A plethora of rain, and the pest problems that may come with it

Dave Pike, Ph.D.
Senior Scientist

A recent abundance of rain has caused some delays in corn planting in the Midwest. While most growers are focused on finding the next planting window, the crop diseases and insects that may have been driven north by the storm fronts could also present a challenge this season. Here’s how this works…

There are several crop diseases and insects that normally are not able to over-winter in the Midwest due to it being too cold, but that could easily survive in states along the Gulf Coast. These pests include some of the most destructive and damaging insects and diseases in corn, wheat, and soybeans. This includes cutworms, armyworms, and spores from rust fungi, just to name a few. As the weather warms up each spring, populations of these pests build in warmer areas, and insects take flight and spores from diseases become airborne. Although we call these pests ‘migratory’ they do not move very far each year by themselves. Left to their own ‘devices’ they may only move a few feet, sometimes up to a mile. However, the strong winds at the leading edge of storm fronts are effective and capable carriers of pests, and may transport them as much as 100 miles. As each storm moves up from the south, rain from the storm deposits insects and disease spores in new areas, infesting developing crops along the way. The rapid development cycle of these pests, aided by the moist and warm spring weather, results in new populations of pests ready to be ‘transported’ by the next storm front coming up from the Gulf states. 

In some years this ‘train’ of successive storms leads to optimal movement of migratory pests. That is; a series of storms occur with sufficient frequency and timing to lift, transport, and then deposit large numbers of spores or insects to new areas. I believe that 2017 could be one of those years! Already a number of Midwestern states, as far north as Wisconsin, are reporting pheromone trap capture of high numbers of cutworm and armyworm moths. The eggs laid by moths in weedy areas now present a threat to emerging corn plants over the next 3 to 5 weeks. 

A high number of moths caught in these traps could also be a bellwether for crop diseases, as those same storms and winds transport disease spores from the Gulf States.  Unfortunately, there is no way to predict a crop disease outbreak with certainty, as we saw with the sporadic outbreaks of southern rust on corn in 2016.  Each disease spore, when it is deposited, must land on a susceptible crop or host plant. Then it must have sufficient moisture to germinate and penetrate the plant and it must arrive in sufficient quantities to create a significant infection. Its arrival also must occur at a stage that results in serious injury to the crop. Disease spores arriving too early or too late may create evidence of a disease but will have little or no effect on the crop. 

Armyworm larva and cutworm damage. Photos courtesy of Purdue University (J. Obermeyer) and University of Illinois Extension.

Our atmospheric scientists here at Agrible believe that 2017 could shape up to be a challenging year for dealing with many crop pests. Our Ag Forecast videos and Morning Farm Report daily emails will help you stay on top of pest issues and help you know when to scout your fields and what to look for.

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