There are two crucial tasks that should be done throughout the year in the rose garden: monitoring for the first sign of disease and pests, and garden sanitation. Every time we cut out, pick up and dispose of infected leaves and petals, we are reducing disease and pest infestation in the garden.
Time spent doing these tasks is well spent, and it brings great paybacks. Here are the issues to turn your attention to:
Botrytis damage to the bloom can range from pink spots on petals to a mass of gray mold. Botrytis is a saprobe, which means it can nourish itself and multiply on live or dead plant material. Spores reproduce quickly and infect other uninfected blooms, so it is imperative to remove affected blooms and fallen petals promptly. A wound to the cane can open an entry for spores that can cause dieback; prune it out.
Blackspot survives on and uses fallen dead leaves as a reservoir for new infections. The conidia (spores) splash up and can infect new living tissue when they have seven hours of wet conditions. An infection in your roses during this year’s rainy season is very likely a continuation of the blackspot breakout you saw last year.
Part of the lifecycle of this fungus is entirely within the leaf. But after about a week to 10 days, the fungi produce numerous small black fruiting domes that each contain thousands of new spores, the spreading agents of the infection. With the release of the spores come a thousand reasons why infected leaves must not remain in your garden.
As with treating the other water-induced fungi, lessen humidity around plants, remove infected leaves on the bush as soon as they appear and dispose of fallen leaves around the plant to reduce spreading disease to other susceptible roses.
Rose rust fungi only grow on live tissue, but they make overwintering structures that survive in leaf debris. In the spring, spores blow or splash up onto newly emerging rose foliage and can germinate with conditions of two hours of moisture.
Cut out leaves with rust pustules rather than pulling them off — doing the latter disperses the spores onto other leaves, into the air and onto the soil. Removing fallen leaves is a must, and so too is a thick layer of mulch laid down after your winter pruning and cleanup.
Powdery mildew infection starts on the surface of the plant, so infection can be reduced by a high-pressure spray of water early in the day to remove spores that haven’t yet imbedded themselves into the leaf. Alternately, cut out infected leaves. Monitoring sanitation throughout the year reduces spores during this and the next growing season.
A number of insect pests overwinter in the soil at the base of the rosebush, and others leave their eggs in the debris of old leaves. By learning about their habits and life cycle, and by…