A 2-year field project was conducted in Thermal, Calif., to investigate cowpea [Vigna unguiculata (L.) Walp.] mulch as an alternative weed control option in pepper (Capsicum annuum L.) production. Treatments included: bare ground (BG) with hand weeding, BG with no weeding, cowpea mulch (CM) with hand weeding, and CM with no weeding. Cowpea was seeded in July on 76-cm beds and irrigated with buried drip line. Two weeks prior to transplanting peppers, irrigation water was turned off to desiccate the cowpea plants. In September, cowpea was cut at the soil line, mulch was returned to the top of the bed, and pepper plants were transplanted into the mulch and fertilized through the drip line. Every 2 weeks, the number of weeds emerged and pepper plant height were recorded. Fruit production, pepper plant dry weight, and weed dry weight were recorded at harvest in December. Fewer weeds emerged in CM than in BG. The final weed population in nonweeded CM was reduced 80% and 90% in comparison with nonweeded BG in 1997 and 1998, respectively. Weed dry weights in nonweeded CM were 67% and 90% less than those in nonweeded BG over the same period. In 1997 and 1998, respectively, pepper plants produced 202% and 156% more dry weight, as well as greater fruit weight, in CM than in BG. There were no differences in mean fruit weight. Cowpea mulch provided season-long weed control without herbicides while promoting plant growth and fruit production.
The phase-out of methyl bromide as a soil fumigant has stimulated research into the use of other soil fumigants for weed control. Methyl bromide, methyl iodide, propargyl bromide, 1,3-dichloropropene (1,3-D) and metam-sodium were tested alone and in combination with chloropicrin in laboratory experiments to determine their efficacy against Cyperus esculentus L (yellow nutsedge) tubers. Propargyl bromide and metam-sodium were the most efficacious fumigants tested, with EC50 values of 3.7 and 6.5 microM, respectively. The relative potencies of methyl iodide and chloropicrin were not significantly different but were 2.6 and 2.9 times more potent than methyl bromide, respectively. The EC50 values for all fumigants other than 1,3-D were significantly lower than that of methyl bromide. Combining each fumigant with 17% chloropicrin resulted in a synergistic interaction. The greatest increase in potency between the expected result and the actual result was a relative potency of 3.8 with the methyl bromide/chloropicrin combination. The smallest increase in efficacy was with propargyl bromide and chloropicrin, with a relative potency of 1.5. There was no significant difference between the EC50 values of methyl bromide/chloropicrin and methyl iodide/chloropicrin combinations. Combining 1,3-D with 17% chloropicrin resulted in an EC50 value for C. esculentus control similar to that of methyl iodide applied alone.
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