Interaction Between Weeds and Insect Pests With Snap Beans (Phaseolus Vulgaris L.)

Abstract

Field experiments were conducted to evaluate the interaction of either redroot pigweed (Amaranthus retroflexus L.) or large crabgrass (Digitaria sanguinalis L.) and bean leaf beetle or potato leafhopper in snap beans (Phaseolus vulgaris L.) cv "Matador". The main treatment was emergence time of either redroot pigweed or large crabgrass relative to snap beans' planting time. Subplot treatments were pigweed or crabgrass density of 0.5, 1, 2, or 8-plants/m row of snap beans. Our data fitted the hyperbola rectangular model for both relative leaf area and snap yield loss. The yield losses were dependent on the year and emergence time. Maximum yield losses at 8-weeds/m row ranged from 29 to 53% in snap bean plots with redroot pigweed, and 46 to 50% in plots with crabgrass. In crabgrass plots, coefficient A (yield loss at high weed densities) and I (percent yield loss at low weed densities) were 53% to 63% with +/-SE ranging from 18.3 +/- 29.3 and 9.3 to 38.7% with +/-SE of 6.9 and 21.1 respectively. Competitiveness of the two weeds was described by the relative damage coefficient ( q). For both the weeds, q was 0.24(+/-0.1) for late emerging pigweed and 2.7(+/-0.008) for early emerging pigweed. The population of the two insects depended on the year, weed type and emergence time. Bean leaf beetle were lower in the weed free snap bean plots by 48 and 58% compared to snap bean plots with early emerging redroot pigweed and large crabgrass respectively. Bean leaf beetle caused pod damage and leaf defoliation of 13 to 24% in weedy snap bean plots compared to weed free plots. Large crabgrass emerging with snap beans reduced the population of potato leafhoppers by 31 to 34% compared to weed free snap bean plots. When properly applied, sub-threshold level of weeds may be used in an integrated pest management system to control low populations of potato leafhoppers in snap beans.