Posted on 13 January 2011.
By Bob Morris, Gardening
Q: Help! I have two ornamental pear trees in my front yard. One is slowly dying back. Each year, more branches are barren. Could the tree have borers? What can I do to save the tree?
They typically don’t get borers that often, but it doesn’t mean they can’t. If they are in rock mulch, then they will not like that. If in a rock mulch, see if you can replace it with wood mulch or select a tree that tolerates rock mulch better than ornamental pear.
You can try putting compost at the base of the tree in early spring. Place it near the water source irrigating the tree. Flood the area under the tree and include the compost so that nutrients move into the rootzone of the tree.
Make sure the tree is getting adequate water each time it is watered and that you wait long enough between irrigations for the soil and rootzone to begin drying before the next irrigation.
Q: During the summer months I noticed most of the plants on one side of my landscaping seem 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, one inch-long, fat, white worms with legs on the front and a brown head. 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 do want to plant herbs next year and see the worms again, is there a ‘natural’ way to get rid of them?
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 system. 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 which can be purchased. This is not a nematode which causes damage to plants.
Q: I have several of the very tall palm trees in my backyard which 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?
From your e-mail it sounds as if they are a palm with a single trunk and not Mediterranean fan palms which is multi-trunked. 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. He can be reached at firstname.lastname@example.org or 257-5555.