Lace Bug Infestation - Ask Extension
Hello!
I’ve had a lace bug infestation on my asters for months. I’ve tried removing them by hand, using a strong stream of water, and applying ...
Knowledgebase
Lace Bug Infestation #879863
Asked August 02, 2024, 10:09 AM EDT
Hello!
I’ve had a lace bug infestation on my asters for months. I’ve tried removing them by hand, using a strong stream of water, and applying neem oil. Nothing has seemed to work and it is killing the plants.
I am looking for advice on something to use. I understand systemic insecticides are a no-go in Maryland but that is all that seems to be recommended when other measures have failed. I also wanted to see if there is a way to make sure these lace bugs don’t over-winter with my plants so that I can try to do a better job controlling for them next year, as this was my first year with the aster. Thank you!
We love in a row home in the city for context.
Baltimore City County Maryland
Expert Response
Chrysanthemum Lace Bug, the particular lace bug species that damages asters (and their relatives in the mum/aster family, like goldenrod), overwinters as adults. They shelter in leaf litter and other plant debris, so while keeping leaf litter in general is beneficial for many organisms, it also can harbor pests like these. Therefore, around plants that have had outbreaks of pests or diseases, a through clean-up of plant debris may help to limit the overwintering population.
If plants become too heavily damaged, where they may not flower well anyway, then you have little to lose by cutting the plants back drastically. They should regrow and be fine (although, depending on when this is done, blooming may be delayed or prevented for that year), and this will be a way to immediately and drastically reduce the lace bug population without having to spray.
While we would not recommend using the Orthene or other systemics mentioned on the page linked above, because they would indeed risk harm to beneficial insects, you could try insecticidal soap or, at most, pyrethrin, though the latter must not contact the flowers since it is an insecticide type (even though organic) that can kill insects that come into contact with the spray residues, unlike the soap and oil options. Granted, those residues do not last as long as the synthetic pyrethroid ingredients used in other products. In general, as you might imagine, the lowest-toxicity spray, if any at all, should be used on a plant as population with pollinators as Aster. Plus, at least one butterfly species can use Aster as a host plant for its caterpillars, though to be fair, a plant riddled with heavy lace bug damage is probably not hosting any caterpillars at that point.
Are you still finding lace bugs after the sprays with water or oil? Leaves cannot heal, so even successful treatments will not result in an aesthetic improvement of the damaged foliage. (Plus, even oil and soap sprays might damage the foliage further if it already has heavy feeding injury.) The best indicator that populations are being sufficiently suppressed is that new growth will remain healthy-looking and not develop lace bug feeding damage.
Miri
If plants become too heavily damaged, where they may not flower well anyway, then you have little to lose by cutting the plants back drastically. They should regrow and be fine (although, depending on when this is done, blooming may be delayed or prevented for that year), and this will be a way to immediately and drastically reduce the lace bug population without having to spray.
While we would not recommend using the Orthene or other systemics mentioned on the page linked above, because they would indeed risk harm to beneficial insects, you could try insecticidal soap or, at most, pyrethrin, though the latter must not contact the flowers since it is an insecticide type (even though organic) that can kill insects that come into contact with the spray residues, unlike the soap and oil options. Granted, those residues do not last as long as the synthetic pyrethroid ingredients used in other products. In general, as you might imagine, the lowest-toxicity spray, if any at all, should be used on a plant as population with pollinators as Aster. Plus, at least one butterfly species can use Aster as a host plant for its caterpillars, though to be fair, a plant riddled with heavy lace bug damage is probably not hosting any caterpillars at that point.
Are you still finding lace bugs after the sprays with water or oil? Leaves cannot heal, so even successful treatments will not result in an aesthetic improvement of the damaged foliage. (Plus, even oil and soap sprays might damage the foliage further if it already has heavy feeding injury.) The best indicator that populations are being sufficiently suppressed is that new growth will remain healthy-looking and not develop lace bug feeding damage.
