Tips to control hard-to-wet weeds

June 15, 2011 - Issue 12

A good test to see how well weeds will retain a herbicide spray is to shower them with water and see how wet they get. If the water sticks, they should retain a coarse spray fairly easily. But if the water rolls off and the plant stays dry, these weeds may be harder to control with larger droplets. Cleavers, kochia, lamb’s-quarters, and volunteer canola are examples of hard-to-wet weeds, especially as they get larger and their waxy cuticle prevents herbicide uptake.

For these weeds:
—Do not use very coarse droplets. Dial down to coarse or even medium droplets if it’s warm, sunny and not too windy.
—Use higher water volumes. With Liberty, use at least 10 gallons per acre. Glyphosate tends to work better with lower volumes, but don’t have the volume so low that there aren’t enough droplets to hit all small weeds.
—Contact products need better leaf coverage than systemic products. Higher water volume and smaller droplets are important for contact products.

Overwintering canola. On the topic of hard-to-wet weeds, some growers with unseeded acres have large overwintered canola plants to contend with. Canola that emerges in the fall can survive the winter and have a head start in the spring. Some of these “weeds” are already bolting. After the 5-leaf stage, canola develops its waxy cuticle and is hard to control. Aerial application now may be the best choice if it will be a few weeks before the ground sprayer or cultivator can get on the field.

Spraying Liberty with no sunshine. Liberty works best on warm sunny days, but some growers have waited a long time for a warm, sunny and calm day. The weeds can’t wait any longer. If you have to spray Liberty on a cloudy day, increase water volumes and consider spraying later in the day when temperatures are at their highest.

Canola Watch