Spraying before a rain

May 26, 2016 - Issue 10

Spraying in the rain is not advised. Product washes off before it gets absorbed. However, spraying just before a rain — allowing enough time to satisfy label requirements — can provide effective control, especially if rains are forecast for a few days and weeds are growing strong.

If rains are coming and you're spraying, keep in mind the required rainfall interval for the product you're applying.

If rains are coming and you’re spraying, keep in mind the required rainfall interval for the product you’re applying.

The rainfast requirement varies by product. Here are required intervals for each common product used in HT canola systems:

—Gylphosate-tolerant (Roundup Ready) canola. Check labels for specific glyphosate products. Roundup WeatherMax is rainfast within 15 minutes, which is the shortest interval of any HT canola product.

—Glufosinate-tolerant (Liberty Link) canola. With Liberty, rainfall within 4 hours may reduce control.

—IMI-tolerant (Clearfield) canola. Ares is 2 hours. Odyssey, Odyssey Ultra, Solo and Solo ADV are all 3 hours.
Tensile is 4 hours because of the clopyralid. Note: With Ares and Odyssey/Odyssey Ultra, rain only affects the foliar efficacy; it doesn’t affect the residual weed control from those two products.

Two things to keep in mind:
1. Some pesticides (including herbicides) are limited to one application per season, according to active ingredient, even if washed off by rain. If efficacy is reduced due to spraying in the rain, options for second chance applications may be limited.
2. When dodging rains during weed management season, keep in mind that a sprayer sitting idle with product in the tank will increase the risk for product contamination. Read more.

Canola Watch