Description
PAN (peroxyacetyl nitrate), an ingredient of smog, damages herbaceous plants mainly on the West Coast. Trees are seldom affected by this pollutant. PAN enters the leaves through microscopic breathing pores causing a characteristic silvering or glazing on the lower surfaces of the leaves. When damage is severe, the injured tissue dies and turns whitish tan. Young, rapidly growing leaves and plants are especially sensitive to PAN exposure. Injury may also occur in bands across the leaf, with each band corresponding to a different exposure. Healthy green tissue separates each band. Plants repeatedly exposed to PAN grow slowly and drop their leaves. Sunscald, frost injury, and damage by mites, thrips, and leafhoppers resemble PAN injury. The most severe injury occurs at midday on sunny days. Plants growing in moist soil in very warm weather (80° to 95°F) are highly sensitive.
Control
Water and fertilize injured plants regularly to help speed recovery. In smoggy areas, select PAN-tolerant plants from the list in Plants Tolerant of Smog (Ozone and PAN).