Posted by Kathy Mc on March 21, 19101 at 08:31:21:
In Reply to: Re: Dormant/sulfur spray posted by Maria on March 11, 19101 at 11:04:08:
Hi Maria,
I use dormant oil spray on my roses every year, about this time of year (as weather warms, but before signs of new growth appear). It's a good tool for disease prevention/control. Black spot spores from last season will overwinter into the new growing season. They can reside on leaves from last season, mulch, soil. etc. Once airborne they infect other plants. I treat my roses only once with dormant oil per season.
You say you've tried every fungicide, have you tried a systemic treatment, such as HALTS? It's a powder that you mix and water in. It's rather expense ($10.00/jar), but I've found it to be quite effective for nasty problems. Systemic treatments work from inside the plants, being carried from the roots through the plant to the leaves.
Here are some mold/mildew/black spot prevention tips I got from attending annual J&P; rose seminars. Some organic treatments work best, so we don't overuse chemicals to harm the environment:
*Never water roses overhead. The preferred method is drip from hose.
*When planting, leave plenty of room for air circulation (lack of air circulation is a major contributing factor of mildew)
*Preferably in fall, if not then spring: clear away all leaves from prior season and throw away in a sealed yard refuse bag, to prevent black spot spores from becoming airborne.
*Remove old mulch around the base of the plant and start fresh each spring.
*When pruning in spring, and anytime during growing season, cut back any canes that are in the center of the bush. Ideally, the base of your rose should be shaped like an upside-down bell when pruning is done. (This does NOT apply to climbers.) A general rule of thumb: You should be able to put your arm in the center of the plant and move it freely without getting stuck by thorns.
*When deadheading, always cut back to an outward facing 5 leaf set. This will allow for better air circulation, keeping the center of the bush open.
*Remove any infected leaves at first sight, sealing in a refuse bag.
*When pruning an infected bush, wipe pruners with rubbing alcohol before going to another bush, so as not to spread disease to your other roses.
*Fungicides are best used as a preventative measure, best not to wait for signs of disease to appear. A tip: alternate between 2 or 3 brands, giving treatments of each 7-10 days apart in the active growing season. This prevents diseases from building up "tolerance" to a particular fungicide.
*For aphid/pest control, buy ladybugs and/or praying mantis eggs. They are nature's insecticide.
*Also for aphids: Use a teaspoon or so of dish detergent mixed with water and squirt on aphids.
Hope this helps a bit ;)
-Kathy