Angular Leaf Spot

Encyclopedia Article

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.

Signs and symptoms of angular leaf spot

Samples often present showing marginal chlorosis (yellowing) of the leaves. The combination of symptoms and the presence of the bacteria in the sample is indicative of a bacterial disease. 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. The combination of symptoms and the presence of the bacteria in the sample is indicative of a bacterial disease. 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. The combination of symptoms and the presence of the bacteria in the sample is indicative of a bacterial disease. 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. The combination of symptoms and the presence of the bacteria in the sample is indicative of a bacterial disease. 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.

Pumpkin leaf affected by angular leaf spot. The causal bacterium has entered the leaf through the hydathodes (pores on the edge of the leaf), causing marginal yellowing. Photo by Dan Carlson.
Pumpkin leaf affected by angular leaf spot. The causal bacterium has entered
the leaf through the hydathodes (pores on the edge of the leaf), causing marginal
yellowing. Photo by Dan Carlson.

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 you 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

 

Angular leaf spot
Angular leaf spot symptoms 

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.

 

 

 

Category: