San Antonio Express News
Sunday, June 20, 2004
By Nathan Riggs
Each year, the transition from spring into summer for San Antonio and South Texas is marked by strange weather events and most of the time, sudden temperature spikes. It is this time of year that two very damaging insects come into their own and at the same time, are also vulnerable for control strategies. The insects referred to are grasshoppers and webworms. Let’s look at these vulnerabilities and how we humans can take advantage of them.
Grasshoppers lay their eggs in loose soil, preferably sandy soil, in sunny areas. These eggs hatch in spring and develop through several stages, or instars, before becoming adults. Grasshoppers feed on plants from the time they hatch until the time they die and when their numbers are very high, they can consume valuable plants in a hurry! While spraying grasshoppers will provide good short-term control, it is unrealistic to expect a spray to control grasshoppers for longer that three or four days. Grasshoppers are too mobile and so numerous that they can re-infest treated areas very quickly. The only sprays that seem to satisfactorily control grasshoppers occur when treatments are 100 acres in size or larger at a time.
There are baits available from nurseries that can control grasshoppers before they reach the adult stage. Look for baits with the name Semaspore or Nolo-Bait. These baits contain spores of a pathogen called Nosema locustae. Nosema locustae will kill young grasshoppers within a few weeks after they eat the bait. These baits are best broadcasted when small grasshoppers are present. As our temperatures increase and rainfall decreases as is the normal summer pattern, grasshoppers will become more numerous and survive better. Semaspore or Nolo-Bait will certainly help reverse that trend. These baits should be broadcasted at one pound per acre for best results. Once grasshoppers reach the adult stage, they are immune to the bait. Semaspore and Nolo-Baits are available at many of the local nurseries.
From grasshoppers, we move to the continuing saga of the webworm in San Antonio. If you all have been keeping up with this article, we mentioned in the March 21 article that Extension, the City of San Antonio, the Texas Forest Service and Bartlett’s Tree Service were working on a project to release microscopic Trichogramma wasps in pecan trees to attack webworm eggs before they hatch. While the results on this study are still pending, there is an important thing that you as readers and pecan tree owners who have been purchasing and releasing the wasps on your own need to know: it is now time to release wasps again to attack the second generation of webworms. Based on what we know about the webworm life cycle, the experts in this program agree that June 21 is approximately the time when new webworm moths will be emerging to lay eggs on pecan trees. Purchasing Trichogramma wasps and releasing them in your pecan trees over the next seven to ten days will afford the best opportunity to affect this next generation. Trichogramma wasps are available from two Texas insectaries: Biofac in Mathis, TX (1-800-233-4914, http://www.biofac.com) and Kunafin in Quemado, TX (1-800-832-1113, www.kunafin.com). They can ship the wasps for delivery within two to three days after the order. The wasps come on little strips as parasitized caterpillar eggs and should be hung in your tree from a limb. Take caution: many species of ants like to remove the eggs from the strips and eat them! To lessen this chance, apply petroleum jelly, tanglefoot or Teflon tape to the wire or string from which the strip is hanging.
Dealing with living creatures is a delicate undertaking. If you choose to purchase these wasps, handle them with care because they are extremely tiny and easily crushed. Trichogramma cannot hurt humans or anything larger than an insect egg, so don’t be afraid to try them or consider them.
With all of the rain we’ve experienced in San Antonio and South Texas, most of the leaf-feeding insects are enjoying a bountiful leaf, weed and vegetation smorgasbord. Of these leaf-feeders, grasshoppers and webworms are the most apparent and probably hated of the group. In this particular case, the biological controls available for grasshoppers and webworms are easily available to homeowners and can be released with a minimum of effort. Any use of biological controls must come with a dose of realism, though: natural organisms are just as positively or negatively affected by environmental conditions as the pests. Keep this in mind and learn as much about your control strategy as you can before you implement it.
This article was written by Nathan Riggs, Extension Agent-IPM with Texas Cooperative Extension in Bexar County.