By Marcia Moffitt

Elm leaves skeletonized by elm leaf beetle turn brown and ugly

Elm leaves skeletonized by elm leaf beetle turn brown and ugly

Are your elm tree leaves turning brown and dying? An initial reaction might be to water the tree more because we are in a drought and other trees are also loosing leaves. That is unless you are familiar with the elm leaf beetle. If you observe that the brown leaves on an elm look different from other tree species’ brown leaves and have a “lacey” appearance, then additional watering will not solve the problem.

Adult elm leaf beetles hibernate over winter in wood piles, crevices and leaf litter; emerge in the spring and fly to elm foliage to feed. They lay yellowish eggs on the undersides of leaves in double rows. The eggs hatch and

Elm leaf beetle larvae, 3rd or 4th instar, feed on elm leaves

Elm leaf beetle larvae, 3rd or 4th instar, feed on elm leaves

the larvae go through three growth stages over several weeks during which time they feed on and skeletonize the leaves. This is what causes the leaves to turn brown and take on the “lacey” appearance. Once the larvae mature, they crawl down the tree trunk and pupate at the base of the tree.   Roughly ten days later, adult beetles emerge fly to the foliage and begin the cycle again.   Adult beetles chew through the leaves and this damage appears similar to shot-hole damage. Multiple generations can occur in one year. In the fall, adults beetles begin looking for places to overwinter and can enter homes through cracks and crevices.

Close up of an elm leaf beetle larva

Close up of an elm leaf beetle larva

Adult elm leaf beetle

Adult elm leaf beetle

When dealing with elm leaf beetles, it is best to use an integrated pest management (IPM) approach. IPM incorporates a variety of techniques to keep populations of elm leaf beetle to a tolerable level. These techniques involve good cultural practices, conservation of natural enemies, regular monitoring and less-persistent chemical usage. University of Nevada Cooperative Extension and University of California fact sheets are very good references detailing IPM techniques for controlling Elm leaf beetles. Both references incorporate preventive guidelines and cultural, biological, botanical and chemical controls as an integrated approach to dealing with this pest. When choosing a biological control, specifically Bt (Bacillus thuringiensis), be aware that there are varieties of Bt and each is effective against certain insects.

Once a tree is infested with elm leaf beetles, take action to maintain the vigor of the elm tree and reduce other stressing factors.   Ensure that the tree is getting sufficient water, don’t compact or disturb the soil underneath the tree and prevent trunk and limb injuries. A healthy elm tree can survive even heavy defoliation if it occurs in late summer and not repeatedly every year.

Peach leaf showing "shot hole" damage

Peach leaf showing “shot hole” damage

Advanced shot hole damage showing how the disease damage progresses

Advanced shot hole damage showing how the disease damage progresses

Our office has been buzzing with calls regarding problems with trees. These problems have been as varied as aphid infestations, browned leaves, holes in leaves and trees with 20-30% of their leaves turning yellow and falling off. All of these problems are caused by one thing: the unusually cool, wet weather followed by a couple of hot, dry weeks.

Fruit trees in our area have been hit the hardest. First, there were the series of frosts after several warm snaps this spring, leaving most people without any fruit on their trees. Next, it has been unusually wet – excessive rains have caused flooding and road wash outs throughout Lyon county. Cool, moist days have increased the incident of fugal and bacterial pathogens, especially in fruit trees. Normally, these pathogens are latent in our area and only appear when trees are irrigated

Leaf scorch on a redmond lindon tree leaves

Leaf scorch on a redmond lindon tree leaves

with a sprinkler system. All of the rain created the same situation.

We have seen many peach trees with shot-hole, a symptom of a fungal disease caused by Wilsonomyces carpophilus. Bacterial leaf scorch bacteria, Xylella fastidiosa, is very wide spread and can infect plants in many plant families. Non-bacterial leaf

Apricot leaf with mild leaf scorch damage that can appear to be similar to shot hole damage

Apricot leaf with mild leaf scorch damage that can appear to be similar to shot hole damage

scorch occurs when the plant cannot take up enough water to compensate for transpiration leaf drying/browning or leaf die-back. It can be caused by not enough water in leaves or soil, fungi or bacteria clogging the plants vascular system, or damage to the roots including rotting because of too much or not enough water. Sometimes there is sufficient water in the soil but the plant cannot take up enough because of salinity or clay in our soils which inhibits water absorption or if roots have not expanded sufficiently to compensate for the sudden new growth from additional moisture then unusually dry hot weather. Signs of root scorch include browning on the edges of leaf and the leaf surface between leaf veins. As long as it is not severe enough to cause significant leaf die-back and over watering does not occur, though unsightly, the plant usually recovers. At times, shot-hole signs can be confused with leaf scorch. If in doubt, email us pictures or bring samples to our office. Proper diagnosis of a plant problem is the first step to planning plant recovery. While there are some treatments for shot-hole, planting varieties which have natural resistance and properly watering are usually the best tools for the home orchards.

Young apricot tree with branch tips damaged by high aphid density and leaf scorch

Young apricot tree with branch tips damaged by high aphid density and leaf scorch

Aphids have also enjoyed this cool wet weather, which has created ideal environmental conditions for a longer period of time. New growth on trees is often the most susceptible. Aphids can vector plant viruses and cause the plant to be covered in sap, which can be unsightly or a nuisance. For the home gardener, most aphid problems will go away in a few weeks when the conditions are too hot or dry. Aphid populations can be decreased by spraying with a strong stream of water or by placing sticky tape around the base of the plant to trap the ants which herd aphids like tiny cows.

Robed locus canopy with yellow leaves caused by heat stress

Robed locus canopy with yellow leaves caused by heat stress

In my yard is a purple robed locust which responded well to all the rain, blossoming several times and putting out new growth. Then the heat wave hit. Almost 50% of the leaves on my tree turned yellow and fell off. Marcia has helped me resolve other problems with this tree, so I was afraid it was struggling from a split in the trunk it suffered 2 years ago. When I asked about it, we decided to go look in our water wise arboretum at the robed locust there. It was also shedding leaves, but only about 25%. The heat was much harder on my damaged tree than the healthy one at the office.

By Joy Paterson and Marcia Moffitt