Strategies for Maintaining Fruit Quality in Northern Highbush Blueberry under Water-limited Conditions: Deficit Irrigation and Reduced Crop Loads

Many commercial blueberry (Vaccinium sp.) fields are irrigated, but mandatory water restrictions may soon limit the availability of irrigation water in several important blueberry growing regions such as California and eastern Washington. New strategies are needed to maintain fruit quality with less water. Two potential options, including crop thinning and deficit irrigation, were evaluated for 2 years in a mature planting of northern highbush blueberry (V. corymbosum L. ‘Elliott’). Treatments included a combination of normal and 50% reduced crop loads and either no drought or 6 weeks of drought (little rain and no irrigation) during early (Stage I-II) and late stages (Stage II-III) of fruit development. Plant water potential declined to -1.2 to -1.3 MPa with drought during the early stage of fruit development and to -3.0 to -3.2 MPa with drought during the late stage. Early drought had no effect on effect on yield, while late drought reduced yield at both crop loads by an average of 40%. Crop load reduction had no effect on plant water potential or photosynthesis during drought at either stage but, compared to the normal crop load, increased berry diameter and average berry weight by 2% to 20%. Plants exposed to early drought had greater fruit bud set than those that were well-irrigated, while plants exposed to late drought had lower fruit bud set. Overall, the results suggest that blueberry may be minimally affected by drought during early stages of fruit development, and thinning the crop to 50% may result in larger fruit at harvest when plants are exposed to drought at any stage of fruit development.