Recently I visited a local facility that had several trees exhibiting severe leaf curl. Trees affected were poplar, catsura, sweetgum and locust. Present were high numbers of aphids and leafhoppers.

Sucking Insects Can Damage Leaves

Leaf hoppers and aphids are both insects that use needle-like mouthparts to suck juices from leaves. When the insects feed on newly emerging leaves the leaves can become distorted. Leaves can curl mildly or even severely.

Sooty Mold Can Be a Nuisance

The insects intake the sugary sap from the leaves and secrete sticky sugary droppings on leaves and objects below the tree. A black sooty mold can grow on the sugary substrate. This can cause problems in public areas such as parks or even in home landscapes.

Interestingly, trees of the same species in natural areas surrounding the site had aphids and leafhoppers but not in the same numbers and were not showing the leaf curl. I suspect the landscape trees are stressed and more favorable to the insects thus they are more severely infested and affected.

Why Are Aphids and Leafhoppers So Bad This Year?

I suspect that with our mild spring, insects will have had earlier and more generations this season. This will lead to insect and spider mite infestations that are more severe than usual. The insects/spider mites likely started their life cycle earlier than normal (it has been relatively warm since February) and were feeding on the newly emerging leaves created the leaf curl we are now seeing. An early start to their lifecycle will lead to more generations of insects/mites this growing season and higher populations.

Control

The affected leaves will not recover but will hang on throughout the season. Although the tree look may bad, the aphid and leafhopper infestation will not affect the longterm health of the trees. Also, ladybugs were very prevalent in these trees demonstrating beneficial insect predation is happening. So, I recommended avoiding insecticides on the landscape trees in question.

The grower was very concerned about the damage since this is a public site however. So I did tell them that if they felt compelled to spray that they should use an azadirachtin product early in the morning just to knock the population of aphids and leafhoppers down. Spraying this biorational insecticide early in the day avoids bee movement and will help preserve beneficial insects.

Update:

I had a client bring in various samples from different species of shrubs and flowers in her landscape. The leaves of the plants are severely curled. It turns out the plants are infested with thrips. Learn more here.