Challenges with mycotoxins in dairy feeds across the region are a growing concern. In our area, the primary mycotoxins we are battling are Deoxynivalenol (DON) and Zearalenone (ZEA), both caused by the fungus Fusarium Graminearum.
This fungus infects many of the crops we grow for feed. In corn silage, it can cause ear rot and stalk rot, both of which can produce mycotoxins. The fungus is also a challenge in small grains where it can infect both the grain causing head scab or the stem/straw. These two are the primary sources of mycotoxins in our feed, but it can also infect alfalfa mostly causing root rot but can infect the stem and produce mycotoxins or grasses growing in your hay field.
Lastly, the fungus can infect soybean fields mostly causing seedling damping off with little concern in soybean grain mycotoxins. Fusarium Graminearum multiplies most rapidly when temperatures are between 59-86 F and relative humidity is about 80%.
Small grains
First, we will address small grains. If you are feeding them as a grain source, this can be a significant area of mycotoxin contamination in your ration. Occasionally, it can be tempting to feed wheat or barley that is cheap because of head scab issues, but this must be done cautiously as it will contain both DON and ZEA. However, when silage is harvested in the boot stage, the DON and ZEA levels are usually low.
At this time, temperatures have not been in the range for toxin development as long and the grain hasn’t emerged to be infected. However, there is a big risk in the straw which we use as both bedding and feed. Straw often has three times the mycotoxin levels as the harvested grain.
If you are planning to feed straw, managing the wheat for low head scab levels is critical. A fungicide application of a product containing Prothioconazole for head scab control during pollination can lower mycotoxin levels. The risk of head scab infection and high mycotoxins development in wheat can be assessed at wheatscab.psu.edu/. This tool can be used as part of an IPM program to determine if you should apply a fungicide.
If the straw is kept dry in storage, mycotoxin growth after harvest is minimal. If it gets wet either waiting to be baled or in storage, the mycotoxins continue to grow.
Corn
The second crop that brings most of the mycotoxins into your milk ration is corn. Unlike corn grain, corn silage can bring mycotoxin concerns in both the stalk and ear. There is no correlation between whether the stalk had DON or ZEA mycotoxins in it or if the ear was contaminated.
Stalk rot infection often occurs early in the growing season from soil that splashes into the corn plant whorl. Ear rot infection then occurs while corn is pollinating and the silks are still wet and green.
Management of corn mycotoxins starts with variety selection. Unfortunately, there is currently not a resistance screening program for corn silage hybrids susceptibility to Fusarium Graminearum along with DON and ZEA production.
Your best tools currently are to use historic experience with hybrids in your area and quiz your seed salesman to find out what they know. We have done a small project looking at hybrid infection and have found that hybrids can have resistance to stalk rot infection but not ear rot infection and vice versa. This has caused hybrids to be the highest when infection occurred in the stalk while low when infected in the ear.
Last year, we conducted a corn grain DON resistance screening program that had 80 hybrids entered in it. This trial was planted in three locations and was inoculated to be sure we had the fungus present during corn pollination.
Across all three locations, there was DON present, with hybrid DON averages between 0-30 ppm. When looking for low DON hybrids it is important to look for the hybrids that were low across all 3 environments as weather conditions are a major driver of DON levels.
Of the 80 hybrids, 13 of them averaged 1ppm or less DON at all 3 locations. Twenty-eight hybrids were less than 2 ppm and 43 were under 3 ppm.
The full report is available at corn.osu.edu Unfortunately, we cannot be certain low hybrids are resistant as the weather may not have been right for disease development, but we can be sure the high hybrids are susceptible. The second management step after the selection of resistant hybrids is a fungicide application containing Prothioconazole while corn silks are still wet.
