If the spots appear as reddish-brown pustules (lesions) with spores (reproductive structures) that will deposit on the hands when rubbed, it is probably a fungus disease called asparagus rust, which is caused by Puccinia asparagi. Another fungal disease with similar symptoms is Cercospora leaf spot caused by Cercospora asparagi, which also causes reddish-brown lesions on the asparagus foliage followed by needle drop and possible dieback in young plants.
The most effective way to control asparagus diseases is to plant resistant varieties. Disease problems can be reduced by providing conditions for vigorous growth; in fall, remove asparagus foliage and compost. Avoid wetting the foliage when watering. Fungicides sprayed weekly after harvest until late summer can be used to prevent infections. Check home vegetable fungicide labels for rates. Contact your local Extension office for fungicide recommendations.
