tt-95 BY DON MEEHAN

BE PREPARED FOR TENT CATERPILLAR INVASION

1988 was a banner year for tent caterpillars in the county. Reports came into our office from most areas of the county. The south end of Whidbey was particularly damaged with infestation so high that complete defoliation took place over many acres in the alder forests. Other areas had only mild infestations and minimal damage reported. 1989 had the potential to be worse than we have seen before based on the degree of infestation the previous year. Our office handled approximately 1500 calls during 1988 from upset homeowners. Keep in mind that I said 1989 year could be potentially worse. It also had the potential to be much better. One thing I think we could say then "is that the caterpillars have not gone away". As it turned out the populations subsided due to a wide number of factors, most of which dealt with Mother Nature doing her thing. Many people have thought county government should be controlling this pest, especially on property owned by the county. Since there are no regulations or laws, state or local, which obligate the county to take action on this pest, the county is not likely to take any. This may be a frustration to many residents. When evaluating the problem, there is only a small threat posed to the county from tent caterpillars. The real and serious risk to the health of the residents living here from the use of chemical sprays is of concern. I can't help but think it is a good choice not to get into a massive insecticidal spray program. One of the things we know about tent caterpillars is that their population will make swings back and forth from year to year. Much of this swinging is dependent on environmental factors of which we have little control. As their population increases, also does the population of their predators. Predators or natural enemies of tent caterpillars are numerous. They include parasitic flies which lay their eggs on the young caterpillars. Birds also play a role in controlling them, and more importantly in preventing large populations from building up. Another natural enemy is a virus that attacks the caterpillar, causing a disease called wilt. The trees which we get most concerned about are fruit trees, which tent caterpillars prefer. They also have a strong preference for Alder, Ash, Birch, Willow, Cottonwood, and Roses. Since we have a significant area of the county covered by red alder, it will come as no surprise to see large populations of tent caterpillars in those tree stands again this year. If your yard is adjacent to a stand of alder, you will want to be more concerned about damage to your landscape and fruit trees. Tent caterpillars generally eat all the leaves on one branch before moving on to the next. The entire tree can be completely defoliated if the infestation is large enough. The important thing to keep in mind is that it is unlikely the tree will die from defoliation. This is especially true if the tree is in healthy condition. Healthy trees will often grown new leaves by midsummer. Unhealthy ones are going to be damaged more by a complete defoliation. Regardless of the health of the tree, defoliation will increase the tree's susceptibility to disease and decrease cold hardiness. When should you start paying attention to tent caterpillar activity in your yard and adjacent areas? April and May are the months which they are most likely to come out of their egg cases. This will be somewhat dependent on the weather. They could emerge sooner or even later depending on weather conditions. You can begin now to locate some egg masses and mark them so you can observe their development in the next few weeks. This is important since insecticides are virtually useless in killing the young larvae protected inside the egg mass. Dormant sprays have no effect on these pests. The egg masses appear as irregular-shaped smooth blobs about one quarter of an inch thick. They have a gray color, and when first encountering them one would be led to believe they might be made of Styrofoam. Once a few have been sighted, take some sort of flag and hang next to the mass. This will help you find them as you observe what is happening with them over the next few weeks. Once you have seen the caterpillars begin to emerge that is the time that you want to begin your spray program. You are probably thinking, Why spray? Why can't I cut and burn them as they emerge? You can! But you must remember that we had a major build-up this last year. You will probably not find all of the egg masses or be able to maintain the shape of your trees if you have to do a lot of severe pruning of limbs to remove the caterpillars. Don't rule out spraying or pruning out the pest. You may find a combination of the two would work satisfactorily for you. Spraying often implies creating an environmental and personal hazard by introducing insecticides into the area. This is true, and must not be overlooked when this control option is used. Two spraying options are available to you as the homeowner. One involves the use of a biological insecticide rather than a synthetic chemical one. This insecticide uses a bacteria called Bacillus thuringiensis ('BT' for short) as the active ingredient. The bacteria is sprayed onto the leaves of the trees you are trying to protect. When the caterpillars eat the leaves they ingest some of the bacteria. The bacteria then creates a big tummy ache for the caterpillar, and it quits eating within an hour or so. A few days later, the caterpillar will die from starvation. This spray is much safer to use and poses much less of a hazard to the environment. Another plus with it is that it is selective for caterpillar-type insects. It will not harm predators of caterpillars, or other beneficial insects like honey bees. Synthetic chemical insecticides which are registered for use on tent caterpillars include Malathion, Diazinon, Carbaryl (Sevin), and Zectran. Carbaryl poses a serious danger to pollinating insects like honey bees. All chemical sprays should be applied in the early morning or late evening to avoid damage to pollinator insects. Be sure to read the label on the insecticide container for application rates and safety information. Do not get these sprays on you since they are all bad for your health. Caterpillars which are left uncontrolled by man will eventually fall to the good graces of Mother Nature's way of controlling pests which have gotten out of balance. Often, for this method to work for us, we have to be willing to be patient and tolerant of the damage that can be caused while we wait. If you were one of the many people who used "BT" last year, and you still have a supply of it remaining, you are probably wondering if you can use the leftovers. Yes, please do, but be aware that the product requires dry, cool storage away from sunlight to maintain its effectiveness. Last year's supply of "BT" in the local stores ran out prior to the end of the season. It is my understanding new supplies have been ordered and are presently on local store shelves. The tent caterpillar problem has the potential to be sever on the mainland again this year as well, and that area will be creating a large demand for the product. Be sure to get yours early while the supplies are good. When using "BT", keep in mind that it works best when the caterpillars are very young. Spray under the leaves to protect the product from degradation by the sun and washing off by the rain and dew. Tent caterpillars have only one life cycle each year. Thank goodness for that. During mid-June they will drop to the ground and spin their cocoons. They will then emerge as adult winged moths in another two weeks or so. These moths have one mission in life; that is to mate and to lay 100 to 300 eggs, hopefully not on your fruit trees or landscape trees. What does the future hold for us in controlling this pest? You will be interested to know that WSU has been conducting some further research on chemicals which might provide success during the dormant season. Test results this last season were favorable, but this year's testing had to be postponed due to low numbers of egg masses in the testing sights. As this research progresses, showing us reliable and effective means, I will share the results with you. As this spring progresses along I will be keeping you posted on the population buildup in this news column. At that time, I will be addressing strategies which will prove useful to you in keeping your yard safe from damage. More information is available in a publication from our office called "Biology and Control of Tent Caterpillars". Call our office to request this 25 cent publication. We will mail it to you, or you can pick one up when you are in Coupeville.




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