New Strategies for Management of Vegetable Diseases in Organic and Traditional Farms

• 2004 annual report
• 2005 annual report

Summary

Phytophthora blight, caused by Phytophthora capsici, is the most serious threat to production of cucurbits and peppers in the North Central region in the United States. Integrated disease management practices developed in this research effectively minimize crop losses of cucurbits and peppers caused P. capsici. An integrated approach of seed-treatment, disking the localized infected areas, and fungicide applications is effective for controlling of Phytophthora blight in cucurbit fields. Phytophthora blight of pepper is effectively controlled by either planting identified resistant varieties or application of fungicides. Red-light treatment is effective for controlling Phytophthora blight in greenhouses.

Introduction:

Introduction Among all states, Illinois ranks first in pumpkin production (2). Approximately 21,000 acres of farmland in Illinois are planted to pumpkins annually. More than 90% of the commercial processing pumpkins (Cucurbita moschata) in the United States (US) are produced on approximately 10,000 acres and processed in Illinois (3). Jack-o-lantern pumpkins are produced in more than 11,000 acres throughout Illinois. In addition, approximately 10,000 acres in Illinois are in production of cucumbers, gourds, melons, squashes, watermelons, eggplants, peppers, and tomatoes (1,2). Peppers are produced in about 1,000 acres. Also, considerable amounts of these vegetables are produced in home gardens throughout the state. Phytophthora blight, caused by Phytophthora capsici, has become one of the most serious threats to production of cucurbit crops (cucumbers, gourds, melons, pumpkins, squashes, watermelons), eggplants, peppers, and tomatoes (2,3,4,13,20). This disease was almost unknown in Illinois before 1998. But, because of unknown reasons, the disease was in epidemics in Illinois during 1998-2003 causing up to 100% yield losses in the above-mentioned vegetables (2,3,4,13). Yield losses up to 100% in pepper, up to 30% in jack-o-lantern pumpkin, up to 100% in processing pumpkin, up to 50% in squash, and up to 80% in melon, tomato, and watermelon fields occurred (2,3). The estimated yield and product losses in Illinois to P. capsici, in pumpkins and peppers, exceeded $10,000,000 per year (2,3). P. capsici was first described on peppers in New Mexico in 1922 (21). The pathogen was subsequently reported on cucurbit crops (cucumbers, gourds, melons, pumpkins, squashes, watermelons), eggplants, tomatoes, and several other crops from vegetable growing areas in the world (2,9,20,32). The pathogen produces coenocytic diploid hyphae, sporangia, zoospores, and oospores (9). Zoospores, which are produced in abundance during the growing season, cause infection in the crops (9). Oospores, commonly produced at the end of growing season, are important in the life cycle of the pathogen both as primary survival structures and as the site of genetic recombination (9,11). This pathogen can grow and infect host plant at 11 to 35C (9,32). P. capsici is a soil-borne and airborne pathogen. It survives in the soil for many years. P. capsici can strike host plants at any time from planting through harvest (2,9,32). Symptoms produced by this pathogen include pre- and post-emergence damping-off, root rot, crown rot, stem lesions, leaf spots, foliar blight, and fruit rot (2,3,5,32). Some of the hosts (e.g., eggplants, peppers, and tomatoes) are more susceptible in early growth stages (5). Phytophthora infections develop and spread rapidly, because sporangia are produced on infected tissues and dispersed by water and air. There was no effective method available to provide adequate control of P. capsici on susceptible hosts. A recommended practice for reducing the incidence of disease in the fields was an approach of combining long-term crop rotation, sanitation, and management of field moisture (9,32). This approach did not provide adequate protection to crops against P. capsici because (i) the pathogen survives in the soil indefinitely, and (ii) in the areas with high relative humidity and/or rainfall, the management of the field moisture for control of the disease is not feasible. Other practices, including amending the soil by adding