Farm406

farm406 58 A number of viruses can infect pulse crops. e symptoms of infection can be subtle and easily confused with other disorders, including nutritional deficiency or herbicide damage, or ignored completely (Figure 13). Viral diseases are much more common in the Pacific Northwest, and are more severe in years when aphid populations are high. A common vector for many of these diseases is the pea aphid (Acyrthosiphon pisum). Montana has been relatively free of viral issues thus far, which is an advantage of growing pulse crops here. However, in a year when aphids are high we may see many of these viral issues. e pea aphid aacks pea, lentil, chickpea, alfalfa, clover, and some leguminous weeds. e aphid can cause direct damage by feeding on plants, but it also vectors several important viruses: Bean leaoll virus (BLRV), Pea enation mosaic virus (PEMV), and Pea streak virus (PeSV). e University of Idaho has an 'aphid tracker' website at www.cals. uidaho.edu/aphidtracker/trackerindex.asp with information on pea aphid thresholds and management. Alfalfa is a very good host of the pea aphid, so exercise caution when planting near alfalfa. It is favored by temperatures of 68 to 75°F and high relative humidity (95 percent or more). Flowers commonly drop from the plant and cause significant losses (Figure 11). e pathogen can also cause a seedling so-rot of chickpea, which is the result of seedborne inoculum. B. cinerea has a very wide host range that includes over 100 plant species including crops and weeds. e pathogen enters a field via seed infection, infested soil and plant debris. e fungus survives on infected seed for up to five years and in chickpea stubble for nearly a year. It also survives on plant debris and in the soil as environmentally resistant sclerotia and chlamydospores. Resistant varieties, compact and erect cultivars, wide row spacing, intercropping with non-hosts such as wheat, reducing irrigation, crop rotation, and deep plowing help manage disease. Seed treatment fungicides including thiabendazole (Mertect) can reduce seedborne inoculum. White mold (Sclerotinia sclerotiorum, S. trifoliorum and S. minor) has a very broad host range (bean, mustard, potato, sunflower, etc.) and infects many broadleaf crops and weeds. It oen enters fields in contaminated seed lots or equipment. Spores can also be windborne short distances from ditches or neighboring fields. It survives as a mass of fungal hyphae covered by an environmentally resistant black rind called a sclerotia. When conditions are favorable, such as at canopy closure when humidity levels in the canopy are high and the crop begins flowering, an inverted mushroom structure called an apothecium produces ascospores which infect the flowers. Hyphae can also grow directly into plant tissues, especially if there is plant-soil contact. e fungus will kill tissue and fill the stem with white hyphae and sclerotia, which then survive in the soil for many years (Figure 12). Sclerotia can be buried with tillage, but repeated tillage will bring them to the soil surface again. Boscalid (Endura) and prothioconazole (Proline) are registered for management of white mold and should be applied at the flowering stage of growth. Check label restrictions before application. Limited variety resistance may be available in dry pea and lentil cultivars. No resistance has been observed among chickpea cultivars. White mold is more common in winter-sown lentils than spring lentils due to their exposure to prolonged wet and cool spring weather. FIGURE 11. A lentil field infected with Botrytis grey mold. FIGURE 12. Symptoms of white mold on chickpea stems. Photo: Michael Wunsch Photo: Weidong Chen, USDA-ARS, WSU VIRAL PLANT PATHOGENS

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