Identify insets correctly to get proper pesticide

: I just read your column about spraying Thuricide early to prevent hornworm damage. Where do you spray, the ground or the actual plant? My problem is that these are in my very large ash trees. I have only actually seen one in the tree because they are so hard to spot up there, but their droppings tell me there are a lot of them.

A: Hornworms are those large, usually green caterpillars that feed on vegetables, grapes and other garden plants. The chemical you mention has to be sprayed directly on the foliage of the plants. This product and the one very similar to it, called Dipel, have a bacterium present in the pesticide solution.

Since you are applying a bacterium, it is considered an organic spray. The hornworms eat the leaves and take in the tiny bacterium that basically consume the insect from the inside out. They will usually stop feeding in about 12 to 24 hours but they may continue to live for three or four days.

To be legal, ash trees or at least ornamental plants, must be on the label.

I have never heard of hornworms on ash trees but there is always a first for everything. It would be very helpful to make sure it is hornworms causing the damage. If the insect is not correctly identified, then the product may not work like it should.

Hornworms don’t stay as hornworms very long and develop fairly quickly into the adult moth, which does no feeding damage. You might want to consider just letting the insects run their course and allow the tree a chance to recover.

Q: I have recently had two adjacent first-year apricot trees die very suddenly. They looked good one day, wilting somewhat the next, then proceeded very quickly to death. The trees are a Tilton and a Chinese apricot. My first hunch is overwatering.

A: It is hard to say exactly what may have caused the death of these trees but let me run down a litany of possibilities.

* Overwatering and poor drainage. As you mentioned this is a real possibility, particularly if they were planted in heavy soils. Apricots are known to have sensitive roots when it comes to heavy soils. It sometimes helps to plant these on hills in these heavier soils.

* Secondly, planting too deep. If these trees are not planted at approximately the same depth they were in the nursery, they run a high risk of getting collar rot, dying at the soil level and then the top dies quickly.

* Fertilizing too close to the trunk. High-nitrogen fertilizers, if applied too close to the trunk, can kill young trees easily.

* Sun damage. In some cases direct sunlight on thin bark trees such as apricot can cause severe sunscald and decline.

* Not staking bare root trees. Although frequently not a direct cause of plant death, leaving trees unstaked can lead to poor root development and struggling trees.

I hope this helps a little bit.

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.