Hoorman: Reduce Corn Tar Spot Disease | Local farm


Most of the farmers had a good corn harvest, but corn tar spot (Phyllacora maydis) was a problem. Tar spot is a corn disease that originates from Central America and appears to be spread by wind in corn-producing states. Tar spot is a fungus that grows quickly when temperatures are 60 to 70 ° F and humidity is 75% or higher with rainy, foggy and cloudy summer weather that spreads this disease. Corn will mature early with reduced cob weight, poor grain filling, stalk rot and possibly lodging with yield losses ranging from 0 to 60 bushels per acre, depending on the severity of the plant. sickness. Unfortunately, not much is known about this disease.

There are several ways you can fight tar stains. No corn hybrid is completely resistant but some varieties (especially early ones) are more tolerant than others. Fungicides can help, but the timing of application is critical for optimal success. The tar spot inoculum can survive the winter, so the rapid decay of the corn husks helps reduce the spread. Crop rotation helps but the inoculum appears to be quite widespread. Reducing stress to plants with optimal fertility helps reduce the severity of tar spots. Some universities recommend tillage to bury the tailings, but it’s not really a long-term solution. About 90-95% of all cropland planted with corn is plowed, so is plowing really efficient? Long-term no-till cultivators who use cover crops can quickly break down corn residue by changing the microenvironment and getting more moisture, microbes and earthworms to incorporate the leaf residue into the soil. simply effective as a tool for cultivating the soil. In addition, a parasitic fungus (Coniothyrium phyllachorae) associates with the tar spot and may be a natural predator.

All diseases attack plants and poorly growing organisms. Healthy plants that grow on healthy soils have fewer pests (weeds, insects, diseases). When plants are not healthy, they have incomplete photosynthesis, which means they do not produce complete proteins. The insects can smell it and they attack the plant, which can open the leaves, stems or roots of the plant to increased infection with the disease. While healthy plants can be infected, yield losses are usually much smaller or much less severe. In the current COVID pandemic, the same principle applies when weak or immunocompromised individuals have the highest severity of illness.

Micronutrients are essential for healthy plants. Most plant proteins converted into enzymes need a certain micronutrient to activate the enzyme. Enzymes speed up biological processes so that plants and animals can function at their highest potential. Why was tar spot disease so prevalent this year? Could he also be exasperated by a micronutrient deficiency? This is unknown at this time, but I will share a few observations.

Almost all of the tar spot images on the internet showed signs of zinc deficiency. Zinc deficiency in corn appears as a white midrib in the center of the corn cob leaf, while the midribs of healthy corn leaves should be dark green. Zinc activates almost 300 different enzymes in plants (luckily many are somewhat redundant). Manganese deficiency manifests as a yellow midrib in corn. Zinc deficiency was rampant this year, I found it throughout the Midwest. The glyphosate herbicide (Roundup) also binds or chelates many micronutrients. The dry weather of 2020 in the fall, winter and spring may have contributed to micronutrient deficiency this year and may be a contributing factor to the increased severity of the disease.

When I visited an Indiana no-till cover crop farmer near Cincinnati this summer, he had some great looking corn. It had a soil type similar to Paulding clay which typically produced 150 to 175 bushels of corn. This farmer regularly gets 240-280 bushels (80-100 bushels more) by supplementing with a total of $ 60 from a micronutrient packet at planting, spreading and sometimes with Y drops later in the season. growth. This farmer had just a small amount of zinc deficiency and only a few tar spot disease lesions on a few plants. The neighbor’s corn (150 to 170 bushels of corn at most) was deficient in zinc, manganese, sulfur, copper, calcium and boron with at least five different corn diseases. The difference in yield could be due to the variety of corn, but soil and fertility management could also be a factor.

Fungicides are known to help, but the timing is critical as most fungicides need to be applied early, before disease becomes serious. Mancozeb is a combination of two fungicides, Maneb and Zineb. The central micro-element of Maneb is manganese with zinc in Zineb (plus a little sulfur). Most fungicides are made up of micronutrients needed to activate the fungicide. You don’t have the answer, but is it possible that micronutrient deficiencies have played a role in the severity of tar spot disease this year? Healthy soils are synonymous with healthy plants and healthy people.

About Marco C. Nichols

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