Reducing the abundance of Mexican bean beetle (Epilachna varivestis) and increasing yields in snap beans (Phaseolus vulgaris) using reflective plastic mulches

Mexican bean beetle (MBB), Epilachna varivestis Mulsant, is a pest of snap beans, Phaseolus vulgaris L., in many regions of North America.  Previous research shows that increasing temperatures and light intensity decreases habitability for MBB.  Plastic mulches with light-reflecting surfaces, such as white and reflective silver (metallized), are known to increase near-ground temperature and light intensity.  We hypothesized that beans grown on reflective plastic mulches would harbor fewer MBB and incur less feeding injury than beans grown on black plastic or bare soil.  Three field experiments were conducted in Blacksburg, Virginia: summer 2014, summer 2015, and fall 2015.  In all experiments, ‘Dragon’s Tongue’ snap beans were grown on beds of either metallized plastic mulch, white plastic mulch, black plastic mulch or bare soil.  Treatment differences were measured from visual insect counts, foliar damage ratings, pod damage ratings, and total pod weights.  Overall, beans grown on metallized plastic, and, to a lesser extent, white plastic had fewer MBB, less injury and produced greater yields than those grown on black plastic and bare soil.  In all experiments, metallized plots harbored fewer MBB adults, eggs and larvae, and also exhibited less defoliation than other treatments.  In both summer experiments, metallized plots produced significantly greater yields than all other treatments, with over 100% yield increases from bare soil plots.  White plastic, followed by metalized, produced the greatest yield in the fall 2015 experiment.  These findings suggest that growing beans on reflective plastic mulches may protect against MBB and increase marketable pod yields.