Alyssa Collins, Extension Plant Pathologist (Penn State), collins@psu.edu; Phillip Sylvester, Kent County Extension Agent, phillip@udel.edu
A cool, dark spring has slowed development of grains across the region, and it shows in the progress of small grain development. However, we are getting close to heading and flowering in small grains, and forecasted temperatures may push them quickly. The environment also has been unfavorable for the development of many of the fungal diseases we usually deal with, so much of the wheat and barley in the region is pretty clean so far.
Our most pressing concern right now will be preparing to control Fusarium head blight (a.k.a. head scab). As many of you know, this is a disease of wheat and barley that can lead to the production of vomitoxin (DON) in grains. If you intend to protect your barley from scab be prepared to spray a triazole fungicide at heading or shortly thereafter, which we could see in the next few weeks. For wheat, once it begins flowering, there is about a 5 to 6-day window to apply a fungicide. The labels state the last stage of application is mid-flower and there is a 30-day to harvest restriction. Do not use any of the strobilurins (Aproach, Headline), or strobilurin/triazole (Quilt Xcel, Stratego YLD) combination products at flowering or later. There is evidence that they may cause an increase in mycotoxin production.
At this point in the season, the only way to reduce the scab problem is to spray. But in general, do not rely solely on fungicides, as they will provide at most a 50–60% reduction in scab severity and vomitoxin. Start with selecting resistant wheat varieties, and time sprays properly to achieve greater control.
Caramba or Prosaro are effective on scab and give control of most leaf diseases and glume blotch. They do not need to be tank mixed with another product to control these diseases. For growers planting lima beans after small grains, Proline is an option since the plant back restriction is only 30 days compared to 120 days for Caramba and Prosaro. Spray nozzles should be angled at 30° down from horizontal, toward the grain heads, using forward and backward mounted nozzles or nozzles with a two-directional spray, such as Twinjet nozzles. We anticipate a new active ingredient will be on the market for the control of scab soon, but it will not be labeled in time for the 2018 season. If you choose to use a fungicide for these or any other diseases on wheat this year, an updated fungicide efficacy chart is included in this week’s issue of WCU and available as a PDF here.
If you have some other diseases prior to heading, like rust or leaf blotches, the question becomes: do you spray for leaf diseases now and come back for a second pass with a head scab product? Or do you hold out and just spray once at flowering?
The answer depends on how close you are to heading, what diseases are present in your field now, and how willing you are to run through your field twice. The goal is flag leaf protection here, but lesions on lower leaves can give rise to spores that can infect higher leaves. If you’ve got a bunch of blotch in your canopy now, and you’re at Feekes 9 or earlier, it may be worth your time to make a trip through the field with a fungicide now, as most of these products are systemic and will give you a few weeks of control. If your wheat is already heading when you discover leaf diseases, it might be more economical to wait until flowering begins so that you can apply Prosaro or Caramba for head scab, since these will also give you great control of flag leaf diseases.
Currently, most of Delaware is at a “low” risk of scab development because it has been so cool to this point. As your crop progresses toward heading, keeping an eye on the FHB Risk Assessment Tool will become critical for those farmers who are trying to make the decision to spray or not. This forecasting site, http://www.wheatscab.psu.edu, is an online model that helps us predict infection risk levels everywhere in the state. It works best in the Mozilla Firefox browser and updates each day around 10am. Visit it at your convenience, or sign up to have updates e-mailed or texted directly to you.
I (Alyssa) will doing some guest commentary while UD searches for a great new pathologist. So, when you visit, please select “Pennsylvania” as your state so that you can see my commentary where I will also be including information for Delaware growers. You’ll still be able to view your Delaware counties from there.