COLOR MULCHES INFLUENCE YIELD AND INSECT PEST POPULATIONS IN TOMATOES

Field studies were conducted for three seasons, Fall 1988 and Spring a nd Fall 1989, on the effect of six mulch colors: blue, orange, red, al uminum, yellow, and white (fall) or black (spring), on fruit yields an d on insect vectors of' Sunny' tomato (Lycopersicon esculentum Mill.), Plant growth and yields were inconsistent with mulch colors during th e three seasons, In Fall 1988, in a once-over harvest, extra-large (gr eater than or equal to 70 mm diameter) and marketable fruit yields wer e higher (P less than or equal to 0.05) on blue than on the convention al white mulch. In Spring 1989, early marketable yields on red mulch w ere higher than on black mulch, and in Fall 1989, under high stress fr om tomato mottle virus (TMoV) transmitted by silverleaf whitefly [Bemi sia argentifolii (Bellows and Perring)], seasonal yield of extra-large fruit was better on orange than white mulch. In Fall 1988 and 1989, f ruit size and marketable yields were reduced on yellow mulch. Aphids ( Aphididae), thrips (Thripidae), and whiteflies were counted monthly in traps placed on the mulched beds. Aphids were least numerous on the a luminum and yellow and most numerous on the blue mulch. Where differen ces occurred, the fewest thrips were captured on aluminum and the fewe st whiteflies were captured on the yellow, aluminum and orange mulches , Although differences were not always significant, the fewest adult w hiteflies also were observed on foliage of tomato plants grown on thes e latter three mulches. Later in the seasons, as plant foliage covered the mulch, differences in the number of insects captured were similar for all mulch colors, Low numbers of whiteflies on the orange and alu minum mulches early in Fan 1989 delayed virus symptom development and increased yields. Virus symptom development was not delayed and yields were low on the yellow mulch, in spite of the low number of whiteflie s. When averaged over all mulch colors, extra-large and marketable fru it yields increased linearly with delayed symptom development. It is p roposed that, under high insect stress, mulches should be selected for their effects on insects in addition to their effects on soil tempera ture and plant morphology.