Black aphids on japanese maple

(Question)

Hello, I’m in Toronto with a west facing garden (full afternoon sun) that has a 4ft japanese (waterfall) maple. I planted it last summer, and it came back this spring very healthy. But today, I noticed swarms of small black ants near the ends of branches mostly where new leaves are growing in. The ants seem to be attracted to a clear gummy substance. Black aphid excrement? Does that sound right? And, how do I get rid of the aphids? …I’ve read about spraying the leaves with a solution of 1tsp of dish detergent mixed into 2L of water. Is that a safe and effective solution?
Any help is appreciated,
Thanks

(Answer)

You don’t mention seeing any aphids, themselves. They would be highly visible if present, clustered on the soft tissues. If they are present, the easiest control methods are mechanical: simply squish them with your gloved fingers and/or knock them off with a strong blast of water from a hose. Inspect your tree from time to time and repeat as necessary.

If not aphids, it will be difficult to diagnose your problem and suggest a solution without seeing your tree. However, here are a couple of possibilities to investigate:

Are the ants all over the tree, or only on certain branches? As this is a maple tree, which produces a sweet sap, one possibility for the sticky substance (and ants) might be sap over-production encouraged by the full-west location on a hot day. Or, if the activity is restricted to only certain branches, could there have been slight damage to a branch, or pruning at the wrong time, opening it to leaking sap? If this sounds like your problem, you can hose down your tree to wash off or dilute sap. Japanese maples tend to bleed from cut or damaged tissues and should only be pruned either while dormant in winter or during midsummer, when sap isn’t running.

Another possibility might be scale, a sucking insect which can be harder to see than aphids. Ants are also drawn to areas where scale feeds. Scale insects get their name from the hard, waxy or sometimes fluffy shells they produce to protect the eggs and female. The scale larvae, called crawlers, can be quite small and move along young branches to feed through thinner bark (such as where twigs branch off) or on leaves.

Inspect the trunk and older branches of your maple, away from these feeding areas, looking for the small, shell-like bumps. Depending on the scale species, these bumps might be round or elongated like an oyster shell or even cottony. If you see anything suspicious like that, try to crush or gently scrape one off with a fingernail. This will confirm a scale problem.

Areas in the U.S. are also reporting a newer species of scale specific to Japanese maples. If scale is your problem, controlling it could be tricky – Japanese maples are said to be sensitive to horticultural oil sprays which are the usual treatment. However, the University of Tennessee suggests that lighter, more refined oils (called summer oils) might be appropriate to use. The insecticides mentioned in this last sheet, on the other hand, are banned for cosmetic use in Ontario.

Check back with us once you’ve had a closer look at your tree and let us know if you have further questions. Good luck!