Hello again,
I sent my second enquiry to you yesterday about ants that are beginning to appear on my Chinese Snowball bush. It is just the beginning of this problem and past years have taught me that the amount will increase and increase. What I have been trying to show you in my pics is the very small pin sized material on the stems near the leaves. They are likely eggs. They are now green/brown and soon the clusters will grow and become blackish. I want to arrest the process as soon as possible and have done 2 applications (weeks apart) of dormant oil and this Morning gave it a strong blast of water with the garden hose. Something else I did was trim out all the dead wood as you indicated the ants might be carpenter ants and feeding on dead branches. I also tried the placement of jam within the bush (your suggestion) – it did not end up showing me where the ants were originating, although lots of the little guys visited the jam but seemed to be coming from within the bus. These pictures may not be satisfactory – hopefully my explanation is. I can re try photos later as the egg clusters grow – but am most concerned about stopping this infestation sooner rather than later.
Thank you for contacting the Toronto Master Gardeners about the ants on your Chinese snowball (Viburnum macrocephalum). I cannot determine from your photo what the tiny pin-sized material that you have referred to is on the stems near the base of the leaves, but I know it is not ant eggs. Most ants (not carpenter ants) live in nests in the ground, often very deep in the ground, where they overwinter. Queen ants lay eggs in the nest. Eggs become larvae which become pupae which finally become adults. All of this development takes place in the nest. Adult ants can be workers (some of which leave the nest to find food to bring back to the nest – note that ants rarely eat plant material), or males (whose only function is mating), and sometimes they are queens. In order to eliminate a nest, all workers and queens must be destroyed. There is more information about ants here. (Please note that the information about pesticides (chemical controls) in this article applies in the US and not in Canada. The use of pesticides in Ontario for cosmetic purposes in home lawns and gardens is strictly controlled by law. Here is the Allowable List of active ingredients that can be used in Ontario.)
Based on your description of what has been happening with ants on your Chinese snowball, I think it is quite likely that you also have aphids, which are very common on viburnum. Aphids (and some other insects) excrete a liquid called honeydew, and honeydew is the most common natural source of food for ants. (Note that a fungus called sooty mold often grows on honeydew, and I think this might be the blackish patches that you have seen on the leaves of your plant.) Ants ‘farm’ aphids, meaning that they protect them from their natural predators so that the aphids can feed on plant leaves and stems and provide an unlimited source of honeydew for the ants. I think what you are seeing is this symbiotic relationship between ants and aphids, taking place on your plant.
I can’t be sure without a clear close-up photo, but I think the tiny bumps you are seeing on your plant could be aphid eggs (they could also be the actual aphids, so I suggest that you take a close look with a magnifying glass). Aphids lay eggs on a preferred plant towards the end of the growing season. The eggs overwinter on the plant and hatch in the spring. Aphids also give birth to live young during the summer. There is more information about aphids in the link at the bottom of this response including the damage (usually not serious) that they cause to plants as they feed and the symptoms of their presence.
So, what to do about what I suspect is your ant and aphid problem: I think the first consideration is that ants are virtually impossible to completely get rid of (and they are also very beneficial in gardens). All queens and workers need to be destroyed in order to eliminate a nest, which could be very deep into the ground. And it is quite likely that a new nest will appear in the vicinity of the previous nest, because the conditions in your garden are probably attractive to ants. Their preferred habitat is dry soil that is low in organic material, so if this is the case in your garden you could remedy this by adding organic matter and/or mulch (at least 4 inches) and keeping it moist. There is more information here about other things you could try in order to get rid of your ants.
While I think getting the ants under some control at least is worth doing, I think you can achieve the best overall results by getting rid of the aphids, so the ants’ preferred source of food is no longer available to them and they will look elsewhere. It is usually not difficult to get rid of aphids, it just requires persistence. Spraying aphids with water to knock them to the ground, every day for as long as you see them (and they are good at hiding especially on the undersides of leaves, so keep checking every day) is usually effective because aphids are not strong insects so they are very unlikely to crawl back onto the plant from the ground. You could also introduce plants into your garden that are attractive to aphids’ predators eg. lacewing, lady bugs. There is more information here about aphids and how to get rid of them. (Please note that the caveat about pesticides included above for the first link in this response also applies to this article.)
Best of luck in reducing the insect population on your Chinese snowball and restoring it to good health!
May 12, 2023