I have found over the years that if you see ants going up or down the trunk of the tree it is a sign of Spring pest. Don't mistakenly dismiss these ants as adventurous climbers looking for a better view to admire your beautiful tree or garden. They have a purpose and it's not beneficial to you or your Japanese maples. The easiest way to spot ants is to look at the trunk of your tree. They use the trunk as a highway to and from. Follow the ants moving up the trunk and they will reveal the pest. Aphids: You may track ants going to the tips, tender new stems or on and under leaves of tender new growth. This is an indication of aphids. A new tree may have aphids from the nursery. The ants are drinking the sugar filled escriment from the aphids. Once established ants will store aphid eggs over winter and then establish a farm on your tree in Spring, by carrying the aphid eggs up the tree and placing them in a designated area, or farm once the aphids mature. The ants also fend off natural predators to keep their farm growing and food source safe. Scale: If you track the aphids to areas on the trunk, old pruning cuts, and more mature areas of branches; look closer and you will likely see scale. Depending on the age of the scale they may be very hard to see or larger and much easier to spot. Scale causes bark damage while sucking the sap. Photo of scale, or see uploaded photo: http://forums.botanicalgarden.ubc.ca/attachments/inkedp5090380_li-jpg.157808/ Both pest can cause cosmetic damage, limit new growth and in more severe cases cause dieback of tender new growth, and introduce disease. In most cases they do not kill your tree, but they can introduce a disease that may. Scale and aphids can be smashed with your fingers. Aphids can be blown off with a hose and stream of water. Most of the time the ants will continue to bring back more and aphids populations can explode, so it takes a huge daily commitment that may last for days or even weeks. topical or systemic insecticides should be used with extreme caution or not at all especially if your trees are in bloom. Insecticides kill pollinators, poison birds, contaminates soil and water. Any chemical can become volatile in hot weather and go from a liquid to a gas that can travel by wind and breathed by us and pets/wildlife. My approach is not perfect and may not be popular, but I try to consider all the above in my approach. I go after the ants and smash the scale or aphid. The key is to catch them now before an infestation occurs. To kill or deter the ants I use a small brush and apply neem oil around the base of the tree creating a connecting ring around the bark. If by the second or third day, if the ants still persist then I use insecticide using the same ring method. The ants or pest have to cross this area at the base of the tree to get to the tender new growth. This eliminates their path and kills them in the process. Most beneficial insects fly so by treating the base of the tree and not using a systemic we are reducing risk. The goal of this post is not to recommend a method for treatment, rather it is to raise awareness of ants on your maple = pests. For informational reasons I thought mentioning methods for treatment were warranted. What you choose to do with the information is really up to you. What's right for me in treatment may not be what's right for you. Photos of ants farming scale in various stages of development along an area where a branch was removed on Acer japonicum. Since the bark of Acer japonicum is thicker and rough, they tend to attach to areas of wounds. Acer palmatum bark is thinner so you may find them anywhere on bark and thicker areas of branches or wounds like in the picture. In the 3rd picture ants are circled in red and scale are pointed out at the end of each red line.
I don't hesitate to use ant poison around the trunk. Ants = aphids, and aphids = limited new growth. Ants don't do any damage themselves, but once they're farming, they reinstall the aphids in a flash and it's impossible to keep up with them. I have not found an insecticide, or even soap, that doesn't to some extent stunt leaf growth. The only exception is, when buds have swelled but not burst, it seems safe to use a mild (!) insecticide. I too remove these and scale by hand. Also caterpillars, it seems I spend an inordinately large part of my gardening time picking them off this time of year! Grrr, bugs. :)
