Plant Pathology Infobytes

November 20, 1998
End-of-Season Strategies for Rose Disease Control

As any devoted Rosarian will tell you, a great looking rose garden doesn't just happen. A lot of plain old hard work is required. Plants have to be fertilized and watered, pruning is required, weeds, insects and diseases have to be controlled, and occasionally, a replacement bush will have to be added to the planting. The task list can be pretty long, but the rewards can be great, since there is a lot of personal satisfaction in growing roses.

One area where attention to detail really pays off in rose growing is disease control, and Rosarians who maintain healthy plants generally use a combination of common sense strategies to keep black spot, canker, powdery mildew, and other diseases under control. The following disease control practices can be carried out this fall and will add to the appearance of your rose garden next season.

Black spot and powdery mildew can be reduced another year by carrying out a sanitation program. This refers to removal of fallen leaves and carrying out recommended pruning procedures before next spring. If you aren't sure about pruning, check with the County Extension Office for a publication on "Rose Growing in Mississippi."

Removing fallen leaves is especially critical in reducing black spot (sometimes referred to as "rose public enemy number one). This chore will cut back on the amount of fungus present in the rose garden next spring. The black spot fungus easily over-winters in fallen leaves, so it just makes good sense to remove diseased leaves from beneath your plants. This will help with other disease microorganisms which also maybe be present on fallen leaves.

While you're in the rose garden, take the time to prune-out canes killed by brown stem canker. This disease also carries over and cutting out (and proper disposal) of those canes killed by this fungus disease is part of a rose health care program. Be sure to cut the dead cane back to sound growth, and don't forget to disinfect pruning tools between cuts to prevent spread of plant disease microorganisms. Rubbing alcohol, or 10% bleach solution (prepared by adding one cup of household bleach to nine cups of water), are good common disinfectants. If you use bleach, thoroughly rinse pruners with water (followed by a good oiling), since bleach is often corrosive.

Later this season, after we've had a spell of cold weather and your roses are dormant, give some thought to mulch replacement. This is particularly true if black spot has become a problem. While removal of diseased leaves will help, mulch removal and replacement may also be necessary as part of your overall rose disease sanitation program.

If new roses are added to your planting, use recommended varieties. Some varieties are advertised as "black spot resistant," and while these probably will suffer less black spot damage, no variety completely escapes this disease in the humid mid-South.

Since periods of heavy dew fall, rainy weather, and high humidity favor development of black spot and other fungus diseases, add any new plants to your planting at recommended spacing distances to insure adequate air circulation in the growing season. Plants which are planted too closely don't dry quickly following rainfall and are vulnerable to black spot attack.

What about dormant sprays? This can help with rose disease control, especially powdery mildew. You'll hear more from the County Extension Office later in the season about this topic, as well as the need for collection of soil samples for fertility analysis (well-fed roses are more resistant to diseases).


Written by the late Dr. Frank Killebrew

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