Miri
Good morning!
Thank you so much for the quick reply! While the newest growth is doing okay and trying to flower (many of the flowers are turning brown and dying before they even open while others are doing okay), you can see the lace bugs making their way up to the new growth. There are many, many live ones on there as well as eggs on the underside of the leaves. I’ve tried my best to be thorough both with water and oil but the water is right next to my goldenrod and it’s hard to make sure I get everything since the growth is fairly dense.
I plan to cut them back at the end of the season for winter but should I do it sooner? Since this was their first year, I was hesitant to prune anything early.
No caterpillars on the two asters and the pollinators have been fewer since my bee balm stopped blooming. Should I give pyrethrin a go? I can make sure I do it at night when there are fewer pollinators and avoid the flowers at all costs. I’m hoping to get this under control because if they move to the wreath goldenrod, I’ll never be able to treat them effectively. The plants are just too dense.
Thank you so much for your help! I’m sorry I’m so full of questions!
Amanda
On Aug 2, 2024, at 11:28 AM, Ask Extension <<personal data hidden>> wrote:
Good morning!
Thank you so much for the quick reply! While the newest growth is doing okay and trying to flower (many of the flowers are turning brown and dying before they even open while others are doing okay), you can see the lace bugs making their way up to the new growth. There are many, many live ones on there as well as eggs on the underside of the leaves. I’ve tried my best to be thorough both with water and oil but the water is right next to my goldenrod and it’s hard to make sure I get everything since the growth is fairly dense.
I plan to cut them back at the end of the season for winter but should I do it sooner? Since this was their first year, I was hesitant to prune anything early.
No caterpillars on the two asters and the pollinators have been fewer since my bee balm stopped blooming. Should I give pyrethrin a go? I can make sure I do it at night when there are fewer pollinators and avoid the flowers at all costs. I’m hoping to get this under control because if they move to the wreath goldenrod, I’ll never be able to treat them effectively. The plants are just too dense.
Thank you so much for your help! I’m sorry I’m so full of questions!
Amanda
On Aug 2, 2024, at 11:28 AM, Ask Extension <<personal data hidden>> wrote:
No worries about the questions - that's why we're here!
It's hard to say which would be better -- pruning down the Asters or trying an evening application of pyrethrin. While the vast majority of bees visit flowers during the day, moths can visit flowers after dark (and potentially other insects...this is an area needing more research). Still, you probably have the best chance at not impacting too many other species much if you aim for about twilight to treat. Otherwise, it's generally safest to avoid pesticide use at all, especially if the plant is expected to outgrow the damage (perhaps not this year, but next year). One downside to broad-spectrum pesticides, even organic ones, is that they can impact different insects indiscriminately, which means that it might harm beneficial predators of the lace bugs just as readily as the pests themselves. Therefore, you may want to just cut the Asters back, and if they are able to regrow enough to flower a little by frost, that's a bonus. Keep the roots alive and healthy by still monitoring them for watering needs, feeling the soil around five inches deep and watering well once it becomes somewhat dry to the touch at that depth.
Miri
It's hard to say which would be better -- pruning down the Asters or trying an evening application of pyrethrin. While the vast majority of bees visit flowers during the day, moths can visit flowers after dark (and potentially other insects...this is an area needing more research). Still, you probably have the best chance at not impacting too many other species much if you aim for about twilight to treat. Otherwise, it's generally safest to avoid pesticide use at all, especially if the plant is expected to outgrow the damage (perhaps not this year, but next year). One downside to broad-spectrum pesticides, even organic ones, is that they can impact different insects indiscriminately, which means that it might harm beneficial predators of the lace bugs just as readily as the pests themselves. Therefore, you may want to just cut the Asters back, and if they are able to regrow enough to flower a little by frost, that's a bonus. Keep the roots alive and healthy by still monitoring them for watering needs, feeling the soil around five inches deep and watering well once it becomes somewhat dry to the touch at that depth.
Miri
