Wild Blueberry Newsletter, March 2017

Wild Blueberry Newsletter header graphic, text and a photo of blueberries and leaves

March 2017

Date Change for Calibration Workshop  

The date for the Cooperative Extension calibration workshop has been changed to April 13, 2017, from 5:00 to 7:00 p.m. (with a rain date of April 20). The workshop will be by the Hope Elementary School, 367 Buzzell Hill Road (Route 235), Hope, Maine.

We will review and demonstrate the calibration of both a tractor mounted boom and airblast sprayer.  Contact the Knox/Lincoln County Extension Office, if you have questions on inclement weather at 832-0343.  Certified pesticide applicators will receive two credits for attending the workshop.

Management Strategies for Reduced Inputs

The decision to rest land, cut back on inputs, or manage for optimal production has to be made on a farm-by-farm and field-by-field basis considering both production costs and productivity of the field. Use the following considerations in determining what management strategy is best for you. It is very important to know your production costs in detail.

Do not manage fields or portions of fields with low cover and low yields.  Do not manage land that must be burned and hand-harvested unless you have markets established or available that provides higher prices.

Consider resting land until prices are above your production costs. If you do rest your land, you should continue to mow (or bush-hog to two to three inches) in the fall or in spring pre-bloom, to cut or wipe any woody weeds, and scout and pull any new weeds to prevent new infestations.  These maintenance costs should go into your calculations of the benefits of resting land.

Manage fields that you keep in production for optimal yields; this will keep your cost/pound low. Evaluate all inputs to reduce costs to the minimum needed:

  • For Fertilizer: Take leaf samples at tip dieback and do not fertilize if your leaf samples indicate you do not need to, or do not apply in this current cycle. Not fertilizing also will reduce your weed pressure.
  • For Weeds: Scout to determine weed pressure and use lower herbicide rates and less expensive herbicides (For example, Velpar 1 lb/a, plus Matrix 2 oz/a, plus Diuron 2 lb/a) and then evaluate control and determine if any post-emergence weed applications are needed. Having a few weeds will not reduce your yields but be sure you do not allow any new weeds to invade, such as milkweed.
  • For Pest Insects: Scout your fields and use action thresholds for deciding if control is necessary. You can also use a more conservative 1.5 to 2 times the recommended threshold. This more liberal threshold means more risk of damage, but because the value of the crop is lower, more damage risk at a lower value balances out the cost of insecticides for control. For example, the blueberry spanworm threshold in a crop field is ten spanworm caterpillars per set of ten sweeps. Using a more liberal threshold of 15 or 20 caterpillars per set of ten sweeps is warranted. We have provided a range of thresholds for SWD. Use the higher end of five to ten males as a more liberal threshold. The other tactic is to use less expensive, but still effective insecticides. Check our recommendations for effective insecticides for each pest insect using:
  • For Pollination: If you have measured native bee foraging densities and fruit set in your fields in previous years using the Schedule for Monitoring Pollinators, see:

and use this information to decide if you can cut back on honey bee rentals or bumble bee purchases. Strong native bee populations measured at 0.5 bees/square yard of bloom/minute will provide 20-35% fruit set. Generally, this level of native bee abundance with an additional two hives of honey bees per acre will provide about 65% fruit set (the result being about 4,000 lbs/acre (range 1800-9000 lbs/acre). Reducing honey bee stocking density to one hive per acre under this scenario (0.5 native bees/square yard) will provide about 45% fruit set, which in a year that has good blueberry fruit production conditions will result in a pretty good crop (about 3,000 lbs/acre (range 1,000-5,000 lbs/acre). Just relying on native bees without honey bees at all will result in about 1800 lbs per acre (range about 1,000-2,800 lbs/acre). The estimates of BOTH fruit set and yields are only averages and they vary considerably with the weather, and inputs such as fertilizer, irrigation, pesticides, and pest and pathogen crop losses. BUT, no matter what the stocking density of honey bee hives you choose, it is paramount that you rent strong colonies. Do not rent less expensive, but weak colonies in order to save money. Weak colonies only send out a fraction of the foragers to the bloom and so it is never worth saving $10-20/hive. Always monitor the field strength of the colonies that you rent, see Fact Sheet 629 – Honey Bees and Blueberry Pollination.

You can also sign up to receive the wild blueberry newsletter by email and receive the disease report on the Wild Blueberry Newsletter Request Form page.

Do not control for Botrytis blossom blight unless you find early symptoms in your field.  The presence of this disease is highly variable and dependent upon early infection and rain around bloom.

Consider skipping control for leaf spots, Septoria, and rust, if you have not seen high levels of leaf loss in late July and August in the past. Scout for diseases, particularly Valdensia leaf spot, which is much less costly to control if it can be caught as a small patch and burned out.

Consider alternatives to selling your fruit to the freezer which includes:

  • Fresh pack which requires investment in cleaning equipment, purchase of boxes and clamshells, trained labor to hand-harvest into half boxes, and labor to pack your fruit. You will also need to find a market for your fruit, such as farm stands, farmers markets, or selling to local stores.
  • Organic production requires certification by MOFGA, with fee and records certifying that no non-OMRI approved pesticides or fertilizers have been used on your fields for the last three years.  If your fruit is sold fresh then you would also have to consider all of the requirements for fresh pack. If you are considering selling your organic crop processed, Merrill Blueberry Farms in Hancock is the only organically certified freezer in Maine.

To evaluate your inputs use the updated Wild Blueberry Fact Sheet No. 260 Blueberry Enterprise Budget which gives examples of organic, low, medium and high input costs and returns. There are interactive Excel budget sheets that illustrate where your major costs occur and allow substitution of your own values to evaluate how adjustments will affect your predicted returns.

These new budgets on the wild blueberry website may be found on the Marketing and Business Management page of Cooperative Extension’s Maine Wild Blueberries website.

Fact sheets from Nova Scotia and an article in the New Brunswick Field Notes newsletter article give additional viewpoints to consider.


David E. Yarborough
Extension Blueberry Specialist

Wild blueberry fact sheets, past newsletters, contacts, resource links, calendar of events, and more can be found on the Cooperative Extension’s Maine Wild Blueberries website.

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 2017

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