University of Missouri Extension

Debbie Johnson
Senior Writer
University of Missouri Cooperative Media Group

Published: Friday, March 29, 2013
Story Source: Jennifer Schutter, 660-665-9866

This is part of an ongoing series, "Your Show-Me Garden: MU Extension brings you gardening tips from experts around the state." To see all entries in the series, go to

The battle to protect fruit from fungi, diseases and insects

KIRKSVILLE, Mo. - Growing fruit is a true labor of love because there are so many pests waiting to deny you the fruits of your labor. Fruit growers are in a constant battle against diseases, fungi and insects.

Spring is the best time to draw battle lines against these invaders. Several types of fungi attack fruit trees. On apple and pear trees, they can harm the roots, foliage, bark and branches.

Do you have peach trees? Peach leaf curl is caused by a fungus that makes leaves curl, pucker and turn red, said Jennifer Schutter, horticulture specialist for University of Missouri Extension.

"To control peach leaf curl, apply a fungicide containing chlorothalonil to the trees before buds swell," Schutter said. "You can also use fixed-copper products, but they may not be quite as effective."

Black knot is a common fungal problem for plum and cherry trees in Missouri. It appears as elongated swellings, or knots, on the limbs of trees. When newly formed, these knots are green and soft, but will harden and turn black with age.

"The most effective control for black knot is to prune out all of the cankers, or knots," Schutter said. "A liquid lime-sulfur spray during dormancy will help control this disease and should be used along with canker removal."

Fungi aren't the only microbial threats to fruit trees. Fire blight can be a serious bacterial disease of apple and pear in Missouri. It kills blossoms, fruiting spurs and, in severe cases, entire branches, limbs and trees. It overwinters in cankers on the tree and spreads to healthy tissue in the spring.

"You can control fire blight with a dormant spray application of a copper fungicide, available under trade names such as Kocide, Bordeaux and others," Schutter said. "Make sure the brand of copper you purchase is cleared for use on apple and pear trees."

Don't forget to read the label before applying any chemical, she said. Apply products at the recommended rates.

Many insects are waiting to take a bite out of your delicious fruit trees. Dormant sprays are a good protection against these pests.

"If insects have been a problem, you might want to consider dormant oil for control. It's a refined, lightweight oil that can be used on woody plants during the dormant season," Schutter said.

Dormant season application of horticulture oil can help control tent caterpillars, leaf rollers, mites, scale insects and aphids, she said.

Schutter warns that oils should not be applied to woody plants during freezing weather. Cold temperatures will cause the emulsion to break down, producing uneven coverage. Also, horticulture oil should not be applied if the tree is wet or rain is likely.

For more information, the following MU Extension publications are available for free download:

Photo available for following caption

Peach leaf curl
Photo credit: Giancarlo Dessi

Photo available for following caption

Black knot on cherry
Photo credit: Robert L. Anderson

Photo available for following caption

Fire blight
Photo credit: Roger Meissen

Photo available for following caption

Eastern tent caterpillar on bark
Photo credit: Public Domain from the U.S. Forest Service

Photo available for following caption

Scale insects on a common dogwood
Photo credit: Gilles San Martin

Photo available for following caption

Raspberry aphids
Photo credit: Public Domain from the U.S. Department of Agriculture

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