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The Potential Impacts of Late Planting on Corn Diseases

06/21/2019
  • Foliar diseases in corn can be detrimental to yields if the infection develops at critical stages of development (mid vegetative stages through R3).
  • Even though we had a wet start of the season, it is the environment around those critical stages of development that will drive disease infection and severity.
  • If weather is favorable, late planted corn can be more susceptible to yield losses due to foliar diseases.
  • When wet conditions and moist environments are prevalent through the early reproductive stages of corn development, a fungicide application can help protect yields and stalk integrity.
  • Scout fields from mid vegetative to R3 stages to determine the need and properly time fungicide applications.

The combination of late planting and wet conditions this growing season has everybody wondering what this means for diseases and the need for fungicide applications. Unfortunately, the answer is not straightforward. Corn yield potential in some areas may be already compromised due solely to late planting, planting in less than ideal conditions, and the resulting poor stands. The fungicide conversation may be a delicate one to have as the idea of spending extra dollars in a year with low yield potentials may not go over well with our growers. We can make predictions based on weather forecasts but in the end it is the interaction of the crop, the pathogen and the environment at critical growth stages that will determine disease development and severity levels. As of June 20, 2019, the three-month climate prediction shows 33-40% probability of below normal temperatures across the Midwest (Image 1), near normal precipitation in WI, IN and parts of Illinois and 33% probability of above normal precipitation in west Illinois, Missouri and Iowa (Image 2). Low temperatures can slow down corn development, grain fill and the time to physiological maturity while wet conditions can favor infection by foliar diseases and compromise carbohydrate supply to fill the ears.

Image 1 below. Three-month outlook of temperature asof June 20, 2019. (Source: NWS, Climate prediction center)

3 month temp outlook.png

Image 2 below. Three-month precipitation outlook as ofJune 20, 2019. (Source: NWS, Climate Prediction Center).

3 month precip outlook.png

The amount of inoculum for pathogens that overwinter in the region such as gray leaf spot, tar spot and northern corn leaf blight may be higher in areas with infested crop residue from the previous year. Periods of high humidity will favor spore release and movement and if these conditions are prevalent during mid vegetative stages through R3, issues with kernel formation or abortion may be observed. Common and southern rust, pathogens that do not overwinter in the region but instead blow in from the south mid-season may land on much younger corn than usual, potentially resulting in increased yield losses. Depending on where you are located across the geography, corn is currently in the early-mid vegetative stages. It is concerning to realize that we are approaching the end of June and most fields are not even knee high. Be diligent about scouting fields during the critical stages of development to protect yields from foliar pathogens. If disease risk is high, scouting will help you make timely fungicide decisions while protecting the profitability of your growers.

For more information on this topic visit the following University resources:

http://bulletin.ipm.illinois.edu/?p=4606

https://extension.purdue.edu/fieldcroppathology/author/dtelenko/

https://crops.extension.iastate.edu/cropnews/2019/05/delayed-planting-and-diseases-2019

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