A few of our maintenance clients have contacted us regarding tent caterpillars in their trees that are now crawling up building structures. Yiiiikes!


According to local horticulturist Darren Strenge, these are the options available to us and anyone else dealing with tent caterpillars in the landscape:

Option 1: Live with it. The majority of affected trees survive and after the caterpillars disappear in June, the trees will leaf out again and be looking normal by August if not sooner.

Option 2: Prune out the silken tents produced by the caterpillars. The best time to do this is when the caterpillars are still young. In Kitsap County, this is usually mid to late April.  With an extension pruner or pole saw, you can reach up and prune out branches with tents on them.

Option 3: It’s too late to do it this year, but NEXT winter when the branches are bare and easier to see, look over your tree’s branches looking for the golden egg masses of the Western Tent Caterpillar. When you find some, scrape them off.

Option 4: Spray the little buggers.

If you elect to spray, here are his rules for spraying:

Rule #1: Don’t do it!  It’s hard for me to justify the use of pesticides for purely ornamental purposes. If you’re growing food that your family relies on, that’s another matter, but no one’s going to actually suffer if your prize roses get defoliated (options 1-3 will be better for that anyway).

Rule #2: If you’re going to ignore rule #1 then PLEASE follow rules 3-5.

Rule #3: Read and follow the label instructions. The pesticide label is a legal document. Deviating from the label instructions is illegal and could land you in hot water. Not to mention that the instructions explain proper use of the pesticide and ignoring them could harm you, your kids, your plants, or create greater harm to the environment.

Rule #4: Don’t spray during bloom. Most pesticides that will kill the western tent caterpillar will also kill bees attracted to your tree’s flowers. Wait until your tree is completely finished blooming. We already have enough problems with colony collapse disorder, a serious situation that’s already impacting agriculture. Seriously. Be proactive and get out there with extension pruners in April and early May or hire someone to do it for you.

Rule #5: Use bt instead of synthetic or inorganic pesticides. Bt, formulated as a pesticide, is spores of the bacterial species Bacillus thuringiensis. It is much safer for everyone. There are various strains of this bacterial-based pesticide depending on what you want to attack. Read the product label to make sure what you buy will actually work on caterpillars (look for B. thuringiensis kurstaki). Perhaps the most important bit of advice here is to apply Bt while the caterpillars are young. Older caterpillars are much more resistant to it. Additionally, sunlight degrades Bt so apply it late in the day before the caterpillars leave their tents at night to feed. For Bt to work, it must first be ingested by the caterpillars so make sure to apply it directly to the plant’s foliage.

Many thanks to Darren Strenge for the very useful information. He provides pest, disease and plant health consultation to Kitsap County and be contacted at pnwbotany@gmail.com.

Thanks for reading our blog.  Northwest Construction & Landscape, LLC is a Kitsap County landscaping company that offers landscaping, decorative concrete and lawn maintenance services to homes and businesses across Kitsap and Pierce counties.