Corynespora blight

Corynespora blight (Corynespora cassiicola) is a plant pathogen.

Cucurbits
The fungal disease is most damaging to cucumber and cantaloupe but may occur on other cucurbits. Lesions on leaves begin as small, watersoaked spots delimited by small veins, but soon enlarge to form large, circular, sometimes zonate spots that range from tan to dark brown in color. As the spots enlarge, the entire leaf turns yellow and dies. Fruit are not attacked.

Tomato
On leaves, the disease first appears as small, necrotic lesions with light-brown centers and dark margins. Symptoms often begin deep within the tomato canopy. On fruit, lesions first appear as brown, slightly sunken flecks. As lesions develop, large, pitted areas appear on fruit.

Non-chemical
Destroy crop residues promptly.

Chemical
New chemistries, including the strobilurins and related compounds (e.g., azoxystrobin and famoxadone + cymoxanil), have given excellent control of target spot in University research trials.

Non-chemical
Avoid overfertilization, especially with nitrogen, as this leads to a lush growth habit, with more likelihood of significant “melting out”. Be certain that fields are scouted thoroughly and that target spot is not misdiagnosed as bacterial spot, early blight, or other foliar diseases. Glasshouse should be decontaminated with a sterilant between crops and good ventilation should be maintained to keep the humidity low during the cropping season. No known resistance to target spot is currently available in commercial cultivars.

Chemical
Chlorothalonil and mancozeb (maneb) provide fairly good control of target spot when applied on a preventative basis.