By Mitchell Japp, PAg, Provincial Specialist Cereal Crops, Regina
Seeding is complete and in-crop spraying is well underway. Some growers may consider including a full or partial rate of a fungicide with the in-crop application of herbicides on cereal crops. Recent evidence suggests that including a fungicide with an herbicide application is not beneficial and could be detrimental in both the current and future years.
Adding a fungicide, such as propiconazole, into the sprayer along with the herbicide seems to make sense theoretically, saving another sprayer pass and the direct cost of the fungicide is relatively small. It may also appear like good insurance against later disease issues. However, both recent and historical studies on the prairies have shown that there is no benefit to either a full or half rate of fungicide, even if that fungicide remains active for another seven to 10 days after application.
Dr. Kelly Turkington, with Agriculture and Agri-Food Canada, led a research project looking at the impact of fungicide and herbicide timing in barley production from 2010-2012. They added a half-rate of propiconazole to herbicide timing at the two to three leaf growth stage and five to six leaf growth stage. Results showed that the disease levels were higher on early treatments compared to flag-leaf timing. Crop yields, along with several key quality parameters for barley, were optimized with the fungicide at flag leaf timing. They also tested a dual application, with an early application and a flag leaf application. There was no improvement compared to a single application at flag leaf. Additionally, they observed that delaying herbicide application to the five to six leaf stage from the two to three leaf stage, barley yield declined due to early weed competition. Weed control was excellent at all sites in the study, but in regular field operations delayed herbicide application could lead to reduced weed control which would lead to increased weed seed production. (CPJS 95:525-537)
Another study by Dr. Sheri Stryhorst updates earlier research conducted in Saskatchewan. The earlier research in Saskatchewan was conducted on irrigated land in the early 1990s. The early Saskatchewan work on irrigated fields did not lead to notable trends in yield, but disease was significantly reduced with fungicide timing at the flag leaf stage compared to earlier applications (at herbicide timing). (CJPS 94: 205-207). Dr. Strydhorst’s, with Alberta Agriculture and Forestry, is using modern varieties in an intensive management system, with zero-till operations, similar to what many producers will be doing on their farms. The study focused on tight rotations that may be more susceptible to disease risk, using a canola-wheat rotation, although two crops is not really a rotation. The study was conducted in 2018 and 2019 at four location includes multiple factors and treatments, including variety, fungicide rates, fungicide timing and fungicide mode of action.
Their findings were similar to other research. There was no yield improvement or disease control improvement with a single fungicide application at either herbicide timing or at PGR (plant growth regulator) timing (GS 30-32). However, there were considerable reductions in disease levels and on average a 9 per cent yield increase when fungicide was applied at either flag leaf timing or anthesis timing. In 2019, the yield response was even more notable, with a 12-17 and a seven to 15 per cent yield benefit with a fungicide application at flag leaf or anthesis timing, respectively. They also looked at dual applications, with the first fungicide application at either herbicide or PGR timing compared to dual fungicide applications when the first fungicide application was at flag leaf timing. In most site years, there was no significant yield advantage of dual fungicide applications over single fungicide applications at flag leaf or anthesis timing. (This study is not yet published, but is discussed on The Growing Point podcast).
These results are consistent with recent research that also found that in most cases a single fungicide application at anthesis (Fusarium Head Blight timing) is sufficient for control of leaf diseases (Crop Protection 112: 343-349). In a severe outbreak, managing leaf disease at flag leaf timing may be advantageous, instead of waiting until FHB timing. Recent work out of the northern Great Plains in the U.S. found that a routine fungicide application at flag leaf when the disease risk is low, only generated a positive net return less than one-third of the time (Plant Health Progress 19:288-294). The goal is to protect the upper canopy from leaf disease as yield is derived from the upper canopy. However, in some unusual conditions, there may be a benefit to an early fungicide application. Research out of North Dakota State University has shown that early fungicide applications may result in a small yield benefit, but only in a continuous wheat on wheat "rotation." They did not observe any benefit to an early season fungicide when a wheat followed another crop. So, just don't grow wheat on wheat.
Farmers are living with the reality of herbicide resistant weeds. Fungicide resistance is also possible. There are reports of fungicide resistant Fusarium in the north-east United States. Now is the time to be cautious to delay fungicide resistance development. Unnecessary applications and applying the fungicide at a lower rate than recommended (which may be sub-lethal) increases the risk of developing fungicide resistance.
So, while the direct costs of early season fungicide are not high, there is no evidence to suggest there are sufficient benefits, economic or otherwise, to justify the expense. And, there may be additional costs due to delayed weed control and the potential for development of fungicide resistance.
Good fungicide management decisions come down to an understanding of the disease triangle. In order to have the disease, you need a susceptible host, a virulent pathogen and the right environmental conditions. Check the leaf disease resistance ratings in the Varieties of Grain Crops. Scout your fields and watch for signs of the disease. Pay attention to weather patterns. The primary goal is to protect the upper canopy so those leaves can be contributing to yield. Determine if the crop is worth further investment to protect it from leaf disease, based on yield potential, price, potential loss due to disease and the cost of the fungicide application. There are a lot of factors to consider, but early-season fungicides generally shouldn’t be one of those considerations.