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| So, I have some ideas for organic fungicides, specifically for blackspot. But I don't want to just spray them and see what happens. I'd rather do something slightly more scientifically rigorous, so I can at least provide a credible anecdote. I'm really not sure how to go about doing this though.
For example, how can I purposely infect several roses with blackspot so that I'm *sure* that they have exposure to the disease at the same time? Is there an easy way to test fungicidal activity on a blackspot infected leaf removed from the plant, or is this best left to laboratories that can culture the organism? Just fyi, my first two tests are going to be turmeric (powder) and ginger (powder) dispersed in water. If I can summon the motivation, I may also try cold extracts of fresh ginger and fresh turmeric root, as these actually have better scientific evidence as far as use against plant pathogens. |
Follow-Up Postings:
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| Unless you can take samples and grow them in petri dishes, black-spot whether dead of not does not disappear. It simply stops spreading which is why one should, or at least I do pick off all affected leaves. If it is gone you will know it. If it is not you will see it. |
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| To inoclulate plants with blackspot, gather blackspotted leaves from several different infected plants (because they may carry different strains of BS), liquify in a blender with water, strain, dilute, and apply the liquid with a sprayer set to a coarse spray. If it clogs, unscrew the nozzle cover and use a toothpick. If you want active infection, apply in the evening when it will stay wet for 10-12 hours at temperatures between 60 and 78. Researchers do use detached leaves in controlled studies. The procedure is described in many research articles--for example you could look at the great doctoral diss. by Emma Gachomo which is on the open web. |
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- Posted by mike_rivers z5 MI (My Page) on Wed, Jun 13, 12 at 14:19
| I think the primary requirement for coming to reliable conclusions is the use of control plants. Ideally, you would use plants of the same variety and located at random among the plants receiving the fungicide spray. These control plants would receive the same treatment, including any inoculation with blackspot spores, except they would be sprayed with water instead of with the fungicide. Your conclusions would be based on comparing some measure of blackspot infection among the control versus the fungicide-sprayed plants. |
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- Posted by mad_gallica Z5 Eastern NY (My Page) on Wed, Jun 13, 12 at 14:28
| This is the problem I have with most anecdotal claims of blackspot control. The tests are done under circumstances where a control plant would not be seriously infected, either because of the climate conditions, or the rose variety. I've heard it referred to as 'elephant repellent'. It must work because I've never seen an elephant in my backyard. |
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- Posted by henry_kuska z5 OH (kuska@neo.rr.com) on Wed, Jun 13, 12 at 15:01
| mad_gallica, that is why the use of "control plants" is recommended. If they do not get blackspot either, the test is not definitive. |
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- Posted by greentiger87 none (My Page) on Wed, Jun 13, 12 at 19:26
| Yes, I definitely am going to use control plants. But theoretically at least, I could have roses of the same variety right next to each other, and have only one get blackspot - so I need to make sure both are infected. I'll do as michaelg suggests and wait for the first signs of blackspot on the lower leaves before I start spraying. I'm kind of excited! Hopefully I can get some plants cheaply since it's so hot right now, and have them growing in time for the early fall blackspot wave. I'll let you guys know how it goes! |
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