Answer: Climbing roses bloom on new stems that grow on old wood. Pruning them back in late winter will encourage new, flowering stems. If you didn't prune, most of the new growth will be at the ends of the main canes instead of lateral stems that produce flowers. Hybrid teas or Grandifloras need to be pruned heavily to encourage bigger flowers. Roses should be pruned in late January or February.
First remove any deadwood down to the nearest healthy bud
eye. Make the cut at least an inch below the dead area. If no live buds remain, remove the entire branch or cane to the bud union.
Cut out weak, spindly and deformed growth. This includes canes that grow straight out, then curve upward (called doglegs). Remove old canes. Old canes are thick and woody, and produce a profusion of twigs rather than strong stems.
Remove all suckers or reversion growth (undesired shoots that come from the rootstock below the bud union). Sucker foliage is different in color and form from the foliage of the rest of the plant. If you do not remove suckers, they will soon be dominant. When cutting them out, take all the sucker base from the crown area along with a piece of the crown, if necessary.
Next, thin out the remaining healthy canes to the shape you want and cut them back to the height you want. Always cut back to an outside bud.
The dusty coating you mention is probably powdery mildew, a fungal disease. By properly pruning you'll open your plants up to better air circulation and more sunlight, which should discourage development of the disease.
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