Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2007
Publication Date: 7/1/2007
Citation: Black, B., Ehlenfeldt, M.K. 2007. Foliar Applications of GA4+7 Reduce Flowering in Highbush Blueberry. HortScience, vol. 42, pp. 555-558.
Interpretive Summary: Some varieties of highbush blueberry produce significant crops immediately after planting in the field. This may adversely affect subsequent cropping by reducing plant size and vegetative growth. Blueberry plants are also susceptible to several pollen-borne viral diseases. For these reasons, growers may remove flower buds from young blueberry plants by hand. A less laborious method to inhibit flowering in the nursery and during field establishment would help new plantings establish in the field and reduce the risk of early virus infection. We investigated the efficacy of foliar applications of commercially produced plant growth hormones for suppressing flower bud initiation in blueberry. In two studies, the greatest response resulted from three weekly applications in late August and early September. Flower bud numbers were suppressed by 70 to 85 percent for ‘Bluecrop’ and 95% for ‘Duke’. This level of inhibition would result in a significant reduction in the hand-labor typically needed for flower bud removal in such plants. This information will be of value to nurserymen and growers all over the U.S.
Technical Abstract: Precocious varieties of highbush blueberry may over-crop during the first few seasons in the fruiting field, adversely affecting plant establishment. Reducing or preventing bloom in the nursery and during establishment would be beneficial in preventing early cropping and reducing the risk of infection by pollen-borne viruses. We investigated the efficacy of foliar applications of GA4+7 (ProVide (registered), Valent BioSciences), for suppressing flower bud initiation in blueberry. One-year-old rooted cuttings of ‘Bluecrop’ were obtained from a commercial nursery and established in 11-liter pots at the Philip E. Marucci Blueberry and Cranberry Research Center, Chatsworth, New Jersey. Experiments were conducted over three seasons with ‘Bluecrop’ highbush blueberry where foliar applications of GA4+7 were made at concentrations ranging from 50 to 400 mg active ingredient per liter, with timing treatments ranging from 7 July to 15 Sept, with 10 replicate plants per treatment. Floral and vegetative buds were counted the following spring. In the first study, the greatest degree of flower bud suppression resulted from applications at 400 mg•L-1 repeated weekly from 7 July to 1 Sept. However, these treatments also reduced total vegetative bud number and plant height. In the two subsequent studies, the greatest response resulted from three weekly applications in late August and Early September, where flower bud numbers were suppressed by 70 to 85 percent for ‘Bluecrop’ and 95% for ‘Duke’.