Azoxsytrobin (Quadris, Tetraban) is the most used fungicide on rice in California. Azoxystrobin has been in use since the late 1990s. This fungicide was registered after rice blast was discovered in California in 1996. More recently, several years of trials showed that when azoxystrobin is used at the late boot to early heading stage, severity of the tiller diseases stem rot and aggregate sheath spot can be reduced. Currently, azoxystrobin is used in over 300,000 acres of rice annually.
A common question I get is about the potential of azoxystrobin to increase yield or grain quality even when disease is absent. I conducted trials in 2023 and 2024 to answer this question. Each year, trials were set up at two locations with very low levels of tiller diseases, no blast, and no smut. Each trial consisted of an untreated control and two rates of Quadris (12.5 and 15 oz/a). In 2023, there was no increase in yield or quality at any of the locations. In 2024, at one of the locations (Yolo County), there was a tendency to have higher grain yield (6 cwt higher) when rice was treated with 12.5 oz of Quadris. Milling yield or head rice yield was not affected. At the second location (Glenn County) grain yield was not affected but milling yield was higher (1 point higher) when Quadris was applied at 12.5 oz/a. Head rice yield was not affected.
Putting these results together, we can say that in one trial out of four we detected an increase in grain yield and in one trial out of four we saw an increase in milling yield. I never detected an increase in head rice yield. The increase in grain yield and milling yield may be due to the “greening” effect of Quadris. This effect has been well documented in other crops and rice growers know it well. Fields treated with Quadris stay greener for longer; this may result in a slightly longer grain filling period that may cause higher yield. However, this does not seem to occur every year or at every location. Most likely, these results are weather dependent. Since we don’t know what type of grain filling weather we are going to have at the time the fungicide is applied, it is difficult to make a recommendation. At most, we can say that under very low disease pressure, you may see benefits from an azoxystrobin application 25% of the time. Given the price of rice, 2026 might not be the year to try your luck. Remember, this is under no disease pressure. If disease is present, then it is a different story.