Gordon Johnson, Extension Vegetable & Fruit Specialist; firstname.lastname@example.org
If growers have not done so already, plasticulture strawberries should be cleaned to remove dead leaves and other dead plant material. Winter injury has left many dead leaves that will serve as a major source of Botrytis spores during bloom (the critical stage for infection). Dead material can also lead to crown rots in strawberry plants.
Plasticulture strawberries should have nitrogen applications prior to bloom. Base recommendations are 25 lbs/a of nitrogen at greenup and another 25 lbs/a of nitrogen 2-3 weeks later. If fertigating weekly, addition of 3-5 lbs of nitrogen per acre per week may be warranted. Nitrogen is critical prior to and during early bloom. Altering between potassium nitrate and calcium nitrate as the nitrogen source will often improve fruit quality.
Growers are also encouraged to take petiole and leaf tissue samples for laboratory analysis. To collect and submit strawberry tissue samples, follow these guidelines:
● select the most recently mature, healthy, trifoliate leaves from uniform field areas and the same variety;
● detach the petioles from the leaves as you collect them and save each separately;
● include leaves and petioles from 20 to 25 plants; and
● then submit leaves and petioles together as one sample.
We have a lab on Delmarva that can run these tissue samples. Leaf tissue nutrient levels should be maintained as follows: N (%) 3–4, P (%) 0.2–0.4, K (%) 1.1–2.5, Ca (%) 0.5–1.5, Mg (%) 0.25–0.45. When in full bloom, petiole tissue nitrate content should be between 4000-6000 ppm and then will decrease thereafter.
Petiole nitrate levels for most plasticulture strawberry varieties in ppm:
● greenup, pre-bloom 600-1500 ppm;
● bloom 4000-6000 ppm,
● main fruiting period 3000-5000 ppm,
● later fruiting decrease each week from 3000 to 1000 ppm.
Note that some varieties, such as Flavorfest, require much lower nitrogen levels.
Further note that day neutral varieties such as Albion that fruit into July should maintain higher levels of petiole tissue nitrate later in the season than June bearing types.