Help with controlling birch aphid infestation - Ask Extension
Hi, looking for any possible help in dealing with a bad case of aphids throughout our .25 acre property in SW Portland. We have 2 very large (60+ft) b...
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Help with controlling birch aphid infestation #800987
Asked July 13, 2022, 6:01 PM EDT
Hi, looking for any possible help in dealing with a bad case of aphids throughout our .25 acre property in SW Portland. We have 2 very large (60+ft) birches, and our neighbor has one that overhangs our driveway as well.
We first noticed the aphid problem last year, when our cars in the driveway started getting sticky spots all over them. Never noticed much else. This year, same thing, with initial signs of heavy amount of honeydew on our cars. Then during the heat wave 2 weeks ago, we realized the issue was severe. Aphids were flying and floating around our yard to such a degree that it looked like it was snowing. Couldn't be outside without getting covered in aphids. We have seen green, black, and white, both winged and wingless.
In the past 2 weeks, we have noticed these on many, if not most of the plants and trees throughout our yard. Luckily we haven't found any significant damage, but they are spreading like crazy, and we also have nearly 100 new plants that went in this spring, including many native grasses, shrubs, trees, flowers, etc. So we are concerned for all our new and delicate plants.
We have noticed some lady bug larvae and now have spotted a few adults as well, but we still are seeing aphids absolutely everywhere. Many common recommendations like water jets or insecticidal soap are impossible due to how large the trees are. Any suggestions for how we can handle the infestation before it's too late?
Multnomah County Oregon
Expert Response
Hmm. This is a difficult problem, in the sense that no single answer will address all concerns.
Aphids tend to be a relatively ephemeral problem. They are phloem feeders, which means that they are feeding on the glucose and other photosynthetic products produced by the trees. And since they are basically feeding on the sugars of the tree . . . and they are defenseless against their predators . . . I sometimes refer to them as the 'Skittles of the Insect World'. Many predators and parasitoids attack aphids. If left alone, the problem often resolves itself in a week or two. The fact that you see ladybugs on the tree suggests that the problem is in the process of being resolved, by the predators.
I'll note that drought stress often exacerbates aphid issues. This is because trees, when stressed, may start to back translocate amino acids to their roots, for storage. During this time, aphids not only get to feed on plant sugars, but also plant proteins. And, since aphids are often starved for proteins, drought stress makes the aphid problems worse. I share this, so that you can plan ahead in future years. When heat waves are in the forecast, it will be important to ensure your trees are well-watered. It won't solve your problem, but it may help.
Now, leaving the problem to resolve itself isn't the best solution in your case, because of the honeydew exudates and droppings onto your car and driveway. Perhaps you may be able to park your car in another location, for a brief period of time? Even if this is the case, however, I've found that aphid honeydew on driveways or sidewalks often presents a tripping hazard. Your shoes get stuck to the ground, like flypaper.
If leaving the issue to resolve itself isn't possible, you will need to look at insecticides. The large size of the trees makes them difficult to treat with insecticides, as you note. If you do choose to use foliar, sprayed insecticides on trees of this size, I would highly suggest hiring a landscape maintenance company or professional arborist, and ensuring that the folks you hire are licensed professional applicators.
One promising pesticide, that could help with your problem, are insecticides with the active ingredient of chlorantraniliprole (http://npic.orst.edu/factsheets/chlorantraniliprole.html#products). This active ingredient is effective against aphids, but has limited impact on bees (see page 18 of this publication: https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/pnw591.pdf). It has some systemic activity, but is not as long term as other systemics, such as imidacloprid (which I discuss, below). The problem is, that you will need to work with a licensed pesticide applicator to apply this product. The only home-use product that contains chlorantraniliprole as the active ingredient is formulated for use on turf.
There is also the option of using systemic insecticides, that are sprayed onto the bark or applied at the root flare of the tree. These insecticides will have the active ingredient of dinotefuran OR imidacloprid, and can be purchased at home and garden stores or big box stores. These products are taken up by the vascular system of the tree, and incorporated (systemically) into the vegetation. Insects that are feeding on the tree (such as the aphids) will get a dose of the insecticide, and die. But, there are a few cautions I need to add about using systemic insecticides, for your situation.
