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Late Planted and/or Maturing Corn, Watch Out!!– (John Obermeyer, Rich Edwards, and Larry Bledsoe)
Suddenly there’s a surge of moth activity that should concern producers with corn that is late in development. Corn earworm and second generation European corn borer moths are becoming quite numerous in pheromone and black light traps. Both of these species are attracted for egg laying to fields that are actively pollinating. This is especially a concern in late maturing seed corn or late-market sweet corn fields. Monitoring for these pests in these fields should commence immediately. Though sampling schemes for these two species differ, they both involve monitoring for moths and eggs, which is tedious and time consuming. Waiting for larval emergence and damage to show up is too late! Though we have not heard much about fall armyworm as of yet, it too will be attracted to later developing corn. High risk fields are typically bottomland fields that have been planted extremely late. Fortunately, fall armyworm damage is almost always spotty in fields, which means it usually looks worse than it really is. Monitor Soybean for Rootworm Beetles Now– (John Obermeyer, Rich Edwards, and Larry Bledsoe)
Ron Blackwell, IPM Surveyor, is actively sweeping soybean fields to sample for western corn rootworm beetle populations. Stay tuned to future Pest&Crop issues as we report the catches by county. Pest managers have been reporting the western corn rootworm variant making its move from corn to soybean fields in many areas of Indiana. Knowledge of beetle numbers in soybean helps one to gauge the potential risk of rootworm damage to next year’s corn. Few beetles mean low risk, thus little need for rootworm protection next year. Lots of beetles means higher risk, and the insecticide “insurance” will likely pay off. Several producers and agribusiness personnel throughout the state have initiated a sampling program for their soybean fields. Because of the variability of beetle numbers from field to field, those willing to inspect soybean now may reap the benefits next spring. Sampling for rootworm beetle in soybean fields does not require sticky traps or sweep nets, but they do make decision making more accurate. Visual inspections during the morning hours, while walking through the field and carefully observing the upper canopy, should help you reach a management decision. Soybean fields should be visited weekly until early September. A full color PDF fact sheet on monitoring soybean with yellow sticky traps is available on-line at <http://www.entm.purdue.edu/entomology/ext/targets/e-series/EseriesPDF/E-218.pdf> |
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Poisonous Plants Reprise– (Glenn Nice and Thomas Bauman) We have been getting some phone calls about problems with toxic plants. Many of the plants regarded as weeds in pastures or roadsides can cause pathology in livestock and pets. Often the toxicity of a plant is only exhibited in certain conditions, or with certain plant parts. Below is a list of some of the more common toxic plants covered in “Indiana Plants Poisonous to Livestock and Pets” (WS-9) that can be classified as weeds. To access this publication I welcome you to visit this web address, <http://www.vet.purdue.edu/depts/addl/toxic/cover1.htm>.
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Corn Anthracnose– (Gregory Shaner)
Last year, anthracnose stalk rot was widespread on corn in Indiana. Will we have a problem again this year? We can look to that much-loved metaphor (at least by plant pathologists), the disease triangle. This metaphor emphasizes that in order to have a serious plant disease outbreak, conditions on three sides of the disease triangle — host, pathogen, and environment – must be appropriate. We certainly have an abundant host – corn. And, based on what was seen last year, many hybrids are susceptible to anthracnose late in the season. The pathogen side of the triangle is what may be quite different from last year. The anthracnose fungus (Colletotrichum graminicola) survives in corn residue. Evidently there was enough of the fungus around last year to infect a lot of corn. This year, the fungus may be even more abundant, because residue of all of that corn that had anthracnose stalk rot last fall will contain the fungus this year. It seemed to me that the early season leaf blight stage of anthracnose was more common this spring than usual, which would support the idea that there is abundant inoculum this year. The other side of the triangle is weather. Anthracnose is favored by wet, cloudy weather. We’ve certainly been having that. Moisture favors production of spores and infection of plants. Cloudy weather seems to render plants less resistant to infection. Diplodia Ear Rot– (Gregory Shaner)
Diplodia ear rot was another late season disease of corn that was widespread last year. Diplodia ear rot is caused by a fungus now known at Stenocarpella maydis (formerly Diplodia maydis), and like the anthracnose fungus, S. maydis survives on corn residue. Stenocarpella maydis produces spores on crop residue under warm, humid conditions. The fungus can infect stalks through the crowns or roots. Ear infection may occur via silks or via husks. Shanks may also become infected, from where the fungus can invade the ear. Last year, I saw severe Diplodia ear rot in a field on August 1st. Many ears had been infected through husks. Infected husks had tan lesions near the base of the ear. Even at that time, when ears were in the milky ripe stage, the fungus had progressed through the husk tissue of some ears and invaded the kernels. A white mat of fungal mycelium was evident over much of the ear. The same argument that I made about anthracnose stalk rot would apply to Diplodia ear rot. The abundance of ear rot last year means that there is probably a lot of the fungus in corn residue this summer. Thus, the risk of Diplodia this year would seem to be higher than normal. The most vulnerable period for ear infection is for about 3 weeks after silking. Gray Leaf Spot– (Gregory Shaner)
Weather over the past few weeks seems to have been ideal for gray leaf spot. Hot, humid weather, warm nights, heavy dew, and frequent rainfall are favorable for production and dispersal of spores of Cercospora zeae-maydis and for infection of corn. Gray leaf spot is certainly present, and has been for some time. However, it does not seem to be developing as rapidly as might be expected given the weather we have been having. Sudden Death Syndrome– (Gregory Shaner)
In earlier issues of this newsletter, I discussed the likelihood that we would see sudden death syndrome in soybeans this year. Symptoms are now appearing in many fields. Based on my limited windshield survey, most fields do not show symptoms (at least not symptoms that can be seen from the road while driving by at 50 mph). However, a number of fields do have symptoms that can be seen during a fast drive-by. Closer inspection of these fields reveals that diseased plants have not quite reached the stage where leaflets are dropping, but the interveinal chlorosis and necrosis are evident. When I dug up symptomatic plants, I could see small patches of light blue on the surface of the taproot just below the soil surface. These are masses of spores of the SDS fungus, Fusarium solani f. sp. glycines. Cutting into the lower stem revealed the characteristic brown streaking in the cortex, while the pith remained white.
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