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All about raspberries


Sun, Sep 24th, 2000
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Diseases of Raspberries By Virginia CooperMonday, September 25, 2000

There are two kinds of diseases that commonly infect raspberries, the serious and the not-so-serious. Of the serious kind, we have anthracnose, cane blight, spur blight and botrytis fruit rot (grey mold). The not so serious list includes: phytophthora root rot, powdery mildew, rust fungi, leaf spot and verticillium wilt. This list sounds pretty imposing but we can break it down and make it simpler.

All of these diseases listed so far are fungal, carried by spores over wind or wintering over in soil. There are three uncommon but potentially damaging viral diseases including raspberry mosaic, leaf curl and tomato ringspot. Viral diseases are carried by insect vectors. Todayís discussion will focus on the fungal diseases.

Before we get to symptoms, letís get a better understanding of how the raspberry grows. There have two kinds of canes, primocanes and floricanes. Primocanes are the first stage of growth with green shoots that mature to grow only leaves. Floricane refers to the second year in the life of the raspberry cane, with leaves, flowers and fruit.

Now, serious symptoms to watch for include checking primocanes in late spring for purple-red lesions, center of lesions turning gray, leaf margins becoming raised and purple. Lesions will girdle canes and cause cane death. This indicates anthracnose and should be treated by total removal of all infected canes.

Primocanes are susceptible to spur blight. Symptoms include lesions that surround the nodes (the point where the leaves join the cane), lesions are brown with yellow margins and cause leaves to fall. It doesnít kill the cane but next years buds will fail. Again, remove all infected canes.

Cane blight is usually seen on wounded or damaged canes. Usually not visible till floricane stage, lesions can be black, brown or grey and cause rapid wilting and death. Canes will be brittle and often break near the lesion.

Grey mold is very common and very serious, especially in cool, wet years. Infection begins on flowers but usually isnít seen until fruit develops grey or brown fuzzy mold. Damaged, bruised or wounded canes are more susceptible. Total removal of fungal material is critical.

Of the not so serious diseases we have rust, leaf spot and powdery mildew. Problems are mostly cosmetic and are remedied by good cultural practices. Root rot has potential to be serious but is rare. Symptoms may be a dark water-soaked appearance near the base of the cane. Over-watering or planting in a poorly drained site are common culprits. Verticillium wilt can also be serious, but usually only amounts to wilting and stunting of a few floricanes, if you suspect wilt, cut into sapwood, it will be stained red-brown.
Control of fungal diseases will always be by following good cultural practices: start with disease free plants from a reputable nursery. Raspberries need well-drained soil; avoid overhead watering, over-fertilizing and wounding plants. Keep weeds down and remove all abandoned or wild brambles nearby as these can harbor disease. Remove any diseased canes and also remove old fruiting canes after harvest. Canes should be burned or landfilled to prevent the spread of spores.

As always, if you need extra help in diagnosing your plant problems, call the Extension office and ask to speak to one of our counties knowledgeable Master Gardeners. Itís the end of the year and we need to get our hours in....

Virginia Cooper gardens and writes from her farm in Mabel. She can be reached at the Extension office at (507) 765-3896, or via email:virgcoop@yahoo.com

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