The first is that it will take time for the insecticide to be moved from the base of the tree, and into the canopy. Imidacloprid can take weeks or months to move into the canopy. Dinotefuran can take weeks. And by that time, as I mentioned, it is quite possible that the problem would have resolved itself, via the predatory activities of the ladybugs.
The second is that once systemic insecticides ~ particularly imidacloprid ~ are in woody plant tissues, they remain insecticidal for long periods of time: months to years. So, even if you are applying an insecticide to deal with a short-term problem, the pesticide persists for a much longer time. Some folks like this . .. because you get long term protection against insect pests.
Third, bees are highly attracted to birches, particularly at certain times of the year, when the birches offer pollen on their catkins. Research has shown that bees are negatively affected by systemic insecticides if exposed to the pesticides in nectar or pollen. Birch trees don't offer nectar to bees. They are wind pollinated plants, and thus don't try to entice pollinators with a nectar reward. But, if small amounts of imidacloprid move into the pollen, it could harm bees.
Sorry for the long winded answer. With a pest management issue, such as yours, there is no 'perfect' answer, and I was trying to offer you options to consider, while also painting the complexity of the problem.
Best of luck to you! I would be very curious to hear what you decide, and how it goes, if you would be willing to circle back and share with me.
Aphids tend to be a relatively ephemeral problem. They are phloem feeders, which means that they are feeding on the glucose and other photosynthetic products produced by the trees. And since they are basically feeding on the sugars of the tree . . . and they are defenseless against their predators . . . I sometimes refer to them as the 'Skittles of the Insect World'. Many predators and parasitoids attack aphids. If left alone, the problem often resolves itself in a week or two. The fact that you see ladybugs on the tree suggests that the problem is in the process of being resolved, by the predators.
I'll note that drought stress often exacerbates aphid issues. This is because trees, when stressed, may start to back translocate amino acids to their roots, for storage. During this time, aphids not only get to feed on plant sugars, but also plant proteins. And, since aphids are often starved for proteins, drought stress makes the aphid problems worse. I share this, so that you can plan ahead in future years. When heat waves are in the forecast, it will be important to ensure your trees are well-watered. It won't solve your problem, but it may help.
Now, leaving the problem to resolve itself isn't the best solution in your case, because of the honeydew exudates and droppings onto your car and driveway. Perhaps you may be able to park your car in another location, for a brief period of time? Even if this is the case, however, I've found that aphid honeydew on driveways or sidewalks often presents a tripping hazard. Your shoes get stuck to the ground, like flypaper.
If leaving the issue to resolve itself isn't possible, you will need to look at insecticides. The large size of the trees makes them difficult to treat with insecticides, as you note. If you do choose to use foliar, sprayed insecticides on trees of this size, I would highly suggest hiring a landscape maintenance company or professional arborist, and ensuring that the folks you hire are licensed professional applicators.
One promising pesticide, that could help with your problem, are insecticides with the active ingredient of chlorantraniliprole (http://npic.orst.edu/factsheets/chlorantraniliprole.html#products). This active ingredient is effective against aphids, but has limited impact on bees (see page 18 of this publication: https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/pnw591.pdf). It has some systemic activity, but is not as long term as other systemics, such as imidacloprid (which I discuss, below). The problem is, that you will need to work with a licensed pesticide applicator to apply this product. The only home-use product that contains chlorantraniliprole as the active ingredient is formulated for use on turf.
There is also the option of using systemic insecticides, that are sprayed onto the bark or applied at the root flare of the tree. These insecticides will have the active ingredient of dinotefuran OR imidacloprid, and can be purchased at home and garden stores or big box stores. These products are taken up by the vascular system of the tree, and incorporated (systemically) into the vegetation. Insects that are feeding on the tree (such as the aphids) will get a dose of the insecticide, and die. But, there are a few cautions I need to add about using systemic insecticides, for your situation.
The first is that it will take time for the insecticide to be moved from the base of the tree, and into the canopy. Imidacloprid can take weeks or months to move into the canopy. Dinotefuran can take weeks. And by that time, as I mentioned, it is quite possible that the problem would have resolved itself, via the predatory activities of the ladybugs.
The second is that once systemic insecticides ~ particularly imidacloprid ~ are in woody plant tissues, they remain insecticidal for long periods of time: months to years. So, even if you are applying an insecticide to deal with a short-term problem, the pesticide persists for a much longer time. Some folks like this . .. because you get long term protection against insect pests.
