White apple leafhoppers (WALH) and rose leafhoppers (RLH) feed on the underside of leaves producing small, whitish spots on the upper leaf surface. This "stippling" may cover the entire leaves and appear silvery. Leafhopper feeding can reduce tree vigor, but of more concern is the accumulation of LH excrement on apple surface. The LH leave dark, "tar spots" and is difficult to remove.
Potato leafhoppers (PLH) do not overwinter in here, but migrate north with summer storms, usually reaching New England in mid June. PLH feed primarily on immature leaves and actively growing shoots in outer part of canopy. Leaves injured by PLH feeding turn yellow on edges, cup upward, and later turn brown or scorched. On mature trees, PLH damage may not be significant, but feeding on young trees stunts shoot growth.
- WALH overwinter as eggs beneath tree bark. Hatching begins just before Bloom and is completed in 10-14 days. Nymphs migrate to leaf underside and feed, advancing into adults by mid-late June. These adults deposit eggs on leaves in July which hatch in early August, producing adults in August and September.
- RLH overwinter on rose species such as cultivated and multiflora rose. First generation RLH adults migrate into orchards from nearby multiflora rose in early-mid June. Second generation adults, present in July and August, deposit eggs mostly in orchards. In September, 3rd generation adults can cause extensive excrement spotting of fruit and be a nuisance to pickers before emigrating to rose bushes to deposit overwintering eggs.
- WALH and RLH adults look similar, but large nymphs of the two species can be distinguished with a handlens. RLH nymphs have rows of small dark spots on their backs. Timing can also be used to distinguish the 2 species. LH found during Petal Fall are most likely WALH.
- PLH nymphs and adults are pale green. When disturbed, nymphs move rapidly in a sideways fashion.
- To monitor WALH and RLH, check 10 interior fruit cluster leaves per tree on 10 trees per block. Tentative treatment threshold is 3 WALH or RLH nymphs per leaf in June. However, growers who have had troublesome LH populations at harvest may want to use a lower threshold of 25 nymphs per 100 leaves in June.
- For PLH, sample the youngest shoot leaves in outer canopy. Tentative threshold of one PLH per leaf.
- LH have developed resistance to several insecticides. Insecticides are most effective against young nymphs. Older nymphs and adults are usually less easily controlled.