Value of Fungicide Application in Wheat Production in Southwest Kansas, 2017 Report

During the past several years, applying fungicide to wheat has become a more common practice. The availability of cost-effective generic fungicides, as well as the positive yield responses often reported, seem to be the potential drivers for the adoption of such practices by producers. A wheat fungicide trial was conducted in Garden City, KS, to answer the following questions: 1) Are fungicide applications profitable? and 2) Can remote sensing technology be used to quantify the efficacy of different fungicide products? The study consisted of two wheat varieties sown on September 30, 2016 (Oakley CL, highly resistant to stripe rust; and TAM 111, highly susceptible to stripe rust) and treated with different fungicide products. Stripe and leaf rust were the major fungal diseases impacting wheat yield in southwest Kansas in 2017. Wheat production in 2017 was impacted by dry planting conditions in late 2016, a winter ice storm in January, and a late snow storm on April 30, and severe wheat streak mosaic virus infestation. There were significant differences in grain yield among fungicide products for both TAM 111 and Oakley CL. The large changes in normalized difference vegetation index (NDVI) values suggest that multiple environmental factors were interacting to impact the wheat plant health. The benefit of fungicide application observed on yield was minimal under the environmental conditions of 2017.


Introduction
In recent years, producers are becoming interested in protecting wheat grain yield from major fungal diseases due to the availability of more affordable generic fungicides. However, it is important for producers to be aware that application of fungicides protects yield potential that is present at the time of application. Fungicides serve as yield protectors by enhancing the plant health. Therefore, it is common for producers to often associate delayed harvest with fungicide application. Fungicides allow plants to stay green and maintain their leaves longer, using more nutrients during the late development stages.
Previous research has reported variable results regarding the value of fungicide application in the Great Plains. In Kansas, several years of research have indicated that a single fungicide application to a susceptible variety, on average, could provide a 10% yield increase, relative to the untreated control (De Wolf, 2013). To maximize the benefit of a fungicide application, producers should know the vulnerability of the variety to be treated. Susceptible varieties are more likely to benefit from foliar fungicides as compared to varieties with moderate to high levels of resistance. It is also important to pay attention to weather conditions and scouting reports within a field, region, and even surrounding states to the south.
Rating the effectiveness of a foliar fungicide application on disease control is often tedious and very subjective. With the onset of remote sensing technology, there are great opportunities to develop more objective approaches for rating varietal resistance to diseases and the efficacy of fungicides. Measurements such as the normalized difference vegetative index (NDVI)-which combines wavebands in the red region of the spectrum that is controlled by the leaf pigment content, and wavebands in the near-infrared region of the spectrum that is controlled by the internal leaf structures-are strongly correlated with plant health. Application of fungicide is reported to enhance plant health that results in the plant staying green longer. Therefore, differences in NDVI before and after fungicide application relative to the control could be used to develop a more objective scale for rating fungicide efficacy.
The objectives of this study were to evaluate the value of variety selection and application of a foliar fungicide as part of an economically optimal disease management plan and to assess the potential for using remote sensing measurements such as NDVI as a tool for rating fungicide efficacy.

Experimental Procedures
An experiment was established at the Southwest Research-Extension Center in Garden City, KS, in fall 2016. The design of the experiment was a randomized complete block design with three replications consisting of eleven fungicide application treatments and two wheat varieties: Oakley CL (highly resistant to stripe rust) and TAM 111 (highly susceptible to stripe rust). The experimental treatments are summarized in Table 1. Experimental plots were sown on September 30, 2016, at a seeding rate of 120 lb/a, and were 7.5-ft wide × 30-ft long. The entire experimental area was fertilized with 100 lb of N/a at green-up in March of 2017, and plots were sprayed with a mixture of 0.4 pints of Starane, 0.375 quarts of MCPA, and 0.1 oz of Ally the first week of April for weed control. Fungicides were applied at a volume of 15 GPA with a CO 2 backpack sprayer when the flag leaf fully emerged and the ligule was visible (Feekes GS 9). A plot combine 7.5-ft wide was used to harvest 25 ft from each plot for yield. A subsample was collected from each plot to determine the test weight and moisture content. The yield was adjusted to 13% moisture.
NDVI was collected before and 15 and 30 days after the flag leaf fungicide application. A handheld Greenseeker sensor (Ntech Industries, Inc, Ukiah, CA) was used to measure the NDVI. The difference between the before and after NDVI values were used to assess the efficacy of the fungicide. The smaller the difference between the before and after application NDVI values of the treated compared to the control was indicative of the efficacy of the fungicide.

Results and Discussion
The 2017 wheat crop overcame many challenges, including a late winter snowstorm that covered the wheat in more than 20 inches of snow for three days, mild leaf and stripe rust, wetter than normal conditions in March and April, and warmer temperatures were the main environmental conditions for the 2016-2017 wheat crop.
The results of this study showed that the effect of fungicide on yield differed significantly among products and across both resistant and susceptible varieties. The variability in response to the fungicide applications may be attributed to the impact of environmental stress on wheat as well as the later application of the fungicide at Feekes 10 compared to Feekes 9 in 2016. Compared to the results of 2016, TAM 111 (the susceptible variety) once again out-yielded the resistant variety Oakley CL. Similar to 2016, lodging was again a problem for the Oakley CL variety ( Table 3). The generic fungicide was the most consistent in producing a net return, with a net benefit of $3.45 for TAM 111 and $9.64 for Oakley CL. Oakley CL is not resistant to leaf rust, so a mild infestation of this fungus likely justified justifying the greater net returns as compared to TAM 111.
In 2016, Foster et al. (2017) reported differences of 0.07 in NDVI 30 days after application in the check TAM 111 plot, but in 2017 differences in NDVI for the check TAM 111 plot were 0.07 15 days after application, and 0.32 30 days after application (Table  3). Contrary to 2016, the changes in NDVI indicated significant differences in efficacy among the different fungicides 15 and 30 days after application for both TAM 111 and Oakley CL. The large changes in NDVI and the significant difference in efficacy among the fungicides in 2017 may be attributed to the later application timing, the impact of the April 30 snowstorm, other diseases (mild infestation of leaf rust), lodging, warmer temperatures in May and June, and the effect of the crop approaching physiological maturity at the time of the 30 day NDVI sampling.

Conclusion
The results of 2017 demonstrate the complexity of environmental conditions on wheat management. Therefore, it is important for producers to manage each crop independently, taking into consideration the environmental condition of that year in making decisions on fungicide application. Scouting the crop and gathering information about the condition of the crop is vital to making an optimal decision. Clearly, in 2017 the challenge of getting fungicide applied on time was a factor. In these situations, a good decision is to go with the generic products to minimize the potential for economic losses. The results observed in 2017 in no way should be interpreted outside of context of the particular growing season from which data were collected-that is, without considering the environmental conditions under which the wheat was grown. Fungicide decisions should take into consideration the current crop growing condition and yield potential, inoculum present in the field or neighboring fields, and weather conditions during that particular growing season. Remote sensing technology shows potential in quantifying the efficacy of different fungicides. However, the result was most beneficial when compared to the control, which might offer some challenges in real-world application.    Treatments  TAM OAK  TAM OAK  TAM OAK  TAM OAK  TAM