sciences, Entomology, Plant Pathology, and Nematology provides students with the fundamental knowledge needed to be successful problem solvers and decision makers. Alongside academic and industry professionals, students apply their expertise to practical situations during multiple internships. In Florida and elsewhere, interns have worked on a wide variety of crops with private corporations, public institutions, and government agencies, in research, regulatory, and extension capacities. Students have the opportunity to tailor their program to reflect specific interests while maintaining a strong foundation in the core courses. Since its inception in 1999, enrollment in the D.P.M. program has grown to over 40 students, and beginning in 2003 graduates will become valued members of the global agricultural community.
Susceptibility of southern highbush blueberry cultivars to Botryosphaeria stem blight. B. J. SMITH. USDA-ARS, Small Fruit Research Station, Poplarville, MS 39470. Publication no. P-2004-0032-SOA.
Stem blight, caused by the fungus Botryosphaeria dothidea, is a destructive disease of rabbiteye and highbush blueberries in the southeastern United States. The susceptibility of 20 southern highbush, two rabbiteye, and two highbush cultivars were compared using a detached stem assay. Fresh isolates of B. dothidea obtained from infected southern highbush blueberry plants were used as inoculum. Succulent, partially-hardened stems were surface disinfected, wounded by scraping away a section of bark, and inoculated by covering the wound with a mycelial agar block of B. dothedia and securing with parafilm wrap. The base of each stem was inserted into moistened, sterilized sand in a 150 × 25 mm tissue culture tube and incubated at 25°C, 100% RH for 30 days. Lesion length was measured after 15 days incubation. Cultivars with the shortest mean lesion length were classified as apparently resistant and included Pearl River, Emerald, Star, Sharpblue, Elliott, Misty, Bluecrisp, Darrow, Southmoon, Ozarkblue, Sapphire, and Brightwell. Cultivars with the longest lesions were classified as apparently susceptible and included Legacy, Gulf Coast, Cooper, Georgiagem, O’Neal, Reveille, Jubilee, and Magnolia. Tifblue, Windsor, Biloxi and Santa Fe were classified as tolerant.
Managing the race structure of the tobacco black shank pathogen. M. J. SULLIVAN, T. A. Melton, and H. D. Shew. Dept. Plant Pathology, NC State University, Raleigh, NC 27695. Publication no. P-2004-0033-SOA.
Deployment of tobacco varieties with single-gene, complete resistance to race 0 of Phytophthora parasitica var. nicotianae has increased field populations of race 1 in NC. Tobacco varieties with high or low levels of partial resistance were rotated with a variety with complete resistance to race 0 to assess the effects on pathogen race structure and disease development in fields containing single or mixed races. Populations of race 1 decreased relative to race 0 populations when varieties with partial resistance to both races were planted, suggesting that race 1 isolates were not as fit as race 0 isolates under field conditions. Rotation of partial and single-gene resistance may thus minimize disease losses while slowing changes in the pathogen race structure. Under greenhouse conditions, race 0 isolates were more aggressive than race 1 isolates on varieties with moderate or high levels of partial resistance. Symptoms, including lesion development, chlorosis, wilting, and root rot, developed sooner and were more severe after 3 weeks with race 0 isolates. Isolates of race 1, however, caused greater stunting of plants than race 0 isolates.
CAY-1, A potential natural fungicide for control of small fruit diseases. D. E. WEDGE (1), K. J. Curry (2), M. Abril (2), B. J. Smith (3), and A. DeLucca (4). (1) USDA-ARS, Natural Products Utilization Res. Unit, University, MS 38677; (2) Dept. of Biol. Sci., Univ. of So. Mississippi, Hattiesburg, MS 39404; (3) USDA-ARS Small Fruit Res. Sta., Poplarville, MS 39470; (4) USDA-ARS So. Regional Res. Ctr., New Orleans, LA 70179. Publication no. P-2004-0034-SOA.
CAY-1 is a fungicidal steroidal saponin (MOL WT 1243) isolated from the ground fruit of cayenne pepper (Capsicum frutescens). CAY-1 is lethal to germinating conidia of Aspergillus flavus, A. fumigatus, A. parasiticus and A. niger. It is also active against agricultural and medicinally important fungi and yeast. In vitro dose-response assays with CAY-1 against plant pathogenic fungi showed that 3.0 microM inhibited growth of Colletotrichum gloeosporioides and C. acutatum by 100 percent and C. fragariae, Phomopsis obscurans, and P. viticola by 90 percent. Detached leaf assays using strawberry leaves from anthracnose susceptible cv. Chandler demonstrated that CAY-1 decreased C. fragariae induced lesion number by 95 percent compared to the untreated control. Dose-response data indicated that CAY-1 appeared to be more active than azoxystrobin in disease control of C. fragariae induced anthracnose leaf spot.