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Technical dossier for a crop rotation system which minimises the abundance of WCR (Western Corn Rootworm)

- The WCR (Western Corn Rootworm) adult population, which is near economic levels 6-8 years after the initial infestation, highly prefers maize stands for adult feeding, egg laying, and larval development.

- The WCR population in continuous maize showed a continuous increase though the rate of increase can differ depending on environmental (rainfall or drought) conditions. Even under extreme dry summer and unfavourable soil conditions, the WCR population can increase in the following year.

- Part of the WCR adult population can immigrate to other crop stands or to other fields (harvested). The reason for such immigration can be to feed on flowers and pollen of the crop, such as sunflower, or to feed on volunteer winter wheat in harvested wheat fields. A small portion of the WCR adult population (5-15%) is active near the ground surface of these crop stands.

- Biologically, the immigration of WCR adults to other crop stands, adult feeding, and/or egg laying in non-maize pre-crops and larval feeding on the roots in the next year’s maize was observed in the crop rotation trial.

- Although there were differences among non-maize pre-crops regarding the robustness of correlations between the adult density of immigrating individuals and the next year’s adult population density in maize, the differences were not enough to demonstrate pre-crop preferences by a critical number of adults to non-maize crops.

- There was no clear preference for non-maize pre-crops by WCR adults and no sign of any special adaptation of the WCR population to the crop rotation system. Rather, a random spread and movement of WCR adults and subsequent egg laying happened under project trial conditions.

- We assume that crop rotation systems in Europe will not result in high selection pressure on the WCR at levels that have been seen in the USA Corn Belt. Diverse landscape with a more diverse plant spectrum in Europe offers broader feeding sources and different egg laying habitats compared to the landscape in the USA Corn Belt, that primarily being a maize/soybean rotation system. We believe that diversity in space, as well as in time, may contribute to the lower possibility for the development of an adapted WCR population. Diversity in time refers to avoiding long-term, narrow, and routine rotations of crops. This may be of special importance in the typical maize growing areas in Europe where maize is cultivated on large areas, over long periods, and in narrow rotation selections (1-2 crops in rotation with maize). Existing IPM (IPPM) rules also support the above.

- While the rotation of maize with other crops is a primary control method of WCR populations and is strongly prescribed (by law or other types of regulations), especially in the population build-up phase, there are still major questions concerning the long-term management of WCR. If, theoretically, all maize plots (or a majority) will be rotated to non-maize crops, we do not allow WCR population to survive! This type of full rotation may pose a very high selection pressure. Therefore, the use of “refuges” of continuous maize for two years within rotation areas to reduce selection pressure and preserve rotation as a means for managing the WCR population needs to be studied and policies developed, if effective.

Reported by

Szent Istvan University Godollo
Pater Karoly 1
2103 Goedoelloe