3/10

Black Spot

Problem: Black spot is a fungal disease commonly found on roses, but also on other flowers and fruits. While it doesn’t kill plants outright, it weakens them and makes them susceptible to other problems. In cool, moist weather, small black spots appear on foliage, which starts to turn yellow and eventually drops off.

Solution: The fungus overwinters in diseased canes and leaves, so remove both before winter. Keep foliage clean and dry by mulching beneath plants, positioning roses where the morning sun will quickly evaporate dew, and watering at the roots rather than wetting the foliage. Consider planting varieties of roses that are resistant to black spot. Plants also can be sprayed with a fungicide to prevent black spot.

4/10

Mosaic Virus

Problem: There are a number of mosaic viruses, but gardeners are most likely to encounter two: tomato mosaic virus and tobacco mosaic virus. The former infects tomatoes, peppers, potatoes, apples, pears and cherries; the latter infects tomatoes, peppers, cucumbers, lettuce, beets, petunias and, of course, tobacco.

Mosaic virus causes mottled yellow and green leaves that are sometimes curled and distorted. Some plants exhibit yellowing, stunted growth, malformed fruits and reduced yield. Mosaic virus is more common in hot weather.

Solution: There are no chemical controls, but resistant varieties exist. The virus can live in dry soil for some time. Remove and destroy infected plants, roots and all, and avoid planting susceptible plants in the same area for two years. Because tobacco is a carrier, smokers should wash hands thoroughly before handling plants.

5/10

Damping-Off Disease

Problem: Damping-off disease, caused by several soil-borne fungi, is most problematic in wet, humid conditions. It infects seedlings and causes them to collapse and decay. It’s often found in greenhouses but can occur outdoors as well.

Solution: There is no treatment, but you can prevent it with good cultural practices. Use new pots, cell packs or trays, or those disinfected with a 10 percent bleach solution. Fill with fresh, bagged, soilless potting mix, avoid crowding seedlings and provide adequate ventilation.

Damping-off disease usually affects newly-sown plants.