CUPS: Managing Small Fruit Size

Ernie NeffCUPS

Laura Waldo shows undersized grapefruit grown in a citrus under protective screen facility.

Fresh fruit has generally grown well in a citrus under protective screen (CUPS) facility at the Citrus Research and Education Center, but there has been an issue with small fruit size. Laura Waldo, a senior biological scientist who works with lead CUPS researcher Arnold Schumann, discusses the problem and likely solutions. 

Waldo says causes of the smaller fruit size have included foliar diseases, overproduction of flowers, lack of fruit thinning and some trees becoming root-bound in pots. Ray Ruby grapefruit planted in 5-gallon pots have been particularly susceptible to becoming root-bound. Trees that become root-bound experience physiological stress and have fewer and smaller leaves and smaller fruit sizes.

“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 says. In addition, workers plan to remove all grapefruit trees, especially those in 5- and 7-gallon pots, and plant them into the ground. Waldo says replanting should “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 also reports that some Honey Tangerine (Murcott) and Kinnow mandarin trees in the CUPS are suffering from collapse. She said those two varieties “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.” Currently, the fruit are thinned by hand.

Waldo summarizes the steps being taken to prevent small fruit size: “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.”

Hear more from Waldo: 

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About the Author
Ernie Neff

Ernie Neff

Senior Correspondent at Large