Boxwood mite

About

A spider mite about the size of a printed period that feeds only on boxwood (NC State). Its damage is often noticed, but the mites themselves are rarely seen.

Spotting it

Damage

Unlike most spider mites, it feeds on both sides of the leaf, leaving tiny pale lines that look like fine scratches, especially on new growth. Leaves can look speckled, yellowish or bronzed and may drop early (NC State, Rutgers).

How to find it early

In spring, look at new leaves with a hand lens for fine, scratch-like pale lines and tiny gray mites (NC State).

When

Mid-spring through early summer, sometimes again in late summer.

Life cycle

Yellowish eggs laid on leaves and twigs in September and October spend winter there and hatch in mid-spring. A generation takes about 18 to 21 days, so there are at least eight a year; mites are busiest in late spring and early summer and may pick up again in late summer (NC State, Rutgers).

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Go easy on nitrogen Prevent

   Keep boxwoods healthy and unstressed and avoid nitrogen fertilizer, which favors mites (Rutgers).

2. Prune and clean up By hand

   Prune off badly infested shoots and remove clippings and fallen leaves (Rutgers).

3. Natural enemies Natural enemies

   Lady beetles, lacewings and predatory mites eat boxwood mites (Rutgers).

4. Insecticidal soap or horticultural oil Organic spray

   In spring when mites are present, spray insecticidal soap or horticultural oil twice, 10 to 14 days apart (NC State). A 2 to 3% dormant oil hits the overwintering eggs; if you find mites later in the year, spray oil then and again the next spring (Rutgers, NC State).

   Oil can harm bees it hits (PNW 591); spray when bees are not flying. Follow the label.

Plants it goes after

Boxwood

Pressure by region

Ratings are estimates based on where boxwood is common.

Ratings come from extension sources where available; some are estimates, as noted above.