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Blueberry Site Preparation

At least one year prior to planting, collect soil samples to determine if soil modifications are necessary. All perennial weeds, including quackgrass, Canada thistle, field bindweed, curly dock, horsetail rush, blackberries, and others need to be totally eliminated. Fall plowing prior to spring planting is not adequate. A broadcast application of herbicide followed by plowing and discing will kill many perennial weeds. Some leveling may be necessary to eliminate low areas in the field. Drain tile may be required on some sites.

Once the field is cleared and drainage problems have been addressed, adjust nutrient levels and/or pH based on the soil tests, if necessary. Spread any required soil amendments or nutrients entirely over the area to be planted and incorporate to a depth of 8 to 12 inches. Avoid treating just the strips into which the plants will be planted. (See Nutrition).

In order to protect the ground from weed invasion prior to planting, cover crops can be sown. Annual cover crop choices include cereal grains such as wheat, barley, oats, or cereal rye (100-120 lb/A); annual ryegrass (15-30 lb/A); or agronomic crops such as corn. Add 40-50 lb/A nitrogen for cover crop establishment. Legumes do not require supplemental N, but they do not establish well on acid soils. A dense cover crop will deplete the food reserves of any perennial root systems that survived the herbicide and cultivation treatment.

Generally, grain crops are sown in the early fall to take advantage of warm soils and rain to speed germination. When the cover crop is turned under by cultivation before planting blueberries the following winter or spring, the stubble will help improve soil organic matter. If cereal rye is sown in the fall, be sure to not let it exceed a height of 9 to 12 inches the following spring because its coarse texture can make tilling difficult.

Any cover crop that grows to a height of 24 to 36 inches will probably need mowing in the spring prior to cultivation. A good stand of corn also can work well because the frequent cultivation of the corn will kill many broadleaf weeds that would otherwise have survived to re-emerge in the blueberry planting. If the previous crop was either sod or a forage legume, wireworm and white grubs (June-beetle larvae) may be present. Deep plowing and use of a cover crop such as corn should reduce these pests. (See Insects).

Ground that has been in cultivation requires considerably less work to bring into blueberry production. Sites with less than 10 percent organic matter (as determined by a soil test) usually require soil amendments.

Sawdust, shavings, compost, manure, cover crops, and other types of organic matter will promote growth of the young blueberry plants considerably during the establishment years. Plow under barnyard manure at the rate of 8 to 12 tons per acre, or 5 to 6 tons per acre of chicken manure prior to planting. Manure from excessively weedy pastures can introduce a considerable amount of weed seeds. Compost represents a better soil amendment because it has been allowed to heat up sufficiently to kill weed seeds.

If raised beds will be used, make them just prior to planting, after the soil has been modified.

Soil pH

Blueberries do best in soils with a pH of 4.5 to 5.2. If the soil pH is too high, iron chlorosis symptoms develop on leaves (green veins, interveinal yellowing). In areas west of the Cascades, the native soil pH is usually acidic unless there has been a previous crop that has required the addition of agricultural lime. Soil pH values in the range of 5.2 to 5.5 can be partially lowered by incorporating elemental sulfur 6 months prior to planting (see Nutrition ).

It is generally impractical to lower a soil of greater than 6.0 with sulfur. Growers should submit a soil sample to a reputable soil testing lab for pH determination. It can take as long as one year to see any changes in soil pH as a result of sulfur additions. Note that the continual use of acidifying fertilizers, such as ammonium sulfate, over a period of years can appreciably lower soil pH. If the soil pH is less than 4.0, use ground limestone.

Nematodes and soil fumigation

In the Pacific Northwest, the two most damaging plant parasitic species include the root-lesion (Pratylenchus penetrans) and the American dagger (Xiphinema americanum) nematodes (see Nematode Management).

While nematodes are not as injurious to blueberries as they are to caneberries or strawberries, their presence or absence should be considered prior to establishing the plantation. The expense of nematode testing is a minor one relative to other establishment costs. Instructions for taking proper nematode samples are described in the nematode section.

Testing for nematodes will determine their presence and identity. If any dagger nematodes are found, growers are advised to either fumigate the soil in the fall prior to spring planting or to grow a shallow-rooted grass species for 1 to 2 years. The cover crop will bring nematodes closer to the soil surface where they can be more easily controlled with fumigation.

If lesion nematodes are found, contact your local county Extension agent for information. Nematode counts may be high following a susceptible crop such as strawberries. Avoid the use of leguminous cover crops, as they can serve as hosts for nematodes. After any cover crop, an additional lab test should be conducted to verify that lesion nematode levels have either been reduced to low levels, or that no dagger nematodes remain.

Fall fumigation remains one of the best methods for controlling high nematode populations. There are disadvantages to spring fumigation. The soil temperature for effective fumigation should be between 45 F and 75 F at the 6 to 8 inches depth. In addition, soil moisture levels should be moist, but not wet, such that the soil barely retains its shape when squeezed in the palm of the hand.

Often during the spring, the soil is too cool and wet for effective penetration of the fumigant. Also, after spring fumigation, growers generally have to wait too long prior to planting to prevent plant injury from the fumigant.

In selecting a fumigant, consider the method of application, effectiveness on different soil types, and cost. Fumigation costs can range from approximately $300 to over $1,100 per acre.

To keep the field free of nematodes in the future, growers should purchase plants that have been grown on fumigated ground. If farm implements must be used in fields where nematodes may reside, all surfaces which have come in contact with soil should be pressure washed thoroughly before being used in the clean field to prevent reintroduction.

This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order