Techniques Tested on Mandarins in CUPS

By Rhuanito S. Ferrarezi and Mark A. Ritenour

Two independent trials were conducted under a commercial citrus under protective screen (CUPS) system. The first trial was to investigate canopy management strategies to improve fruit yield and quality of mandarins. Canopy management is essential for CUPS since the environment stimulates vigorous vegetative growth, posing operational challenges to mechanization that can be overcome by selectively controlling plant growth. The second trial was to evaluate the effect of colored netting on tree growth, fruit color and internal quality of mandarins cultivated inside and outside the CUPS.

TRIAL 1
In the first trial, a combination of pruning practices were tested. These included:

• Mechanical hedging/topping after budbreak stage (bloom) and late summer
• Hand pruning at bloom and late summer
• Mechanical hedging and hand pruning at bloom and late summer
• Hand pruning only at bloom

Sugar Belle® and W. Murcott on C-35 rootstock were planted in January 2017 and spaced at 8 feet by 15 feet (363 trees/acre). Mechanical pruning was performed using a gas-powered 3-foot-long sickle-bar knife. Hand pruning was done with lopping shears, saws and clippers.

Canopy management using hand pruning of W. Murcott approximately doubled yield compared to summer mechanical pruning two out of three years, and the trend was similar for the third year. However, there were no significant differences for Sugar Belle, nor were there consistent effects on either cultivar related to trunk diameter, canopy volume, or sugar and acid content.

TRIAL 2
In the second trial, four screen colors [red, blue, gray, and no netting (control)], were tested in a different set (inside a CUPS facility and open air) of Sugar Belle® mandarins grafted on C-35 rootstock. Colored screens can alter the spectral wavelength of light reaching leaves and fruit and transform direct light into scattered/diffused light.

Unfortunately, there was no significant benefit of using colored nets on yield or internal quality, with the use of gray netting significantly reducing salable yield. Furthermore, the netting often significantly reduced the amount of light reaching the leaves and fruit. This resulted in reduced trunk growth (diameter) and canopy volume. Thus, there appears to be no benefit of using photoselective netting on Sugar Belle mandarin under CUPS or in open-field production.

Rhuanito S. Ferrarezi is an associate professor at the University of Georgia College of Agricultural & Environmental Sciences in Athens. Mark A. Ritenour is a professor at the University of Florida Institute of Food and Agricultural Sciences Indian River Research and Education Center in Fort Pierce.

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