Ascochyta Blight (Wet Weather Blight)

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Symptoms of Asochyta Blight on cotton leaf. Note dark border and also small, embedded fruiting struc-tures in the spots.

Caused by: Ascochyta gossypii (Phoma exigua)

Foliar Symptoms: Ascochyta Blight forms lesions on cotyledons, leaves, stems, and bolls. Lesions on the cotyledons and leaves approach 2 mm (<0.1 in) in diameter, are white to light brown and circular in shape. Elongated can-kers on the stem are reddish-purple to black or ash gray in color. Small, black fruiting structures are likely to be embedded in symptomatic tissue.

Diagnostics Note: Margins of necrotic regions on leaves and cotyledons will have dark borders. Spots may have a target-like appearance. However, Ascochyta Blight typically occurs early in the season and small black fruiting structures are observed in the lesions.

Range and Yield Loss
Ascochyta Blight has been reported in most major cotton producing regions. Yield loss is rarely reported, but is possible under conditions such as prolonged cloudy weather with cooler temperatures and rainfall.


Use fungicide treated seed, avoid planting in cool wet weather, and incorporate cotton residue to encourage decomposition, which helps in fields with a history of Ascochyta Blight.

 


Photo Gallery:

 

Symptoms of Asochyta Blight on cotton leaf. Note dark border and also small, embedded fruiting struc-tures in the spots.

Early-season symptoms of Ascochyta Blight on coty-ledons of cotton. (Photo credit S.M. Brown).