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J.C. Palumbo and C.A. Sanchez

Imidacloprid is a new, chloronicotinyl insecticide currently being used to control sweetpotato whitefly [Bemisia tabaci Genn, also known as silverleaf whitefly (Bemisia argentifolii Bellows and Perring)]. Large growth and yield increases of muskmelon (Cucumis melo L.) following the use of imidacloprid have caused some to speculate that this compound may enhance growth and yield above that expected from insect control alone. Greenhouse and field studies were conducted to evaluate the growth and yield response of melons to imidacloprid in the presence and absence of whitefly pressure. In greenhouse cage studies, sweetpotato whiteflies developed very high densities of nymphs and eclosed pupal cases on plants not treated with imidacloprid, and significant increases in vegetative plant growth were inversely proportional to whitefly densities. Positive plant growth responses were absent when plants were treated with imidacloprid and insects were excluded. Results from a field study showed similar whitefly control and yield responses to imidacloprid and bifenthrin + endosulfan applications. Hence, we conclude that growth and yield response to imidacloprid is associated with control of whiteflies and the subsequent prevention of damage, rather than a compensatory physiological promotion of plant growth processes. Chemical names used: 1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro-1-H-imidazol-2-amine (imidacloprid); [2 methyl(1,1′-biphenyl)-3yl)methyl 3-2-chloro-3,3,3-trifluoro-1-propenyl]-2,2-dimethylcyclopropane carboxylate (bifenthrin); 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodiaxathiepin 3-oxide (endosulfan).

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A. Galadima, C.A. Sanchez, J. Palumbo, B. Tickes, M. Matheron, and M. McGiffen

Experiments were conducted during 1998–99 seasons to evaluate the potential for organic vegetable production in the low desert of the southwestern United States. The experimental design included three summer management options [fallow, cowpea (Vigna sinensis), and sudangrass (Sorghum vulgare)] in factorial combination with alternative production systems, which included organic and conventional systems. The crops cultivated were iceberg lettuce (Lactuca sativa L) during the fall–winter period and melons (Cucumis melo Reticulatus Group) during the spring. The organic plots were managed with strict adherence to California Certified Organic Farmers (CCOF) guidelines. Summer cover crop management seemed to influence the early growth and N uptake of lettuce, but had no final effect on yield and quality. The organic production system resulted in lower yields and inferior product quality compared to the conventional system. Generally, disease and weeds were not limiting factors, although labor costs for weed control would be slightly higher in organic plots. Insects, primarily aphids (various types) and thrips (Frankliniella Occidentalis Perancle), and fertility, primarily N, were factors limiting yield and quality in organic systems. Control of whiteflies (Bemisia argentifoli) was the limiting factor for melons. Studies during 1999–2000 are focused on overcoming the challenges of the insect and fertility management in organic systems.