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Photosynthetic Balance/Stress Leads to Harvest Problems in Corn
Dr. Tom Hoegemeyer, Chief Technology Officer
The six weeks from mid-July through August 2007 were unusually and continuously warm and humid for the Western Corn Belt. Later in July, we started getting widespread rains—along with cloudy, dank weather—that continued through August. Some areas have seen storms, resulting in root lodging, but all of us are experiencing the impact of weather-related problems.
The first of these problems is fungal diseases. Plant pathologists describe the “Disease Triangle,” that is, the combination of the host plant, the virulent pathogen, and the environment. If the host plant is very resistant to the pathogen, or the pathogen is not virulent on the particular variety, or the environment isn’t favorable, there will be no disease problem. However, this year we have had an extremely favorable environment for the development of Southern Rust, Gray Leaf Spot, Anthracnose and several leaf blights. The pathogens causing these diseases are always here. The disease resistance/susceptibility among varieties is relative, and the range of responses depends upon the environment. With the environment we drew this year, some fairly resistant/tolerant varieties have damaging levels of disease. And as hybrids mature, this becomes more apparent.
Leaf diseases reduce the amount of active leaf area, which consequently reduces photosynthesis. Cloudy August weather also reduces photosynthesis at the time when grain filling is reaching its peak. This results in a second crisis for the corn plant, especially when high yields have already been established by good weather and management earlier in the season. The plants try to fill all the kernels, even if they have to starve the stalk tissues to do it. If photosynthesis is continually low, they will cannibalize stalk tissue and use the energy for grain filling.
This leads to a third problem, root and stalk rots. Many of the root and stalk rot-causing organisms are not good pathogens; they are not very good at attacking healthy tissue. However, they are excellent saprophytes, that is, they are very effective at attacking dead or stressed and dying tissue. The organisms that cause root/stalk rots are the same ones that decay last year’s crop residue. The less tillage and crop rotation we do, the more risk we have of continuous cycles of leaf disease, and subsequent root and stalk rot. This whole issue is staring us in the face this fall.
As we harvest we need to be planning for next year. Plan to balance risk and opportunity. Only a fixed amount of solar energy can be harvested by a plant, and that energy must be divided among roots, stalks and grain. How it is partitioned will vary by year, by location and by other environmental factors. Some of the highest yield potential hybrids also carry significant risks for root or stalk problems. There are no perfect hybrids in anyone’s bag, so it is important to plant a package of hybrids, rather than just the one or two with the highest yield this year. Hybrids such as 9679Hx and 9777Hx have solid leaf disease tolerance combined with outstanding root/stalk strength and consistent yields. 7016RRBt and 8778HxRR have tremendous top end yield potential, but are more vulnerable to agronomic issues and need to be managed more carefully. Try to plant corn-on-corn ground to hybrids with solid disease tolerance. Plan to harvest first fields with more apparent disease issues. Watch your fields carefully as harvest proceeds, and select harvest order by stalk/root health as well as maturity/moisture.
If you have questions, send an email to: askus@therightseed.com, or directly to Dr. Tom at drtom@hoegemeyer.com. |
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