Lace bugs

Damage symptoms

Adults and nymphs push their mouthparts in through the pores on the leaf underside and empty the chlorophyll-bearing cells just below the upper surface. That is why the damage shows on top while the insects sit below. UF/IFAS notes that adult females do more damage than males or nymphs. Light feeding looks like fine stippling; heavy feeding bleaches whole leaves, which can dry and drop. UC IPM calls it mostly cosmetic, but UKY adds that repeated years of infestation can weaken a shrub and contribute to its death. Buyers notice it early: in a survey cited by Graham et al. (2020), consumers could see damage on 2% of the leaf surface and rejected plants with 11% of leaves damaged.

• Fine pale stippling on the upper leaf surface, merging into bleached or silvery leaves
• Shiny black, varnish-like spots of excrement under the leaves, often with cast skins
• Black spiny nymphs in groups on the leaf underside in spring
• Leaves that yellow, dry and drop early after heavy feeding
• Damage that is worst on shrubs in full sun and becomes obvious by mid to late summer

Lifecycle & degree days

Azalea lace bugs overwinter as eggs laid in the leaves of evergreen hosts under a dark crust, and the first nymphs hatch in spring. How fast the generations turn over depends on temperature. In Florida lab work, egg to adult took 22–45 days between 20.6 and 31.7 °C, and each female laid more than 300 eggs at 5–7 a day. There are two to four generations a year, and development speeds up with warmth. A western Washington degree-day model (Garrison and Tobin 2022, base 10.2 °C / 50.4 °F from 1 January) puts 5% of the first-generation nymphs out at 69 °C degree days and 50% at 171.

Host crops

The azalea lace bug attacks the heath family, and UF/IFAS singles out evergreen azaleas as the most badly hurt, though deciduous azaleas and rhododendrons are also attacked. Some Rhododendron species resist it, and nymphs develop more slowly on those. Other lace bugs have their own hosts, each feeding on one plant or a few relatives. At least 17 species damage ornamental trees and shrubs in the US. Examples include the andromeda lace bug on Pieris, the sycamore, hawthorn and avocado lace bugs, and in California the Christmas-berry lace bug on toyon.

Monitoring & action thresholds

Check the shrubs weekly from spring into autumn, and start in late winter if they were damaged last year (UC IPM). Early stippling is easy to miss, so turn leaves over and look for black nymphs and excrement spots with a hand lens. You can also tap a branch over a sheet of white paper and look for adults and nymphs. Check shrubs in sunny spots first.