Preventive sprays for spruce usually consist of a mix of horticulture oil and carbaryl insecticide (sold as Sevin). Horticulture oils (refined mineral oils) smother small, soft-bodied insects that overwinter on the tree (i.e., aphids and spider mites). An application of carbaryl, when timed properly, will prevent attack from certain wood-boring insects as well as the well-known cooley spruce gall adelgid. Preventively spraying spruce with the mixture is not recommended unless there has been a previously identified problem that needs to be managed. Most of the problems for which the spray is effective are cosmetic; in other words, not a big deal. Preventive sprays for aspen likely consist of a fungicide or insecticide mixed with horticultural oil. Other than a fungal disease called cytospora (a disease that attacks stressed trees), aspen pests are going to cause only minor cosmetic problems. See fact sheet Aspen and Poplar Leaf Spots. Preventive fungicide applications are not likely to prevent cytospora infestation. See fact sheet Cytospora Canker). Preventive insecticide sprays on aspen may be helpful in preventing poplar borer, a common and destructive insect of aspen and cottonwood in Colorado. See fact sheet Shade Tree Borers), and also, Aphids on Shade Trees and Ornamentals.

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