Pennsylvania, USA
November 4, 2014
Source: Penn State Extension
As you finish up your harvest and sit down to think about your seed options for next year, consider your options when it comes to genetic resistance to disease. Most seed companies offer resistance ratings for their hybrids and varieties when it comes to the more common diseases for corn and soybeans. Keep in mind that resistance does not mean immunity. Varieties with even the best ratings for a disease can still get that disease in high pressure situations. Often the symptoms will be milder and yield may be impacted to a lesser extent. The nice thing about selecting varieties with good resistance ratings is that you are not usually paying extra for this. The resistance to disease is conferred through traditional breeding as opposed to genetic engineering, so there is no associated tech fee. On the other hand, those varieties that have excellent resistance to a disease sometimes won’t come with some of the other traits you may like to have such as drought tolerance or high yield potential—we can’t have it all! As you explore your options, know that one company may have a different rating scale than another. For example, a rating of “1” may be the best for one company, while a rating of “1” may be the worst for another.
For corn, most companies provide ratings for Grey Leaf Spot and Northern Corn Leaf Blight. These are our most problematic leaf diseases in PA, and it can be worth investing in some genetics to manage them. Elements that contribute to high pressure for these diseases include no-till, continuous corn and bottomlands where humidity is high. Using a hybrid with good resistance in any of these situations can be a good strategy.
If you often have issues with ear and stalk rots, some companies offer ratings for Anthracnose Stalk Rot and Fusarium and Giberella Ear Rots. However, also consider choosing something with insect resistance. Stalk and ear rots are more common in situations where feeding damage or mechanical damage has allowed the fungus to get into the plant. By minimizing the wounding, you minimize the opportunity for these fungi to gain entry.
For soybeans, the best help for some of the soilborne pathogens comes in the form of genetic resistance. Many of us experienced problems with White Mold, Sudden Death Syndrome, Stem Canker and Brown Stem Rot this year. These diseases are all caused by fungi that enter the plant early in the season, but don’t cause symptoms until much later in the year when water and nutrients become limiting, like in the heat of August. Since 1) seed treatments don’t offer much help with these pathogens because of the timing, 2) fungicides are not effective in most cases, and 3) these pathogens are going to be present in the field for many years, a great option is to select a resistant variety. Especially in the case of White Mold, whose survival structures can live for 10 years, choosing a resistant variety should be a key part of your management strategy if you have confirmed the disease in a field.
Companies may also offer ratings for diseases that are not typically problematic in our area. This is because they may be marketing them in other regions where this disease is important. If your crops have never had a disease on the list, don’t worry about selecting for resistance to it. Think about your most common issues from year to year and decide what you could use some extra help with. Then work with your dealer to find the best options for your farm.
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