ladybug infestation on mature rhododendrons - Ask Extension
I had a professional look at the trees and she diagnosed it as lacebug infestation. She recommended a chemical injection into the
soil. It was quite...
Knowledgebase
ladybug infestation on mature rhododendrons #863366
Asked April 04, 2024, 4:27 PM EDT
I had a professional look at the trees and she diagnosed it as lacebug infestation. She recommended a chemical injection into the
soil. It was quite expensive, but I am willing to do it if it saves the trees. MY question to you is if you think this method is at all effective? Have you seen any positive results with this treatment ? Foliar spray would be too difficult as the trees are very large and full,
Thank you!
Multnomah County Oregon
Expert Response
Hi,
I don't have direct experience as to the effectiveness of systemic insecticides to control lace bugs on rhododendrons, so I did some research. This is from a webpage from the University of Minnesota (which I consider a credible source) about lace bugs on rhododendrons...
"Systemic insecticides, like imidacloprid and dinotefuran, are effective. These products move through the plant to the leaves."
However, systemic insecticides need to be used with a great deal of caution so that pollinators are not affected. This is a warning about the dangers of systemic insecticides that is also from the same University of Minnesota webpage....
"CAUTION: These products are very toxic to bees. Avoid treating plants when possible. If making an application, wait until after the trees or shrubs have finished flowering to reduce pesticide exposure to bees. Do not apply systemic insecticides to the soil when bee attractive flowers are planted directly adjacent to trees."
Here is a link with more information about the risks of systemic insecticides to pollinators...
https://xerces.org/systemic-insecticides-reference-and-overview
Other non-systemic pesticides applied during flowering could also harm bees and other pollinators, so it would be best to apply any pesticides you think are necessary after the flowers have dropped off.
The other thing to consider is whether pesticides are necessary.
Here is some information about lace bugs on rhododendrons and azaleas from the PNW Insect Management Handbook...
"Damage is usually apparent by early to mid-July. While almost never fatal, repeated infestations of rhododendron lace bugs may result in yellowed, sickly plants."
And from this same source, here are some non-pesticide methods that can be used to manage lace bug damage....
Management-cultural control
Maintain plant health by providing proper water and nutrition. Stressed plants are more susceptible to insect damage. Grow azaleas in shady areas to minimize damage. Remove leaves with brown patches of eggs along the midrib. Hosing plants with a strong stream of water directed at the underside of leaves will help to remove some adults and wingless nymphs.
Management-biological control
Release of lacewing larvae have proven successful in one experimental test. Select insecticides to preserve populations of beneficial predators that will help control lace bugs.
So, sorry to not have a completely clear-cut answer for you. I would say that if you choose to go with a systemic insecticide, have it applied after flowering. That would protect pollinators this year and allow time for the pesticide in the tissues to degrade so that it is not present in pollen or nectar of next year's flowers.
Hope that helps!
I don't have direct experience as to the effectiveness of systemic insecticides to control lace bugs on rhododendrons, so I did some research. This is from a webpage from the University of Minnesota (which I consider a credible source) about lace bugs on rhododendrons...
"Systemic insecticides, like imidacloprid and dinotefuran, are effective. These products move through the plant to the leaves."
However, systemic insecticides need to be used with a great deal of caution so that pollinators are not affected. This is a warning about the dangers of systemic insecticides that is also from the same University of Minnesota webpage....
"CAUTION: These products are very toxic to bees. Avoid treating plants when possible. If making an application, wait until after the trees or shrubs have finished flowering to reduce pesticide exposure to bees. Do not apply systemic insecticides to the soil when bee attractive flowers are planted directly adjacent to trees."
Here is a link with more information about the risks of systemic insecticides to pollinators...
https://xerces.org/systemic-insecticides-reference-and-overview
Other non-systemic pesticides applied during flowering could also harm bees and other pollinators, so it would be best to apply any pesticides you think are necessary after the flowers have dropped off.
The other thing to consider is whether pesticides are necessary.
Here is some information about lace bugs on rhododendrons and azaleas from the PNW Insect Management Handbook...
"Damage is usually apparent by early to mid-July. While almost never fatal, repeated infestations of rhododendron lace bugs may result in yellowed, sickly plants."
And from this same source, here are some non-pesticide methods that can be used to manage lace bug damage....
Management-cultural control
Maintain plant health by providing proper water and nutrition. Stressed plants are more susceptible to insect damage. Grow azaleas in shady areas to minimize damage. Remove leaves with brown patches of eggs along the midrib. Hosing plants with a strong stream of water directed at the underside of leaves will help to remove some adults and wingless nymphs.
Management-biological control
Release of lacewing larvae have proven successful in one experimental test. Select insecticides to preserve populations of beneficial predators that will help control lace bugs.
So, sorry to not have a completely clear-cut answer for you. I would say that if you choose to go with a systemic insecticide, have it applied after flowering. That would protect pollinators this year and allow time for the pesticide in the tissues to degrade so that it is not present in pollen or nectar of next year's flowers.
Hope that helps!
