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Silk and Pollen Snackers– (John Obermeyer and Larry Bledsoe)
Rootworm and Japanese beetles continue to emerge throughout the state, although high numbers have not yet been reported. If beetles are present in commercial cornfields during pollination, control may be necessary if the silks are clipped off to within ½ inch or less of the tip of the ear before 50% pollination is completed. It has been suggested that 5 beetles per plant can result in the need for control, however, many fields have had higher numbers during pollination with little or no silk clipping activity. This is because the rootworm beetles prefer pollen to silks for a food source. So, don’t judge the need for treatment based on beetle numbers. Highest risk fields, or areas of fields, are those that have been delayed in growth from flooding or replanting and pollination will be later than surrounding fields. Beetles will flock to these pollen-laden plants and potentially interference with fertilization by severely clipping silks. Research with inbreds in seed production fields has shown that 2 to 3 rootworm beetles per plant can significantly reduce ear fill. For additional information on rootworm beetles see Extension Publication E-49-W, Managing Corn Rootworms - 2004 (Rev. 1/04) at: www.entm.purdue.edu/entomology/ext/targets/e-series/fieldcro.htm. First Spider Mite Report Received – (John Obermeyer and Larry Bledsoe)
While some fields in the state are still draining off the excess from gully-washers a couple weeks ago, some areas could use some moisture. This became evident when I received a call from Mark Evans, Owen County Extension Educator, about spider mites in soybean. He was alerted to the mites presence by the discoloration of the plants along the field edges. His question was, can treating of borders prevent damage throughout the field? Unfortunately, there’s not an easy answer. Before considering control, it is very important that spider mites are identified as the source of the problem. Shake some discolored soybean leaves over a white piece of paper. Watch for small dark specks moving about on the paper. Also look for minute webbing on the undersides of the discolored leaves. Once spider mites have been positively identified in the damaged areas of the field, it is essential that the whole field be scouted to determine the range of infestation. Sample in at least five different areas of the field and determine how far the spider mites have moved into the field from the grassy borders by using the “shake” method. Stressed plants actually provide a better nutritional feast for spider mites thus they thrive and quickly colonize areas or whole fields. The best spider mite control is to eliminate plant stress, this easier said than done. Sandy or high clay soils will express moisture stress first in the plants, with or without the presence of spider mites. Other stresses on soybean include pests such as soybean cyst nematode or nutritional imbalances, such as manganese deficiency. Obviously the best plant stress reliever under dry conditions is rain. Rain indirectly controls spider mites. Pounding rains can physically beat spider mites off the plants where they meet their doom by drowning or to ground dwelling predators. More importantly, rains increase humidity that slows the spider mite reproduction and favors pathogenic fungi. Several days of relative humidity above 70% may induce an epizootic wiping out the spider mite population. On the other hand, warm temperatures and low humidity returning after rain may only delay the spider mite infestation. Above all else, significant rain helps the soybean crop to grow and provides less of a “protein broth” for the spider mites. Reduction of crop yield is directly related to duration and intensity of the mite attack. The most severe damage occurs when the infestation starts in the early stages of plant growth and builds throughout the season (extended drought). Before applying controls carefully consider that, depending when damage is noted, multiple insecticide applications may be necessary. This is because surviving spider mites are able to repopulate a field faster than can the natural predators that are often prevalent in infested fields. If leaf discoloration is apparent, spider mites are positively identified as the culprit, and hot, dry conditions are expected to persist, it is recommended that a control be considered. Spot treatment may be effective if infestations are caught early enough and the mites have not yet moved across the field. Success of spot treatments depends on spraying beyond the infested area, not just the discolored plants. Spray a buffer zone of at least 200 feet beyond colonized plants. If a control is warranted, two pesticides are recommended for use. These include dimethoate (Dimethoate 400 and 4 EC) and chlorpyrifos (Lorsban 4E). Proper placement of these pesticides is the key to successful control results. Nozzle pressures of 40 psi and 30-40 gallons of water per acre for ground application helps distribute the pesticide throughout the foliage. If using aerial application, the control material should be applied in 3-5 gallons of finished spray per acre. Normally, aerial applications are not as efficacious as ground applications due to limited surface-area coverage. So where possible, use ground application. Also, research has shown that mite controls work best in the early morning or evening hours. This is primarily due to more stable weather conditions, less convection currents and evaporation, resulting in better targeting of the pesticide.
Soybean Aphid Update – (John Obermeyer, Larry Bledsoe, and Bob O’Neil) We haven’t given a soybean aphid update in several weeks; no news is good news! Purdue’s soybean aphid researchers have found very low numbers of aphids in Cass, Miami, and Tippecanoe Counties. Pest managers throughout the state have reported looking for the soybean aphid and finding little to none. The elevated aphid numbers in Eastern Iowa several weeks ago apparently has subsided. It certainly is too early to write this pest off for the 2004 season, but suppressed aphids numbers and excellent soybean growth and development are certainly in our favor. FREE: Soybean Sweep Net Sampling! – (John Obermeyer) In a couple weeks we will begin our sweep net sampling of soybean fields for the presence of the corn rootworm beetle. This helps us determine the spread and/or density of the variant western corn rootworm beetles throughout Indiana and assess the risk to next year’s first-year corn. We need soybean fields to sample, generally 2-3 fields per county separated by several miles. We especially are in need of field locations in southern and central counties. We will make every attempt to share field insect counts with you once completed early this fall. If you are willing for us to sample your soybean fields, please contact me ASAP with specific locations (road intersections, GPS coordinates, marked plat book pages, etc) to: John Obermeyer |
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Weed Control Timing Issues in Roundup Ready Soybeans- (Bill Johnson, Glenn Nice, and Tom Bauman) Postemergence weed control operations in soybean should be well underway in most of Indiana. With over 85% of our soybean acres planted to Roundup Ready soybean, we have seen the use of postemergence weed control products shift from photosynthetic inhibitors (Basagran), diphenylethers (Cobra, Blazer/Status, Reflex/Flexstar) and ALS inhibitors (Scepter, Pursuit, Classic, Synchrony, etc.) to glyphosate-based products. Although we are shifting use patterns, we must still use sound judgment in selection of controllable spray application variables. Obviously, weed management strategies have shifted with the use of the Roundup Ready technology. Before Roundup Ready soybean, weed control programs consisted of utilizing either soil-applied herbicides plus early-post (weeds less than 3 inches tall) treatments for broadleaves and/or mid-post (weeds 3 to 6 inches tall) treatments for grasses or utilizing total-post programs targeted at a mid-post application timing. |
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Soybean Sudden Death Syndrome – (Andreas Westphal, Scott Abney, and Gregory Shaner)
Sudden death syndrome has been a problem in many Indiana soybean fields in recent years. Since the disease was first identified in the southwest corner of Indiana in the mid 1980s, it has spread to affect fields in nearly all of the state. The distribution of past outbreaks suggests that the disease may show up in virtually any area of Indiana, when conditions are favorable. |
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