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
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
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.
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.
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.