yard-waste, using cover crops, straw mulching, and soil solarization, and using antagonistic fungi for protecting crops in the fields have been investigated, but none of them have provided adequate protection against P. capsici (5,23,24,32). Fungicides might be used to protect plants against P. capsici (18,2829). However, the efficacy of fungicides in protecting the crops against P. capsici varied considerably from one area to another. It has been reported that light of long wavelengths (red region; 600-700 nm) induces strong resistance in plants against Bipolaris oryzae, Botrytis cinerea, and Alternaria tenuissima (15,17). Red-light treatment resulted in production of anti-fungal substances in leaf tissues, suppressed the germination of fungal spores. Another report indicated that red-light treatment induced anti-fungal substances in plant tissues that suppressed the germination of spores of several plant pathogenic fungi, including soilborne pathogens (16). One other report has indicated that red-light treatment induced resistance in eggplants, peppers, and watermelons, which were suppressive against P. capsici (31). A unique feature of Phytophthora species throughout the literature is the higher incidence of vegetable diseases in soils low in calcium (8,9). Calcium nutrition affects the incidence of diseases in several ways. First, Ca is essential for stability of biomembranes; when Ca is low, the efflux of low-molecular-weight compounds from the cytoplasm to apoplasm is increased. Second, calcium polygalacturonates are required in the middle lamella for cell wall stability. Most parasitic fungi invade the apoplasm by releasing pectolytic enzymes, which dissolve the middle lamella. The activity of these enzymes is strongly inhibited by Ca (7). The susceptibility of plants to infection with pathogens is therefore inversely related to the Ca content of the tissue (22). For example, preharvested pod rot in peanut, caused by P. myriotylum, has been closely linked to the Ca content of the pod tissue, and can be controlled by soil application of Ca sources, such as gypsum (10). The effects of calcium compounds on the incidence of seedling blight of pepper, caused by P. capsici (26,27), black shank of tobacco, caused by P. parasitica, (19), and Phytophthora diseases in plants in general (27,30), have been studied. References: 1. Anonymous. 2004. USDA Agricultural Statistics. USDA, National Agricultural Statistical Service, Washington, DC. Http://www/usda.gov/nass/pubslhtm. 2. Babadoost, M. 2000. Incidence and Impact of Phytophthora diseases on Illinois vegetables - SIU Horticulture Day 2000:22-25. 3. Babadoost, M. 2000. Outbreak of Phytophthora foliar blight and fruit rot in processing pumpkin fields in Illinois - Plant Diseases - 84:1345. 4. Babadoost, M. and Islam, S.Z. 2001. Seed-treatment for control of seedling death of pumpkin caused by Phytophthora capsici. 2001 annual meeting of the American Phytopathological Society (Abstract). 5. Baucher, T.J., and Ashley, R.A. 2000. Northeast Pepper Integrated Pest Management (IPM) Manual. University of Connecticut Cooperative Extension System. 136 pp. 6. Barksdale, T.H., and Papavizas, G.C. 1984. Resistance to foliar blight and crown rot of pepper caused by Phytophthora capsici. Plant Disease 68:506-509. 7. Bateman, D.F., and Lumsden, R.D. 1965. Relation between calcium content and nature of the pectic substances in bean hypocotyls to susceptibility to an isolate of Rhizoctonia solani. Phytopathology 55:734-738. 8. Brady, N.C. and R.R. Weil. 1999. The nature and properties of soils. 12th ed. Prentice Hall, NY. 9. Erwin, D.C., and Ribeiro, O.K. 1996. Phytophthora Diseases Worldwide. APS Press, St. Paul, MN. 562 pp. 10. Hallock, D.L. and Garren, K.H. 1968. Pod breakdown, yield and yield quality of Virginia type peanuts as affected by Ca, Mg, and K sulfates. Agron. J. 60:253-257. 11. Hwang, B.K., Kim, Y.J., and Kim, C.H. 1996. Differential interactions of Phytophthora capsici isolates with pepper genotypes at various plant growth stages. Korean Journal of Plant Pathology 102:311-316. 12. Illinois Specialty Growers Association. 1993. Fruit and Vegetable Statistics. Illinois Agricultural Statistics Service, USDA/IDOA. 34 pp. 13. Islam, S.Z., Babadoost, M., and Honda, Y. 2001. Red light therapy for management of seedling death caused by Phytophthora capsici in pumpkin and tomato. 