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Decisions made throughout the entire 12-month production cycle can make a big impact on the success of each strawberry season, however, very close attention to detail is required during the pre-plant and planting stages. The pre-plant and planting periods are times when growers should anticipate at least $5,000 per acre in operating expenses for pre-plant fertilizers, fumigants, plastic mulch, drip tape and plants. Plants will be the principal cash outlay and costing as little as $1,350 per acre for bare-root fresh dugs to as much as $3,750 per acre for plug transplants (assuming a planting density of 15,000 plants per acre, based on average prices from 2009).
Ensure fertility. Complete a soil test several months before planting to determine how much dolomitic lime is needed to raise the soil pH and how much potash (K2O) fertilizer to apply before bedding. If a soil test was not taken prior to shaping the beds, use these standard recommendations: Apply 60 pounds nitrogen (N) per acre, 60 pounds phosphate (P2O5) per acre and 120 pounds potassium (K2O) per acre. Broadcast these fertilizers and lightly incorporate before bedding and fumigation.
Ammonium nitrate is recommended for the pre-planting nitrogen application. A broadcast application of 175 pounds per acre of ammonium nitrate will deliver 60 pounds of nitrogen per acre. In general, a P2O5 application of 60 pounds per acre should be incorporated, even on soil with a high phosphorus index. However, on soils that have ultra high levels of phosphorus (typically areas where large amounts of poultry manure have been applied), this application can be deleted.
A pre-bedding broadcast application of 120 pounds triple superphosphate (50 percent) can supply 60 pounds of P2O5 per acre. Soil testing also determines the need for potash (K2O). Potassium sulfate is a very good source of K2O for strawberries (50 to 53 percent), and it provides some sulfur as well (18 percent). If the soil test recommends 60 pounds K2O per acre, then a broadcast application of 120 pounds of potassium sulfate fertilizer (50 percent K2O) can be applied to meet the crop’s potash requirement. Other nutrients can be injected as called for (preferably as the result of tissue testing) through the drip irrigation system.
Shape the beds. Avoid using a vegetable bed-maker. Instead, stick with the bed-making equipment that is specifically designed for deep strawberry plasticulture beds. Reddick and Kennco are two of the leading suppliers. A deep bed will produce higher yields and fruit with less soil splash. The 10-inch deep beds mulched in plastic are typically 30- to 32-inches wide at the base and 28- to 30-inches wide on top. Beds are slightly crowned so water will run off and not rest on the plastic. For example, a bed with a 28- to 30-inch top should slope from the center to the edge with a drop of 1.25 inches. Applying straw mulch to the aisles to keep the berries clean is not necessary with 10-inch deep beds. Bed centers are usually 5 feet.
Most machines have some specific advantages, and it is worthwhile to investigate these differences. Almost all of the machines sold will form the bed, fumigate, lay plastic mulch and install drip tape in one operation. In general, the single-row bed-making and plastic-laying machines are appropriate for most strawberry operations. Be sure that enough soil is pulled up so that the bed has good, sharp corners and no depression in the center (it is not usually possible to get these sharp corners on clay soils). You may find it beneficial to pre-bed the rows to make sure that enough soil will be pulled up for the bed-shaper-the same disk hillers used for making tobacco beds work nicely for strawberry pre-bedding. The extra pains involved in getting your land “just right” for forming beds, such as laying plastic and fumigating, will pay off in better plant growth in the fall and winter seasons.
Install plastic mulch. Ideally, strawberry beds have the plastic mulch in direct contact with the soil beneath. If there are air pockets beneath the plastic, plant growth will be slow in the fall and winter. Heat from the black plastic will not be conducted into the soil if there are air pockets. In fact, the black plastic will have a cooling effect if it is not in good contact with the soil beneath. In very recent years most of the N.C. strawberry industry has transitioned to higher barrier plastic films such as virtually impermeable films (VIF) or mulches that allow very little methyl bromide and other fumigant gases to pass through it. These nearly impermeable films make it possible to significantly reduce fumigant application rates by helping to contain the fumigant within the soil and reduce overall emissions into the atmosphere.
Use black plastic 1-mil to 1.25-mil VIF for strawberry plasticulture production. On 5-foot row centers there are 8,712 linear feet of row per acre, so you will need about 3.5 rolls (2,400 feet) of plastic mulch per acre. For 6-foot centers, 3 rolls of plastic mulch will be required per acre. It is important that the plastic fit tightly on the bed and that the edge of the plastic, or the tuck, be held firmly in the soil. These measures reduce the chance of wind getting under the plastic and causing it to blow off or float up and down, which injures plants.
