CUPS operations have had great success in growing citrus and combating citrus greening but have had issues with small fruit size.

Citrus Under Protective Screening, CUPS, hold great promise for the Florida citrus industry in combating citrus greening, but the Citrus Research and Education Center (CREC) facility has had issues with small fruit size. In a Growing Produce article, Laura Waldo, a senior biological scientist with CREC, shared the steps the facility has taken to manage the issue, including fertilizer management, with fruit size. See details below.

Small Fruit Size Management

According to Waldo, the smaller citrus fruit size in the CUPS facility are caused by:

  • foliar diseases
  • overproduction of flowers
  • lack of fruit thinning
  • some trees becoming root-bound in pots

“We’re working to prevent the disease cycle that causes leaf drop, so we’re trying to work with keeping greasy spot to a minimum,” Waldo said. Similarly, the facility is planning on replanting all citrus trees in pots in the ground. Waldo maintained this would “allow them to have more space for the roots and improve tree quality and ultimately fruit quality … Our trees that are in the ground already have much better fruit size to them because the trees are healthier, they have larger leaves; they’re better able to support the fruit that are on the trees.”

Waldo shared also shared that those trees that over-produce and suffer from collapse are thinned of their fruit. Varieties like Murcott Honey Tangerine and Kinnow mandarin “tend to set too much fruit, which causes the collapse in the tree health from a deficiency of potassium … The closer we get to harvest time, those trees start to decline, their leaves wilt, and then ultimately the trees succumb while the fruit are still hanging on the trees. So the only way to solve that problem is fruit thinning,” she said.

Waldo added that fertilizer management is a key part of the process as well. a“Managing fertilizer, making sure we keep potassium levels appropriate; fruit thinning when necessary; and in the case of our grapefruit, just making sure that we don’t lose the leaves from greasy spot this time of year.”

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