Fungicide Options to Combat Fusarium Head Blight

By Robert Battel

Universities have recommended using group 3 fungicides Prosaro (prothioconazole plus tebuconazole) or Caramba (metconazole) applied at early anthesis (Feekes 10.5.1 or flowering) or within the first six days after flowering to combat Fusarium head blight. There is a newer fungicide on the market that wheat growers can use against Fusarium head blight: the group 3 and group 7 premix Miravis Ace (Propiconazole and pydiflumetofen). Miravis Ace has been found to be just as effective at controlling Fusarium head blight as Prosaro and Caramba when applied at flowering.

Miravis Ace is marketed by Syngenta as being effective against Fusarium head blight when applied to wheat as early as 50% head emergence (Feekes 10.3). University plant pathologists in 10 U.S. wheat growing states, including Michigan, in 2018 and 2019 conducted field trials to compare the efficacy of Miravis Ace when applied at, before or after flowering, or sequentially with a DeMethylation Inhibitor (DMI) (group 3) fungicide to that of a standard flowering-only application of Prosaro or Caramba.

Treatments included:

1. Untreated check
2. Prosaro at 6.5 fluid ounces per acre at flowering
3. Caramba at 13.5 fluid ounces per acre at flowering
4. Miravis Ace at 13.7 fluid ounces per acre at 50% head emergence
5. Miravis Ace 13.7 fluid ounces per acre at flowering
6. Miravis Ace at 13.7 fluid ounces at flowering followed by Prosaro at 6.5 fluid ounces four to six days after
7. Miravis Ace at 13.7 fluid ounces at flowering followed by Caramba at 13.5 fluid ounces four to six days after

Optional treatments were:

1. Miravis Ace at 13.7 fluid ounces at flowering followed by tebuconazole at 4 fluid ounces four to six days after
2. Miravis Ace at 13.7 fluid ounces four to six days after flowering
3. Prosaro at 6.5 fluid ounces four to six days after flowering

The goal of this work was to ascertain the efficacy of Miravis Ace applied at, before or after flowering compared to standard-single application of Caramba or Prosaro applied at flowering. Fusarium head blight index is a visual rating system to quantify the number of heads showing Fusarium head blight and the severity of infection on each head. Fusarium head blight index is a good rating of how much disease is present but does not always correlate with DON (vomitoxin).

In these trials, all fungicide applications and timings lowered Fusarium head blight index compared to the untreated check. Single fungicide treatments applied at flowering reduced Fusarium head blight index by about half compared to the untreated check. Prosaro, Caramba and Miravis Ace applied at flowering were all similar in Fusarium head blight index reduction. Likewise, results of Prosaro and Caramba applied at flowering and Miravis Ace applied at 50% head emergence were similar in Fusarium head blight index. Treatments with two fungicide applications (treatments No. 6 and 7 in the first list above) were significantly lower in Fusarium head blight index than single application treatments.

While an application of Miravis Ace at 50% head emergence can be good to control the amount of Fusarium head blight in the field (index), this early application is not very effective in terms of DON (vomitoxin) suppression. Low levels of scab does not automatically mean DON is low. DON levels can be high even when disease levels are low. While Fusarium head blight index is useful in quantifying the presence of Fusarium head blight in the field, actual reductions in DON are the most important because that is what affects farmer payments.

In this case, Miravis Ace reduced Fusarium head blight Index from head emergence (Feekes 10.3) through late flowering, which is encouraging because it widens the window for application. However, the application at head emergence had higher DON levels compared to the flowering or late application timings.

It is also important to select varieties with Fusarium head blight resistance. There are no varieties that are completely resistant to Fusarium head blight, but there are some varieties that are better than others. Selecting the most resistant varieties in combination with applying fungicides is the best strategy for reducing DON levels. Consult the Michigan State University Wheat Performance Report for ratings and results for more than 80 commercial wheat varieties.