Uptake of Foliar Nutrients Applied to Productive Southern Highbush Blueberry (V. corymbosum, Interspecific Hybrids) Emerald

Foliar applications of nutrients are used to correct deficiencies, improve fruit quality, and amend nutrient programs. However, many growers apply nutrients foliarly to blueberry plants, although the efficacy of foliar applications is not well demonstrated. The objective of this study was to determine uptake of nutrients applied foliarly to healthy southern highbush blueberry ‘Emerald’. In 2015, two applications of chelated [Albion Metalosate Crop-Up (AMC), Clearfield, UT; Mg: 0.05%, B: 0.025%, Cu: 0.25%, Mn: 2.50%, Fe: 0.25%, Zn: 1.25%] and sulfate salt chemistries [R.W. Griffin Industries (RWG), Douglas, GA, Mg: 2.0%, B: 0.1%, Cu: 0.25%, Mn: 1.0%, Fe: 2.0%, Zn 1.0%] were applied on 29 May and 18 Aug at 4.7 l^.ha^-1 and 27.8 l^.ha^-1, respectively. For each treatment, an application without and with a non-ionic surfactant was included [Loveland Products LI 700 (L), Greeley, CO].  The 29 May application was after harvest and before hedging on 8 Jun. The treatments were sampled 3 and 10 d after application (DAA). The leaves sampled were fully expanded, from new growth, washed with 0.1% solution of non-phosphate soap, dried, and sent to an agricultural testing lab (Waters Lab, Camilla, GA). Chlorophyll (Opti-Science, Hudson, NH) indices were measured at each leaf sampling. Shoot length and count were measured after 28 Aug. Both Mg and S were not deficient in plants and only AMC/L had 17% more Mg on 8 Jun by 10 DAA. All other treatments were statistically equivalent to the untreated plants by 10 DAA. The only micro-nutrient that was deficient in the untreated plants was Fe (≤ 50 ppm); Fe was lowest (45.1 ppm) on 21 Aug. The micro-nutrients applied generally showed higher concentrations when compared to the untreated plants at 3 DAA than 10 DAA.  Applying a higher rate, the micro-nutrients increased foliar concentrations of Cu, Fe, Mn, and Zn at 10 DAA; however only RWG/L consistently increased nutrient levels at 47%, 37%, 21%, and 59%, respectively compared to the untreated plants. Chlorophyll indices were similar among treatments within each leaf sampling date except on 1 and 8 Jun when there was a 14% and 12% increase for AMC, respectively, relative to the untreated plants. Shoot length and count were suppressed in all the treatments with application of L. In conclusion, foliar macro-nutrients Mg and S are unwarranted for healthy ‘Emerald’. Both Fe and Cu showed efficacy as a sulfate salt or chelated compound and LI-700 showed inhibit growth.