2001. Annual Meeting of the American Phytopathological Society (Abstract). 14. Islam, S.Z., and Honda, Y. 1996. Influence of phototropic response of spore germ tubes on infection process in Colletotrichum lagenarium and Bipolaris oryzae. Mycoscience 37(1):331-337. 15. Islam, S.Z., Honda, Y., and Arase, S. 1998. Light-induced resistance of broadbean against Botrytis cinerea. J. Phytopathology 146(10):479-485. 16. Islam, S.Z., Honda, Y., and Arase, S. 1999. Some characteristics of red light-induced substance(s) against Botrytis cinerea produced in broadbean leaflets. J. Phytopathology 147:65-70. 17. Islam, S.Z., Honda, Y., and Sonhaji, M. 1998. Phototropism of conidial germ tubes of Botrytis cinerea and its implication in plant infection processes. Plant Disease 82:850-856. 18. Johnston, S.A. 1989. Evaluation of fungicides for the control of the foliar phase of Phytophthora blight, 1988. Fungicide and Nematicide Tests 44:117, p. 115. 19. Kincaid, R.R., Martin, F.G., Gammon, N., Breland, H.L., and Pritchett, W.L. 1970. Multiple regression of tobacco black shank, root knot, and coarse root indexes in soil pH, potassium, calcium, and magnesium. Phytopathology 60:1513-1516. 20. Latin, T., and Rane, K. 1999. Identification and Management of Pumpkin Diseases. Purdue University, BP-17. 15 pp. 21. Leonian, L.H. 1922. Stem and fruit blight of peppers caused by Phytophthora capsici. Phytopathology 12:401-408. 22. Marschner, H. 1995. Mineral nutrition of higher plants. 2nd ed. Academic Press. 23. McGrath, M.T. 1995. Evaluation of Gliocladium virens as a biocontrol agent for managing Phytophthora in cucurbits. 1994. Biological and Cultural Tests. 10:146. 24. McGrath, M.T. 1997. Evaluation of solarization and sorghum grass for managing Phytophthora crown rot and fruit in pumpkin, 1995-1996. Biological and Cultural Tests, 12:159. 25. McGrath, M.T., Superak, T.H. 1999. Susceptibility of pumpkin varieties and experimental to Phytophthora fruit rot in pumpkin, 1998. Biological and Cultural Tests, 14:173. 26. Muchovej, J.J., Mafia, L.A., and Muchovej, R.M.C. 1980. Effect of exchangeable soil aluminum and alkaline calcium salts on the pathogenicity of Phytophthora capsici from green pepper. Phytopathology 70:1212-1214. 27. Schmitthenner, A.F. and Canaday, C.H. 1983. Role of chemical factors in development of Phytophthora diseases. P. 189-196. In: Phytophthora: Its biology ecology, taxonomy, and pathology. D.C. Erwin, S. Bartnicki-Garcia, and P.H. Tsao (eds). American Phytopathological Society, St. Paul, MN. 28. Shishkoff, N., and McGrath, M.T. 1999. Evaluation of fungicides for Phytophthora fruit rot and tip blight of summer squash, 1998. Fungicide and Nematicide Tests 54:192. 29. Stevenson, W.R., James, R.V., and Rand, R.E. 2001. Evaluation of selected fungicides to control Phytophthora blight and fruit rot of cucumber, 1200. 2001 MWFPA Processing Crops Manual and Proceedings: 145-146. 30. Swiader, J.M., Ware, G.W., and McCollum, J.P. 1992. Producing Vegetable Crops. 4th ed. Interstate Publishers, Danville, IL. 31. Umezu, H., Islam, S.Z., and Honda, Y. 1999. Red light-induced resistance in some plants. Bull. Assoc. Plant Protect. Shimane pref. 24:55-57. 32. Zitter, A.T., Hopkins, D.L., and Thomas, C.E. 1998. Compendium of Cucurbit Diseases. APS Press, St. Paul, MN. 87 pp.

Objectives/Performance Target

Objective 1: Evaluate the effectiveness of plant resistance induced by red-light treatment for control of Phytophthora blight and other diseases in pumpkin, watermelon, and pepper.

Objective 2: Determine the effects of calcium on the incidence and severity of Phytophthora blight and other diseases in pumpkin, watermelon, and pepper by soil application of CaSO4 and foliar application of CaCl2.

Objective 3: Determine the efficacy of a new copper compound (Cuprofix Disperss) on controlling Phytophthora blight and other diseases in pumpkin, watermelon, and pepper.

Objective 4: Determine the effectiveness of seed-treatment for control of seedling death caused by P. capsici in cucurbit crops.

Objective 5: Determine the effectiveness of integrated approaches of red-light treatment, calcium application, cooper spray, and seed-treatment on controlling Phytophthora blight and other diseases in vegetable farms.