Borers can be controlled without using chemicals

Q: You mentioned controlling borers with chemicals, but can borers in trees be controlled without using chemicals?

A: Yes, it is possible. But it requires diligence. Damage to trees by borers may linger for several years before it comes to our attention. Sometimes extensive damage happens quickly. But this should not stop us from being proactive.

Use chemicals to control boring insects (borers) in trees as a last resort, not the first line of defense. Our understanding of pesticides and their use has changed over the years. There are other treatments that can work before the damage gets extensive.

When the death of an entire limb is seen in midsummer, borer damage in this area of the tree was already extensive. Extensive damage tells us we should have started looking for borer damage a few months earlier.

Discover borer damage as early as possible. Start in early spring when borers have first entered the trees as babies or have woken up after a long winter sleep. Begin looking about one month after leaves first emerge from the trees.

Look for sap oozing immediately from limbs and trunk after a good rain. At this time the bark around the trunk and limbs becomes soft. Sap oozes easily from inside the trunk and upper sides of limbs where damage occurs from borers because of tunneling and feeding just under the bark.

Sap oozing from trees is not always a clear sign of borer damage but instead a problem indicator. This indicator says, “Hey, look here!” Begin a borer search and destroy mission where this sap is located. Use a sharp, sanitized knife and cut into the trunk or limb at these locations at a sharp angle like you are whittling wood.

These cuts are shallow and clean, not ragged. Clean cuts from a sharp, sanitized knife allow the tree to heal quickly from these wounds. The damage created by your knife is much less than damage already done by borers. And destroying these borers may save the tree.

What about no rain? Try spraying the trunk and limbs with water from a hose-end sprayer near dusk.

Perhaps spraying will soften these areas enough for sap to begin oozing by the next morning. Combine this water with insecticidal soap (or unscented liquid detergent in a pinch) and start controlling aphids with this spray as well which are always a problem in the spring.

Q: You recommended a granular insecticide for controlling borers in fruit trees. What is it and how do you apply it?

A: I don’t remember recommending a granular insecticide for this purpose. The insecticide I recommend for controlling borers inside trees contains the active ingredient imidacloprid. This insecticide comes in several different forms for application, made by several different companies, and marketed under several trade names.

Read the label before buying it. Be sure it’s what you need. When deciding to use it, read the application instructions and follow them.

Use insecticides when no other options to save the tree exist. Don’t use pesticides carte blanche. Remember, one of the options available is to remove the tree.

Another option is to start looking for this pest earlier before damage is extensive. When damage is extensive, removal of a limb or the tree may be the best option and should be done as soon as possible.

My recommendations for the application of this pesticide do not contradict the label but are intended to supplement it. Following these directions may help reduce environmental and human safety problems.

Apply this pesticide after the tree has finished flowering for the season. This pesticide has been implicated in a serious problem with honeybees. It has not been proven, but it has been implicated. To avoid this problem, know when your tree flowers and apply it afterward.

If you decide to apply it, several methods of application are available. I suggest the soil drench method rather than spraying it all over the tree. Pouring the diluted liquid pesticide onto the soil helps prevent its wider distribution in the total environment.

The label may allow eating the fruit later in the season. In my opinion, I would avoid eating fruit.

The label tells you to wear protective equipment when handling it, such as unlined rubber gloves. Be sure to rinse any supplies or equipment in contact with pesticides multiple times after use and apply this rinsate rather than flush it down the drain.

Never apply any pesticide when flowers are present. Applications are best done during early morning hours or late in the evening.

Q: About 10 years ago, a beavertail cactus started to grow in front of my house. Last spring, ugly boils started appearing on the pads. The nursery told me it was being attacked by insects and recommended I spray it weekly with an insecticide until it is cured.

A: I looked at the picture sent to me of your cactus. I could see the damage to the pads done by an insect called cochineal scale. The white cottony residue that surrounds this insect was gone, but the damage done by its feeding near the thorns remain.

Even though the insect might be gone, the damage may be permanent on these pads. This insect releases immature forms of itself called crawlers and will infest the new growth causing the same problem.

Protect new pads growing from the old ones or start a new plant using pads removed from the mother plant. Your choice.

Cochineal scale doesn’t feed on smooth surfaces of plants but congregates in small colonies on or near the spines, aka glochids. The areas surrounding glochids are called areoles. The succulent flesh of the cactus is close to the surface at these locations so these tiny bugs feed with less effort at these spots, and the spines help protect them from predators.

You can continue to spray this insecticide to protect the new growth or wash off the new growth with a strong stream of water from a hose sweep. Do this twice each week during the summer months. This forceful stream of water knocks the crawlers off the new growth, protecting it.

Dormant oils and soap sprays are recommended by many, but they must be repeated every three to four days, as the pads become repopulated. Controlling ants, which move them around on plants, is also recommended.

The old-fashioned way was to apply insecticides, as you are doing, to cover the plant with a poisonous barrier. Repeat sprays according to the label, but it is usually applied less often.

Q: If I can find an apricot tree at the nursery now to replace one I lost, can it be planted soon? I saw a variety called Mormon, but it requires 600 hours of chilling for fruit production.

A: Chilling hours do not appear to be as important on many apricots as some other fruit trees. Even though Las Vegas has perhaps 200 to 400 chilling hours each year, I have had good luck growing apricots that require more chilling hours than this. With some varieties, I have had good luck at even 800 chilling hours.

Mormon apricot, also called Chinese apricot, is a good, old-fashioned apricot for our locale. The Mormon cultivar has the traditional apricot flavor, cans well and is a heavy producer of good-sized fruit without much thinning.

Plant it as soon as the weather cools off a bit, holding off as late into September and early October if you can wait that long. If you can’t wait, then go ahead and plant now but have the hole dug and the soil amended before planting it.

Buy it in a 5-gallon nursery container if available. Select a tree that has lower branches on the trunk, not overgrown for the container, appears healthy and has good form.

Plant it in the prepared hole wet and don’t let the roots dry or contact very dry soil when planting. This method reduces transplant shock.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at Send questions to

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