Question
Hi Jim,
We have 4 old birch trees in our SF Bay area landscaping (3 in a group/1 large alone) and as always at this time of year tremendous amounts of sugary drip from the aphid infestation. I should have sprayed when dormant in the winter/spring but let it go this year (has used malthione 2x separated by a couple of weeks). I wonder if I should just take a hose to them to wash it off, spray them with malathione, or just accept it? In the future, what is the best timing/substance to use? Thanks for you thoughts.


Answer
There are a couple of insecticides that will work well. (Malathion is not one of them). It will take an insecticide called a systemic to have an effect on the population. Contact insecticides like malathion have to be sprayed on each insect and with aphids this is difficult to do. If you do not kill them all the population will come back fast.

I would either spray the foliage (both sides and the stem) with Orthene or treat with Bayer Advanced Tree and Shrub Insect Control. Both are systemic and will be absorbed by the plant and kill the insects as they suck the plant juices. Orthene is sprayed on the foliage and the Bayer product is applied to the soil around the tree and the roots will absorb the insecticide and transport it to the leaves and twigs killing the insect when it feeds on the juices. The Bayer will last longer and will not need to be applied again until next spring. The spray will need to be applied at least twice to insure all are killed.

Here is the web link to more information the Bayer product. Both can be purchased at your local nursery.  http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html