STRAWBERRY PRODUCTION SYSTEMS

(Click here for another article on organic research in berry crops)

Marvin Pritts
Department of Horticulture
Cornell University, Ithaca, NY

and

Joe Kovach
Fruit IPM Program - NYAES
Geneva, NY 14456

Demand for organically grown produce has been increasing significantly over the past decade as the public often perceives organic produce to be healthier than conventional fruits and vegetables, and a portion is willing to pay extra for organics. Tomatoes, sweet corn, lettuce, onions, carrots, melons and strawberries already are produced by organic growers in significant quanities. States with the most organic production are California (30%), Oregon (16%), New York and Texas (11%) and Michigan (8%) (1994 Chemical Use Survey, USDA Marketing Service).

Can strawberries be grown organically for a profit? Organic strawberry systems have 5 characteristics in common, regardless of the location in which they are grown.

1. several years between successive crops of strawberries
2. short production cycle (1-2 fruiting years)
3. high labor requirements
4. lower yields
5. greater variability in yields

All of these characteristics result in a greater expense for the organic grower than the conventional grower, but if the price of berries is higher, then production can be profitable.

For example, organic and conventional annual strawberry production systems were examined in California over a three year period (Table 1). Both systems cost a similar amount to establish ($22,000/acre-year), and the organic system yielded less (27,100 lb/A vs. 40,200), but the organic system averaged a higher return because the price received for fruit was 50% higher (Calif. Ag. 50:24-31).

In an attempt to determine the costs of production and breakeven price for organic matted row strawberries, a comprehensive spreadsheet developed by Alison DeMarree and Regina Rieckenberg of Cornell Cooperative Extension was used to calculate production costs and profit for matted row strawberries, and the assumptions were changed to conform to organic production. For example, any costs for synthetic inputs such as fertilizers and pesticides were eliminated, but yields were reduced by 30 - 70% as well - with the greatest decrease in later years. For example, in fruiting years 1 - 4, conventional yields were set at 7,000, 7,000, 4,000 and 3,000 qts/A, whereas organic yields were set at 5,000, 4,000, 2,000 and 1,000 qts/A. 104 hours of labor we assigned to weed the organic fields, but only 52 hours per year to weed the conventional fields. All fruit was hand harvested for sale. Conventional prices were set at $1.75/qt. Organic prices were set at $2.00, although significantly higher prices can be obtained at urban markets (up to $3.50/qt.).

The breakeven price for the conventional system was $1.10/qt. (Table 2), whereas the breakeven price for the organic strawberries was 34% higher at $1.47/qt (Table 3). By the 4th bearing year, however, organic strawberries were losing money. This supports the practice of many organic growers of fruiting their fields for only 2 years. If fields are rotated out of strawberries after 2 fruiting years, then a positive cash balance is obtained.

The enterprise budget for organic strawberries does not include the costs of a fallow period between cropping cycles, which is a real expense for organic growers. On the other hand, the fixed costs of both systems were set at equivalent values, even though an organic grower is likely to have less equipment (e.g. herbicide sprayer). Regardless of the details of the budget, one can conclude generally that organic strawberry production can be as profitable as conventional production if the price differential for fruit approaches 35 - 40% (Table 4). This is consistent with the price differential required in the annual production system as well. The size of the market for $2.40/qt. berries is limited in many regions of North America, but not all. Therefore, a profit opportunity does exist for organic strawberries in certain marketing niches.

Organic production systems of the future - New techniques of nutrient and pest management are under development that could be used by organic strawberry growers to enhance their production and improve soil quality.

Use of specialized rotational cover crops - Planting berries through strips in a rye residue can enhance weed control in lighter soils. Recent work with marigolds, sudangrass, brassicas, and certain native prairie species (e.g. Rudbeckia) have found them to be suppressive to nematodes, pathogens and weeds. Certain of these may be particularly suited for rotations with strawberries, but might be too expensive for lower-value crops.

Use of interplanted cover crops - Interseeding oats and sudangrass between rows after harvest can supplement weed control, help improve soil structure, and improve winter mulching practices.

Use of bees to deliver biological control agents - Bees are being used to deliver spores of Trichoderma fungus to strawberry flowers to provide protection from Botrytis infection. Tests show that this works in the field as well as fungicide sprays. Bees also could be used to distribute predatory insects throughout a berry field. Such work is no longer limited to honey bees as bumble bees and orchard bees are being developed for use in fruit plantings.

Use of entomopathogenic nematodes and fungi to manage insect pests - Special strains of nematodes are being developed that will attack grubs and weevil larvae in strawberry fields. Similarly, pathogens of insect pests are being developed and tested in strawberry fields. Once robust delivery methods are identified, then the use of these organisms will become routine.

Use of parasites/parasites to manage insect pests - Parasites of tarnished plant bug and sap beetle have already been tested in strawberry fields. The use of predatory mites is routine in some areas of Florida and California where the climate is mild. Development of hardy, adapted predators is a next step in achieving acceptable control. The techniques of molecular biology are being used to improve the adaptation of predatory mites in Florida.

A better understanding of thresholds - Strawberries appear to be able to tolerate more weed pressure in late August and September than earlier in the season. Also, recent work has suggested that strawberry plants can compensate for clipper injury by increasing the size of remaining fruit, indicating that for most growers in most years, strawberry clippers are not economically important pests. Improved scouting techniques, such as the use of white pan samples rather than sticky cards, have enabled growers to identify more precisely when tarnished plant bug damage actually occurs. This knowledge allows organic growers to make better management decisions.

Improvements in varieties - Many of the new strawberry varieties are resistant to several races of red stele and verticillium wilt, show tolerance to nematode feeding, and resist gray mold infection. Some show tolerance to feeding by tarnished plant bugs, and certain selections appear to be tolerant to black root rot. Most of these newer varieties have improved postharvest qualities, yet have maintained a high degree of flavor.

Use of analytial techniques to monitor nutrition - Soil and leaf testing services are available and being refined to enable organic growers to determine if nutrient levels are adequate, and to monitor long-term trends in soil fertility.

Research needs

The advances mentioned above have been developed separately, under tightly manged conditions, but have not been combined under field conditions. At Cornell, we have a large systems trial in which an organic production system, a futuristic IPM system, and a conventional IPM system are being compared. We hope to learn about the gaps and synergies in these systems in order to identify improved production systems in the future.

A pressing reserach need is to understand the relationship between system diversity, stability and productivity. How much diversity must be sacrificed in order to achieve acceptable levels of crop production? How is diversity related to long term stability of the system? How important are soil microorganisms in maintaining a stable system? What are the roles of these bacteria, fungi, mites and nematodes, and how can their activity be managed to positively influence crop production?

Clearly there is much to be done, but we are making progress.