Strawberries do well in areas where they have some drying breeze every
day. Though they prefer cool, moist nights, excess free moisture on the fruit and
leaves for long periods can lead to fungal and bacterial diseases. At the
same time, heavy wind can be a damaging to berry flowers and can rub
leaves against the fruit causing chafing and bruising. We look for planting
locations that offer the least amount of heavy winds, but are not completely
void of breezes.
Less is best! By that, I mean that if I selected the best soil in the first place, very little physical ground preparation will be necessary. The soil environment, though quite stable and resilient, can become somewhat inhospitable to plant growth if it is disturbed too much. Years ago, I found that plowing the soil created an antagonistic environment for berries and have not plowed a berry field since the mid-eighties.
With respect to soil amendments, I test soil samples for nutritional content,
salts, pH, cation exchange capacity, organic content, etc., at least
annually. Corrective and preventative amendments are then made to the soil
based on lab results, soil type, varietal needs and my experience. This is
part of the art of berry growing, and cannot be "cookie-cuttered" for all
conditions. That is, one size does not fit all.
In general, our plantings do best with annual applications of composted organic matter (certified for organic food crops), gypsum (calcium sulfate), and a balanced blend of controlled release fertilizer containing nitrogen, phosphorous and potassium. Controlled release fertilizers are uniquely well suited for berry production, as well as other crops. Briefly, they allow the nutritional needs of the crop to be applied prior to planting, yet continue to supply nutrition for up to seven months.
Raised planting beds are formed with heavy furrow shovels like those to the left (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].
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. CultivatingOnce 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. IrrigationSince 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.
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.
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.