Our rhododendrons and azaleas have been looking sick lately. What is going on? In the last few years we have seen the damage by the azalea lace bug on the ericaceous plant family (e.g., rhododendrons, blueberries, azaleas). This tiny, almost transparent insect sucks fluid from the underside of the leaves, resulting in pale, sickly looking leaves and a brown fecal residue on the underside of the leaves. Over time this can kill a susceptible plant.
Entomologists from the Oregon Department of Agriculture are concerned. Severe damage was first seen in this area in 2009, but scientists are not sure why areas like Portland and Salem have been hit especially hard by the lace bug. Right now entomologists have more questions than answers. Their research is ongoing to find some answers.
What should we do now?
- Don’t plant azaleas and rhododendrons in full sun. Walking around the neighborhood, I have seen the most damaged plants are in full sun.
- Situate, water, and fertilize your plants appropriately so they grow as strong as they can.
- Consider planting rhododendrons that have lots of fuzz on the underside of the leaves. This may act as a physical barrier to the lace bug.
- Use horticultural soaps and oils as soon as you see lace bugs on the leaves. (This is a lot of work because the soap/oil must cover the undersides of the leaves.)
- Do not use neonicotinoid insecticides (http://en.wikipedia.org/wiki/Neonicotinoid). The ongoing effects can last more than one growing season and may kill bees and many other insects that feed on lace bugs.
- Plant a diverse flower garden that encourages lots of different kinds of bugs to live there. Most bugs are helpful, especially in a garden with lots of different types of plants.
The best actions to take at present: plant rhododendrons and azaleas that seem less susceptible to lace bug and use good growing techniques to support strong healthy plants.
Additional information including pictures:
http://oregonstate.edu/dept/nurspest/azalea_lace_bug.htm
http://oregonstate.edu/dept/NWREC/sites/default/files/em9066.pdf
http://portlandnursery.com/service/brochures/solutions/azaleabug.shtml