1997 Research Results
Effective weed control in full-season, no-till soybeans -- a variety of treatments were examined for knock-down and residual weed control in full-season, no-till soybeans in 1996. For knockdown, Sencor (metribuzin) was effective on various emerged weeds at planting. Tank-mixes of Sencor with Gramoxone Extra or Roundup, particularly when 2,4-D was added, provided excellent control. Select, particularly in combination with another knock-down herbicide, provided good early season control of annual grasses. For residual grass herbicides, a split application was, in most cases, better for control than a single pre-emergence application. When half the recommended rate was applied two weeks prior to planting, followed by the other half at planting, better annual grass control was observed.
Genetically engineered soybeans for weed control -- In narrow row soybeans, the performance of genetically engineered soybeans such as Roundup-Ready soybeans was improved, possibly by allowing less chemical application to be made due to the shading effect of the soybeans.Timing can be a problem, though, due to the fact that most fields have annual and perennial weeds. Annual weeds need to be controlled early n the season, while perennial weeds need to be treated later in the season. Thus, in many cases, particularly with Roundup-Ready soybeans, two applications may be necessary. With STS and Liberty-Link soybeans, a preemergence grass "base," followed by Synchrony or Liberty herbicides, provided good control of many annual broadleaf weeds.
Can Brassic crops control nematodes? In the first year of this study, canola and oilseed radish were planted in April 1996 on two farms in Caroline County and allowed to grow and flower until June 20. The cover crop was then killed and soybeans were planted. Nematode samples were taken twice, once at planting and again as soybeans matured. At the first farm, radish and canola both seemed to suppress juvenile cyst nematode and full cyst better than no cover crop. With both crops, lesion nematode actually decreased to a zero population. On the second farm, radish and canola seeemed to suppress juvenile, full cyst and lesion nematode better than no cover crop. Root knot nematode increased with the radish crop on one farm and the canola crop on the other.
Transgenic corn may help reduce soybean podworm -- Corn earworm or podworm causes significant damage to Maryland soybeans and also infests corn which serves as the primary nursery for population recruitment. As corn matures, earworm moths shift their egg-laying to soybeans. Because of this close association, any measure used in corn to reduce earworm population may also suppress podworm injury. Monsanto's YieldGard Bt corn showed a significant reduction in the ear damage caused by corn earworm, both in terms of damaged ears and surface area of kernels consumed. Bt protein expression in silk and kernels also significantly reduced the density of larvae and drastically delayed development.
Recruitment of larvae that reached prepupal stage was reduced by more than 90 percent in Bt ears. Results clearly indicated that corn earworm survival and development were suppressed to the extent that very few larvae completed development in Bt corn. The data suggest that, if corn earworms survive Bt corn to adult state, those moths may be competing at a repreoductive disadvantage compared to unselected moths from non-Bt corn. Furthermore, in cage studies, some of the prepupae in Bt corn took longer to emerge. This delay and reduction in moth emergence may significantly lower the chance of corn earworm colonizing in soybeans later in the summer.