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Don’t let new diseases distract from old threats

Tar spot has been the hot disease topic in recent years and for good reason. It is a new threat that can cause devastating yield losses in corn.
However, with an important new disease on the loose, it can be easy to forget about others we’ve managed for in the past.

KevinMoore                       Kevin Moore
              Senior staff agronomist
Think about it this way. During the COVID-19 pandemic, we tended to focus on that disease and forget other things necessary for good health, such as exercising and eating nutritious foods. So, while focused on keeping COVID at bay, we lost sight of other health issues. While tar spot is proving to be something we need to manage, let’s not forget about other important corn diseases.

Good disease management begins with planting. The standard corn seed treatment package does a great job of protecting the crop from early-season diseases such as seedling rots, blights and damping off. Keep in mind, however, that planting into good conditions is necessary to give corn the best chance of coming up quickly and evenly, which gives pathogens less time to take hold. Another strategic management practice is adding a fungicide to the in-crop herbicide application around V5. Corn begins determining its yield potential at V6 when the number of ear rows is established, so protecting against early-
season foliar diseases like anthracnose will help that yield potential.

The reproductive stages are the most important time to keep the plants healthy and disease-free. Our most devastating diseases, such as tar spot, rob the corn crop of green foliage during these stages. Gray leaf spot and northern corn leaf blight have typically been the main foliar diseases of concern. They tend to be first seen around tasseling, and lesions continue to develop through the rest of the season. We recommend applying a fungicide with multiple modes of action around VT (full tassel) to R1 (beginning silk).

“Every time we get a new disease in our area, the old diseases will remain. It is important to manage for the disease spectrum as a whole.”

Southern rust will not survive our winters and moves from south to north with wind currents each year. That means infection timing varies from year to year. Fortunately, new advancements have led to fungicides that can be sprayed at VT-R1 timing to combat southern rust, even if it shows up later in the season. Further, these newer premium fungicides also offer the best yield protection from tar spot when applied during that timing. The new formulation allows growers to incorporate tar spot protection into management practices for historic diseases.

As we move into the season, stalk and ear rots become diseases of concern. Anthracnose, fusarium and giberella are three of many stalk rots that hinder the standability of a corn crop. We can’t directly fight these diseases with a fungicide, but that VT-R1 application can improve overall plant health and reduce the negative effects of these rots. Maintaining good soil fertility will also help. Adequate levels of nutrients, especially potassium, contribute to a healthy stalk and make it more difficult for pathogens to infect.

Ear rots such as aspergillus, diplodia, fusarium and giberella decrease grain quality. Some fungal pathogens produce mycotoxins that can negatively affect human and livestock health. As with stalk rots, fungicides will not directly protect against ear rots. However, we can defend against them with good soil fertility for general crop health.

If ear rot does occur, damaged kernels tend to be light and can be discarded by making combine adjustments. Proper storage is also important to keep any mold from spreading to healthy grain in the bin. Drying immediately to less than 15% moisture and then cooling to under 50 degrees will help maintain good grain quality in storage.

Every time we get a new disease in our area, the old diseases will remain. It is important to manage for the disease spectrum as a whole. The best way to start is a sound cropping plan, which not only covers disease control strategy but also fertility, insect and weed management. Contact MFA’s knowledgeable location managers and agronomy personnel to help develop your cropping plan.

CLICK TO READ MORE FROM THE 2024 MAY ISSUE OF TODAY'S FARMER MAGAZINE.

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