Q: I have a 33-year-old birch tree that I have treated for birch leafminer for many years using a Ross Root Feeder and Systemic Insecticide Root Feeder cartridges. The product contains 2 percent Di-Syston. I cannot seem to find the cartridges anymore. Are there other products that I can use?
A: Di-Syston (disulfoton), the active ingredient in Ross Systemic Root Feeder cartridges, is no longer available for home use. The Environmental Protection Agency continues to review pesticides under the Food Quality Protection Act of 1996, using stricter limits for human exposure to these products. As a result, a number of pesticides are no longer sold to home gardeners. They may still be available to licensed pesticide applicators for commercial use, but often they cannot be applied to residential properties.
Fortunately, there are other products that control birch leafminers effectively and safely. One that is particularly easy for home gardeners to apply is Bayer Advanced Tree & Shrub Insect Control. It contains the systemic insecticide imidacloprid as the active ingredient.
One application in late winter will provide season-long control of birch leafminer, bronze birch borer and other pests. The product is mixed with water and applied with a bucket or watering can to the tree's root system. Like the root feeding system you have been using, there is no spraying involved.
You have to measure the circumference of the trunk of the tree, or add up the circumferences of all the trunks of a multitrunked specimen, to determine how much of the concentrated product to use. You mix it with 1 gallon of water (2 gallons for trees with a circumference greater than 50 inches), and then apply the mixture slowly and evenly around the base. Stay close to the trunk, but try to get the product on the ground where it can be absorbed by the roots. Refill the bucket or watering can with plain water and go over the area where you applied the mixture to water it into the root zone.
It does take time for the product to be absorbed, anywhere from a week to three months, depending on the size and health of the tree. Bayer Advanced Tree & Shrub Insect Control can be applied any time the ground is not frozen or waterlogged. It is also important that there is adequate soil moisture prior to application. If we have not had rain, be sure to water the area under the tree the day before you make the application.
Adult leafminers are active and laying eggs as birch trees leaf out in the spring (May). A second generation hatches out in mid-to-late June. You want to be sure to apply the Bayer product early enough, so that tree has time to take it up and transport it through the branches before the adults become active. It will not be effective if applied after you see leafminer activity.