Effectiveness of Sunn Hemp (Crotalaria juncea L.) in Reducing Wireworm Damage in Potatoes

Wireworms are a major threat to potatoes. Agronomic prevention is always the first IPM strategy to be implemented. This work assesses whether a bioactive cover crop, sunn hemp (<i>Crotalaria juncea</i> L.), a tropical leguminous plant, reduces wireworm damage risk when cultivated as a crop preceding potatoes. The effects of <i>Crotalaria</i> plants (alive, chopped, and incorporated) on wireworms and tuber-damage prevention were studied in semi-natural (pots) and open-field conditions. The survival of a set number of reared wireworms feeding on <i>Crotalaria</i> plants or potato tubers in soil with incorporated <i>Crotalaria</i> chopped tissues was assessed. Wireworm damage on tubers was assessed in fields where <i>Crotalaria</i> had been cultivated, chopped, and incorporated the previous year. The tuber damage assessment involved counting all the erosions/scars caused by wireworm feeding. The prevalent wireworm species studied was <i>Agriotes sordidus</i>. Our research is the first to demonstrate that <i>Crotalaria</i> as a cover crop can significantly reduce potato damage by wireworms. A major role is likely played by the high pyrrolizidine alkaloid content in <i>Crotalaria juncea</i> tissues, but this has to be specifically proven. <i>Crotalaria juncea</i> may thus represent an effective means for use alone or with complementary ones to produce potatoes with low wireworm damage without using synthetic insecticides.