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Borers

Garden pest

Description​

Borers are the larvae of various moths, beetles, flies, and other insects that feed inside plant tissue. “Borers” is a general name, not a single species. Depending on the insect, larvae may tunnel through stems, trunks, branches, roots, or fruit. Their feeding can interrupt the movement of water and nutrients, weaken stems, and open wounds to decay. Affected plants may wilt, grow poorly, or lose branches; fruit may be damaged from within. Some borers favor particular hosts, such as squash vines or peach trees, while others attack a wider range of plants. Adults usually lay eggs on or near a suitable host, and the young larvae enter the plant soon after hatching. Once inside, they are sheltered from many sprays and predators. Damage varies greatly by species and plant age: a single larva can kill a young vine, while an established tree may survive a limited infestation.

Symptoms​

  • Wilting
  • Stunted growth
  • Leaves dropping
  • Stems chewed or cut through
  • Insects visible on the plant
  • Rotting fruit

How to Identify​

Look for small entry holes, sawdust-like frass, sap or gum around wounds, and tunnels beneath bark or inside stems or fruit. A split, damaged stem may reveal a pale larva with a distinct head, although its appearance depends on the species. Sudden wilting despite moist soil is a clue when a vine’s stem has been hollowed out. Unlike drought or a root disease, borer damage often has a localized entry point and feeding debris. Inspect the affected tissue before cutting it away. The host plant, location of the tunnel, and time of year can help identify the particular borer and guide control.

Prevention​

Inspect susceptible plants regularly, especially when adults are active locally; eggs and new entry holes are easier to address than established larvae. Keep plants appropriately watered and avoid injury from mowers, pruning tools, or sunscald, which can make some woody plants more vulnerable. Remove dead or heavily infested wood and dispose of it before emerging adults can reproduce. Follow good pruning practices rather than leaving damaged stubs. For crops such as squash, a lightweight insect net can keep egg-laying adults away if installed before they arrive; remove it during flowering if pollinators need access, or hand-pollinate. Rotate annual crops where the pest overwinters nearby, and avoid moving infested wood or fruit to new areas. Prevention depends on the borer species.

Treatment​

First, confirm where the larva is feeding. Hand-pick eggs or exposed larvae, and remove and discard infested fruit or badly damaged stems. On a squash vine, an early, localized infestation can sometimes be treated by carefully opening the stem, removing the larva, and covering the wounded section with soil to encourage rooting; this may not save a severely wilted plant. Prune infested branches from woody plants when doing so will not cause greater harm, and dispose of the cuttings promptly. For certain borers, beneficial nematodes applied according to their label may help, but results depend on species and conditions. Insecticides generally work best against newly hatched larvae before they enter the plant; spraying an occupied tunnel is often ineffective. Use a product labeled for the identified pest and plant, follow its timing and directions, and protect pollinators. Severely infested plants may need removal.

Plants Affected​

African Mahogany, American Elm, Ash, Aspen, Basmati Rice, Bhutanese Red Rice, Birch, Black Ash, Black Cottonwood, Black Locust, Black Oak, Black Rice, Blue Ash, Blue Gum, Brown Rice, Bur Oak, Camargue Rice, Chestnut Oak, Cork Elm, Dogwood, Eastern Cottonwood, Elderberry, Elm, Eucalyptus, Flowering Dogwood, Forbidden Rice, Green Ash, Green Rice, Hickory, Honduran Mahogany, Honey Locust, Indian Sandalwood, Indica Rice, Iris, Japonica Rice, Jasmine Rice, Kalijira Rice, Laurel Oak, Lilac, Locust, Mahogany, Mountain Ash, Oak, Overcup Oak, Paper Birch, Peach, Pine, Poplar, Purple Rice, Quaking Aspen, Red Oak, Red Rice, Rice, River Red Gum, Rock Elm, Sambucus, Sand Cherry, Scarlet Oak, Shagbark Hickory, Shumard Oak, Slippery Elm, Sticky Rice, Swietenia, Syringa, Tasmanian Blue Gum, Teak, Trembling Aspen, Walnut, Water Oak, White Ash, White Birch, White Rice, Willow, Yellow Birch, Yellow Rice

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