Which application method is characterized by trunk injection and frill treatments?

The method characterized by trunk injection and frill treatments is indeed the cut-surface application. This technique involves creating cuts or frills on the surface of the tree, allowing the pesticide to be directly delivered into the vascular system of the tree. Trunk injections involve inserting a pesticide directly into the tree's trunk. Both of these methods are effective for targeting specific tree pests or diseases while minimizing exposure to surrounding vegetation and non-target organisms.

Cut-surface applications are particularly useful because they can deliver a concentrated dose of pesticide directly to the affected area, facilitating faster uptake and increased efficacy against pests that may be entrenched in the tree. Additionally, these methods allow for precise targeting, which is essential in forestry management to protect valuable trees while maintaining ecological balance.

Other methods listed do not utilize these direct injection techniques. High-volume ground sprays usually involve dispersing pesticides over a larger area, which is less targeted. Low-volume sprays use smaller amounts of pesticide but still cover broader areas rather than focusing on specific trees. Summer foliage sprays are meant to treat pests on leaf surfaces rather than directly affecting the tree's trunk or core.