Most borers are the larval form of large group of insect pests that tunnel into stems and feed on the plant tissue from the inside. They can attack trees, shrubs, perennials, and vegetable crops. They leave open wounds at the entry points but are often undetected until the damage to the whole plant is noticed. This usually includes yellowing and wilting of leaves, loose bark on trees, and eventually wilting of branches and stems and leaf drop.
Here are several different controls:
Trees and shrubs
- Borers will go after plants that are stressed due to poor growing conditions or poor nutrition so be sure to feed and water your plants adequately and provide them with the proper growing conditions.
- Avoid mechanical injury to your trees, especially from lawnmower nicks, as borers often enter through wounds or scars.
- For cane borers which infest roses, blackberries and raspberries, the best solution is to prune the canes several inches below the wilted stems (back to healthy solid green wood) as soon as you see the damage. Destroy canes or discard in the trash.
- Rhododendron and lilac borers damage stems and branches. Prune out and destroy infested branches.
- When you see the bore holes in trees and shrubs, you can often kill the borer larvae by inserting a sharp wire into the hole.
- Ornamental trees and shrubs can be treated with a drench of Bayer Advanced 12 Month Tree & Shrub Protect & Feed or Bonide Annual Tree & Shrub according to the label directions. These products are systemic and will protect for a year. Always read and follow the label directions!
In the vegetable garden - vine borers:
- The best defense is a good offense! ROTATE your crops is one of the best control measures against many vegetable garden pests and diseases!
- Once the vine borers are inside the stem, insecticides have little effect.
- Squash vine borers can infest more than just squash. Keep an eye on your cucumbers, melons, and pumpkins, too. If you notice borers in the stems, you can use a wire to poke in and stab them or carefully slice the stem lengthwise with a knife, pick out the borer, then push the stem back together and cover with soil or compost.
- If you have a history of borer problems, spray the base of the stems early on with Bonide Captain Jack's Deadbug Brew or Bonide Eight. If they are in flower, spray early in the morning or later in the evening when bees are less active and try to avoid spraying on the blooms. Always read and follow the label directions!