Weed control in perennial strawberry

Renovate strawberry fields after harvest to improve crop production next year.

Much of the 2017 Michigan strawberry crop was lost as a result of a frost in early May. The blossoms had not yet opened, so many growers did not take frost control action. Cool, wet conditions throughout May also may have reduced honey bee activity, and the few remaining blossoms were poorly pollinated.

The crop was about two weeks late in mid- Michigan, coming primarily from scattered individual blossoms. There were few fruit clusters, as is common in normal strawberry production. Statewide, the crop was in the 25-30 percent range. For more information on the poor strawberry crop, see the Michigan State University Extension article, “Why are the strawberries so small this year?

With no fruit to support, strawberry plants grew very well. Plants 10-12 inches tall are not unusual. Now that spring bearing strawberry harvest is over for the year, growers should renovate the fields to encourage new growth and prepare for production next year. Those beautiful, tall plants need to be mowed off to about 2 inches, the field fertilized, the rows narrowed and residual herbicides applied. The renovation process extends the productive life of a field of "matted row" spring strawberry production for two to four years.

Weed control is an important factor in renovation. If there are many large weeds standing above the strawberry, apply 2,4-D (Formula 40) before mowing. Wait three days, then mow the field. If the weeds are smaller than the strawberry, apply the 2,4-D after mowing. A post-emergence grass herbicide, such as sethoxydim (Poast) or clethodim (Select Max), should be applied to kill annual and perennial grasses. Include an adjuvant with the grass herbicide.

Before narrowing the rows with a rotary tiller, broadcast 50 pounds of actual nitrogen per acre over the field. The nitrogen can be in any form since the field will be rotovated and watered soon. An adjustable tiller that straddles the row is the most effective machine for renovation. Narrow the rows to about 10 inches. The remaining plants in the rows will then regrow and send out runners that take root and become the fruiting plants the following year.

After the renovation process is complete, apply residual herbicides to control weeds for the rest of the summer. Herbicides labeled for use at renovation include Devrinol, Dual Magnum, Spartan, Prowl H2O, Sinbar and Ultra Blazer. For broad-spectrum, full-season weed control, include two residual herbicides in the post-renovation application. Effective mixes include a primarily grass herbicide (Devrinol, Dual Magnum, Prowl H2O) and a primarily broadleaf herbicide (Spartan, Ultra Blazer). Read labels to determine which weeds will be controlled for your situation.

Sinbar is a very effective herbicide, but may stunt strawberry on light sandy soil. Do not use Sinbar on soils with less than one percent organic matter or over 70 percent sand. Chateau also may be used on strawberry, but should only be applied to aisles between rows. It is most appropriate for strawberry grown on raised beds on plastic mulch.

Spartan, Sinbar and Ultra Blazer may be applied in late fall before spreading of straw mulch. Apply only one residual herbicide in the fall. After removing mulch in the spring, apply another single or tank mix herbicide.

Clopyralid (Stinger) is the only post-emergence broadleaf herbicide labeled for strawberry, other than 2,4-D. There are several generic clopyralid herbicides available. Apply clopyralid in early to mid-fall to control legumes, composites (asters and daisies), nightshades (including groundcherry) and smartweeds (including prostrate knotweed, red sorrel and wild buckwheat). Another grass herbicide application may be made at this time. Some weeds will escape all of these herbicide applications, and should be removed by hand.

On light soils, another application of 50 pounds nitrogen will give the plants a boost and prepare them for fall dormancy. This should provide more vigorous growth in the spring. Timely irrigation during summer and early fall will promote plant growth and health. This will result in production of many fruit buds in the spring and a larger crop.

Drs. Zandstra and Hanson’s work is funded in part by MSU’s AgBioResearch.

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