Impressive autumn foliar color among the silver maples is nearly as incredible as lemons on shattuck trees during this weather change during this time of the year. The silver maple is one of my favorite trees but disappoints those expecting it to color as other maples do. However, this year, the foliage that typically becomes dingy gray, brown and pale yellow has been unusually yellow. Although the color still does not compare to that of other species with more remarkable color, it has been drawing attention.

I briefly thought I learned something new while reading a previous gardening column. “Among dwarf citrus, the understock is shattuck, which produces wicked thorns and very large, insipid lemons.” Wow! Lemons from a shattuck tree! Actually, shattuck trees can only produce shattuck fruit. Lemons grow on lemon trees. I hope this misinformation did not cause much confusion.

Red oaks have also been coloring better than normal. However, the Pacific maple (bigleaf maple) that has colored more impressively during the previous two autumns has not done so this autumn. I can not explain why the various species behave as they do, only that they are much more aware of climactic conditions than I am. Each species reacts uniquely, so each autumn features a different cast of star performers.

The dingy brown among the normally bright yellow tulip trees may have involved more than weather conditions. Many throughout the Santa Clara Valley have been infested with aphid and scale. Both are homopteran insects (of the family Homoptera, which is perhaps more than one needs to know) that disrupt vascular activity among the foliage and emerging stems. This disruption causes premature abscission and defoliation. Necrotic (dead) foliage becomes brown before there has been sufficient time for it to yellow in response to autumn weather.

The sticky substance that falls from infested trees is ‘honeydew’ that is excreted from the insects. Honeydew is attractive to ants and may become infected with sooty mold. It is particularly bothersome on cars parked below infested trees. Fortunately, honeydew is rinsed away by the recent rain and will not appear while the insects are over-wintering. Unfortunately, any grunge that accumulates on cars will need to be washed off.