A commonly asked question posed by many growers is, “Does it pay to apply a fungicide to my wheat?” This question is particularly important with recent reductions in commodity prices. Fungicide applications are useful in protecting wheat from fungal diseases affecting the foliage and head. Commonly encountered diseases include the residue-borne members of the Leaf Blotch Complex (Tan Spot, Stagonospora leaf and glume blotch, Septoria (speckled) leaf blotch), as well as Fusarium head blight, leaf rust, powdery mildew, and stripe rust. Although these diseases differ in many ways, they all have similar effects on the plant in that they can reduce grain fill and quality if a susceptible variety is planted and conditions favor disease. In small grain production, the most important tissues involved in providing carbohydrates to support grain fill include the flag leaf (45%), upper leaf sheath (25%) and glumes (25%). Thus, if a fungicide is applied, you will likely get the most “bang for your buck” by applying a labeled product between flag leaf emergence (FGS 8) and flowering (FGS 10.5.1-FGS 10.5.1 + 6 days). However, the likelihood that a fungicide will pay is dependent on many factors, including environment, disease present, arrival of disease, disease pressure, and variety. University of Delaware Master’s student and Kent County, Delaware Agricultural Agent, Phillip Sylvester has conducted a set of replicated studies to better understand fungicide utility and profitability under Mid-Atlantic growing conditions.
The study consisted of 5 commonly used fungicides (Tilt, Quilt Xcel, Priaxor, Stratego YLD, Prosaro) applied to FS 815 wheat according to Table 1. An untreated control was used as a reference and each treatment was replicated six times per site. In 2015 four sites were planted and in 2015 six sites were planted. VA, MD, DE, and S. PA were included. Treatments were applied at labeled rates at either FGS 8 (flag leaf) FGS 10.5.1 (Flower-Prosaro only) or a combination of FGS 5 (greenup) and FGS 8 OR FGS 10.5.1.
Plants were rated for disease in the canopy over the course of the growing season. A final disease rating was made on the flag leaf and glumes at soft dough. Yield and test weights were determined. Phillip obtained average application costs by surveying multiple distributors and custom applicators in the region. Then, the overall profitability, or net returns, for each program averaged across all sites and years was determined. In addition, the percentage of times that a particular treatment produced a yield benefit sufficient to cover application costs was determined. Net return data were assessed at $3.00, $4.00, and $5.00 per bushel. Phillip saw a diverse range of environments between sites and years, ensuring a wide, diverse set of observations. Diseases observed, in order of frequency, included : Leaf blotch complex, Glume blotch, powdery mildew, Fusarium head blight, and rust.
Overall the data showed that any fungicide product or program can result in a yield increase relative to an untreated control (Table 2), with programs increasing average yields between roughly 3-9 bushels per acre. However, profitability and yield increase were not related, particularly at the lower commodity prices tested. In general, the data showed that applications at flowering (FGS 10.5.1) which are geared towards protecting the glumes and head, were just as efficacious as flag leaf applications in terms of protecting yield. This is likely because many of the diseases we encounter do not reach the flag leaf until after heading in many cases and, as mentioned earlier, the majority of the carbohydrates for grain fill are derived from tissues above the flag leaf. Consequently, the FGS 5 applications in many instances were less profitable than a single application at FGS 8 or FGS 10.5.1 (Table 2). Applications made at only FGS 8 will not be efficacious against glume blotch or FHB.
Data also indicated that the likelihood of a fungicide application paying for itself varied for programs, but even at high commodity prices, returns are not a sure thing (Table 3). In sum, fungicides can be useful in Mid-Atlantic wheat production, but overall profitability is influenced by many factors. Multiple fungicide applications may not be profitable in many instances, especially under low commodity prices. Protection of the flag leaf, upper sheath, and glumes is critical to maintaining yield and applications targeting FGS 8 or FGS 10.5.1 are most likely to provide a beneficial yield response.
As always, growers need to pay attention to labels and only apply fungicides labeled for application at a given timing. Also note that fungicides containing a group 11 (Strobilurin) mode of action have been shown to increase vomitoxin, produced by Fusarium head blight, in many instances. Application of Strobilurins after FGS 8 is not recommended for this reason.