Yesterday I found the first azalea caterpillars of the year. These tiny caterpillars had just hatched from the white eggs you see
Newly hatched azalea caterpillars. Notice white eggs on the leaves in the background. Photo: SD Frank
in the background. You can scout for these bright eggs in August before the caterpillars hatch and remove them. I think these caterpillars are worth having though since they are very beautiful. Actually the caterpillars are prettier than azaleas tend to be this time of year and they will eat all the leaves stippled by lace bugs! You can read more about these caterpillars that feed on azaleas and blueberries in a post from last August.
This week I have gotten three samples from the clinic with sycamore lace bug, Corythucha
Adult sycamore lace bug. Photo: SD Frank
ciliata. I had just taken some pictures of these beautiful critters last week when I was in Asheville. They really do a number on sycamore leaves and this time of year heavily infested sycamores look pretty bad. The other lace bugs that are important landscape pests are the azalea lace bug and hawthorn lace bug. Like these, the sycamore lace bug causes stippling damage by piercing the underside of leaves with its stylet and sucking out the fluids. Large yellow and gray areas develop on the top of the leaves. In some cases, most leaves on a tree can be entirely covered in stippling damage.
Yellow blotch of stippling damage caused by sycamore lace bugs. Photo: SD Frank
Sycamore lace bugs are a native insect. They overwinter as adults under bark or in other sheltered spots and become active soon after bud break. They lay eggs in leaves and complete their lifecycle in around 30 days. However, research from China, where this is an invasive pest, shows that at high temperatures this happens much faster, even twice as fast. This suggests that it could be more abundant in hot urban areas where sycamores are often planted in parking lots and along roads. Our research shows that lecanium scales and gloomy scales become much more abundant on hot urban trees than cooler trees nearby. My anecdotal observation is that this hold true for sycamore lace bugs too. Sycamores are wetland trees and probably are not very happy in hot, sunny, dry spots but lace bugs clearly are.
Sycamore lace bug nymphs. Photo: SD Frank
Management of sycamore lace bugs will be similar as for other lace bugs but you are typically dealing with large trees instead of small azalea bushes or cotoneaster. Thus systemic insecticides applied as a drench can be a good option. Applications of horticultural oil should also help keep abundance low just by killing adults and nymphs that are present.
This time of year arborvitae plants may get a little shabby. Many branches get short brown
Damaged tip from arborvitae leaf miner. Photo: SD Frank
tips. Other branches may turn brown and just hang on the plant. Arborvitae leaf miners, Argyresthia spp., are tiny moths responsible for brown tips. Moths lay eggs on new growth which is why the tips of plants are damaged. Larvae burrow into leaf scales and mine foliage as they feed and develop.
Larvae overwinter in the mines and resume feeding in spring. Damage is most evident in winter and early spring so the damage you see now is likely from mines initiated last year. Mines can be differentiated from other damage by looking for exit holes and by opening damaged tips to look for larvae.
If you have larger brown branches that are hanging, barely attached to the tree, you
Flagging branch from bark beetle feeding. Photo: SD Frank
probably have damage from Phloeosinus spp. bark beetles. Commonly called cypress bark beetles, eastern species attack arborvitae. These beetles chew branches 15-30 cm from the tip making a groove or short tunnel that weakens the branch. The branch then breaks easily in the wind and turns brown, a condition called flagging. You can look for the hollowed end of branches you suspect were damaged by these beetles.
I have gotten several phone calls about leaf notches on redbud trees. This characteristic damage is caused by leaf cutter bees in the genus Megachile. Leafcutters in Megachile
Leafcutter bee. Photograph by Sam Droege, USGS
and other genera are solitary bees that nest in hollow grass stems or other pithy stems they can easily excavate. They will also make nests in existing holes in wood but do not bore their own holes in wood (those are carpenter bees). Adult leaf cutter bees can be about as big as honey bees. They cut out round pieces of leaves to line their nests and pack in between brood cells. Damage by leaf cutter bees is general insignificant. In this area they seen to prefer
Leaf notches cut by leafcutter bees on a redbud tree. Photo: S.D. Frank
redbuds but will cut other plants including maples and roses. I have never seen more than a few leaves damaged on any particular tree and the damage is not enough to affect tree growth or health. Leafcutter bees are important pollinators of many native plant species and fruit and vegetable crops. In many urban and rural areas the plant species bees use for nesting have become less common than they used to be. Thus, bees cannot find suitable reedy grasses of tree holes to nest in. You can help conserve leaf cutters and other bees species by creating nest tubes. These are fairly simple contraptions that just require tying together bundles of reeds or drilling holes in blocks of wood to replace the nest substrate that used to be provided by plants. Visit April Hamblin’s other recent blog post for details. April is conducting research on how urbanization and urban warming affect bee communities, individual survival, and nesting. Visit her guest blog on yourwildlife.com or project description for details of her work.
