Predicting crop damage caused by wireworms and the effect of tillage on trap efficiency

Abstract

A novel wireworm ‘probe’ trap is described, characterized, and used in field trials to (i) determine effects of different spring tillage treatments on its efficiency capturing Agriotes obscurus L. Coleoptera: Elateridae wireworms; and (ii) assess its ability to predict crop damage. In pot trials, its attractiveness to other wireworm species was determined. In a forage/grass field, spring tillage treatments included: ploughing, rototilling, glyphosate-sprayed then ploughing, glyphosate-sprayed then rototilling, glyphosate-sprayed untilled, and untilled. The number of wireworms captured in tilled treatments increased until 20 October. The number of wireworms captured in untilled treatments remained low. Subterranean CO2 levels in tilled treatments decreased after tillage and over the trapping period, suggesting the increase in captured wireworms occurred because trap CO2 levels were not overwhelmed by soil levels. The decrease in subterranean CO2 was less pronounced in untilled-glyphosate and relatively unchanged in untilled-no glyphosate, corresponding to the lower number of wireworms captured. In a separate trial determining the trap’s ability to predict crop damage, a 2 m-wide section was rototilled in grass/forage fields in the spring of Year 1. Probe traps assessed wireworm levels in August and October of Year 1 to predict crop damage for potato and corn planted in Year 2. The y-intercept of linear equations suggested that wireworms captured in October better-predicted potato damage and corn emergence although equations were significant only for August. October-captured wireworms ≤ 21 mm in length correlated better with crop damage than larger wireworms. Pot studies revealed the probe trap to also attract A. litigiousus, A. sordidus, A. brevis, and A. ustulatus.