Pennsylvania Wheat: When to Pull the Trigger on Fungicides

From a wheat disease perspective, many of us are looking at wheat that is approaching heading or flag leaf. Hopefully, you are scouting, and if so, you may be seeing some leaf diseases in the lower canopy. We also know that it’s now time to prepare for managing Fusarium head blight. The fungus that causes this disease enters through the wheat flowers and infects the developing grain. Warm and humid environmental conditions during wheat flowering or barley heading favor the growth of the fungus.

So 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, which will also give you great control of flag leaf diseases.

Most areas of PA are now at a “Low or Medium,” but steadily increasing risk for the development of scab in wheat. While the temperatures have been high, the humidity until this week has not been high enough for the fungus to make spores. This will change very quickly this week, so keeping an eye on the FHB Risk Assessment Tool will become critical for those farmers who have wheat beginning to flower in the next few weeks.

This forecasting site is an online model that helps us predict infection risk levels everywhere in the state. It has been improved over recent years to include some new features and better accuracy. Visit it at your convenience, or sign up to have updates e-mailed or texted directly to you.

Use your judgement based on your experience and your local conditions. Be prepared to spray a fungicide on fields that are at medium to high risk at flowering. Remember, sprays applied PRIOR to flowering will NOT provide significant suppression of scab or toxin production, however, a spray up to a week after the beginning of flowering can offer good disease and toxin reduction.

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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. If either these products is unavailable, Proline and Folicur (which together provide the same chemicals as Prosaro) may be tank mixed at a rate of 3 + 3 fl oz/A.

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.

Once wheat begins flowering, there is about a 5-6 day window to apply a fungicide. You can also spray a bit later and still get some efficacy from these products, but not as much as targeting early flowering. 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 (Quadris, Headline), or strobilurin/triazole (Twinline, Quilt, Stratego) combination products at flowering or later. There is evidence that they may cause an increase in mycotoxin production.

If the weather is challenging you with impending storms, you should know that these products are quite rainfast shortly after drying. So if your only opportunity to spray is an hour before rain, you can still do so.

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. Choose resistant wheat varieties, and time sprays properly to achieve greater control.

If you choose to use a fungicide for these or any other diseases on wheat this year, an updated fungicide efficacy chart can be found on the chart below.

Table 1. Efficacy of fungicides for wheat disease control based on appropriate application timing. Click Image to Enlarge

1. Efficacy categories: NR = not recommended; P = poor; F = fair; G = good; VG = very good; E = excellent; NL = not labeled for use against this disease; U = unknown efficacy or insufficient data to rank product efficacy.
2. Product efficacy may be reduced in areas with fungal populations that are resistant to strobilurin fungicides.
3. Efficacy may be significantly reduced if solo strobilurin products are applied after stripe rust infection has occurred.
4. Application of products containing strobilurin fungicides may result in elevated levels of the mycotoxin Deoxynivalenol (DON) in grain damaged by head scab.
5. Multiple generic products containing the same active ingredients also may be labeled in some states.
6. Products with mixed modes of action generally combine triazole and strobilurin active ingredients. Priaxor and the Trivapro co-pack include carboxamide and strobilurin active ingredients.

The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) developed the above information on fungicide efficacy for control of certain foliar diseases of wheat for use by the grain production industry in the United States.

Efficacy ratings for each fungicide listed in the table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy is based on proper application timing to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application.

Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. Table includes most widely marketed products and is not intended to be a list of all labeled products.

This information is provided only as a guide. It is the responsibility of the pesticide applicator by law to read and follow all current label directions. No endorsement is intended for products listed, nor is criticism meant for products not listed. Members or participants in the NCERA-184 committee assume no liability resulting from the use of these products. This table was revised April 2018.

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