Angular Leaf Spot

Need To Know 

• Common bacterial disease of pumpkins and other cucurbits. 
• Signs of infection are water-saoked angular leaf spots and yellowing of leaves. 
• The disease expands during rainy weather and temperatures in of 75 to 82 degrees F. 
• Use disease-free seed, avoid handling wet plants, and rotate crops to manage angular leaf spot. 

Overview of angular leaf spot

Angular leaf spot is a common bacterial disease of pumpkins and other cucurbits that causes chlorosis and necrosis (death) of leaf tissue.

Symptoms of angular leaf spot

Symptoms of angular leaf spot usually first appear as water-soaked lesions bound by the veins of the leaf, so they are angular in shape. As they progress, the lesions may turn yellow and then brown and the leaf tissue may tear. Lesions may have yellow haloes. During wet weather, bacteria may ooze from the spots and later dry to a white residue.chlorosis (yellowing) of the leaves.

Signs of angular leaf spot

During wet weather, bacteria may ooze from the spots and later dry to a white residue.

Not to be confused with Cucurbit anthracnose.

Disease cycle of angular leaf spot

The bacterium that causes angular leaf spot, Pseudomonas syringae pv. lachrymans, can enter the leaf through the stomates (breathing pores), hydathodes (water-excreting pores on the edge of the leaf), or wounds in the leaf tissue.

Angular leaf spot is favored by rainy weather and temperatures of 75 to 82 degrees F. High nitrogen levels also favor the disease.

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents.  If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us. 

Want to submit a sample? Follow the instructions at submitting annual herbaceous plants page.

Management of angular leaf spot

Angular leaf spot can be managed by using disease-free seed. Some resistant varieties of cucumber are available. Crop rotation helps to lower inoculum levels. Avoid handling plants when they are wet, and limit overhead irrigation. Copper compounds can be applied preventatively before symptoms appear, and every 5-10 days during weather that favors disease. Insecticides may also be used to manage insect pests, which may cause wounds that serve as entry points for the bacteria.

Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.