HORTICULTURAL ENTOMOLOGY Impact of Straw Mulch on Populations of Onion Thrips (Thysanoptera: Thripidae) in Onion

Development of insecticide resistance in onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), populations in onion (Allium spp.) Þelds and the incidence of the T. tabaci transmitted Iris yellow spot virus have stimulated interest in evaluating alternative management tactics. Effects of strawmulch applied in commercial onion Þelds in muck areas of western New York were assessed in 2006 and 2007 as a possible onion thrips management strategy. In trials in which no insecticides were applied for thrips control, straw mulch-treated plots supported signiÞcantly lower T. tabaci populations comparedwith control plots. In both years, the action thresholds of one or three larvae per leaf were reached in straw mulch treatments between 7 and 14 d later than in the control. Ground predatory fauna, as evaluated by pitfall trapping, was not increased by straw mulch in 2006; however, populations of the common predatory thrips Aeolothrips fasciatus (L.) (Thysanoptera: Aeolothripidae) were signiÞcantly lower in straw mulch plots in both years. Interference of straw mulch in the pupation and emergence of T. tabaci was investigated in the lab and their emergence was reduced by 54% compared with bare soil. In the Þeld the overall yield of onions was not affected by the strawmulch treatment; however, the presence of jumbo grade onions ( 77mm)was increased in 2006, but not in 2007. These results indicate that populations of T. tabaci adults and larvae can be signiÞcantly reduced by the use of straw mulch without compromising overall onion yield. The use of this cultural practice in an onion integrated pest management program seems promising.