June 27, 2017

Growing organic strawberries in Minnesota

by Emily Hoover, Carl Rosen, Jim Luby, and Suzanne Wold-Burkness.

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Many of the practices in conventional strawberry production are applicable to organic growers as well; starting with site selection and planting healthy, virus-indexed plants obtained from a reputable nursery.

Organic strawberry production methods are determined by the USDA organic certification standards. In general, the standards allow the use of natural methods and products and forbid the use of synthetic products. Because of this, pest management options may be limited for organic growers. Natural fertility sources such as manures, organic amendments, and mineral powders can require changes in fertility management strategies.

Cultivar Selection

According to the USDA organic rules, in perennial cropping systems, “nonorganically produced planting stock that is used to produce a perennial crop may be represented as organically produced only after the planting has been maintained under a system of organic management for a period of no less than one year”.  These cultivars have proven successful in Minnesota. However, please verify all information with your certification agency.

Table of June bearing strawberry cultivars. Click to enlarge. 

Junebearing Strawb Cvs

Nutrient Management

Organic soil fertility management is achieved by increasing soil organic matter, biological activity, and nutrient availability. By increasing soil organic matter through the use of cover crops and crop residues, the soil contains the nutrients needed for strawberry plant growth. In addition to increasing soil organic matter, commercially available organic fertilizers may be needed. Sources of organic fertility options can be found at ATTRA’s Sources of Organic Fertilizers and Amendments.

Weed Management

One of the major challenges facing all strawberry producers is weed control.  Controlling weeds in organic farming systems requires the use of many techniques and strategies in order to achieve economically acceptable weed control and yields. In general, perennial weeds are of particular concern. Once establishedSimilar to the conventional grower, hand weeding, hoeing, cultivation, and mulching are the most effective weed management options. Alternative options include the following:

Stale seedbed

The stale or false seedbed technique of flushing out weed seeds from the soil works by depleting the seedbank. Following cultivation the emerging weeds are either killed by flaming or by light cultivation. This technique may need to be repeated numerous times the year before planting to reduce the seedbank and perennial weeds.

Flame Weeding

Flamers can be used for weed control in the establishment year of strawberry production. Heat causes the cell sap of plants to expand, rupturing the cell walls; this process occurs in most plant tissues at about 130º F. Weeds must have less than two true leaves for greatest efficiency of the burner. Grasses are harder to kill by flaming because the growing point is below ground.

Alternative Cultivation Options

Researchers in Ohio have found success with the brush hoe in matted row strawberry production. By using two well-timed passes, the brush hoe was able to provide excellent season long weed control. They also found that the dust created by the brush hoe “mulched” the field and suppressed weed seed germination (M. Pritts and M. Kelly, 1999. Trials and tribulations of weed management in strawberries. New York Fruit Quarterly. Vol. 7, No. 3).

Alternative Systems

University of Minnesota researchers have found that plastic mulch, low tunnels, and woolen landscaping fabric are effective alternative weed control methods. In research trials, one-ply woolen fabric centered over the crop nearly eliminated weeds from rows, promoted daughter plant rooting, and allowed for maximum fruit yield. In addition, in a related study, researchers found that a combined wool-canola ground cover to have greater colonization of arbuscular mycorrhizal fungi, which have been found to increase nutrient uptake and protect against plant pathogens.

wool mulch strawberries

Wool mulch inhibits weed growth, but allows water to pass through and permits the rooting of daughter plants

 

Low tunnels provide protection from rain which prevents many fungal diseases. Plastic mulch virtually eliminates weed growth in the rows and prevents many diseases due to the lack of contact between foliage/fruit and the soil.

low tunnel strawberries

Low tunnels and plastic mulch facilitate organic production of strawberries.

Weeder Geese

Geese have been used for weed management in a large number of crops for many years. At Michigan State, researchers studied the impacts of populations of domestic geese and chickens in a non-chemical orchard system. They found that geese fed heavily on weeds, and preferred grasses. In addition, if the geese were confined, they will dig up and eat Johnsongrass and bermudagrass rhizomes. For more information on aspects of weed management:

Disease Management

Soil health and management are the keys for successful control of plant diseases. A soil with adequate organic matter can contain numerous organisms such as bacteria, fungi, nematodes, protozoa, arthropods, and earthworms that may suppress soil-borne pathogens. Increasing soil organic matter by incorporating cover crops or adding compost and organic fertilizers will help maintain beneficial organisms. Rotating strawberries with other crops is critical. The site should be plowed and planted to a crop that is not susceptible to Verticillium wilt for a minimum of two years.

Many soil-borne pathogens form specialized survival structures and are capable of surviving for several years in soil, even when strawberries are not present. Crop rotations lasting longer than two years are encouraged, however, crop rotation is not enough to provide adequate control of red stele. It is essential that disease resistant varieties and improved soil drainage are used. See the ATTRA publication Sustainable Management of Soil- Borne Plant DiseasesMost organic fungicides and biological control agents are not highly effective against the overall disease complex on strawberry. Copper fungicides have been recommended and used for control of angular leaf spot; however, once the disease is established in the planting, copper fungicides will do little to control it. Many products are currently available or currently being introduced as “biopesticides”. These include living microorganisms, natural chemicals such as plant extracts, and “plant activators” that induce resistance in plants to disease. For more information on biopesticides and disease management, see the following publications:

Insect Management

Management of insect pests begins with proper identification of the egg, larva, and adult stages of both insect pests and beneficial insects. The correct identification of insects will aid in the grower’s efforts to prevent economic damage to the crop. A scouting program with regular monitoring can help growers determine both the pest pressure and presence of beneficial insects.

Beneficial insects such as predators and parasites are important in preventing outbreaks of insect pest populations. To encourage the presence of beneficial insects it is important to increase plant diversity in an agricultural setting. Crop diversity can be achieved by using crop mixtures, crop rotations, border crops or windbreaks, or plants known to be attractive to beneficial insects. To assess insect pest and beneficial activity, use of sticky traps or visual plant samples. These traps are sheets coated on both sides with a sticky non-toxic compound.Most flying insects are attracted to the yellow or blue color of sticky traps. Traps can be used for detecting presence of arthropods or for mass trapping of pests such as aphids and thrips.

Some insect pests can be managed by establishing trap crops near the field. Trap crops are plants that are typically more attractive to the target insect. The trap crop is established next to, or surrounding, the field that is to be protected. By planting a more attractive crop, the expectation is that the insects will fly to the more attractive trap crop, where they can then be treated with an insecticide, or vacuumed using a Bug vac (bug vacuum).

Bug vacuums are an interesting non-chemical approach to insect pest management, and can range from tractor- mounted machines to small hand-held devices. Understanding how the insect uses and moves in its environment is crucial in designing a successful trap crop system. For more information on bug vacuums, see the ATTRA publication Bug Vacuums for Organic Crop Protection. For a list of OMRI approved pesticide options, see the The OMRI Products List.

Biological Control and Trap Information

General Organic Resources

Note: Prior to using any material in the organic system, it is important that the grower consult his/her organic certification agency or program to be positive that use of the material or technique is permitted in the certification. Growing strawberries organically may sound challenging, however, organically grown berries may command a price premium since the demand for organically grown produce has increased significantly over the past decade. Before starting, put yourself in the best possible situation by researching your intended market area. If you have a large potential market, the increased price that you will be able to charge for your berries is acceptable, and the chances of successfully growing organic fruit are fairly high, then organic production may be promising.

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