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Dr. Michelle Moyer, Washington State University

Dr. Michelle Moyer, Washington State University

When trying a new product, conducting an on-farm spray trial is critical to determine if the new treatment was effective, says Washington State University’s Dr. Michelle Moyer.

“Any time you use a new material—for whatever reason—it’s important to have your own trial so that you know if it really worked. Otherwise, positive results may not be related to the product, but could be that it was a low pressure year for the disease or insect,” Moyer said.

Spray trials are easy to do on your own and don’t have to be complicated with randomized replications, she said. They can be as simple as leaving a few rows for the control.

When designing a spray program, first understand your target and know why you are spraying. Next, consider resistance management and know what you are spraying. Third, build your program by identifying when to spray, timing applications when the target is most ­susceptible. Lastly, test new products and be able to interpret results to judge how well your program is working.

She outlined key points to follow when designing an on-farm spray trial:

1 Make sure you’re doing things right. If your powdery mildew program wasn’t effective last year, before making radical changes, first make sure the sprayer is calibrated, nozzles are properly working, and tractor speed is appropriate (2.5 to 3 mph).

2 Only test one thing at a time. If trying out a new fungicide, only test the fungicide. Don’t change two things together, like trying a new surfactant or combining the new fungicide with leaf removal. If you have more than one thing to test, set up multiple controls.

3 Always have a control. A control can be a few rows if you want to apply the new product to the majority of the vineyard, or it can be most of the vineyard with the new product applied to a few rows. Control means your standard practice and allows you to directly ­compare results.

“If you don’t have a control, you don’t have a baseline. You won’t know if the change you saw was due to weather or other practices,” Moyer said.

For example, if you used lime sulfur as a dormant spray in 2012 and saw little powdery mildew in 2013, you may believe the product was effective. But the lack of powdery mildew last year was likely related to the hot, dry weather.

4 Have an information collection plan. Know what kind of data you are going to collect and when you will collect it. Build in a “busy” time factor.

5 Interpret your results. Look at the variations of your data, not just the averages, to figure out if the change was worthwhile. For example, four fruit samples of the treatment and control analyzed for Brix could show variation of two to three degrees but result in the same average.

Suppose the control fruit had Brix of 24, 25, 23, and 23 over four years, while the treatment fruit had Brix of 26, 22, 21, and 26 in the same four years. If you look only at the average, they would both be the same at 23.75 Brix.

6 Repeat and replicate. Replicating the experiment means having the treatment and control represented several times in the same block. Repeating refers to doing the exact same experiment for another or multiple years, or doing it at another separate location or with a different variety. “Replication aims to capture any site variation, while repetition aims at capturing variation due to weather or microclimate,” she explained. •