When is the best timing for contact insecticides for boxwood leafminer?

When is the best timing for contact insecticides for boxwood leafminer?

• A. When adults are first observed in early spring.
• B. In mid-summer after leaves have fully expanded.
• C. In late autumn after leaf drop.
• D. In mid-winter when temperatures are low.

Answer: (A)

Target the stage that is exposed to the spray. Boxwood leafminer adults emerge in early spring and lay eggs on new growth; the larvae, which cause most of the damage, develop inside the leaves and are protected from contact sprays. Spraying when adults are first observed kills them before they lay many eggs, reducing the number of larvae that will hatch and begin tunneling. If you spray later in mid-summer, the larvae are already inside the leaf tissue, where contact insecticides can’t reach them, so the control is much less effective and you may need repeated applications. Autumn, winter, or periods of low activity are ineffective because there’s little or no active pest on the plant to contact. So, the best timing is early spring, as adults first appear, to intercept the next generation at the surface.

Target the stage that is exposed to the spray. Boxwood leafminer adults emerge in early spring and lay eggs on new growth; the larvae, which cause most of the damage, develop inside the leaves and are protected from contact sprays. Spraying when adults are first observed kills them before they lay many eggs, reducing the number of larvae that will hatch and begin tunneling. If you spray later in mid-summer, the larvae are already inside the leaf tissue, where contact insecticides can’t reach them, so the control is much less effective and you may need repeated applications. Autumn, winter, or periods of low activity are ineffective because there’s little or no active pest on the plant to contact. So, the best timing is early spring, as adults first appear, to intercept the next generation at the surface.