Suggestions for a good fungicide for Black Spot Disease that can be sprayed when the temperatures are above 80 degrees.
Bayer Disease Control for Roses (etc.) containing only tebuconazole. It works and doesn't burn.
Betty, I'm with Michael. In both hot hot Texas and here I have relied on Bayers Disease Control. Our temps are above 80 virtually the entire growing season!
Note I do N O T recommend Bayers 3 in 1.
Thanks Barbara and Michael. I have 30 roses and the temp in Louisville Ky were over 100 degrees for many days last summer, and I stopped spraying and boy did I get Black Spot. This year I will get Bayer Disease Control and stay on top of the spraying.
That's what I use also. When the temps are over 100 though, I find that I don't need to. Our summer baked last year and there was no rain, so I don't think I sprayed at all in July & August. I think everyday in August was over 100.
Once every two weeks is enough with the Bayer tebuconazole product.
Blackspot can spread in very hot weather if you have a thunderstorm in the evening that lowers temperatures into the 70s, allowing germination. Barring that, many people have found they can cut back on spraying during brutally hot weather.
I have been using Serenade, much cheaper if you buy the large commercial containers, and have had very good luck with it against black-spot plus it seems to work well for many squash, tomato and such problems also.
It is my understanding that the state of New York has taken the following action: "When used as labeled, this product could cause unreasonable adverse effects to humans. The Department hereby denies the application to register Bayer Advanced Garden Disease Control for Roses, Flowers, and Shrubs Concentrate (EPA Reg. No. 72155-14)."
Does this apply to all Bayer formulations with tebuconazole?
Here is a link that might be useful: one commercial add with NY restriction
The Bayer product "Natria" is similar to Serenade and may be more widely available. I don't know how effective it is.
Does the use of a fungicide have an effect on the important soil properties? This recent research paper reports that for tebuconazole there is an effect.
The concentrations used were 5, 50 and 500 mg per kg. The 5 corresponded to the maximum spray rate recommended for wheat.
The following is the Conclusion section from the full paper.
Tebuconazole degradation was accurately described by a bi-exponential model (degradation half-lives varied from 9 to 263 days depending on the concentration tested). The addition of tebuconazole has a strong negative impact on soil microbial biomass and activity: basal respiration, substrate-induced respiration, microbial biomass C and enzyme activities involved in the major biogeochemical cycles were strongly inhibited by tebuconazole. Values of the ecophysiological indices qCO2 and QR increased as a result of tebuconazole application, indicating a stressful condition for the soil microbial communities. In addition, nitrification was also inhibited during the first 30 days of incubation and functional community profiles revealed a shift in the composition of soil heterotrophic cultivable bacteria. Soil microbial properties have shown to be most valuable monitoring tools to assess the impact of tebuconazole application on soil health."
It would be interesting to see a research report where everything was held constant except the application/no application of fungicide on the growth, health, and flowering characteristics of three groups of identical roses (control, tebuconazole sprayed, and Serenade sprayed).
Here is a link that might be useful: Tebuconazole application decreases soil microbial biomass and activity