The practice of monoculture corn represents the highest risk of infestation by one of the two species of corn beetle present in Quebec. They are: the western root beetle and the northern root beetle. Considered as secondary pests, their larvae cause damage to the roots while the adults feed on pollen and silks, thus harming pollination. For more information on these pests, we invite you to consult the bulletin of the Phytosanitary Warning Network (No 1, February 10, 2020):

https://www.agrireseau.net/rap/documents/101962

The main risk factors favoring their presence in the field are:

• The cultivation of corn on previous corn : the larvae must feed on corn to be able to complete their life cycle. Following the laying of adults in corn in the previous fall, the larvae emerge in the following spring, and if the field is still sown in corn, they can feed on the roots and cause more or less damage depending on the intensity of infestation.
• History of infestations : fields with a history of economic damage are more at risk, as well as those having experienced a significant presence of adults during the previous season.
• Soil type : heavy textured soils are more at risk. The effective and applicable control methods are:

The effective and applicable control methods are: 

• Crop rotation is the best method of preventive control of this pest. Its effectiveness in reducing populations of beetles is greater than that of insecticides. A return of corn should not be carried out on a field considered to be at risk having a corn precedent.
• The use of Bt corn hybrids is an alternative that allows these pests to be controlled when it is not possible to rotate the crop. You can consult the list of corn hybrids and Bt traits available in Canada to find out about the different resistance genes available on the market and the requirements for setting up shelters. Be careful however, because cases of resistance to certain Bt hybrids have been reported and new cases could be observed. It is therefore important to rotate the Bt hybrids in order to limit the development of resistance.

The role of the agronomist

In fields where there is a history of the presence of the corn beetle, the intervention strategies are as follows:

• Recommend a crop rotation to avoid sowing corn on a previous corn.

• Guide the agricultural producer to buy a hybrid of Bt-chrysomele corn available in his region.

In the event of a limited supply of Bt-chrysomele corn from your client’s usual seed supplier, you are required to offer one of the two control methods mentioned above or to refer it to another seed supplier.

Caution

Considering that these two control methods mentioned above are effective and applicable, the recommendation and the sale of a corn hybrid coated with neonicotinoids cannot be justified on an agronomic level to control corn chrysomeles.

The president,
Michel Duval, agronomist