The battle to protect fruit from fungi, diseases and insects

Wednesday, May 1, 2013

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.

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 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.

The following MU Extension publications are available for free download: "Fruit Spray Schedules for the Homeowner" (G6010), extension.missouri.edu/G6010; "Insect and Mite Pests of Apples" (IPM1008), extension.missouri.edu/IPM1008; "Insect Borers of Fruit Trees" (G7190), extension.missouri.edu/G7190; and "Fruit Production" (MG6), extension.missouri.edu/p/MG6.

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