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Friday, May 23, 2008

Strawberry Farming from California

Strawberry from California

Coastal California is home to more acres of strawberries than anywhere else in the world. This is due in part to its temperate climate, which favors strawberry production. Cool, moist nights (45-55°F, 60-90% RH) coupled with cool, sunny days (60-70°F) are ideal. This is why most acres of strawberries in California are located within 15 miles of the coastline.But, soil and water are other important components. Berries like a well drained, sandy-loam to loamy-sand soil with good fertility. Being somewhat sensitive to salts in the water, berries do best where water is low in dissolved salts (ECw < href="">(see MPEG video of bed shovels) . These beds are shaped and smoothed before controlled release fertilizer is shanked in beneath the surface. Two rows of drip irrigation tape are buried near the surface (see E. Irrigation below), and the beds are sealed with a layer of clear or colored plastic bed mulch. Once the drip irrigation system is connected and activated soil fumigants, such as Dow Chemical's Inline®, can be injected through the drip lines to kill harmful pests, diseases and weeds in the root zone.
Note: Beginning in 2002 methyl-bromide, the most popular soil fumigant in California strawberry fields, is no longer used on Manzanita Berry Farms fields. Though still a thorough and effective soil sterilant, political decisions forcing the phase out of methyl-bromide use in the developed countries has caused the price of the material to skyrocket beyond the cost/benefit range for our crops. [Read more about methyl-bromide and soil fumigation in a letter to a friend of ours].
C. Planting Just prior to planting, the beds are irrigated with subsurface drip water to provide proper moisture to help start the young, dormant transplants. Holes are then poked through the plastic mulch with a machine designed to space the plants properly. Spade-shaped points are arranged on steel wheels mounted behind a tractor. As the tractor travels down each row, the "poker wheels" make holes in the plastic mulch and the indentations to put the plants into. Workers, at left, push each individual plant into the poked holes, then press the surrounding soil tightly to close the hole around the plant roots. Sprinklers are then activated and run long enough to saturate the soil, further sealing the soil around each root. Sprinklers continue to be the primary irrigation method for only about 6 weeks following planting, or until plants become established.
D. Cultivating Once planted, the young plants need little help for the next month or two. Watering the fields and pulling weeds are the normal winter and spring cultivation activities. We lightly chisel the soil in the furrows to knock down weeds and smooth out the surface to make walking between the rows easier once harvest begins.
E. Irrigation Since the seventies, drip has become the essential method of irrigating strawberries as well as many other crops. After the intial post-planting irrigations with overhead sprinklers, drip accounts for 100% of applied water on strawberries. Drip irrigation reduces the amount of water needed to raise a crop, reduces weeds in the field and allows a grower to apply supplemental plant nutrition directly to the root zone, all of which promote crop growth uniformity. We also use the irrigation system to inject gypsum through the water during the season to maintain good soil tilth and improve the water penetration pattern around the roots. ( Note the uniformity of plants at left )
F. NutritionWith normal cold winter temperatures, strawberry plant vigor increases. But, occasionally, warm winter temperatures can reduce plant vigor, requiring additional applications of plant nutrients to augment the pre-plant fertilizer program. This demonstrates a management decision that must be made before planting -- predicting (guessing) the winter climate in advance is helpful in adjusting the pre-plant fertilizer amounts to apply. If a grower thinks the winter will be warm, he may put in a little more fertilizer. If cold weather is predicted, he might lighten up a little on the rates.
But, predicting the weather is not an exact science. Fortunately, drip irrigation allows for additional nutrients to be added to the roots during the season if needed. That is, if warm weather reduces plant vigor, fertilizer can be injected through the water system. Since fertilizer cannot be taken from the soil if unusually cool winter weather increases vigor, it makes sense to apply slightly less than you think you will need. You can always add a little, but you can't take it back.
As you can see, the weather determines many of the activities needed to raise a profitable strawberry crop. Late in the season, warm spells are common and cause the plants' metabolism to accelerate, stressing the roots to keep up with the plants' demand for water and nutrients, especially potassium, calcium and certain other minor nutrients. These nutrients may be augmented with foliar applications, but to do this requires experience and care so as not to injure the delicate flowers.
G. Crop and Pest ManagementThis is the most demanding and technical part of strawberry farming. Strawberries are extremely susceptible to a relatively small number of disease and insect pests. Although the number of pesticides registered for use on strawberries is huge -- 2,376 -- very few of them actually have any affect on real pest problems. We use 11 or 12 pesticide materials each season, 3 of which are registered for organic growing, and 7 of which are "bio-rational" or environmental/worker friendly. Preventing pest problems from becoming uncontrollable is key to a healthy crop. Prevention requires a good crop management program which includes regular field inspections, sampling plant tissues and soils and water, and recently we've begun to monitor infra-red radiation reflected from the field to gauge certain aspects of plant health.
Infra-red aerial photography below clearly illustrates the lack of vigor in a small bright green block where we suspended methyl-bromide fumigation four years ago. Surrounding areas are planted in the same soil with the same plant varieties and watered and fertilized and sprayed equally with the non-fumigated test plot. The non-fume plot did have an abnormally high amount of weed pressure which contributed to the lack of plant vigor.

In the infra-red photo below, the lack of vigor shows in the darker black/grey area of the black and white portion of the photo. This is where a different strawberry variety was planted this past season, which we won't be planting again.

Pest management in all of modern agriculture relies on the regular monitoring of plants to evaluate pest populations. Strawberries are no different. I survey all the fields at least weekly, more often where I have detected pest populations building up. I also rely on the work of two other trained pest management specialists to help monitor for pests. Plant tissues are tested at least monthly during the season to ensure proper pant nutrition and to identify potential nutrient related maladies before visual plant symptoms might occur. The soils are tested at least annually and nutrients, organic matter, salts and pH are watched carefully.
During the late winter and early spring, rainy periods make regular applications of plant disease prevention materials essential. Allowing a buildup of any plant disease early in the season would be disastrous later in the season when problems can become uncontrollable.
Later in the season, the two-spotted spider mite becomes the arch enemy of the berry plants. Strawberries are notorious hosts for this insidious pest and must be monitored closely until pest populations have stabilized below damaging levels. Though highly technical, suffice it to say that no two years are treated the same with respect to mite control.
That said, we typically begin our mite management program in late January with applications of beneficial mite predators, such as P. persimilis.
We apply approximately 30,000 of these beneficials per acre, over a 6 week period ending by late March. This method will usually reduce the amount of chemical applications by two-thirds, and maintain pest populations at lower levels all season than with chemical-only programs.
In the spring, the daily presence of workers in the fields greatly reduces the available options for pest management, as chemical applications can require workers to stay out of treated areas for up to three days. When we are picking fruit every two to three days, many chemical treatments are no longer feasible. This is when our reduced risk Integrated Pest Management (IPM) program really pays off, both in workers safety and comfort and in economic pest management.
Our biological, non-chemical and reduced-risk pest management techniques are continuing to be improved and we take pride in being a leader in reducing hazardous chemical use. We have reduced total pestcide use each of the last five years and seem to be on track to make it six in a row.
Good field observations are critical to reducing pesticide use. But so is our pesticide/nutrient application equipment, designed for more efficient pesticide application. The Gearmore ® Air-assisted sprayer in the picture works similar to an compressed air paint sprayer, depositing a concentrated water-chemical mixture on the plants, with less drift to non-target areas. We find a 33-50% reduction in the amount of chemical needed to manage pests with this sprayer when compared to high-volume, dilute sprayers. From :

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