The combination of certain herbicides with insecticides can inhibit crop growth. Greenhouse studies were conducted to evaluate interaction effects of herbicides and insecticides with/without protectant, on corn and weed species. ‘Northrup King 9283’ hybrid corn showed greater sensitivity to acetanilide herbicides than ‘Cargill 7567.’ Neither the insecticides terbufos nor isazofos appeared to enhance this sensitivity. Both hybrids were sensitive to the combination of chlorimuron, nicosulfuron, or primisulfuron with terbufos. Cargill 7567 was more tolerant than Northrup King 9283 to the growth inhibiting interaction of sulfonylurea herbicides with terbufos. Imazaquin at 70 g/ha reduced height of Northrup King 9283 corn, but there was no interaction with terbufos. The protectants CGA-154281 and NA reduced corn injury from metolachlor and the combination of nicosulfuron and primisulfuron with terbufos, respectively. Nicosulfuron and primisulfuron treatments combined with metolachlor showed less corn injury than metolachlor alone, but these herbicides increased corn injury when combined with terbufos. The inclusion of terbufos did not enhance primisulfuron activity on barnyardgrass, giant foxtail, or velvetleaf.

Glyphosate [N-(phosphonomethyl)glycine] toxicity to bermudagrass [Cynodon dactylon (L.) Pers.] increased as 0.84 kg/ha of the herbicide was applied in decreasing volumes of diluent from 374 to 47 L/ha. Visible injury to bermudagrass varied from 18 to 91% depending upon the spray solution formulation and diluent volume. The addition of surfactant to glyphosate (MON 0139) formulated without surfactant increased bermudagrass injury at each diluent volume tested. Glyphosate commercially formulated with surfactant (MON 2139) was the most toxic of the three formulations to bermudagrass. Regrowth of bermudagrass clipped at the soil surface 48 h after treatment ranged from 10% of the untreated control with MON 2139 at 47 L/ha to 100% of the control with MON 0139 at 374 L/ha. The MON 2139 formulation showed as much as a six-fold increase in foliage regrowth when the diluent volume was increased from 47 to 374 L/ha.