Program PL480: Enhancing the implementation of IPM to improve farmer competitiveness, minimize environmental risks and ensure food security and safety Project 1.7: Evaluation and dissemination in integrated weed management strategies in vegetables grown after rice (88-B08-21)

Results of the study revealed the following: 1) The post plant application method of applying glyphosate using a shielded noozle shows promise as a viable control option for vegetable farmers because it reduces the cost of weed control inputs by as much as 50% compared to farmers' practice of three to four or even weekly hand-weedings. However, for the past several seasons that have been conducted, the authors have been getting yields lower than that of the farmers' practice and other control methods such as the stale-seedbed technique. Low yields in the postplant glyphosate applications in onion and okra could be due to either inadequate weed control (needs follow-up handweeding) or due to herbicide injury (glyphosate is non-selective to vegetable crops) in spite of the use of nozzle shields to prevent the herbicide spray from getting in contact with the crop stems and leaves. 2) of the three crops (onion, okra and eggplant) tested for efficacy of postplant herbicide application method, eggplant showed the most promise, which yields at least comparable to yields obtained from farmers' practice. Apparently, eggplant is less susceptible to the herbicide and is also highly competitive against weeds than either onion or okra. 3) Results of the fourth study showed the potential of Spoladea recurvalis as a biological control agent against horse purslane (Trianthema portulacastrum) if release of the larvae could be timed within the first one to three weeks after planting when crop competition with the weed is critical. The authors' studies showed that the larvae can consume the weed in sinificant amounts enough to reduce weed populations. However, we need to determine how to integrate use of this biological control agent in combination with other cultural weed management strategies to control weeds other than T. portulacastrum which are also dominant in onion fields. In cases where T. portulacastrum is the only dominant weed, S. recurvalis will be effective as biological control agent and 4) Results of the fifth study on control strategies against lowland purple nutsedge showed that several broadleaf herbicides such as bensulfuron, 2,4-D, MCPA, bentazon, and metsulfuron + chlorimuron provided excellent control against lowland purple nutsedge. Purple nutsedge shoot densities of plots treated with herbicides were reduced by 70 to 90% at 20 DAT and by 90 to 100% at 40 DAT, over those of untreated plots. Initial tuber densities, which averaged 257 tubers/sq m at the start of the cropping season were 30 to 50% lower in herbicide-treated plots, compared to tuber densities in untreated plots at the end of the cropping season. Rice yields from these treatments were higher than, or comparable to, yields obtained from weed-free control plots and higher than yields obtained from plots treated with butachlor, the standard herbicide used by farmers in the area. Although bensulfuron costs more than the other herbicides, it provided net incomes higher than net incomes obtained from the other herbicide treatments because of the high yields obtained from the bensulfuron treatment.