Drought '02 Ohio State University Extension Drought and Soybean Diseases Anne Dorrance - Extension Plant Pathologist Drought's provide an opportunity to locate those problem areas in fields. Areas of fields with poor drainage as well as high populations of soybean cyst nematode will show signs of stress first. Soybeans in these areas will appear yellow or off-color, begin to wilt and in some cases die before other areas of the field. In areas that are poorly drained, the root rotters, Phytophthora sojae, Pythium spp., Rhizoctonia and Fusarium can all gain a foothold in the plants early on when soils were moist. When soils are saturated for a long period of time, the Rhizobium that is essential for nitrogen capture in the nodules will also die. Healthy nodules are firm and pink but those from wet areas of fields (the rain that fell back in May that saturated some areas of fields) are gray and soft and easily removed from the roots. Roots from these areas of the fields have several lesions on the roots and stems, but if you take a knife and scrape the roots they are clear and healthy on the inside. Many of these root pathogens are opportunistic and are growing on the weakened roots. The exception is Phytophthora. In infected plants where the resistance gene (Rps) is not effective against that pathogen population, there will be a discolored area in the stele of the root. Soybean cyst nematode is reeking havoc on some soybeans this season. The poor growing conditions combined with cyst is more than some of these plants can stand. Fields where there are pockets of soybeans that look especially worse for the wear may be suffering from SCN as well as the weather. You can see cyst females in some of these roots. Carefully dig plants and shake the roots gently, then look for the tiny "pearls" on the roots. This will work much better in the lighter soils. Take notes on these fields - these are the ones that should be sampled for SCN this fall following harvest. SCN fields must be managed by CROP ROTATION - by keeping the SCN populations low optimal yields can be obtained. Soybean cyst nematode and one fungus, Macrophomina phaseolina, which causes charcoal rot are the only two pathogens that thrive under these drought conditions. The diagnostic key is the small black microsclerotia which can be found in the pith of the stem as well as on the seed. The last time Charcoal rot caused widespread losses in Ohio was during the 1988 drought. Soybean cyst nematode, however, is becoming more and more widespread. This little beast has great potential to build high populations which can cause substantial yield losses in a short period of time. The best time to sample soil is in the fall following harvest. C. Wayne Ellett Plant and Pest Diagnostic Clinic fees for SCN testing for a single shipment of soil samples from an individual farm the fee will be: $15.00 for the first soil sample, $10.00 for each additional soil sample in the shipment. Sampling Instructions: 1. Use a 1-inch diameter soil probe to collect soil samples (6-8 inches in depth) 2. Following a zig-zag pattern, collect 10-20 soil cores per 10-20 acres 3. Collect cores from areas of similar soil type and crop history 4. Dump cores from each 10 to 20 acre area into a bucket or tub and mix thoroughly 5. Place 1 pint (2 cups) of mixed soil in a soil sample bag or plastic zippered bag and label with a permanent marker; and 6. Store sample in cool, dark place until shipped to a lab doing SCN analysis. 7. Samples may be sent to: C. Wayne Ellett Plant and Pest Diagnostic Clinic 110 Kottman Hall 2021 Coffey Road Ohio State University Columbus, OH 43210-1087 All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status. Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension. TDD No. 800-589-8292 (Ohio only) or 614-292-1868   | C.O.R.N. | Newsletter | Ohioline | Publications |