Two of our rhododendron plants in large planters have parts eaten out of the leaves. We have never seen any insects on or around the plant or planters. Do you have any idea what might be doing the damage and how to prevent any more leaves from being eaten in the future?
According to UC master gardener Carol Rogala, a variety of pests enjoy rhododendrons including snails, foliage-feeding caterpillars, cutworms and black vine weevils (the latter pictured here).
A sample of the foliage and pest damage are necessary for an exact identification. However, the photos you supplied look like black vine weevil as the culprit. This pest feeds on many landscape plants such as azalea, rhododendron, euonymus and liquidambar.
Adult weevils generally feed on foliage. Leaves or flowers appear notched or ragged like yours. The most serious damage is done by larvae, which feed on roots and can kill or weaken some plants, especially azalea and rhododendron.
Destroy adults to prevent more serious damage. For rhododendrons, plant less-susceptible species. Provide cultural care to keep plants vigorous and better able to tolerate damage.
Check roots before planting to make sure they are free from larvae. Trim branches that provide a bridge to other plants or the ground and apply a 6-inch band of sticky material to trunks to prevent flightless beetles from feeding on foliage. Trapping may help.
Parasitic nematodes also may be effective in controlling larvae. Timed insecticides applied to leaves can control adult weevils.
Mulberry trees are planted because they grow relatively fast, need little pruning once established, require minimal fertilization and are generally free of pests and diseases, said master gardener Rogala. The fruiting varieties offer both shade and fruit.
The problem is the messy fruit. One possible solution is to knock the flowers off with a strong jet of water before they set fruit. If it doesn’t completely eliminate the fruit, it may decrease the amount of fruit so that the problem is tolerable.
A product called Florel Brand Growth Regulator and Fruit Eliminator by Monterey is effective on a fruiting mulberry tree. The active ingredient is ethephon and is registered for use on ornamental and landscape trees. The manufacturer recommends that the chickens be removed from the coop before spraying and not returned until the Florel has dried. Monterey indicates that it is not hazardous even when the ground is re-wetted by chicken urine, rain or water.
Look for it in nurseries and home improvement stores. Please read the label carefully and follow all instructions carefully.
Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to email@example.com. Please put “Garden Detective” in the subject field and include your postal address.
To read past Garden Detectives, go to www.sacbee.com/gardendetective