Third, bees are highly attracted to birches, particularly at certain times of the year, when the birches offer pollen on their catkins. Research has shown that bees are negatively affected by systemic insecticides if exposed to the pesticides in nectar or pollen. Birch trees don't offer nectar to bees. They are wind pollinated plants, and thus don't try to entice pollinators with a nectar reward. But, if small amounts of imidacloprid move into the pollen, it could harm bees.
Sorry for the long winded answer. With a pest management issue, such as yours, there is no 'perfect' answer, and I was trying to offer you options to consider, while also painting the complexity of the problem.
Best of luck to you! I would be very curious to hear what you decide, and how it goes, if you would be willing to circle back and share with me.
Hi Gail! Thank you so much for your time and detailed response! It's very helpful. I do agree that, at the moment, insecticides are still in our "last resort" category. As for this year, it seems the honeydew we are seeing has greatly decreased, so I think the issue is at least improving, although we are concerned the issue has seemed to get worse each year.
You noted one thing was to make sure the trees do not get drought stressed to help in the coming years. I was wondering if there are any other preventative measures we can take, to try to help control the aphid populations before they can grow as large?
I saw an article on your site that mentioned a number of different plants and flowers that may attract more ladybugs to the area. Do you think planting a large number of these will help foster a larger population of ladybugs that will deal with the issue quicker? Is there a way to help encourage the ladybugs and larvae to take care of the aphids before they have a chance to populate so quickly?
And also the other question I had was in supplementing more predators as needed. I have read very mixed things regarding purchasing ladybugs - from hearing they will instantly migrate away, as well as they could potentially harm the existing native population. I have also heard purchasing lacewing larvae may be more helpful instead?
Thanks,
CJ
Buying and releasing adult ladybugs will generally be of no help. Ladybugs do have an innate behavior . . . where they need to migrate before their eggs develop ('flight-oogenesis syndrome'). Also, to get the best results from natural enemy releases, you generally need to release the natural enemies ON (or at least near) your pest problem. If your aphids are high above, in the canopy, I can't see that releasing any natural enemy will help.
Lacewing larvae are great aphid predators. However, once again, you have the problem of how do you get the lacewing larvae into the tree canopy? (They can't fly). Lacewing larvae are also UBER expensive. They eat just about any other insect!!! Including each other!!! That means that the biocontrol company has to pay someone to individually pick up one lacewing larvae at a time, and place it into an individual hex cell . . . so that they won't eat each other during shipping.
Incorporating plants that attract a diversity and abundance of natural enemies into your yard can help, but don't expect to see results overnight. Our research, and others, shows that it takes about 3 years for the plants to establish to the point that you attract in a large number of natural enemies. Our specific research has shown that yarrow, goldenrod, and Douglas' aster are the three native plants (of the ones that we tested) that attract the most abundant and diverse assemblage of aphid-eating parasitoids, predaceous bugs, and spiders.
Good luck!
Lacewing larvae are great aphid predators. However, once again, you have the problem of how do you get the lacewing larvae into the tree canopy? (They can't fly). Lacewing larvae are also UBER expensive. They eat just about any other insect!!! Including each other!!! That means that the biocontrol company has to pay someone to individually pick up one lacewing larvae at a time, and place it into an individual hex cell . . . so that they won't eat each other during shipping.
Incorporating plants that attract a diversity and abundance of natural enemies into your yard can help, but don't expect to see results overnight. Our research, and others, shows that it takes about 3 years for the plants to establish to the point that you attract in a large number of natural enemies. Our specific research has shown that yarrow, goldenrod, and Douglas' aster are the three native plants (of the ones that we tested) that attract the most abundant and diverse assemblage of aphid-eating parasitoids, predaceous bugs, and spiders.
Good luck!
Hello,
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You reached out to the OSU Extension Service Master Gardener program with a household pest, plant, garden, or landscape question(s). Providing the public with research based information to help you make informed decisions is our primary public service. We are following up with you to learn if our advice helped you.
We welcome your feedback, which shapes how we provide reliable information for the public. This anonymous, quick survey takes under 5 minutes to complete (see questions below).
Thank you in advance for taking the time to provide this valuable information.
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