Knockout Rose Fungus

History

• The knockout rose is a shrub which a Wisconsin man originally created. He wanted a rose that could survive cold temperatures and which would be less prone to a common rose fungus, black spot. Because this is one of the primary features of the knockout, they are much less likely to suffer from this disease. However, it is not impossible for knockouts to become diseased.

Black Spot

• Black spot is a fungal disease which weakens rose plants to the point that they bloom less and are less able to combat the cold. This is especially damaging to knockouts, which are often grown in colder climates due to their hardiness. Knockouts are at risk for this disease if they stay wet for eight hours or more. Symptoms include yellowing leaves and tiny black spots.

Mildew

• Another fungus which can affect knockouts is powdery mildew. As the name suggests, knockouts affected with this disease look like they've been powdered with spots of mildew. The mildew is caused by a deficiency of sunlight. It can affect rose health and growth, so it is important to treat powdery mildew as soon as possible.

Treatments

• Luckily, treating knockouts for both black spot and powdery mildew is fairly simple. In each case, you should remove any leaves or blooms that look yellow or damaged, or that seem infected in any way. After this, spray the plant with a fungicide appropriate for whichever disease you're trying to cure. You can also make sure that all plant debris (leaves, etc.) is clear of the area, as this often provides a breeding ground for fungi.

Climates

• All knockouts are susceptible to these diseases, but those in some climates are at higher risks than others. Because of the nature of fungus, knockouts grown in warm, humid climates are more likely to develop problems. However, since the diseases make knockouts less likely to survive the winter, those in colder climates which do get diseased are at more risk of serious consequences.