Hill System Plastic Mulched Strawberry Production Guide for Colder Areas

Authors: Charles R. O'Dell Extension Horticulturist, Department of Horticulture, Virginia Tech; Jerry Williams, Teaching Hortculturist, Department of Horticulture, Virginia Tech

Publication Number 438-018, Posted March 2000

TABLE 11 - Calendar of Jobs for Carry-Over Strawberries on Plastic Mulch
  1. July 1 - After harvest, by 7/01, broadcast spray 2,4-D amine, labeled formulation, 1.5 Qts/A. NOTE: If plant-killing diseases are present, destroy planting, do not carry-over.

  2. July 14 - 2 weeks after spraying 2,4-D mow berry plants 2" above plastic mulch.

  3. July 14 - After mowing off as above, if you have more than 5 branch crowns on average, set shielded sprayer so shields expose outer 1/2 of plants on each row on the beds, set shield height to just clear the crowns, spray with 2 pints/acre of Gramaxone and crop oil to thin crowns for better fruit size next year.

  4. July 15 - Drip irrigate to wet beds shoulder to shoulder (7 hours of drip @ 12" in-line emitters, beds on 5' centers = 1 acre inch to beds). No fertilizers in summer months. Goal: keep plants alive, but not fast-growing (controlled moisture stress).

  5. August 15 - Drip irr. beds as above. Goal: same as above.

  6. September 1 - Take plant tissue analysis or soil test the carry-over beds. Typically in this area, beds will test high in nitrogen, medium or medium-low in both phosphate and potash.

  7. September 15 - Drip irrigate to wet beds shoulder to shoulder, but this time at 2/3 of the way through the drip cycle, fertigate nutrients as per tests needs, typically may need to add 15-20 #/A of phosphate and potash, smaller amounts of nitrogen. One option is to fertigate with solubles such as 12-48-8 or 9-45-15 followed by 8-15-36. Mixing them can cause salting out or heavy fertigator-clogging precipitates, use in sequence. Other options are liquids such as 11-48-0 followed by 0-0-30. Note: see examples at end for calculating how much/acre to fertigate.

  8. September 20 - Spray row middles with Gramoxone, shielded sprayer as per VCE Pub. 456-420, for all vegetation including rooted berry runners filling row middles. If foxtail or other tall grasses have filled middles, use Poast, crop oil plus ammonium sulfate activator as per Poast label prior to use of Gramoxone in middles. Remove crop shields for Poast spray to cover grass over beds and raise spray boom to high position to completely spray overtop of grass in middles.

  9. October 1 and 15 - Last drip irrigations of the season, wet beds shoulder to shoulder. If you didnšt pre-plant fumigate to kill soil insects in beds, field mice and voles may move into beds to feed on grubs and bugs or just to overwinter, even in fields that were fumigated, destroying drip tape and plants. Adults of the May Beetle family lay their eggs on sod. Their grub larvae devour strawberry roots, one of their favorite food host plants. They have nearly ruined some fields, so best to use a soil insecticide labeled for strawberries (VCE Pub. 456-420) or plan to bait beds with mouse poison placed under the plastic mulch. Injury has been most severe where strawberries rotate behind sod with no fumigation or soil insecticides.

  10. October 16 - Winterize and drain all drip components, filters, lines. Order winter/spring crop covers or obtain a frost control sprinkler system. Don't bet on another 'Carolina winter.'

  11. October 20 to December 1 - Apply crop covers if needed. Colder areas of the state generally apply crop covers in October. Warmer areas usually get by with no winter covers.

  12. Early February - Remove winter crop covers, leave windward side secured to pull covers later when severe freeze events are expected, also later to re-pull for frosts during bloom.

  13. February - (If you use sprinkler irrigation for frost control). Set up and test sprinkler system well ahead of expected bloom season.

  14. Early Feb. to early March - As weather permits clean off dead runners plus dead leaves from each of the 2 rows per bed, back to original mother plants. Check out mechanical brushes and/or high-vacuum mowers to reduce hand labor of this chore. Dead leaves and runners are the primary source of spores of Gray Mold to infect new spring leaves and blooms.

  15. Late March - Early April, depending on area and season - At first flush of new plant growth after cleaning beds, spray protective/preventative fungicides as per VCE Pub. 456-420 for prevention/management of Botrytis Gray Mold fruit rot as follows: 1st. spray before first bloom on new vegetative growth; 2nd spray at first to 10% bloom; 3rd spray at full bloom; 4th spray at final bloom. Gray Mold spores infect the blooms, then the fruit rot appears later on ripening fruit, especially following periods of wet weather during bloom and harvest. The preventative program of 4 sprays as above has allowed growers to make no further sprays during harvest season so there are no sprays on fruit or visible spray residues on plants for U-Pick.

  16. Early April through harvest season - Every week, once per week or every 5 days in very dry, sunny, windy weather, drip irrigate beds to move water plus fertigations to rows, not just to wet the bed centers near the drip tape. Weekly spring months irrigations/fertigations take at least 4 hours per cycle on our heavier silt loam soils in this area. Fertigate 3 lbs./acre of actual nitrogen, phosphate and potash per week on carry-over beds over a 12 to 14 week spring time period. Many growers either use 8-8-8 liquid fertilizer or soluble 20-20-20 dissolved in water for weekly fertigation of carry-over beds.

Fertilizer calculations: How much N, P and K are in a bag of 20-20-20 soluble fertilizer? Multiply 25 lbs per bag X .20 for 20% = 5 lbs. each of N, P and K. How much N, P and K are in a gallon of liquid 8-8-8? Check with your bulk supplier for the weight per gallon. For this example, let's use 12.5 lbs/gal. so multiply 12.5 X .08 for 8% = 1 lb of each major element/gallon of 8-8-8. To apply 3 pounds of N, P and K/acre per week means you need 3 gallons/acre per week of liquid 8-8-8. Let's go back to page 1 to the September fertigations of high phosphate and high potash fertilizers your beds may have needed: How much phosphate is in a 25 lb. bag of 12-48-8? Multiply 25 lbs X .48 = 12 lbs. of phosphate. To apply 15 lbs. P/acre means you will have to use 1.25 bags per acre. How much P in a gallon of 11-48-0? If it weighs 12.8 lbs/gal, multiply 12.8 X .48 for 48% P = 6.14 lbs. P per gallon. To apply 15 lbs. of P/acre in September means you need 15 divided by 6.14 = 2.44 or 2 and 1/2 gallons of 11-48-0 per acre. Since 1 gallon of 0-0-30 weighs 12.15 lbs/gal., how much 0-0-30 do you need per acre to supply 15 lbs. K/acre? Multiply 12.15 X .30 = 3.75 lbs. K/gallon. To apply 15 lbs. K/acre, divide 15 by 3.75 = 4 gallons of 0-0-30 per acre.


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