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What Impact Will Late Planting Have on Crop Diseases?

Much hinges on growing season weather.

Persistent rains and cool temperatures are combining to delay corn and soybean planting this spring in Illinois and other Corn Belt states. Nathan Kleczewski, University of Illinois 
Extension field crops plant pathologist, outlines below what this means for Illinois farmers the rest of this growing season. Many of the maladies he addresses could also occur in other states.

Keep in mind that disease occurs when you have the correct host, plant pathogen, and environment together. The longer those three factors are together, the more disease will occur.  Although we cannot speculate much on the long-term environmental conditions we will face this year and how that will impact diseases, we can make some educated guesses on how late planting could potentially impact some diseases.  

Let’s take a look at our magical plant disease crystal ball, shall we?

1. Soybean cyst nematodes in soybean and other nematodes in soybean and corn  

These organisms grow and reproduce in/on crop roots, and will continue to reproduce and damage plants over time. One potential impact of late planting is that these organisms will have less time to damage plants prior to harvest, and therefore their overall impacts may be reduced compared with other seasons.

2. Sudden death syndrome (SDS)  

The fungal pathogen that causes this disease is favored by cool, wet soils. These conditions also reduce soybean germination, growth, and development early in plant development. Planting later in the season hedges your bets of encountering warmer soils, which are not as favorable for the SDS pathogen.

3. Pythium species on corn and soybean  

Similar to SDS, Pythium diseases tend to be favored by cool, wet conditions. However, unlike SDS, Pythium seedling diseases are caused by a complex of fungi. We now know that a single field can host many different pathogenic species of Pythium, which may differ in terms of their optimal temperatures to cause disease. Consequently, if wet weather is encountered soon after planting, regardless of temperature, issues with these pathogens may still occur.

4. Residue-borne foliar diseases and stem diseases  

There are numerous foliar diseases that can impact soybeans and corn, and many stem diseases that may cause issues in soybeans. Unlike some of the other diseases I mentioned earlier, many of these diseases will be affected by the environmental conditions during the growing season when favorable conditions occur relative to plant growth and development.

5. Rusts

The rusts that can impact corn and soybeans blow in from warmer regions to our south. Many rusts arrive later in the season, typically after yield has been made, or after in-season management decisions have been made and fungicides applied. A good example of this is common rust in corn.  

This does not always happen, though. As many Illinois farmers who experienced southern rust several years ago know, early arrival of these diseases may coincide with conducive conditions that can result in yield losses. 

Consequently, late planting could potentially result in plant exposure to rusts earlier in growth and development. There has been little activity with rusts in the South this season, which hopefully translates to less potential issues with these pathogens during the season. 

Similar to the residue-borne foliar diseases, favorable weather conditions are essential for disease development during the growing season.

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