Garden Guides, Insects That Harm Pecan Trees

Insects That Harm Pecan Trees

By: April Sanders

21 September, 2017

The pecan tree (Carya illinoinensis) is the official tree of the state of Texas and is desirable for its large size, bright green leaves and, of course, delicious nuts. The production of those nuts can be reduced or damaged, however, if the pecan tree is attacked and infested by insect pests, which feed on the sap and even use the nuts to house their young.

Hickory Shuckworm

Hickory shuckworm is a major pest to pecan trees. This insect harms the pecans of the tree and attacks midway through the season. The larvae tunnel into the shucks of the nuts, stopping the flow of nutrients and interfering with kernel development. The pecans end up malformed and immature, or they drop prematurely from the tree.

Treat affected trees with an insecticide. Because the effects of this insect are sometimes hard to spot at first, it is a good idea to spay the tree with a preventative pesticide or insecticide in the spring, before the nuts begin to develop.

Stink and Leaf-footed Bugs

Stink bugs and leaf-footed bugs love to feast on pecans. These insects overwinter under fallen leaves, only to emerge in the spring and lay eggs on nearby crops, such as soybeans, or common weeds. When the eggs hatch, the larvae make their way to nearby pecan trees, where they latch onto the developing nuts and suck out the sap. If the shells of the pecans are not yet hard, the nuts will drop prematurely from the tree. If the shells have hardened, dark spots will appear on the kernel, and the pecan will develop a bitter taste.

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These pests are easily spotted with the naked eye. Once spotted, the tree should be treated with a powerful insecticide to kill the insects.

Black Pecan Aphid

The black pecan aphid can devastate a pecan tree in just one season. These aphids suck the sap from the bottom, or underside, of the leaves of the tree. Black aphids are more dangerous to the tree than yellow aphids because they inject a toxin into the leaves when they pierce the leaves to suck out the plant’s juices. The toxin kills the tissue between the veins of the leaves, first turning it bright yellow, then brown. In this way, defoliation can quickly occur, especially since it only takes three of these tiny bugs to kill one leaf, according to horticulturists with Texas A&M University.

Defoliation of a pecan tree greatly reduces nut development and production. Black pecan aphid infestations should be prevented with the application of a preventative insecticide in the spring.


Sawflies look similar to tiny bees. Their larvae are voracious eaters and will consume the leaves of the pecan trees, leaving them full of holes or ragged along the edges. Often, entire leaves are eaten. When the larvae are satiated, they drop to the soil, where they burrow into it and overwinter. In the spring, the adults lay eggs on the newly emerging leaves, continuing the cycle. Pecan trees should be sprayed with insecticide in the spring to kill the larvae before they hatch or shortly thereafter.

Fall Webworm

Fall webworm is a type of caterpillar. Hundreds of these can build large webs on a pecan tree, swathing the tree in sheets of white silk. These caterpillars consume the leaves of the tree and can defoliate even large trees in one growing season, which severely limits nut production. Between two and four generations of caterpillars can infest pecan trees each year.

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Beetle infestation puts Joburg’s tree canopy at risk

Johannesburg City Parks and Zoo is investigating an outbreak and infestation of borer that is killing trees in several suburbs.

Residents in Hurlingham‚ Craighall Park‚ Dunkeld‚ Sandton‚ Parkview‚ Kensington and Houghton have reported diseased trees in their yards and on the street‚ mayoral committee member for community development Nonhlanhla Sifumba said on Wednesday.

“Polyphagous Shothole Borer … is a minute beetle that embeds its eggs deep in the inner layers of the tree. The larvae‚ once matured‚ then make their way out of the tree by tunnelling holes‚” a statement by the MMC read.

“The holes resemble ‘gunshots’ that stifle the flow of nutrients through the veins of a tree‚ resulting in a tree that is visibly diseased from the top. This is eventually fatal for the tree and can destroy a cluster of adjacent trees once the young beetles start to nest.”

The city’s parks and zoo department is working closely with institutions such as the Forestry and Agricultural Biotechnology Institute (FABI) to survey the extent of the spread of the infestation.

Pesky bug brings a plague to city trees

Sifumba appealed to residents to report diseased trees to [email protected]

“We are in the process of identifying the extent of the infestation of the Shothole Borer to the tree canopy of the City of Joburg‚ and the environment as a whole in order to mitigate the far reaching implications” said Sifumba.

The beetle has been devastating in other parts of the world but Sifumba was cautious not to cause panic until the true extent of the infestation was ascertained.

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“Pesticides are not effective as well‚ because the beetle bores deep into the wood. The only known method of managing the spread is to cut down infested trees hosting the beetle‚ and to dispose of them in a controlled manner‚ through burning‚” Sifumba explained.

Symptoms vary in different tree species — from patches of white powdered wood called frass to blotches of oozing resin or gumming. This weakens the trees’ immune system causing stress and die-back on the bark surrounding the hole.

While the city evaluates the extent of the infestation‚ it is also training personnel to identify the borer and other fungal hosts that accompany the beetle‚ disposing of trees in a designated area for controlled dumping and burning and ensuring that a tree replacement strategy is in place.

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