Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
Imidacloprid Protects Trees & Shrubs from Borer Damage
Nearly all shade trees and many shrubs are subject to borer attack, the tunneling of immature beetle or moth larvae through the cambium, sapwood or heartwood of the host plant. Adult insects lay eggs on the bark of a host plant, which hatch into very small, caterpillar-like larvae. Their tunneling causes disruption of water and food movement through the plant's vascular system. Insects often re-infest affected plants causing branches to decline and die, and potentially killing the entire plant.
Traditionally, borers have been treated with a trunk spray application of insecticide that kills the newly hatched insects before they tunnel into the plant. However, a new product is making borer control easier and targeting the small larva as they chew their way into the plant. Imidacloprid, sold as Bayer Advanced Tree & Shrub Insect Control or Ortho Max Tree & Shrub Insect Control, is a systemic insecticide that is applied as a soil drench around the base of target plants. It has a twelve-month residual effect, so should only be applied once per year. Depending on the size of the plant, it can take from one week to three months (for large trees) to reach full effectiveness so should be applied 3-4 weeks before the targeted insect's egglaying period.
Imidacloprid is effective against beetle borer larva, such as redheaded ash borer, bronze birch borer, roundheaded apple borer, and flatheaded apple borer. It is NOT effective against moth borer larvae, including lilac borer, banded ash clearwing or peachtree borer.
Egg laying periods for common native Nebraska beetle borers:
- Redheaded Ash Borer - (hosts ash, oak and hackberry) late April
- Bronze Birch Borer – (particularly damaging to paper and European white birch) mid to late May
- Roundheaded apple borer – (wide range of hardwood trees) late June
- Flatheaded apple borer - (attacks all hardwoods) mid May
Follow label directions to determine how much product to apply. As a soil drench, imidacloprid is mixed with water and applied to the soil at the base of the plant. The chemical is absorbed by the plant's root system and moved throughout it's trunk, branches and foliage.
Cultural practices can also reduce borer infestations. Usually, borers attack plants that are already in a weaken state from improper care and transplant or environmental stress. Healthy, vigorously growing trees are not especially attractive to borer attack. To maintain healthy trees, apply one inch of water weekly if the area has not received a similar amount of rain. During the periods of drought, water plants deeply with a slowly trickling hose or small sprinkler. Protect plants from other pests particularly during the first two or three years of growth. Do not plant trees too deeply. Finally, apply mulch around the base of your trees to preserve moisture and to prevent the most common and serious injury of all- lawn mower damage.
Note- Emerald ash borer, a non-native insect that has caused widespread death of ash trees in several states, has not been found in Nebraska as of June 2010.