Stemphylium Leaf Spot

On parsley initial symptoms of Stemphylium leaf spot consist of small (1/8–1/4 inch or 3–6 mm diameter), circular to oval, gray-green leaf spots. As the disease progresses leaf spots enlarge and turn tan in color. Older spots coalesce, dry up, and become papery in texture. Visual signs of fungal growth are generally absent from the spots. On parsley, Stemphylium leaf spot can be confused with bacterial leaf spot and late blight (Septoria) diseases.

Stemphylium leaf spot is a cool-season foliar disease. Cool temperatures (60° to 70°F) and moist weather favor infection and spread. The disease is usually found in first and second cuttings. Because defoliation occurs only under heavy disease pressure, Stemphylium leaf spot is not considered as serious as some other leaf spot diseases. Following a parsley harvest, loose, cut debris falls onto the plant crowns; if such debris is diseased, the subsequent re-growth may be exposed to Stemphylium inoculum however future plantings will not be affected after infected residue has decomposed.

To prevent disease development:

• Avoid planting back-to-back parsley, especially if the first crop had significant disease.
• Use irrigation systems (furrow or drip irrigation) that eliminate splashing of water.
• If sprinkler irrigation is used, irrigate in the morning instead of at night, so that the canopy dries rapidly, thereby minimizing duration of leaf wetness.
• Curly leaf cultivars typically have less severe symptoms than flat leaf varieties.

Use cultural controls in an organically certified crop.

Pesticides are not effective against Stemphylium leaf spot of cilantro and parsley.