Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
It may not be too late to take tissue tests for your blueberries. Tissue tests are important tools for monitoring blueberry fertility. Leaf samples should be collected from mature leaves in the mid-portion of current season’s growth the first two weeks after last harvest. A double hand full of leaves should be harvested from across the field, washed in tap water, dried and sent to a testing laboratory. Below or critical nutrient values for blueberries.
If values are below normal or deficient use the following recommendations:
• Low N (if N is below 1.7 percent): Increase rate of N application by 10 percent for each 0.1 percent that sample is below desired level. If soil pH is above 5.0, use ammonium sulfate; if below 5.0, use urea. Apply half of the nitrogen fertilizer at bud break and the remaining half four weeks later.
• Low P (below 0.06 percent): Apply 180 pounds per acre superphosphate (45 percent P2O5) at any time.
• Low K (below 0.40 percent): Apply 400 pounds per acre potassium magnesium sulfate or 160 pounds per acre potassium sulfate in fall or early spring.
• Low Ca (below 0.4 percent): Refer to soil test and apply lime as needed if soil pH is below 4.0. Apply 1,000 pounds per acre calcium sulfate in fall or early spring if pH is above 4.0.
• Low Mg (below 0.2 percent): Refer to soil test and apply dolomitic limestone if pH is below 4.0. If pH is above 4.0, apply 250 pounds per acre magnesium sulfate or use Sul-Po-Mag (400 pounds per acre) if K is also low. Apply in fall or early spring.
• Low Mn (below 50 ppm): Apply a foliar spray of manganese chelate at 6 pounds per 100 gallons per acre twice during the growing season. If product label offers a different recommendation, follow label recommendation.
• Low Fe (below 70 ppm): Apply a foliar spray of iron chelate at 6 pounds per 100 gallons per acre in late summer and again after bloom the following year, but check product label and follow its recommendation.
This information was taken from the Mid-Atlantic Berry Guide http://pubs.cas.psu.edu/freepubs/pdfs/AGRS097l.pdf