Abstract

Plants of the 'Elliott' highbush blueberry (16-year-old, planted at 3 × 1 m) were grown in a sandy loam soil under colored shade nets (white, red, black and no net) of different density (25, 50 and 75% of shading) in Gobles, Michigan, USA, during 2006-07. Treatments were assigned randomly with 3 reps, and established as a continuum of 4 rows with 6 plants in each row. Nets (provided by Polysack Plastic Industries, Israel) were established horizontally from July to October at 3 m height. Leaf chlorophyll content increased and the ratio Chl a/Chl b decreased as shading intensity increased, with the black nets giving the largest changes. Also, leaf photosynthesis, measured at the actual light intensity under the nets, decreased as shading intensity increased, with the red and black 70% having the lowest values. Fluorescence (Fv/Fm) was significantly lower in plants without shading (control) compared with plants under 70% shading (white, black or red). Nets retarded fruit development; thus, on August 10th, the proportion of ripe fruit was 26.9% without shading, while less than 10% of the fruit were ripe under black 70%, black 50%, red 70% and red50%. On August 23rd, the separation between the controls and the most delayed fruit development (black 70%) was over 30%. In general, the various shading treatments increased fruit weight compared to the controls, but decreased fruit soluble solids, with the black 50 and 70% having the greatest impact. Thus it is clear that colored shade nets alter blueberry physiology and could be a valuable tool to displace peak harvest season in blueberries.