and get honeydew around the ground. And that can attract other pests that the tree can’t protect against.” Arborists use preventive measures, such as pruning, mulch, soil amend- ments, and proper watering, to support plant health. This work can continue with the introduction of friendly in- sects, quarantine to limit the spread of diseases, and pesticides to directly counteract pests. When treating trees against pests, the biggest mistake an arborist can make is “not getting out there early enough,” says Stringfellow. He points to apple scab ( Venturia inaequalis ), a fungus that appears in early spring, with full effects seen in June or July. “By that point, it’s too late to do anything. You treat in the fall to reduce the amount of pathogens in the spring.” Pests and diseases can leave a wide range of clues and footprints to indi- cate their presence. Signs can include chewed, distorted, or stippled foliage, white spots or masses, holes or boring tracks in bark, sticky substances, and leaf spots.
The Wedgle is a syringe-like applicator, used here to inject imidacloprid (Pointer) to control emerald ash borer.
attacking a tree. Aphids, for example, are oen a harbinger of more destruc- tive pests to come. “Do aphids kill the tree? No,” says Bill Stringfellow, managing director at Quest Products, LLC, which provides pesticide and fertilizer products. “But what they do is suck the juices out of the leaves
multiplying in spring, most pests sink into hibernation, a sliver of time that gives arborists the perfect opportunity to shore up defenses and mount a coun- terattack. “Fall is an interesting time because there’s not a lot of pest activity going on,” says Mark Ware, an "arborologist” who provides product tech support for Rainbow Ecoscience, which provides treatment products, equipment, and research. “But what I really like about fall is that it’s a great opportunity to alleviate plant stress.” GIVING TREES A FIGHTING CHANCE A healthy tree offers a variety of nat- ural defenses against pests, including structural barriers, such as sap or wax, toxic chemicals, and the attraction of pests’ natural enemies. However, these barriers can be over- come when a tree is stressed or suffers damage. It can be hard to see this dam- age when a tree is lush with foliage. So, winter is the perfect time to observe pest infestations when fallen leaves ex- pose a tree’s limb structure. In protecting trees, an arborist’s work begins with simple observation and tracking to accurately identify what is
Wooly ash aphids attack the underside of a curled American ash leaf (Frazinus americana) . The aphid colony has been largely parasitized by Aphelinus sp ., as noted by the black aphid “mummies.”
30 | ArborTIMES Fall 2023
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