Pruning class scheduled

Q: During the summer months I noticed most of the plants on one side of my landscaping seemed to be not thriving, regardless of what I did such as adjusting water and fertilizer. It was when I decided to replace a couple of bushes that just wouldn’t “grow” (leaves were shriveling, little or no new growth) that I think I found the reason.

When digging up the bushes I found about a dozen, 1-inch-long, fat, white worms with legs on the front and a brown head. Please see the picture I sent. When a neighbor saw them, he immediately said they were grub worms and that they were eating the roots of the plants.

I bought and applied a systemic insecticide containing imidacloprid in the ingredients, which I read was effective in fighting grubs. However, I’m not sure what else I can do and wonder if I resolved the problem or need to do additional treatments. I currently don’t have food crops in my landscaping, however, if I do want to plant herbs next year and see the worms again, is there a “natural” way to get rid of them?

A: From your picture your identification was correct and they do in fact eat the roots of many different kinds of plants, including lawn grasses. The common accepted name for the insect is “white grub” when in the immature or “worm” stage as you call it. These white grubs mature or pupate into a beetle we commonly call chafers or “June bugs.”

The insecticide you used is a plant systemic and neurotoxin, which means it is absorbed by the roots and moved around inside the plant. Neurotoxins poison varmints by short circuiting their nervous systems. That application should take care of it. White grubs can be difficult to control with pesticides.

They could have come in on some compost or any decomposing soil amendments as well as the container soil of the plant at the time of planting, particularly because you found them so soon after the planting. Normally you should not see those types of numbers in grubs attacking plant roots so soon after planting unless they were brought in somehow.

The chemical you purchased is a good one for that purpose. Of course, it would not be wise to apply it to anything that produces food although imidacloprid is sometimes labeled for food crops. I just don’t like the idea of using these types of insecticides on food crops when other treatments are available.

Usually tilling the soil prior to planting crops exposes these grubs to predators such as birds and the natural elements, which help in control. There is a beneficial nematode in the genus Heterorhabditis that controls white grubs that can be purchased. This is not a nematode that causes damage to plants.

Q: I have several of the very tall palm trees in my backyard that have been sending out little sprouts all over the place. I let a couple start growing and now see that they will interfere with some concrete. Is there any way to stunt their growth?

A: From your e-mail it sounds as if they are a palm with a single trunk and not Mediterranean fan palms which are multitrunked. These are probably new plants resulting from seed. They start from seed easily.

There is a no good way to keep them small. They are going to be the size Mother Nature dictates to them, which is tall.

If you want to keep them at bay while they are young, just behead them and take off the tops. They cannot grow and will die once the central bud has been removed.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.