Downy mildew—Peronospora sparsa
Downy mildew initially causes a yellow discoloration on the upper leaf surface that progresses to red
and purple. Lesions are often angular, restricted by veins. Light pink to tan areas and white spore masses
may be present on the lower leaf surface. Leaves may show a mosaic of small yellow and red angular lesions
as well as distortion. Fruit is dry, shriveled, and split.
The downy mildew fungus overwinters in roots and shoots and grows into new growth in spring. If possible,
avoid planting in sites with a history of the disease. Roses and wild blackberries are alternate hosts
for the disease. Once the planting is established, remove suckers and weeds to reduce humidity at the
base of the plant. Remove affected plants and destroy old fruited canes after harvest. Copper
sprays may be applied to protect developing fruit, flowers, and foliage from infection when conditions are wet.
blotched of mildew along veins
symptoms on boysenberry