The bloom period is progressing very rapidly in all blueberry varieties. Excellent weather conditions from the past week have propitiated a steady plant growth and development. It is important that growers pay special attention to pollination, disease and insect control.

After the slight frost from the previous week, some early season varieties may have suffered some flower bud damage in the form of a partial frost of the flower internal organs. This will cause some pollination problems that will result in a large “June drop” of non-pollinated flowers. If you think you have a problem with low pollination, there are two alternatives to ameliorate it: increase the number of beehives per acre or try some gibberellic acid.

Blueberry fields with light frost damage to stamens and styles may benefit from the application of gibberellic acid. Michigan State University Extension small fruit horticulturist Eric Hanson has shown that application of gibberellic acid may decrease the impact of low pollination. Gibberellic acid applications results in greater retention of some parthenocarpic (seedless) fruit that would have dropped and also increases the size of berries without a full complement of seeds. Gibberellic acid can be applied in a single spray during bloom – 80 grams active ingredient per acre – or two 40 gram sprays, one during bloom and the second 10 to 14 days later. The commercial formulation of this product is marketed under different names; several gibberellic acid products (ProGibb, GibGro, etc.) are labeled for highbush blueberries. For more information, see the MSU Extension article “Gibberellic acid use on blueberries”.

Growers that attended the May 14 twilight meeting in West Olive, Mich., may have received a copy of the actual gibberellic acid recommendation from Eric Hanson. If you can’t download the recommendation, call Carlos Garcia at 616-260-0671 or email garcias4@msu.edu to obtain a copy of the recommendation.

Regarding blueberry insect control, cherry fruitworm is emerging in the southern counties and the time for the first insecticide application is approaching rapidly. Among the choices for fruit worm control, Intrepid 2 F is one of the recommended products. It is important to note that this insecticide is considered problematic for some endangered species of butterflies. The restrictions are outlined in the revised specimen label for Intrepid from April 22, 2013. In Michigan, counties where this insecticide requires special considerations include Allegan, Muskegon, Oceana, Newaygo and Montcalm, among others. Growers interested in using this insecticide in the restricted areas should obtain a copy of the Endangered Species Protection Bulletin from the EPA website. Growers should request the bulletin valid for the month when the insecticide will be applied.

If you have problems accessing this information, please email or call your Michigan State University Extension local office for assistance. If your blueberry field is located in one of the restricted areas, confirm if another similar product is available for fruitworm control.

For more insecticide options, please check the MSU Extension bulletin 2013 Michigan Fruit Management Guide (E154).