lace bug infestation on azaleas
I have 6 azaleas out front of my home, infested with lace bug damage. It has now apparently spread to a large Rhododendron nearby. Should I attempt to use an insecticide to treat these, or are they too far gone and should I dig them all up and remove them all?
Lane County Oregon
The stippled appearance on the leaves in the third photo would indicate lace bug or spider mites. To confirm that they are lace bugs look on the underside of the leaves for a sticky black fecal substance or for crusty brown patches of eggs along the midrib, or bring a plant sample to the OSU Extension Lane County plant clinic at 996 Jefferson St in Eugene (call the plant clinic at 541-344-0265 for more information). Lace bug infestations are typically due to plants being stressed due to lack of water or fertility, or the azaleas being placed in the full sun instead of a partially shady location. Typically more than 14% leaf canopy damage will impact growth and flower production. In terms of whether you should remove the plants, I think it will depend on what lengths you are willing to go to to control the pest. For management options, please refer to the following: https://catalog.extension.oregonstate.edu/em9066 and https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/azalea-rhododendron-azalea-rhododendron-lace-bug.
Thank you for your reply. There is indeed, a lot of brown spots on the underside of most of the leaves. The azaleas are in a partially shaded area and both plants I believe received adequate water this summer. At down to Earth, they told me if I used a pest management system it could hurt the pollinators in the spring. Do you know about that?Thank you again for your help.
I assume by pest management they meant pesticides specifically. In terms of toxicity to bees, it really depends on the type of pesticide you use. The publications I sent to you lists insecticidal soaps, horticultural oils, neem based products, pyrethrins, and acephates as chemical control options. Of those listed, insecticidal soaps and neem oil are the low toxicity options with respect to bees. Acephate and pyrethrins are high toxicity to bees and horticultural oils are moderately toxic to bees. If you are uncomfortable using an insecticidal soap or neem based product, then you need to ensure you are using cultural options, such as maintaining plant health with proper water and nutrition or trying to spray adults off the plant with a hose. Otherwise, your best option may be to replace the infested azaleas with resistant cultivars. For more information about resistant cultivars, please see https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/azalea-rhododendron-azalea-rhododendron-lace-bug, and for information on pesticides and toxicity to bees, please see How to Reduce Bee Poisoning from Pesticides: https://catalog.extension.oregonstate.edu/pnw591.
Thanks again. The information about the least harmful pest management are great suggestions. I also appreciate the link to pesticides.
Happy to help Deborah. I will add one more thing to regard to protecting bees when using pesticides...it is best to spray pesticides to plants when they are not in bloom, which is the time that the bees would be visiting the flowers for nectar and pollen. Another good practice is to spray in the evening, near dusk, when the bees are less active. This will reduce the possibility of spraying the bees directly, and it also gives the pesticide time to dry overnight. Please let me know if you have additional questions.