Vegetable Growers News
May-June 2000, Vol. 7, No. 3
Charlie O'Dell
Department of Horticulture, Virginia Tech
Before his untimely death this spring, Dr. Eric Bish, Extension Horticulturist at NCSU had worked out a system for use of cold-conditioned strawberry plugs to be planted in late Sept., in the field of SE North Carolina, protected during cold fall weather periods with low tunnels, for field harvests from late October through Christmas season. In colder areas, cold-conditioned plugs were planted in un-used greenhouses such as tobacco float bed transplant production houses. Growers direct marketed at the farm to consumers, some delivered to local restaurants who appreciated flavor of vine-ripened strawberries by paying premium prices to be able to get them. Customer acceptance was extremely favorable, and, this is an ebb-time in the year-round California field production cycle. Prices reported were in the $3 to $4. range per pint. Eric and an on-farm cooperating grower presented their work last Dec. at our SE Veg Expo at Greensboro, contained in the published proceedings.
We honor our memory of Eric and his work by hoping others will take up this work, including our growers who want to try it in greenhouses in our colder region. Plugs of Sweet Charlie, a variety having a low chilling requirement, excellent taste further enhanced by the cool nights, warm days of greenhouse production, plus Anthracnose resistance, was found in the earlier work to be best adapted to off-season production. It is very early into production, then provides sustained greenhouse fruiting over several months. In the short days of mid-winter there will be a reduced amount of blooming and slower rate of fruit development, ripening and harvest, that will again accelerate with the coming of longer days by late January on into May in the un-used greenhouses. Where those facilities are needed for spring tobacco transplant production, plants, drip irrigation lines and artificial soil media such as "bag culture" or "grow bags" would need to be removed by late winter-early spring.
In Eric's work, they cold-conditioned plugs as soon as they were received from the commercial plug plant producer in September by either a) placing them in growth chambers at 45 degrees F. for 2 weeks, high light intensity for short days, normal long dark period by night, then planted out immediately after acclimation to warmer outside conditions, or b) taking plug plant trays to high elevation, cooler areas of Western NC in the Blowing Rock area for 3 weeks, outdoors in full sunlight, watered as needed. We have areas around Mt. Rogers in SW Virginia, and around Monteray in Highland County and Bath County, Va. that could naturally condition plug plants for such production.
There are almost no traditional crop protectants registered for use on greenhouse food crops, including strawberries. Costs are too high to obtain EPA approval for such minor use, would not be cost-effective for the manufacturers. However, successful use of predators for controlling 2-spotted mites on greenhouse strawberies have been widely reported by entomologists and cooperating grower tests. Mites are probably the #1 pest of greenhouse strawberries, they love to spend the winter in such cozy quarters luxuriantly feeding on one of their favorite host plants, it's like a long winter Florida paid vacation! Likewise, there are new, environmentally safer natural product-mimicking fungicides for Botrytis Gray Mold control on greenhouse strawberries, such as Switch, a new strobilurin natural product type, and Armicarb 100 potassium bicarbonate, also carrying an EPA exemption for zero re-entry and pre-harvest time interval for use on strawberries. Plus, consider that for older, registered crop protectants for strawberries, if the cover is off the greenhouse, they are truly outdoors, right? I must go figure. Also, bumble bee colonies, commercially available for such pollinator use, are used in the houses for increased fruit set and berry production.
Our Greenhouse Extension Horticulturist, Joyce Latimer, may have some ideas on best grow-bags to use for this application, they should be black in color or spray painted black for maximum heat gain during off-season months. Plants should be spaced 12" apart with a drip tube placed midway between each double row of berry plants on the bags, drip lines may be secured to bags with U-shaped, 6" length sod staples, a staple over each tube about every 15' of drip line length, but not pushed into the bag far enough to constrict the tube's water flow. Only enough floor space to get through for culture and harvesting is not covered with bags and plants. In a typical 35' X 200' tobacco greenhouse (some are smaller, some are larger), a grower may achieve at least 70% crop use of square footage of total floor space for bag culture off-season strawberry production. In this example, 70% of 7,000 sq. ft. = 4,900 sq. ft. Using only 18" aisles after every 4 rows of strawberry plants, bags laid end to end tight, 12" space between plants in-row and between rows or 1 sq. ft. per plant, provides space for 4,900 plants in such a greenhouse example.
Grower ingenuity will figure a way to get an extra 100 plants into that house to make it an even 5,000 plug plants, since they are purchased by the thousand, so let's just figure it that way now: Greg Gordon at Aarons Creek Farms, Inc. at Clarksville has the most experience with greenhouse strawberry production in Va. With conditioned plants, growers may get up to 3 pints per plant of total fruit over a 7 month period in a greenhouse not used for spring tobacco or other transplant use. This may not be realistic for first time berry growers, but for experienced, successful outdoor berry growers who know strawberries, it has been done. So, 10 to 15 thousand pints at retail sounds like a lot of money from a house just sitting there. It is also a mighty lot of intensive work for 6 to 7 months, growers will earn every penny! However, I will volunteer to work with Dr. Latimer to be of any assistance to you, this is stepping out, daring to risk failure, hey, it is what we should do! On a lighter note, I would like to be able to volunteer to take your freshly transplanted into cells-plugs to Mt. Rogers area or to the Bath and Highlands County area and camp, fish and shepherd your clients' plugs for 3 weeks in September, ahh, beautiful foliage, cool nights, sparkling waters, leaping trout, now we are onto something needing this type of research! Let me go figure, my ole bread van will hold 100 flats, 50 plants per flat, hey, that is exactly 5,000 plugs!
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