Q.How Long Do the Chemicals Stay Effective? Have
Funginex and Malathion that have not been effective on the black spot on roses.
Funginex is an older fungicide for roses that sometimes does not appear effective and may not be if you have had it on the shelf for some time. Keep in mind that once you have black spot, the black markings on the foliage do not just go away. The fungicide can kill the fungus but its nasty marks still remain. The key is that the new foliage should not have any such markings if the fungus has been killed. If black spot has a real hold on the rosebush, I recommend using a product called Mancozeb, it can be purchased from http://www.rosemania.com . It will stop black spot in its tracks! Part of how it works is that it leaves a yellowish powder on the foliage, but it does work. You can mix it with Immunox (another fungicide) to lessen the yellow powder impact on the foliage. I like to use a product called Green Cure first thing in the spring when the leaves first start to come out, to keep the funguses away. The Malathion is not a fungicide it is an insecticide, thus will have no impact on blackspot. It is only to help get rid of some of the bugs that can attack your roses and other plants. Some say it stinks them to death! It does indeed have quite the smell to it!! When I did use Funginex several years ago, it had mixed results for me. Thus I moved on to other products.
