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What's bugging you? June 19, 2019

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Pinyon tip moth terminal shoot damage

This spring I looked out my window and to my dismay I noticed many brown terminals on one of my two pinyon trees. Now this might not sound like a big deal to you but remember, I am an entomologist and insects are never supposed to get the upper hand over me.

Some basic facts about tip moth caterpillars is that they kill back the new growth on various pines. While their damage can be quite ugly, rarely does this damage threaten the demise of your tree. Tip moth damage does help keep new growth in check if that is what you want.

While the southwestern pine tip moth infests Scotch, mugo and ponderosa pines, the one we are interested in, the pinyon tip moth, is a different beast. Although little real injury to the health of the infested tree results from tip moth attacks, tree growth can be delayed and their form altered to a bushier appearance.

Tip moth injury can be diagnosed during late spring to midsummer by examining suspect shoots that have dried and shriveled. At this time, the damaging stage of the insect or old discarded skins can be detected. If the insect is not present, examine the damaged terminal growth to see if there is evidence of the internal tunneling typical of most tip moth injuries. Do not mistake winter desiccation due to lack of winter watering for tip moth damage.

Tip moths infesting pinyon overwinter as partially grown larvae either in stem tissue or on the bark. The common tip moth (Dioryctria albovitella) lays its eggs during midsummer. The larvae emerge shortly afterwards but do not feed. Instead, they form a silken cocoon on the bark for passing the winter. The larvae resume activity in May, boring into the base of unopened buds.

Often the larvae destroy the initially-infested bud and move to a new shoot or developing cone, which they also mine. Irregular pitch masses often form at the injury site. Pupation occurs within the infested area, with the adult moths emerging to mate and lay eggs. There is but one generation per year.

Numerous natural enemies of tip moths exist and often reduce infestations to acceptable levels. In particular, various parasitic wasps develop within tip moth larvae, killing a large percentage of the population. As a result of these natural controls, tip moth infestations can vary widely from year to year.

Even though two years ago my pinyon tree had a few damaged terminals, there was nothing to be concerned about. Last year my pinyon had a few more infested terminals so I sprayed the tree with a pyrethroid insecticide. Based on the dramatic increase of brown terminals this year, I must have mistimed my application.

Treatment timing for the pinyon tip moth is not well known. Thorough insecticide coverage in May should be effective if applied to new growth before overwintering tip moth larvae enter buds. Somewhat later treatments can still be effective at killing some larvae moving from buds to developing shoots. Pyrethroid insecticides that are labeled for use on shade trees, contain such products as bifenthrin, permethrin, or lambda-cyhalothrin, and can be very effective against exposed larvae. The key to success then is to thoroughly spray your tree when larvae are exposed. Once in their feeding tunnels, insecticides are generally not effective. However, the systemic insecticide acephate (Orthene) may kill small larvae that have already begun to tunnel into pine tips.

My spray timing recommendations in a nutshell; spray a pyrethroid about mid-May, followed by a second application in late July or early August. Hopefully I will be able to report back next year to tell you I was successful with my treatments.

Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.

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