Source: Chad Lee, Grain and Forage Center of Excellence director 

May is the prime time to scout and take action for wheat for diseases, insects and weeds.  

While approximately 10,000 acres of wheat that were underwater for several days in April are lost, most farmers across Kentucky have reported only a small portion of their wheat fields were impacted.  Further good news is that the condition of Kentucky’s surviving wheat crop has improved, according to the May 5 USDA-NASS Crop Progress and Condition report.  

By May, wheat is typically flowering and developing seeds. This grain-filling period is critical for producing high yields because kernel size and weight are determined during this stage. Yields will be reduced by any stress (high temperatures, low soil moisture, nutrient deficiencies and pests) occurring during grain fill.   

Even though we have little control over weather scenarios, decisions can be made to address pest stressors.     

Pre-harvest Weed Control  

After wheat has headed, watch for emerging warm-season weeds. A preharvest treatment after the hard-dough stage, where the crop has 30% or less grain moisture, may be needed to control weeds and improve harvesting wheat efficiency, especially where wheat stands are poor and weed infestations are heavy. However, research has shown preharvest treatments are not effective in preventing the production of viable seed of winter annuals weeds such as Italian ryegrass.  

Glyphosate and specific formulations of 2,4-D are examples of herbicides registered for preharvest weed control in wheat and should be applied as a weed control tactic and not as a harvest aid to reduce wheat grain moisture. Preharvest applications of glyphosate or 2,4-D require a 7-to-14-day preharvest interval. Preharvest treatments can also injure wheat or reduce seed germination or seedling vigor and are not recommended for wheat grown for seed production.   

Late Season Insect Pests  

Scouting for insect pests, such as aphids, armyworms, and the cereal leaf beetle, should continue through May. Early detection, correct identification, and assessment of pest problems allow appropriate management decisions to be made. Regular field monitoring is the best means of getting the information needed to follow the recommended treatment guidelines.   

Late-season disease  

The risk of Fusarium head blight (FHB) has increased due to rains and generally cloudy weather that occurred in early May. According to the FHB risk map (www.wheatscab.psu.edu), large differences in risk can be observed for susceptible varieties compared to moderately resistant varieties. In May, wheat is generally beyond the time where a fungicide application can be made several days past early anthesis, except for a few exceptions with later-maturing wheat varieties. It will be important to start monitoring for symptoms of FHB in wheat fields over the coming weeks to determine if adjustments to combine fan speeds should be made, which can help blow out the lightweight "tombstone" kernels, which may have the highest levels of vomitoxin.  

Other diseases that have been observed this year include Stagonospora and Septoria leaf blotch, leaf rust, and symptoms that resemble viral diseases. Other diseases that may be present include powdery mildew, glume blotch, black chaff, bacterial leaf streak, and stripe rust. 

In general, management of important wheat diseases includes an integrated approach such as planting the most disease-resistant varieties available and applying an effective fungicide at the appropriate wheat growth stage if warranted from disease risk and/or scouting observations.      

Additional recommendations on managing late-season wheat and preparing equipment for harvest can be found at https://graincrops.ca.uky.edu or contact your local (COUNTY NAME) Extension office for more information.      

 
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