Borers

Borers are generally the larvae form of various beetles or moths that feed inside stems, trunks, branches or twigs. A few adult beetles will bore into plants. Borers are most destructive in trees and shrubs, but will feed on annuals, perennials and vegetables as well. Some common borers in this area attack Dogwood, Cherry, Lilac, Pine and Rhododendron. Borers are among the most destructive and difficult to control insect pests in the landscape.

The borer life cycle begins when eggs are laid in the cracks and crevices of bark, preferably in open wounds and protected locations, i.e. under tree wraps or mulch. Once the eggs hatch, the larvae begins to chew its way into the plant. This is when the damage occurs.

When borers feed, they destroy the tissues in the plant needed to conduct water and nutrients. The result is slow, stunted growth, branch dieback or death of the entire plant. Sap or sawdust may be visible at the entry or exit holes of the borer. When the borer reaches maturity, the adult moth or beetle will chew an exit hole, emerge from the plant and begin looking for a mate. This process, from egg to adult can take several weeks or several years, depending on the type of borer.

CONTROL

Non-Chemical Controls
Borers will infest weak, stressed plants. To reduce borer infestation, maintain plant health through watering, fertilizing and pest control.

• Remove any mulch piled up against the base of trees and shrubs
• Avoid wounding the bark and closely monitor any existing wounds for signs of borer activity
• Remove and destroy heavily infested plants
• Inject Parasitic nematodes into borer galleries as a biological control
• Use floating row covers to prevent borers in vegetable crops

Chemical Controls
Spray the stem, trunk, branches or twigs of the susceptible plant during the egg-laying season of the borer. Timing is critical to successfully controlling borers. Once the borer has gained entry into the plant, pesticide applications are ineffective. The accompanying chart lists the treatment dates for several of the most common borers.

Recommended Pesticides
Borer-Miner Killer - applied every 4 weeks
Advanced Garden Tree & Shrub Insect Control - applied once per growing season. Flathead, Roundhead and Bronze Birch Borers only. Not for edibles.

Please bring plant or insect samples to Merrifield Garden Centers' Plant Clinic for assistance identifying borers and selecting pest control products. ALWAYS READ AND FOLLOW LABEL DIRECTIONS WHEN USING PESTICIDES.

Borer	Treatment Dates *	Primary Host Plants
Banded Ash Borer	Mid July -  Early September	Ash
Bronze Birch Borer	Mid May - Early July	Birch
Conifer Bark Beetle	Early April - Mid August	Cypress, Pine, Spruce
Dogwood Borer	Early May - Early July	Birch Cherry, Dogwood, Hickory, Willow, Oak, etc.
Dogwood twig Borer	Early May - Early July	Blueberry, Dogwood, Crabapple, Viburnum, etc.
Elm Bark Beetle	Early April - Mid June	Elm, Zelkova
Lilac Borer	Early May - Early July	Ash, Ligustrum, Lilac, Privet
Oak Borer	Early June	Oak
Pine Shoot Borer	Early April - Early June	White Pine, Mugo Pine
Peach Tree Borer	Early July - Late August	Apple, Cherry, Cherry Laurel, Peach, Plum
Rhododendron Borer	Mid June	Rhododendron, Mtn. Laurel, Azalea
Round-headed & Flat-headed	Early May - Early July	Fruit, Ornamental and Shade Trees
Shot-hole Borer	Mid April - Early June	Apple, Cherry, Plum, Mtn. Ash, Serviceberry
Two-lined Chestnut Borer	Early May - Late June	Oak
Willow Borer	June - September	Birch, Poplar, Willow
European Corn Borer	At first sign of damage	Corn and peppers
Squash Vine Borer	When vines begin to run	Squash

* Treatment dates are approximate for Northern Virginia, Washington D.C. and Central Maryland. Pesticide applications need to be repeated throughout the treatment times at regular intervals as directed on the product label.