Install drip tubing. Install drip tubing with the orifices facing upwards. The tubing is typically buried 1 or 2 inches deep in the bed center. During installation several workers should be watching to insure that the tubing maintains its orifice-upwards orientation. The workers are responsible for assisting if the tubing becomes tangled in the injector and signal when the drip tape reel is empty. Tubing ends should be closed off by kinking or knotting until the tubes are hooked up to the system. Growers have the option of using only overhead sprinklers in the fall, but the drip system should be functional by late winter.
Fumigate. Fumigants such as methyl bromide and chloropicrin have been used in combination with plastic mulch row covers since the early 1980′s for broad spectrum soilborne pest and disease control in strawberry plasticulture. New land that has been subject to good crop rotations and best management practices (such as cover cropping and good drainage strategies) can, under optimum conditions, generate yields that are 85 to 95 percent of the yields in fumigated soil. Weed control, however, can be a serious problem. Strawberry plasticulture production on the same site year after year is not advisable without pre-plant fumigation because of potential weed and disease problems.
With rising cost and scarcity of methyl bromide, which is being phased- out nationally and internationally under provisions of the Montreal Protocol (effective January 1, 2005), there has been an intensive search underway for a broad spectrum replacement fumigant for methyl bromide over the last decade. Methyl bromide is a stratospheric ozone depleting compound. A newly registered broad spectrum fumigant that has potential to replace methyl bromide is methyl iodide:chloropicrin (Midas 50:50). Similar to methyl bromide, Midas 50:50 has a two-week plant-back period. This product has performed well in comparison to methyl bromide in university research trials. Other registered fumigants for strawberries have plant-back intervals of 21 days or more. As a general rule, you should begin land preparation for bedding and fumigation at least six weeks ahead of planting with the use of methyl bromide:chloropicrin (50:50), and seven weeks ahead of planting for Telone C-35.
Schedule fumigation far enough in advance to allow for plant-back restrictions for the particular chemical used as well as unexpected setbacks that can occur with weather. If adverse weather prevents fumigation, it may be better to plant on time and not fumigate than to fumigate and plant extremely late; if the site is fairly free of noxious diseases and weeds, such as nutsedge.
Stay on schedule. Here is a sample schedule for a grower in Zone 6 who wants to set out Chandler plugs in the second week of September, and where the producer has decided to use methyl bromide. For growers using a fumigant requiring a 21-day plant-back, plan on starting at least one week earlier.
July, week 4. Whenever there is adequate soil moisture, begin preparing the soil so you can shape the beds and fumigate in early August. In an unusually dry July, you may be forced to irrigate overhead to get the land ready for chisel plowing and sub-soiling. Sub-soiling is needed every few years on heavy soils. This should be done in two directions, north-south and east-west, and it needs to be done deeply to loosen the soil and break up the plow layer (at 10 to 12 inches deep). Breaking up this layer will require setting the draft control so the V-ripper doesn’t come up easily when it hits the hard spots. This operation requires extra horsepower. Be sure to incorporate your lime at this stage if you haven’t done so already. Ideally, the lime should be spread in June, just after the plastic is pulled and the beds are knocked down.
August, week 1. Have fumigant cylinders delivered to the farm and complete fumigation rig safety checks. Check with your fumigant supplier to be sure the cylinders are delivered on time and to ensure that the proper safety checks are used.
August, week 2. Broadcast N-P-K fertilizers and disk them into the soil to prevent nitrogen loss. Disk to a depth of 6 inches, breaking up clods until the soil has a “fluffy” texture. Don’t use equipment that will compact the soil (a rotary hoe or rototiller may cause compaction).
August, week 3. Shape the beds and fumigate with methyl bromide + chloropicrin. Lay plastic mulch and drip tape. As the fumigant is injected, the beds should be immediately “tarped” with an embossed 1-mil black plastic mulch film that can be “stretched” by the mulch-laying and fumigation unit to give an extra tight fit over the bed. Also, if rooting your own plugs, now it the time to stick tips. It is time to sow annual ryegrass if you want to ensure erosion control in the field aisles.
September, week 2. Transplant plugs. Always try to allow three weeks between fumigation and planting, even though methyl bromide: chloropicrin (50:50) is a two-week plant-back material. This extra week will provide a “cushion” for possible weather delays that may occur. Likewise, for a 21-day plant-back fumigant, you really need to allow a four-week waiting period between fumigation and planting. Thus, fumigation with Telone C-35 should be done in the third week of August for an area that will be planted in the third week of September.