HomeStrawberriesStrawberries: Angular Leaf Spot

Strawberries: Angular Leaf Spot

Angular leaf spot

The bacterium Xanthomonas fragariae causes an infection that starts off as small, angular, dark green ,”water-soaked” spots on the undersides of leaves.

Strawberry leaf underside with muddy appearance, caused by many brownish, wet-looking spots. Spots are scattered across leaf like a mud splatter. One leaflet is almost entirely brown, one leaflet has a large brown area on one half and only a few speckles on the other half. The third leaflet is evenly scattered with many disparate speckles.

Strawberry leaf with brown speckling across its surface. Speckles are small, but merge along veins to form long lines of discoloration. The discoloration is not present on top of leaf veins.

The angular spots between the veins are visible with top lighting …

Top lighting on strawberry leaf mottled with red and dark green spots. Spots have sharp edges and are distinctly non-spherical.
Top lighting on strawberry leaf infected with angular leaf spot (Xanthomonas fragariae).

…and back lighting.

Back lighting on strawberry leaf mottled with red and translucent green spots. Spots are distinctly angular in shape, with sharp edges and square or trapezoid shapes.
Back lighting on strawberry leaf affected by angular leaf spot (Xanthomonas fragariae). Note the translucent “windowpane” effect.

Eventually these coalesce, and the leaf appears scorched.

Close-up of strawberry leaves that appear shriveled and discolored. Many brown-colored spots are scattered across the leaf, often bordered by yellow tissue. Many spots spots have merged to form large necrotic areas along the leaf margins. The tissues closest to major leaf veins, particularly at the base of the leaf, are still green.
Photo courtesy of Kathleen Demchak, Penn State University.

Note: There are several methods to differentiate angular leaf spot from leaf scorch.

The presence of angular lesions between veins on the lower sides of leaves is indicative of angular leaf spot. These symptoms are not caused by leaf scorch.

Strawberry leaf with large necrotic center surrounded by yellow tissue marked with red spots.

Strawberry leaves with red spots visible on outer edges of leaf surface. Individual spots are about the size of a pin-head, but some have merged to form a reddish patch on a leaf tip.

Sometimes strawberries can be attacked simultaneously by leaf scorch fungus and angular leaf spot bacteria. It is hard to distinguish between scorch  and angular leaf spot  when viewing leaves from above. Holding leaves up to the light contrasts the “windowpane” effect of angular leaf spot to the dark spotting caused by scorch.

Brown and red spotting on two lobes of strawberry leaf. The right lobe has yellow and red discoloration and is slightly more colorful than the left lobe, which has only purple-brown discoloration. The spots on the left lobe are slightly more spherical in shape than those on the right.
Leaf scorch (Diplocarpon earlianum) on left, and angular leaf spot (Xanthomonas fragariae) on right. Photo courtesy of Kathleen Demchak, Penn State University.

 

Underside of strawberry leaf held up to the sun. Sunlight shines through the right lobe, creating "windowpanes" with yellowish and red color. The lesions on the right half of the leaf do not transmit any light and appear deep reddish-purple..
Leaf scorch (Diplocarpon earlianum) on left, and angular leaf spot (Xanthomonas fragariae) on right. Photo courtesy of Kathleen Demchak, Penn State University.

Sepals or “caps” may also be infected by angular leaf spot.

Green strawberry fruit with uniformly grayish-brown cap.
Photo courtesy of Kathleen Demchak, Penn State University.

Use these resources if you need additional help with diagnosis and to find solutions to your problem.

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Use these resources if you need additional help with diagnosis and to find solutions to your problem.