Highbush Blueberry E-Bulletin 2012-3

Wednesday, May 16, 2012

A. Fertility rates and timing:

Early varieties are now in full bloom in the Annapolis Valley and many growers will have already applied granular fertilizer down their rows; however, new research suggests that there must be leaf emergence and growth before you have any significant uptake of nitrogen by the blueberry plant. As such, the correct timing for the first N-P-K application is now considered to be at bloom or early petal fall. A second application should be made 4-6 weeks later.

Most mature plantings require 50 – 70 pounds of actual nitrogen per acre annually but rates vary according to soil type, organic matter content, mulching practice and management. For example, if sawdust or high carbon mulching materials are used, standard nitrogen rates are recommended to be doubled as most mulching materials make the nitrogen temporarily unavailable. Also, remember that nitrogen should be in an ammonium form – either ammonium sulfate or urea. I highly recommend that grower’s tissue test to verify if your tissue nutrient levels are in the optimum range and make adjustments accordingly. The procedure and timing for tissue testing can be found on the AgraPoint website.

B. Fruit rot management:

The two main fruit rot diseases in highbush blueberry are anthracnose and Botrytis fruit rot. If anthracnose has been a problem in the past, consider a program of targeted Bravo sprays at green tip stage (now past), pink bud, and petal fall followed by Maestro/Captan (pre-harvest interval of 2 days) just before harvest as fruit ripens. Bravo should not be applied beyond petal fall as it can burn developing fruit. The Bravo treatment timings are also effective for Phomopsis canker control.

Where Botrytis blight and fruit rot have been a problem, consider an early bloom fungicide application and again 7-10 days later. Registered fungicides for Botrytis blossom blight and fruit rot include Maestro/Captan, Elevate, Lance, Ferbam, Switch, Pristine, and Serenade. Consult the AgraPoint Highbush Blueberry Insect and Disease Management Schedule for more details on the specific formulations and rates. Read labels carefully for application requirements and warnings.

AgraPoint`s Insect and Disease Management Schedule

C. Late weed control options

Hopefully earlier applications of herbicide have your fields in good shape but if you are unhappy with some, Callisto 480SC is a relatively new herbicide that may be helpful in messy fields prior to bloom. It has both “pre-emergent” and “post-emergent” activity on weeds and controls a number of broadleaf weed species including redroot pigweed and common ragweed. Only one application of 0.30 L/ha is permitted per year but the window for application is relatively long, extending up to the 8 leaf stage of weeds and “pre-bloom” for the crop. Application should be a ground application directed down the base of the row.

For more information on Callisto and other herbicides registered for use on highbush blueberries, consult AgraPoint`s Guide to Weed Management in Highbush Blueberries found here!

Note: Read all pesticide labels carefully for application rates, timings, requirements and warnings!