Risk assessment of soil-pest damage to grain maize in Europe within the framework of Integrated Pest Management

The management of soil-pests relies largely on conventional insecticides. Within the framework of the EU's PURE project, data were collected to assess the risk of soil-pest damage to grain maize in Europe in order to implement Integrated Pest Management (IPM) of soil-pests in a more practical and sustainable manner, thus optimizing the use of soil insecticides (in-furrow or as seed-dressing) at sowing. Plant density and soil-pest damage to maize seeds and/or plants during the growing season were determined in fields with no or some risk factors. Risk assessment on a sample of sixteen experimental sites (a total of 109.95 ha of maize) located in five European countries (Germany, Hungary, Italy, Slovenia and the Netherlands) from 2011 to 2014 showed a low risk of soil-pest damage to maize. In all fields, wireworms (Agriotes spp. larvae) caused 99.5%–100% of the plant damage, meaning that damage by other soil-pests was negligible. The fields studied were divided into two groups: those with no risk and those with risk factors. According to previous research, the risk factors were Agriotes brevis Candeze and Agriotes sordidus Illiger as prevalent damaging species, soil Organic Matter content over 5%, rotation including meadows and/or double crops, as well as surrounding landscape being mainly meadows, uncultivated grass and double crops, cover crops, and poor drainage. In the fields with no risk factors, wireworm plant damage (mainly holes in the collar causing central leaf wilting) never exceeded 15%, a threshold value for potential yield reduction. Furthermore, plant damage was much lower or even negligible in the vast majority of the fields (i.e. over 90% of fields had less than 5% wireworm damage to maize plants). Risk factors, such as rotation including meadows and/or double crops, led to the percentage of cultivated land with significant wireworm plant damage being even lower than predicted (8.7% instead of 14.7%) and almost 50% of that predicted for the whole sample (2.7% instead of 4.9%). In the few cases where plant damage was higher than 15%, yield was not affected when untreated strips were compared with strips treated with soil insecticides. In all trials, the soil insecticide Tefluthrin did not significantly increase the density of healthy maize plants or grain yield. In more than 99% of cases, no economic damage to maize by soil-pests was recorded. These results demonstrate that the occurrence of risk factors may increase the risk of wireworm damage to maize crops, while the probability of damage to a field with no risk factors is always very low (less than 1%). This highlights the importance of integrating risk assessment of soil-pest damage to maize into IPM strategies, which would include: i) an “area-wide” risk assessment evaluating the possible presence of risk factors, including click beetle population monitoring with pheromone traps, and ii) “complementary field monitoring” with bait traps where risk assessment has identified the presence of risk factors. In fields with no risk factors, treating maize with soil insecticides was found to be pointless. Therefore, IPM strategies in maize that include risk assessment of soil-pest damage may lead to a significant reduction in soil insecticides use and, consequently, to a reduction in environmental impact.