Is Scouting For Rice Diseases Effective?

Scout for presence and level of disease in each field

By Don Groth
LSU AgCenter

In times when rice prices are low, producers must keep production costs low. One area to save money is on fungicide applications. Applying a fungicide when needed can greatly improve the return you receive from a crop. But applying a fungicide when it is not needed will not increase yield, milling or the second crop.

Prediction of fungicide use is based on the susceptibility of the variety and, more importantly, scouting for presence and level of disease in each field. Remember, the only reason to apply a fungicide is to make more profit.

Field Test Results

Here’s an excellent example of how scouting can improve the return from fungicide applications: Sheath blight fungicide trials were conducted in 2008 and 2009 at three locations – the LSU AgCenter Rice Research Station at Crowley, Lake Arthur and Fenton.

Four varieties – CL151 (susceptible), Cheniere (susceptible), Catahoula (moderately susceptible) and Neptune (moderately resistant) – were treated with four fungicide treatments at mid-boot.

Screen Shot 2015-05-14 at 9.56.32 PMThe four treatments were an unsprayed check, Quadris at 9 oz/A, Quilt at 28 oz/A and Stratego at 19 oz/A. Plots were scouted for sheath blight infestations at panicle differentiation based on the percent positive stops method. Sheath blight severity, infestations and rice yield were determined.

Over all the trials and treatment combinations, fungicides significantly increased yields 50 percent of the time with an average yield increase of 592 lb/A (Table 1).

Neptune did not require spraying five of six times because of its moderate resistance to sheath blight. When Neptune was eliminated from the calculations, fungicides significantly increased yield 63 percent of the time with an average yield increase of 729 lb/A. The Lake Arthur location did not exceed the treatment threshold, and when it was eliminated from the calculations, fungicides significantly increased yields 67 percent of the time with an average yield increase of 782 lb/A.

When Neptune and Lake Arthur were both not included in the calculations, fungicides significantly increased yields 86 percent of the time with an average yield increase of almost 1,000 lb/A – plus we only used about twothirds of the fungicide as blanket applications to all fields, reducing costs.

Factors Contributing To Need For Fungicide

Knowing the disease reaction of a variety and scouting for sheath blight allowed for a more accurate prediction of fungicide needed and greatly increased fungicide yield response compared to blanket applications on every variety, every location and every year.

Fungicide applications were counterproductive (yield losses) in cases where severe sheath blight was not present. The story is the same for blast if the variety is not susceptible and no leaf blast is present; a fungicide application is seldom profitable. You may see some disease in the field at the end of the season, but it takes a lot of disease to cause a significant loss.

That is why you should scout for sheath blight and other diseases. Less costs, more profits.

Dr. Don Groth is a plant pathologist, LSU AgCenter in Crowley. Contact Dr. Groth at dgroth@agcenter.lsu.edu. This article was published in the May 1 issue of the LSU AgCenter Rice Research Station News.