A friend of mine has some roses that I noticed looked a bit brown. Upon closer inspection, the leaves looked skeletonized, like the damage a Japanese beetle does, but this was sucked dry, but not chewed through. It’s also a bit too early for Japanese beetle. Keep looking…
The rose sawfly has one generation a year, with larvae appearing in mid to late spring.
The larvae fall from the plants and tunnel into the soil by mid-June, but it’s a bit earlier this year. They remain dormant underground until next spring, when the adults emerge and lay eggs on the new rose foliage to begin the cycle over again.
Larvae can be effectively controlled with a neem oil product or an insecticidal soap. Spray only the leaves (both sides), in the morning as neem oil can possibility hurt pollinators (More research needs to go into that). The strategy is to find larvae while they are still small and before damage becomes severe, like my friend’s roses! There is no need for control after the larvae have finished eating and left the plants, give or take mid-July.
One last note, these are not caterpillars, they are actually primitive wasps, so Bt or Bacillus thuringiensis will not work.
Any time there is a drought the previous summer/fall, Austrian, Scots, and red pines of the Midwest are susceptible to the Zimmerman pine moth (Dioryctria zimmermani). Why? In a nutshell, if a tree has enough water (turgid), any boring insect would get pushed out via the high pressure of fluids in the tree. This is why it it important to be sure your trees are getting enough water in the autumn.
White, tan or rust-colored resin flowing on the trunk could indicate the presence of the moth’s caterpillar-like larva. Finding one or two boring points is usually of no concern. Heavier infestations could cause weakened trees to become susceptible to other pests and diseases, eventually killing the tree. Heavily infested trees should be removed, so they don’t become a nursery for the moths.
It is critical to understand the life cycle of the Zimmerman pine moth [ZPM] for proper management. The tiny caterpillar over-winters in a silken cocoon-like structure just under the bark. Now, in the early spring, the caterpillars feed on the bark for a week or two, then tunnel into the main trunk, usually in a whorl area. Resin is pushed out by the insect causing a ‘pitch tube’. Fresh pitch tubes are white to tan, the consistency of lard and have a shiny appearance. Old tubes are yellow to grey, crystallized and hard, with a dull appearance. It is important not be confused by old tubes and new, which all together, may look like an infestation.
In mid-summer, the caterpillars pupate either inside the external resin or within their tunnels. At this time, it may be possible to kill the pupa by hitting the resin with a rubber mallet. I love organic cures!
The adults emerge as small grey moths in mid to late August. These moths fly at night and are rarely seen. Females lay their eggs on the trunk under the bark, thus beginning the cycle.
Management of ZPM begins with tree care including proper mulching, watering, pruning and fertilization. Healthy trees do not get attacked.
Insecticides should be applied during the two vulnerable times in the ZPM cycle. These times are mid to late April, as the over-wintering caterpillars become active, and in August, when the female moth has just laid her eggs and the caterpillars are searching for over wintering sites. Indicator plants for these spray times are when the saucer magnolia is in pink bud to early bloom, or in mid to late summer when panicle hydrangea is pink. Spraying branches and foliage is not necessary & wasteful. Permethrin or bifenthrin are preventative sprays that are available for use by homeowners. Spraying at any other time is inefficient, as it has no effect and the insecticide may kill predators of the Zimmerman pine moth.