Tuesday, June 21, 2011

Head Scab Present in Darke County’s Wheat

Rainy and moist conditions persisted through wheat anthesis this year. As a result head scab is once again present in Darke County’s wheat. However, initial results from a survey conducted by THE Ohio State University show disease incidence may be lower than last year. With harvest approaching it is important to be prepared to deal with scab by knowing some best management practices (BMPs) to deal with scab at harvest.

As many farmers are aware, head scab is a disease that affects both grain yield and grain quality of wheat. The disease is caused by the fungus Fusarium graminearum. The fungus infects wheat during anthesis if wet conditions, either rain or high humidity, persist. Once the kernel is infected the disease limits growth causing shriveled kernels. The disease also produces several toxins, the most widely known is vomitoxin. The toxin is also referred to as DON which is an abbreviation for deoxynivelanol. At the time of sale farmers lose money from the sale price for the reduction in yield and quality. Grain is tested for vomitoxin so the risk to consumers of wheat products is non-existent.

On Monday June 13, 2011 Alissa Kriss, a PhD candidate with the Department of Plant Pathology at OSU, traveled to Darke County and completed a survey of wheat fields for head scab with the assistance of Justin Petrosino, OSU Extension Darke County. Initial results from 2011 show that the incidence of head scab ranged from 8 to 15%. Incidence indicates the number of heads per foot of row with symptoms of the disease. Although last year only one field in the county was surveyed incidence was reported around 47%. This was similar to results from other nearby counties with multiple fields surveyed in 2010. Thankfully initial results show a lower level of incidence than the bumper crop of head scab observed last year.

The amount of vomitoxin or DON present in the wheat is still to be determined. The presence of head scab in wheat indicates that some amount of vomitoxin will be present. However, conditions during the maturation of wheat will determine the total amount of toxins present. Recent research has shown that wet conditions after flowering can increase the amount of vomitoxin present so the rains over the last few weeks have not helped the situation. The only way to know the level of vomitoxin is to test at harvest.

There are several best management practices for dealing with scabby wheat at harvest. There is no way to treat for head scab or vomitoxin at this point. Best management practices revolve around limiting the number of scabby kernels that are harvested and limiting any further growth. During harvest it is recommended to spend some time adjusting the combine. Turn up the air to blow out light kernels that are infected with the disease. If handling scabby wheat be sure to wear gloves to limit exposure to the toxin. Once harvested make sure to dry the wheat down to 13.5%. Below this level of moisture, fungal growth and toxin production will be drastically reduced. Be sure to test grain for vomitoxin levels, and if the straw is to be baled have it tested. Scabby wheat blown out the back of the combine will still germinate this fall. A fall herbicide program should be implemented this year to control scabby wheat. With the right combination of products it is an optimal time to control fall emerged marestail, too!

For more information on head scab and current agronomic concerns in Ohio keep an eye on the CORN Newsletter available at http://corn.osu.edu/ or visit the Agronomic crops website at http://agcrops.osu.edu/. There are also factsheets and other publications available at the OSU Extension, Darke County, office. Questions and concerns can be directed to Justin Petrosino by calling (937) 548-5215 or emailing petrosino.3@osu.edu.

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