Eastern black nightshade is a problem weed in soybeans primarily due to interference with harvesting operations and reductions in crop quality. Field and greenhouse studies were conducted in 1990 and 1991 at Harrow, Ontario, to determine whether sublethal rates of imazethapyr and metolachlor could suppress growth and berry production by eastern black nightshade. In the greenhouse, plants treated with metolachlor PRE at 0.8 kg ai ha−1 or imazethapyr POST at 30 g ai ha−1 (1/3 to 1/2 the labelled rates) produced significantly fewer berries in the first flower cluster, with fewer seeds per berry, than untreated plants. When a surfactant was added to the imazethapyr, almost all flower buds in the first cluster were aborted. Treated plants recovered from the damage, however, and did not differ significantly from control plants in dry weight or berry production 110 DAP. In the field, application of 50 g ai ha−1 imazethapyr POST (2/3 of the lowest labelled rate), with or without a surfactant, resulted in delayed flowering, abortion of most of the flower buds in the first cluster, and greatly reduced growth and total berry production between soybean leaf abscision and harvest. Application of metolachlor + metribuzin PPI in the field at 2/3 of the labelled rate (1.6 + 0.25 kg ai ha−1) was not sufficient to reduce nightshade growth and berry production after soybean leaf abscision. Sublethal rates of imazethapyr and metolachlor did not reduce seed viability in either the greenhouse or the field.

Knowledge of how reduction in the rate of herbicide application or rotation of their mode of action influences weed growth will provide insight into how successful these practices will be in an integrated weed management program. Field experiments were conducted in 1996 and 1997 to quantify velvetleaf growth response to three postemergence herbicides, each with a different mode of action. A monoculture of velvetleaf was treated with halosulfuron, dicamba, and flumiclorac at 0, 0.10, 0.25, 0.50, 0.75, and 1.0 × the labeled rate for weed control in corn. Percent plant mortality increased with rate of application; the greatest mortality occurred in flumiclorac treatments in 1996 and in halosulfuron and flumiclorac treatments in 1997. Growth rate temporarily decreased as application rate increased. Maximum height decreased as rate of application increased, with the dicamba treatment resulting in the greatest (27%) reduction. Early-season leaf area index decreased with increasing rate of application, the greatest reduction occurring with halosulfuron (1997) and flumiclorac (1996 and 1997) treatments. The number of leaves produced per plant was temporarily reduced by all treatments, but treatment with dicamba later resulted in larger numbers of small leaves. The number of velvetleaf seed capsules produced per surviving plant was not reduced by any treatment, but the number of capsules per square meter was reduced by the 0.5 × rate of flumiclorac (1996) and the 0.5- and 1.0 × rates of halosulfuron (1997). Research is needed to evaluate whether the temporary suspension of velvetleaf growth after herbicide treatment is sufficient to prohibit crop yield reduction and velvetleaf capsule production.

The effect of topical application and oral administration of diflubenzuron on the feeding budget in the fifth instar larva of Papilio demoleus has been studied. The LD50 and LC50 values of diflubenzuron were 13.50 and 9.00 μg/larva/48 hr respectively. Topical application was found more efficacious in producing 50% mortality at a comparatively minimum dose of 9.00 μg. The growth efficiency was reduced by 44.54% in oral administration and 38.19% in topical application at the highest sublethal dose over that of control larvae. Not only the growth of the larvae of P. demoleus was inhibited, but the adults showed morphological deformities.