Wheat crop looks good, but ...

Recently, I met with members of the agricultural community at OSU Extension's monthly Agriculture Leadership Council. This open meeting at the 50 North Senior Center occurs on the second Monday of every month to discuss current and local agriculture issues. The crop situation was the main topic this month. As many of you have observed, weather conditions have not been the best for planting corn and soybean. Some individuals have taken a chance to plant some corn and soybean in April — those plantings are just beginning to emerge. But the consensus at the meeting indicated that most fields have not been planted in the area. However, farmers at the meeting reported that the wheat crop was looking good and were surprised that the grain heads were already beginning to appear — about seven to ten days earlier than most years. When the heads or spikes poke through the canopy, flowering will soon follow about seven to ten days later. The head or spike (the botanical term for head) is the flowering structure of the wheat plant. Each spike contains about 50 flowers, which will pollinate and form grain. Most people do not notice the flowering period because wheat flowers have no petals. But the flowering period is critical to farmers because it is the time that one of the most devastating diseases may infect wheat: Fusarium Head Blight, more commonly known as Head Scab. Not only can this disease dramatically lower yields and grain quality, but it can also produce a toxin in the grain that is harmful for human consumption. Head scab is caused by the fungus Fusarium graminearum. Infection does not occur unless the wheat variety is susceptible, fungal spores are abundant in the air, and weather conditions are conducive for spore germination and development. Corn stalks are the common source of fungal spores in wheat. The same Fusarium fungus that causes head scab also causes stalk and ear rots in corn. Prior to the 1990's, farmers generally plowed under corn stalks burying the fungal spores. In the 1990's farmers began to adopt conservation tillage practices to reduce soil erosion that left corn stalks and residue on the surface. These surface corn stalks can harbor the fungus for many years. Since soybean and wheat are often planted no-till, these stalks are still present to provide spores that can infect the wheat at flowering. Even if a farmer plows his field before planting wheat, fields many miles away with surface corn stalks can provide spores for infection. Thus, weather at the time of flowering heavily determines whether wheat becomes infected with head scab. Spores are produced and released from the residue when temperatures are above 59°F and the relative humidity is more than 90%. Thus, conditions are right for wheat infection if a warm and rainy period sets in several weeks before and during flowering. Under these right conditions, the fungus infects the wheat head during flowering and will cause developing kernels to shrivel and have a chalky white color. Infected heads may also have a bright pinkish color. Evidence of head scab infection is often not visible until about two to three weeks after flowering. At this time, infected kernels will have a dull white color, and uninfected kernels will be green. It is common for only part of the head to be infected. Infected kernels may produce a vomitoxin called deoxynivalenol (DON). Monogastric animals such as swine and humans are sensitive to this toxin. As you can imagine, the word vomitoxin refers to how the animal (or person) responds to the toxin. Farmers, grain merchants, and processors work together to insure that DON concentrations are below toxic levels in the food chain. Farmers have only a few fungicides available to partially control head scab, but they have to be applied at flowering to be effective. They do not work if applied before flowering. Some benefit may be seen if the fungicide is applied within five days after flowering. These products are quite expensive, and the farmer may face a logistical application problem since fields may be too wet at flowering for land application and then can only be applied aerially. Extension researchers from Ohio State University and other land grant institutions have developed an Internet tool that predicts the risk of head scab for a given area based on current weather and crop information. The risk tool may be found at http://www.wheatscab.psu.edu. As of last Monday, this model showed a medium risk for susceptible varieties. Producers may be surprised that the risk is not higher because of recent rain events; however, spore activity has been reduced because of the abnormally cooler temperatures we have seen the past several weeks. Four fungicides are labeled for head scab in wheat: Caramba, Miravis Ace, Proline and Prosaro. These products will provide some control of head scab and reduce the amount of vomitoxin. Farmers need to apply these fungicides when 50% of the heads have anthers exposed in the middle part of the spike. Unfortunately, these fungicides will not provide 100% control since individual flowers on the spike (head) do not pollinate at the same time. Farmers can improve success against head scab by planting moderately resistant wheat varieties and apply fungicides. At this time, plant breeders have not released a variety with complete resistance to head scab. It may cost farmers more to produce wheat if they have to use a fungicide. However, if head scab occurs and they do not apply fungicides, vomitoxin levels may be high enough that farmers will be unable to sell their wheat. Even if head scab does not materialize, the fungicides will protect the wheat from other potentially yield reducing disease such as Stagonospora glume blotch and rust, which often become a problem in wet years during grain fill. In summary, for the next ten days, farmers will be watching their wheat closely during flowering and checking the Head Blight Assessment tool for head scab risk. They hope that conditions will not be favorable for head scab at flowering. However it the risk for scab is high, they may want to apply a fungicide. Thus, if fields are too wet for ground application, you may see aerial vehicles applying fungicide to wheat in the rural areas for the next two weeks. Ed Lentz is agriculture and natural resources educator with Ohio State Extension Office — Hancock County.