Summary and discussion– Takeda 1999

“Out-of-Season Greenhouse Strawberry Production in Soilless Substrate”

F. Takeda

Published 1999, Advances in Strawberry Research. Volume 18, pp 4-15.

http://www.ars.usda.gov/SP2UserFiles/Place/19310000/FTakeda/1999Advances%20in%20Strawberry%20Res%20feature.pdf (link directly to paper via Fumi’s ARS website)

Summarized by Anita (Teena) Hayden, PhD (UTK, June 2007)

About the paper and author – Fumiomi Takeda is a researcher with the Agricultural Research Service at the Appalachian Fruit Research Station in Kearneysville, WV. His focus is small fruit production, and he has been publishing technical papers on greenhouse strawberries for many years. This paper provides a good overview of the strawberry production in protected agriculture

Protected Cultivation of Strawberries – In other parts of the world, strawberries are more likely to be produced under plastic than in open fields. Japan, Korea, northeastern China, western Europe and some parts of Australia all utilize either high tunnels or greenhouses and various types of soilless systems for production of strawberries.

Rationale for Soilless Systems – Methyl bromide has been an important soil fumigant to control soilborne pathogens, insects, nematodes and weeds in field strawberries. However, with regulations restricting use of methyl bromide, various alternative methods of producing strawberries are being developed and adopted. The loss of methyl bromide will likely lead to decreased yields in field systems, opening market opportunities for greenhouse-grown strawberries. Soilless media can be used in place of soil in protected agriculture and greenhouse systems, thereby eliminating the source (soil) of many of the problems. These systems also provide an opportunity for producing out-of-season fresh strawberries when their market value is highest.

Most greenhouse systems involve growing the strawberry plants as annuals by establishing them in late summer in the greenhouse and harvesting fruit from November through January. Unfortunately, crowns are difficult to obtain during the summer months, so some research has been done on using cold-storage transplants or propagating runner tips specifically for mid- and late-summer planting. Propagating tips locally in greenhouses permits growers to produce their own propagation material on an ideal timetable as well as reducing the plants’ exposure to soil pathogens and pests.

Strawberry Production in Soilless Systems – There are two basic strategies in hydroponic systems – “closed” and “open” systems. In “closed” hydroponic systems, plants are grown in pipes or channels so the fertilizer nutrient solution can be recirculated in a “closed” loop. The solution may be supplied continuously, as in NFT (nutrient film technique) where a small amount (“film”) of the fertilizer solution flows by the roots at all times. Alternatively, the solution may be supplied intermittently in a closed system, as in “ebb and flow” or “flood and drain” systems where the plants are grown in pots and irrigated by flooding the table containing the pots. In “open” systems, fertilizer is supplied to the plants, usually through a dripper, and drains through the medium and is not recovered or recirculated. Open systems may be preferable for varieties especially susceptible to root-zone pathogens.

The timing for greenhouse production is critical in order to compete in the marketplace. California field strawberries dominate the market from early spring through fall. Shipment of field grown berries from Florida peaks in February and March. Although berries can be air-freighted from the Southern hemisphere in November and December, niche markets can be developed for local production of high flavored, attractive out-of-season berries.

Cultural Systems – The author evaluated productivity of bare-root dormant, bare-root fresh-dug, and plug plants in NFT in West Virginia. The plants were placed in 12 foot long troughs suspended 4 feet above the greenhouse floor on October first. The two varieties tested, Camarosa and Chandler, produced 2 pounds and 1.5 pounds of marketable fruit per plant (respectively) in a December – May time frame. Due to some technical concerns for the root zone of long-term crops in small NFT channels, it is advised that channels with a width of at least six inches be used for strawberries.

Vertical hydroponic systems have also been tried for strawberries. Vertically-hung bags and PVC pipes, as well as columns of stacking pots are examples of vertical systems. Nutrients are applied at the top and the solution passes through the substrate and drains from the bottom. Note that the composition (relative concentrations) of individual fertilizer ions can change as the solution passes through the media, so plants on the bottom may not be getting the same fertilizer mix as those on the top. Light distribution is also uneven in these vertical systems, and yields can be dramatically delayed and/or reduced on the plants at the bottom of the column. Plants at the lower level may receive only 10% of the light falling on the uppermost plants. In winter months in the mid-Atlantic region of the US, sunlight is often the limiting factor in strawberry yield. In very cloudy areas, supplemental light is essential.

Bench-top production of strawberries has been evaluated in Europe in the US. In Europe, bags and buckets of peat and peat mixes have been used with drip irrigation, and a closed ebb-and-flow system using pots of vermiculite, sphagnum peat and perlite was successful for several years. The author experimented with pots of ‘Camarosa’ and ‘Chandler’ strawberries transplanted on November 5^th and grown in a peat mix and drip irrigated. Yields averaged 1.1pounds per plant from mid-February through the end of May. Over a seven-month period, large two-gallon pots with 5 plants per pot yielded 23.4 pounds per square yard of bench space.

Enhancing Winter Fruit Production – Different approaches to improving yield of winter-grown strawberries have been investigated. It was found that plants grown from second-order daughter plant cuttings produced similar yields than third-order daughter plants over a three month period, although the second-order plants produced a larger harvest in the first month of the fruiting period. Plug plants out-performed fresh-dug, bare-root plants in all three cultivars investigated (Sweet Charlie, Camarosa and Chandler). When plants were transplanted on October first, Sweet Charlie was the first to produce fruit, followed by Camarosa and Chandler. Camarosa out-performed the other two varieties during the heaviest harvest period in March. Sweet Charlie and Chandler are short-day plants requiring less than 14 hours of daylight and/or temperatures below 59F to produce flowers. Two weeks of short-day (16 hours of dark) conditioning in early September hastened the first harvest date of Camarosa by three weeks. However, that high early yield was balanced by low yields in April.

Pest and Disease Management – The absence of weeds and the ability to minimize and prevent pest problems makes greenhouse production very inviting. However, plants may be dipped into an insecticidal and fungicidal solution before planting, and a plastic barrier between the leaves and the substrate can also help to reduce pest and pathogen problems. The most common problems encountered are two-spotted mites, flower thrips, and powdery mildew. Since no pesticides are currently registered for greenhouse strawberry production, biological control agents are the best approach. Phytoseiulus persimilis is a natural predator of two-spotted spider mite, and should be released at regular intervals even before an outbreak is observed. Another predator mite, Amblyseius cucumeris was effective against flower thrips, although it did take over one month of treatment with the predators before the thrip population declined. Powdery mildew on leaves of strawberry plants can become severe under conditions of low light, low temperatures and high humidity. Weekly foliar treatments of a biological fungicide were as effective as sulfur treatments.

Another strategy investigated to manage pest and diseases was to bring plants into the greenhouse at one-month intervals and remove them after the initial cycle of fruiting, thereby staggering the cropping cycles over the 6 to 8 month production period.

Conclusion – goals of a successful system include maximizing profitability with minimum energy inputs, minimal maintenance, high yields of high-quality fruits during the highest value season, high plant density and minimal or no need for pesticide applications. High capital costs and skills are needed for hydroponic systems, and the currently available strawberry cultivars need further R&D for adaptation to greenhouse winter production systems.