Scab, rust threatens rain-soaked wheat fields

Managing Editor

(May 10, 2016) Pesistent rain throughout much of the Mid-Atlantic region last week has Extension plant pathologists urging wheat growers to scout their fields closely as the crop hits a critical growth stage for disease development.
Stripe rust has been observed on susceptible wheat cultivars in some fields for several weeks now, but levels remained low due to dry conditions, according to Dr. Hillary Mehl, Virginia Tech Extension plant pathologist, but the recent weather has caused it to spread in some areas.
The wet weather also comes when much of the wheat planted in the region is at or near the flowering stage when the crop is at greater risk of wheat head diseases such as fusarium head blight or scab and glume blotch.
“Unfortunately, due to continued wet and humid conditions, even though temperatures are somewhat below normal, enough spores are likely to have developed and conditions are suitable for infection,” Dr. Arv Grabauskas, retired University of Maryland Extension plant pathologist emeritus, wrote in a May 4 alert to growers and Extension staff. “The weather forecast for the next week to 10 days is favorable for scab.”
With more rain projected for this week, growers are facing the decision of applying fungicide to reduce the development of vomitoxin which can bring down grain quality, and also trying to seize the chance to make applications when the weather is favorable.
“In the eastern portions of the state, scab risk is projected to be high for susceptible varieties over the next week,” Mehl wrote of Virginia in a May 2 blog post, “and it will likely be necessary to work in fungicide applications between rain events.”
Economics also play a factor as growers weight the cost of the application against the crop’s value in the marketplace and Grabauskas said fungicide applications at the optimum timing have only reduce vomitoxin levels by 40 to 60 percent.
Complicating the matter further is the relatively short application window where a fungicide application has the best results.
The plant pathologists said applications for scab should come within five or six days of the early flowering stage, when 50 percent of main tillers starting to flower from the center of the head.
“Growers who are concerned about diseases of the head such as glume blotch and fusarium head blight should be thinking about when flowering will occur, so that they can properly time their fungicide applications if these are required,” said Dr. Nathan Klecwezski, University of Delaware Extension plant pathologist.
Triazole-based fungicides Prosaro, Caramba, and Proline are the most effective products for reducing scab and vomitoxin contamination, the Extension experts added and also help control leaf blotch, stripe and leaf rust and powdery mildew.
Along with scouting, the online Fusarium Head Blight Prediction Center at is another tool for growers to use in making a decision on if and when to apply fungicide.