by Andrea Laine, EMGV
I recently learned about leaftiers and leaf rollers. These plant pests may be confused with one another as at first glance the damage they do to leaves looks similar.
This was a scene on my Hydrangea paniculata ‘Limelight’ in early May (see photo below). A tiny creature was cocooned on the leaves where a flower would hopefully form later this summer. Surrounding the creature the leaves were crinkly and curled in a deformed way as were leaves at the tips of other flower stems. I instinctively snipped the stem tip to minimize damage to the plant and get a closer look.
I had a hunch that the creature was the pupa of an insect. But what insect and how much damage could it potentially wreak to my, otherwise healthy, hydrangea? I was curious enough to research further; and it was a good time to re-educate myself about insect lifecycle.
Insects look different in each stage of their development. Typically, there are four stages: egg, larva, pupa, adult. The process by which insects move from stage to stage is called metamorphosis. Most of us know that the butterflies (adult stage) we admire in our garden were once caterpillars (larva stage). We are probably less familiar with recognizing insect eggs and pupa. I know I am.
“My” pupa is likely a developing moth (insect order Lepidoptera). I believe this because of the way in which it wrapped itself in the leaves at the branch tip of the hydrangea. For protection while they morph from pupa into adults, moth larvae, i.e. moth caterpillars, spin cocoons or silky webs (behavior indicative of leaftier caterpillars), while others roll a leaf around their bodies (leaf rollers). The caterpillar feeds on the developing flower bud and leaf surfaces within their reach. The damage may be unattractive and limit bloom, but it will not kill the host plant.
By the time I took note of the distorted leaves on my hydrangea the moth had advanced to the pupa stage and ceased feeding. According to Durham County Agriculture Agent Ashley Troth, leaftier caterpillars drop to the ground to pupate and leaf rollers largely pupate where they have been eating. No activity on the outside belies much activity internally. During pupation many tissues and structures are completely broken down and structures of the adult are formed.2 The following spring the adult moth will emerge.
Since becoming an Extension Master Gardener Volunteer in 2015, I have become hesitant to destroy an insect lest it be one of the beneficial ones. (Prior to my EMGV education I didn’t acknowledge that many are beneficial.) Given that there are 11,000 species of moth3 in the U.S., I may never learn to distinguish between a good one and a bad one. But, so long as the nibbling of their larvae stays within reason and lets my plant produce most of its blooms, perhaps we can co-exist.
Leaftiers and leafrollers are found on a wide range of plants, including many fruit trees. Prune out the effected foliage, webbing and remove caterpillars from plants. Bacillus thuringiensis (BT) is an effective control for recurring problems, particularly if applied as soon as larvae hatch.4 Trees infested with leafrollers can furthermore be sprayed with horticultural oil.5
Footnotes, Sources & Further Reading
1, 4, 5 http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/insects/caterpillars/caterpillars-leaf-tiers-bagworms-and-web-former.aspx
When you are stumped about something gone wrong in your garden, remember Durham County Cooperative Extension’s Ask an Expert resource. Send photos and an explanation of what you are seeing to: firstname.lastname@example.org.