Weed Control Primer

“You really have to know the weeds in your fields when you are growing cole crops,” said Bernard Zandstra, a professor in the Department of Horticulture at Michigan State University, to a roomful of people at the Great Lakes Fruit, Vegetable & Farm Market Expo last month in Grand Rapids, MI.

To help growers get a handle on the products available to control those weeds, Zandstra walked through the preemergent herbicides labeled for broccoli, cabbage, and cauliflower and well as the post emergence products labeled on cole crops.

Preemergent Products
Starting with Treflan (Dow AgroSciences), Zandstra said this herbicide provides good control of annual grasses but can stunt plants if it is used when the temperature is below 50° F. Devrinol (United Phosphorus, Inc.), which Zandstra said is equal to Treflan, doesn’t cause stunting and is most effective if used on the soil surface. Devrinol, however, is more expensive than Treflan but Zandstra recommended it for growers who are planting early in cold weather to avoid stunting issues with transplants.

The next preemergent herbicide on the list was Dual Magnum (Syngenta Crop Protection) which controls annual grasses, nightshades, pigweeds, and nutsedge. Zandstra told growers to use a low rate of this product on sand. He cautioned, however, that post transplant applications may cause foliar burn.

Command (FMC Corp.) a product that is only labeled on cabbage, gives good control of velvet leaf, morning glory, etc., said Zandstra. “Command picks up some weeds missed by Dual Magnum and Treflan, but don’t use Command within 200 feet of a dwelling, fruit trees, and greenhouses because of drift issues,” he added.

Goaltender (Dow AgroSciences), he said, should be used before transplanting. He warned growers that this herbicide should not be used with Dual Magnum as that may cause stunting.

The last herbicide for preemergence use in cole crops, said Zandstra, is Spartan (FMC Corp.), which is labeled only for processing cabbage. “We have been working to get the label expanded,” he added. “In really weedy conditions, Spartan can be a big help.”

Postemergent Herbicides
Goaltender, also on the postemergent herbicide list, Zandstra said should be applied alone to avoid foliar burn. “Goaltender may be applied over the top of broccoli, cabbage, and cauliflower transplants after they are well-established. It will control many small broadleaf weeds but misses most of the weedy mustards and has no effect on grasses.”

Next on the list is Stinger (Dow AgroSciences), which is very similar to 2,4-D. “This product is very safe to use and can be applied at any crop stage,” he explained. “Although it has no effect on mustards, Stinger does a good job controlling pineappleweed, hairy vetch, horseweed, and ragweed.”

The last two on the list, Poast (BASF) and Select Max (Valent USA), are known as the grass killers. “They are more effective on young grasses, so don’t wait to long,” Zandstra added.

Weed Control Guidelines

Bernard Zandstra, a professor in the Department of Horticulture at Michigan State University, told growers to use the following as a guide to effective weed control in cole crops.

1. Work the soil twice before transplanting. “In other words, work two weeks ahead of time,” he explained.

2. Apply Treflan (Dow AgroSciences) or Devrinol (United Phosphorus, Inc.) and incorporate before final tillage. Zandstra suggested growers go about 1 inch into the soil.

3. Apply Goaltender (Dow AgroSciences) to the soil surface after tilling.

4. Transplant crops.

5. Three to six weeks after transplanting, apply Goaltender or Stinger (Dow AgroSciences) for broadleaf control. “Or apply both if you need it,” he said.

6. Apply postemergence grass herbicides as necessary.

A Michigan State University researcher tells growers what they need to know to keep their cabbage, cauliflower, broccoli, and fields of other cole crops free of weeds.