Weed control at strawberry renovation

June is the most critical time for residual weed control in strawberries.

Residual herbicides are applied to strawberries in early spring, at renovation after harvest and in late fall. Herbicides applied at renovation in June or early July should control annual and perennial grasses and broadleaves until the strawberry plants become dormant after frost in November or December. Thus, the applications made now need to maintain weed control for five months while the strawberry plants expand with new runners and fill in the rows. Inadequate or ineffective weed control at renovation results in poor strawberry plant growth during the rest of the summer, and reduced fruit production the following spring.

A weed control program for strawberries should be developed and implemented in the fall. The late fall herbicide application will help maintain weed control through harvest the following spring. An early spring application provides additional preemergence protection from annual weeds. However, it is often difficult to remove straw mulch and apply the herbicides before the strawberries and weeds begin to grow. Herbicides broadcast over the field in the spring often are applied over the straw mulch, which reduces the effectiveness of the herbicides.

Several herbicides are effective and labeled for use at renovation. Sinbar, Spartan, Prowl H2O and Ultra Blazer may be applied at renovation or in late fall. Spartan plus Prowl H2O is a good combination for use at renovation. Sinbar may be used at renovation, but is more effective if applied in the fall as a dormant application. Ultra Blazer is most effective when used in fall.

After harvest is complete, the field should be renovated within one week. If there are many large, broadleaf weeds, the field may be sprayed with 2,4-D (Formula 40) after mowing off the plants. Mowing reduces the leaf surface of weeds, but usually there is enough leaf surface to absorb sufficient 2,4-D to kill them. Broadcast 300 lbs 20-20-20 fertilizer or the equivalent. Then, rotovate the rows to reduce width to 10 to 12 inches. After tilling, apply Spartan plus Prowl H2O or Spartan plus Ultra Blazer.

Grasses often emerge during the summer. If so, they can be controlled with Poast or Select Max. Use the highest labeled rate of these herbicides for quackgrass control. Include 1 percent crop oil concentrate in the mix. If composite or legume weeds become a problem in late summer or fall, apply Stinger alone.

In late fall, apply herbicides that will maintain weed control through harvest the next spring. Sinbar at 8 oz (0.4 lb ai) plus Ultra Blazer at 1.5 pt (0.375 lb ai) will control most annual broadleaves and grasses the next year for about two months.

Chateau is labeled for application to strawberry row middles. It may be applied in the spring if carefully applied with a hooded or shielded sprayer. It should not be applied over the top of strawberry plants at any time. Devrinol may be applied in the spring to established plantings. It provides about three to four weeks of weed control. A new, UV light-resistant formulation of Devrinol should be available within the next year. It will provide weed control for about double the control period of current Devrinol.

By rotating herbicides and using both preemergence and post-emergence applications, it should be possible to keep weeds to a minimum and produce a large crop of strawberry fruit.

Dr. Zandstra’s work is funded in part by MSU’s AgBioResearch.

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