Strawberry

Weed Control

An effective weed control program combines initial identification of the weeds with appropriate cultural and chemical control procedures. Consult your provincial weed guide for recommended herbicides, rates of application and spraying procedures.

Precaution - Phytotoxicity

Note: The following is an excerpt from the "Guide to Chemical Control For Strawberry Production In Atlantic Canada 1989, Publication 1012".

Herbicides must be applied at the recommended rates to avoid injury. Cultivars vary in their sensitivity to herbicides at certain stages of the plant growth cycle. Application of a trial strip in the field before overall treatment is recommended when specific cultivar recommendations are not available. A chance of phytotoxicity from excessive rates on the stage of growth of the plants is much greater with herbicides than with most other pesticides.

Crop injury from use of herbicides is not uncommon, particularly on light soils. Post emergent application injury can result from use of a high rate on light soils, improper timing of sprays, improperly calibrated sprayers, sensitive cultivars and weak plants growing under favorable conditions. Injury can take the form of temporary chlorosis or yellow "haloing" of margins around the leaf edge. This is followed by complete chlorosis and finally death of the plant.

Newly planted and actively runnering strawberries are especially sensitive to herbicides. Crop tolerance increases in late summer and fall. Light soils (sandy soils) require lower rates than heavy soils for comparable levels of weed control. Strawberries growing on soils low in organic matter are especially prone to herbicide injury. Lower rates of herbicides should be used on fields containing less than 2% organic matter. Do not exceed maximum recommended annual application rates or overlap areas during application. The use of a flat fan type nozzle is recommended.

Straw Fumigation

Weed seeds tend to be killed in straw when it is treated with ammonia. This reduces weed seed introductions from straw used as mulch. Fumigated straw is also somewhat less rigid than nonfumigated straw.

Mulching with fumigated straw is an excellent way to reduce weed problems in production of day neutral strawberries where herbicide options are limited due to days-to-harvest restrictions.

To fumigate, straw is tarped with plastic and ammonia gas is injected at the rate of 2% of the straw?s dry weight. For example, a 60 lb (27 kg) bale of wheat straw with 20% moisture has a dry weight of 60 x 0.8 = 48 lb (22 kg). Therefore, the amount of ammonia to inject into the bale would be 48 x 0.02 = 1 lb (0.44 kg) of ammonia gas. This calculates to 42 lb/ton (20 kg/t) of straw.

Preparing the Land

To ensure optimum weed control throughout the entire life of the strawberry field, the crop must be established in soil that is as weed free as possible.

In fields with perennial weeds such as quackgrass and thistle, do not cultivate in the fall prior to a fallow year. Short- term cultivation tends to propagate rather then control these weeds. Chemical control may be an option for late summer-fall use. In the spring, till at a shallow depth to control annual weeds. Allow perennial weeds to recover and apply herbicides as recommended.

Applying a registered pre-plant herbicide in the spring will reduce labor requirements for weed control in the first year.

On Newly Planted Strawberries

When preparation for a new strawberry field includes recommended summerfallow practices and use of a pre-plant herbicide, only the few weed seeds which germinate should be a problem after transplanting. It is important to realize that the herbicide treatments recommended in the summer after transplanting will not control perennial weeds that grow from underground root structures. Most weeds growing from seed can be controlled if a recommended herbicide is used.

After Transplanting

Cultivation will be necessary to control weeds until plants are established. Once plants are well set, herbicides can be applied two ways: as an overall spray, or as a band applied over the row combined with cultivation between the rows. The latter procedure minimizes the cost of herbicide application.

Four to Six Weeks After Transplanting

Several excellent herbicides can be applied after mother plants are well established. At this stage, care must be taken with certain pre-emergent chemicals to ensure full rooting of the mother plant and daughter plants.

Several post-emergent herbicides can also be effective when applied at the correct growth stage of weed seedlings.

In Established Beds

Applying pre-emergent herbicides in the fall, prior to mulching, will give effective control of weeds germinating in the spring. Perennial weeds should be controlled with spot application of herbicides. Registered post-emergent herbicides for broadleaf and grass control can be applied in the bearing year prior to harvest, providing the "days to harvest" are observed.

Several pre-emergent herbicides and be applied after renovation to control germinating weeds up to strawberry dormancy. However, care must be taken to ensure the planting is strong enough to withstand the potential herbicide injury.

For more information, consult the Fruit Crop Protection Guide for Commercial Growers.