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.