Leafcutter bee nest with cells divided by rolled up leaves. Each cell holds a pollen ball and one egg to develop into an adult bee one day. These bees are also solitary.
Photograph by Joel Gardner, Wild Bees and Building Homes.
Overall leafcutter bees are far more beneficial than harmful (they also rarely sting unless handled). My suggestion is to tolerate the subtle damage these bees cause and use it to teach other people about bees. If you are growing plants for sale you may not be able to do this but I rarely see leaf cutting on nursery stock.
MS student April Hamblin contributed to this post.
This week I found severe damage by hibiscus sawfly. Larvae and adults were present on
Damage caused by hibiscus sawfly larvae. Photo: S.D. Frank
the plants I surveyed. The adults are active throughout the summer. The larvae feed on hibiscus and related plants. The larvae skeletonize leaves when they are young but quickly defoliate plants as they grow. Insecticides for management include bifenthrin, spinosad, acetamiprid, azadirachtin and others listed in this insect note.
Plants around campus were also damaged and I noticed these adults present. Sawflies are actually wasps (Order: Hymenoptera) which is why not all insecticides labels for caterpillars are effective. They are not caterpillars they are wasp larvae. Other sawflies I have reported on are the pine sawfly and rose sawfly both of
Adult hibiscus sawfly. Photo: S.D. Frank
which I have found at the JC Raulston Arboretum and on Main campus.
Somehow I got this far in the season without posting anything about euonymus scale.
Euonymus scale on a heavily infested leaf. Photo S.D. Frank
Maybe because this is the first year I have not been conducting research on it or writing papers about it. Euonymus scale has three generations per year in North Carolina the first of which occurs around May. It is best to treat euonymus (or any) scale in the crawler stage. So if you forgot in the spring or didn’t get sufficient control (or were waiting for an alert from me) you still have a chance. Crawlers are active at sites on campus and in Raleigh neighborhoods. In the first generation crawlers come out all at once but become less synchronized in second and third generations. Thus you may find all developmental stages present at this time. There are a number of products that can be used to treat armored scale. You can read an article in Nursery Management about scale control here. Our research (published here) has found neonicotinoids Safari, Flagship, and TriStar to be very effective and also plant growth regulators Distance and Talus. Note that imidacloprid is not labeled for, or effective against, armored scale. Please check the updated insect note for recommendations http://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/note15/note15.html
The first round of flowering is about over for my native columbine, Aquilegia canadensis. Columbine is a great early spring flower that flowers profusely and spread easily by seed. Spring bees and humming birds visit columbine flowers particularly in early spring when it is one of the only flowers present.
Heavily mined columbine leaves. Photo: SD Frank
The columbine leafminer, Phytomyza aquilegivora, overwinters as pupae. Adults emerge in early spring and oviposit in new columbine leaves. Small white maggots mine the leaves creating white or grey serpentine pathways. Often entire leaves are discolored. Larvae pupate after about 10 days on the underside of leaves. Columbine leafminer has at least 4 overlapping generations per year in North Carolina. There are at least 13 species of parasitoids that become more abundant as the summer progresses.
Braman et al. (2005) reported that the native species, A. canadensis, is more resistant to leafminers than many other species of cultivars. Removing and destroying infested leaves before adults emerge may help reduce damage to subsequent leaves. Leafminer control is often best to left the parasitoids become established and just accept some damage. If you are a grower than there are several insecticides available to help reduce leafminer damage.