ROSE FUNGI
HOW TO PREVENT & CONTROL MAJOR ROSES DISEASES of SPRINGTIME
Worldwide roses are one of the most popular flowering plants, cherished by avid rosareans and casual gardeners alike. Unfortunately, roses are sometimes afflicted with diseases that damage their aesthetic appeal. We have put together some tips to help battle these common problems. As with most things in life, the best control is a good defense.
DOWNY MILDEW usually occurs in late winter and early spring in years with heavy rain. An air-born fungus, downy mildew is first apparent as irregular shaped purple to purple-brown, tan or even bright pink spots on the leaves. At this early stage its difficult to distinguish from other fungi problems. If weather conditions are right the plant will yellow and drop leaves. A white downy fungus may be seen on leaf undersides.
As with other fungus diseases, certain varieties will be more susceptible to downy mildew. It can appear almost overnight and severe outbreaks can take off before preventive steps can be taken.
- Keep rose beds clean from all leave litter, spores can over winter in leaves.
- Space roses so that bushes have good air circulation. Try not to let the bushes touch each other.
- Water at a time of day that will promote the fastest drying time and avoid watering overhead if possible.
- Apply fungicides preventively and repeat. Always read labels to make sure you apply at the correct rate on the correct interval.
BLACK SPOT is considered by many to be the most serious disease of roses. Symptoms are circular black spots with indistinct or jagged margins that are frequently surrounded by a yellow halo. This fungus is spread by splashing rain or when watering and allowed to sit for 6 hours or more. Leaf spots develop within 5 to 10 days.
- Water at a time of day that will promote the fastest drying time and avoid overhead watering if possible. During the hot summer days watering on the leaves may burn them.
- Remove all infected leaves that have dropped, and do not compost this material.
- You may have to apply fungicides weekly during warm, rainy months. Always read labels to make sure you apply at the correct rate on the correct interval.
BOTRYTIS BLIGHT affects roses at all stages most commonly during early spring. They start as translucent spots that look like blisters or sunken area which turn tan and have a dark margin. This then becomes worse under ideal conditions becoming a mass of gray-brown powdery spores.
- Remove any dead flowers and leaves. Prune dieback on canes.
- Feed roses with a fertilizer with a calcium additive.
- Do preventative spraying and rotate over time to avoid fungicide resistance. Always read labels to make sure you apply at the correct rate on the correct interval.
POWDERY MILDEW is found on young leaves, shoots and buds and occasionally on fully opened flowers. Stunted and distorted growth is also a telltale sign. Usually wind-borne powdery mildew is difficult to eradicate completely when conditions are optimal.
- Check roses regularly, and prune infected parts and place in garbage; do not compost.
- Again when growing roses to give proper spacing for good air circulation.
- Avoid overhead watering and water during the time of day that would promote fastest drying time.
- Do preventative spraying. Always read labels to make sure apply at the correct rate on the correct interval.
ROSE RUST is one of the most easily recognized diseases because of the bright yellow or orange pustules on leaf undersides. Long, narrow orange spots may be found on young canes and sepals as well as leaves. Rust spores spread through the air in temp. between 65 and 70F. Standing water on the leaves helps it germinate, so again plant spacing and irrigating correctly is important.
- Check roses regularly and keep rose beds clear of leave litter.
- Water during the time of day that would promote fastest drying time.
- Rotate between types of fungicide used to avoid developments of resistance.
