Evaluating Shade Effects on Primocane Blackberry Flowering and Fruiting

Primocane blackberry production in the upper south is limited by high temperatures during the bloom and early fruiting period, resulting in poor fruit set and poor fruit quality. Shade may have the potential to delay bloom and flowering to a more favorable season by reducing temperatures that cause poor fruit set and quality. A greenhouse study was established to evaluate the effects of shade on primocane blackberry growth, physiology, and fruiting. Canes of ‘PrimeArk® 45’ were planted in 11.3 liter pots. At approximately 0.25m in height, one of the four following treatments was imposed with eleven replications: 1) an untreated control [CK], 2) unshaded for 30 days then shaded for 30 days [US], 3) shaded for 30 days then shaded for 30 days [SS], and 4) shaded for 30 days and unshaded for 30 days [SU].  After treatments ended, plants were grown without shade for 30 days. Plants in the SU treatment were significantly taller than the US while the control and SS treatments were intermediate. A similar trend was seen between the height and cane diameter with the SU treatment as the largest and US as the smallest. The SU had the largest total leaf area of all treatments and CK was the lowest. Dry weight of leaves was consistent for all treatments except for SS which was significantly lower than the others. Shading reduced net photosynthesis measured, but plants readjusted to unshaded conditions. At the conclusion of the greenhouse study the US had the most flower formations of all the treatments with nearly four times as many as the SS. The CK treatment recorded the highest number of fruits when potted plants were harvested and the SU had the least amount. There was a direct correlation between shade and increased water use efficiency which improves the sustainability of blackberry production. First bloom dates for each treatment was recorded. The CK bloomed first followed by US and SS. The last to bloom was the SU, 26 days after the CK. At the conclusion of the experiment the CK had the largest number of fruits and SU the least. The US displayed nearly four times as many flowers as the SS, CK and SU when all potted plants were harvested. In conclusion, there was significant delay of flower and fruiting when 50% shade cloth was implemented and removed in the SU treatment.