WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Alternaria

Alternaria Fruit Rot

(Alternaria species)

Diseases

 

Symptoms

Alternaria fungi can cause fruit rot and leaf spot. The leaf spot is usually not a serious problem, however it will produce spores that cause fruit infections. Leaf lesions are circular to irregularly shaped, tan to gray, 1/16” to 1/4” (1-5 mm) in diameter, and surrounded by a reddish brown border. In most cases only lower leaves are affected, but a severe infection can defoliate the plant.

The surface of the infected berries is often covered with a greenish-black spore mass, making it easy to differentiate from the orange spore mass on an Anthracnose ripe rot-infected berry. On ripe fruit, sunken areas near the calyx are covered by a dark green, velvety growth. On stored fruit, a grayish-green mold may appear on the stem scar or calyx end and spread over the entire berry. Infected fruit becomes soft and shriveled. Infected berries also tend to break open easily.

 

Life History

Alternaria overwinters as mycelium and spores in old, dried-up berries, in dead twigs from the previous season's crop and on other plant debris. Leaf infections occur in the spring during periods of cool, wet weather. Infected tissue produces spores that are transferred to fruit by wind blown rain. Fruit infection may occur before harvest, as berries start to ripen, or during the post-harvest period. Spores can easily spread between stored fruit. Disease development is optimal at 68ºF.

 

Monitoring

During the spring, check for leaf infections if weather has been cool and wet. As fruit begins to ripen, look for a shriveling or caving-in of the side of the berry near the flower end of the berry. Infections have greenish gray mycelium and dark olive-green spores. If fruit infection was severe, watch for leaf symptoms the following spring.

 

Thresholds and Management

Threshold varies according to end product usage and processor. Processors of IQF fruit have zero tolerance for alternaria infected berries. Talk to your buyer for their threshold.

Do not let fruit become over-ripe before harvesting. Minimize wounding or bruising during harvest. Cool fruit rapidly after harvest.

Chemical control should be applied after bloom when fruit is forming.

 

Resources

Michigan State University, Michigan Blueberry Facts, Alternaria leaf spot and fruit rot
http://www.blueberries.msu.edu/alternaria.htm

Michigan State University Extension, Blueberry Fruit Rot Identification Guide
http://web2.msue.msu.edu/bulletins/Bulletin/PDF/E2847.pdf

Oregon State University Extension, An Online Guide to Plant Disease Control, Alternaria Fruit Rot
http://plant-disease.ippc.orst.edu/ShowDisease.aspx?RecordID=175

Secondary content using h2 tag. Column 2

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Heading using the h3tag

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu