What You Can Do Now To Reduce DON In 2015

Alyssa Collins
Research Associate, Southeast Ag Research and Extension Center

Variety selection can be as important as your management practices when seeking to limit fusarium head blight and toxins.

Most of us are well aware that Fusarium Head Blight (FHB, or “head scab”) and the toxin that can accompany it (DON, or “vomitoxin”) can be serious problems in Pennsylvania wheat. Farmers in PA have done a good job getting the right fungicides on at the right time in recent years. However, this only gets us about halfway to where we could be with toxin reduction. If you really want to get serious about clean wheat, you’ll want to start with selecting a resistant variety right out of the gate.

Here’s how this disease works. The fungus blows in as a spore from where it survived the winter on some leftover plant residue. When the weather is mild and humid, that spore can germinate and enter the plant through an open flower. That fungus can then infect the developing wheat kernel, causing it to abort or reducing its quality. Also (and we don’t yet understand all the factors involved), the fungus may produce a toxin as a byproduct of its growth and metabolism. The level of infection (how many heads or how much of the head is affected), does not necessarily correspond directly to the amount of toxin in the harvested grain.

Keeping these things in mind, we can use some information gathered over the last few years on wheat varieties to inform our seed selection. When they are available, I think it’s important to use the DON levels on each of these varieties rather than just a scab resistance rating. That’s because it is possible to have a large amount of DON even when you have a small amount of scab. A variety that is resistant to the development of the toxin may even be more important than one that shows fewer of the white heads.

The data shown in Table 2. are from data gathered during 2012 and 2013 in Virginia and Maryland (courtesy of Carl Griffey, Virginia Tech and Jose Costa, USDA-ARS). In these wheat nurseries, the researchers account for differences in flower timing and environmental conditions by misting the plots, so they always have a disease-conducive environment. You’ll see a color coding that indicates the relative control of toxin versus the average DON level in the study. Those varieties that are dark green gave excellent control of DON. There are differences from year to year and site to site, probably as a result of general inoculum levels and site variability, as well as the way the resistance works.

As you know, it is difficult to get excellent agronomic traits and high levels of disease resistance in the same variety—otherwise we’d all be growing that one! But cross reference this table with the PA Wheat Performance Trial closest to you. You will hopefully find some options that give you at least some DON resistance while preserving some of the other qualities you want.

As you review the yield results from the PA wheat and barley trials, you may ask yourself, “Well, if we know a fungicide can help yield and quality so much, why aren’t they spraying those variety trials?” The answer is two-fold. The variety trials include grain varieties with dozens of different flowering and heading times, and these are all randomized in the field. If a fungicide is applied to the field to protect against FHB, chances are very good that a few varieties would receive the proper protection, while the rest of the varieties would not, resulting in inaccurate quality and yield comparisons. And because of the variation in flowering times, a situation would also exist in which certain varieties would have an unintended advantage since some varieties would flower when the weather was conducive for the disease and some would not. By not applying a fungicide to the trial, we know that all varieties are on an equal playing field, and we can make management decisions based on this understanding.

Source : psu.edu