The Institute of Ecosystem Studies, prefers to recommend organic solutions to plant problems. This is not always possible, especially when organic solutions are few and often provide less than satisfactory results. When I wrote "Suppression of Black Spot On Roses Part I", which appeared in the November 2003 "From the Gifford Garden", chemical sprays were the accepted answer for controlling Black Spot, Diplocarpon rosae, on roses. Since then a new product has been added to the choices of fungicides labeled for use against many fungal blights and bacterial infections. Marketed under the name Serenade® SolutionsTM, AgriQuest Inc has formulated a biopesticide containing 10% live Bacillus subtilis bacterium. This product is available though the mail order company Gardens Alive! (www.GardensAlive.com)! A biopesticide employs beneficial microbes to control many fungal and bacterial diseases and is currently labeled for use on field crops.
I would like to define Black Spot again, just to refresh our memories. The disease is a fungal infection of the leaves on roses. Black Spot develops when environmental conditions are present which favor the proliferation of Diplocarpon rosae. These are cool nights and hot, humid days. While the fungal spores of Black Spot are always present in the soil, these conditions enable spore germination and populations to rapidly increase. When water, either from rainfall or irrigation, is splashed onto the leaf surface black spots will appear and infection can occur in six hours. Total leaf defoliation can happen in days. Yellowing leaves and a general appearance of stress will be observed with Black Spot infection. Because of the aggressiveness of this disease, it is widely considered to be the bane to rose growers.
Typical black spots and yellow leaves on a rose bush. Diplocarpon rosae, Black Spot
A preventive spray program is essential for controlling Black Spot. Diligent continuance of the spray program is likewise a must for controlling Black Spot infection. Even with good rose hygiene (careful watering to minimize water splashing, removal of infected leaves, proper fertilization, etc.) spraying is typically necessary.
Choosing an organic fungicide can be confusing. Some of the popular choices include neem oil, from the Neem Tree (Azadirachta indica), baking soda, copper and sulfur. We decided to test the relatively new class of organic pesticides, biopesticides, on roses in the Shankman Rose Garden and on roses planted in a test site on the Rose Mound. The results were surprisingly better than expected.
For generations using strong chemical fungicides to control fungal diseases on roses has been the standard practice. Many rose growers have been looking for safer and environmentally friendly alternatives, and they just might have found one with biofungicides (biopesticides with fungicidal properties). Remember when you were looking for something, you were told, it was probably right in front of you. What is in front of you when you are cleaning up all those fallen rose leaves? What is in front of you is soil, of course. What is in that soil? Bacteria. The biofungicide used in Serenade® SolutionsTM is the bacterium Bacillus subtilis, QST Strain 713. When sprayed on target plants it manages to create an inhospitable environment for the proliferation of fungi which cause many blights, scabs, molds, several mildews and bacterial spots. It creates this environment by competing with disease microbes for nutrients and growing sites. It also attaches to the disease pathogen thereby weakening it. It may also induce a plant's natural systemic resistance to disease or it can create a systemic acquired resistance (SAR) against disease pathogens. Bacillus subtilis QST Strain 713 is a gram-positive (non-pathogenic), aerobic, mobile bacterium found in aquatic and soil environments. It is not harmful to human and most animal populations. When the wettable powder is tank mixed it ay cause dermal or respiratory irritation to applicators. Further information can be found on the Environmental Protection Agency's web site (www.epa.gov).
The Trial:
Applications of Serenade® SolutionsTM were done with a manual hand sprayer. Applications were made every 7 to 10 days as per label directions. Visual observations showed no sign of tip-burning on leaves. There were no post application odors connected with this product. A slight powdery residue was left on leaf surface. Since the product did "puff" when moved from container to sprayer, the applicator used a particle mask and wore eye protection when mixing.
The test site on the Rose Mound consisted of six assorted rose varieties.
CONTROL (No Spray) SPRAYED J.P. Connell (shrub) Piñata (floribunda) Knock Out (shrub) Lavaglut (floribunda) Scentimental (floribunda) Nancy Reagan (hybrid tea) Conclusions:
Black Spot was slowed or halted in all cases where Serenade® SolutionsTM was used. This is significant given the fact the design features used in the trial were intended to foster the proliferation of Black Spot. The spacing used to plant the trial roses was too close compared to standard planting practices. Further, infected cast leaves were not removed from the test site. Despite these conditions we were able to maintain 75% of the foliage on infected roses with our spray program. Rose growers can expect defoliation of 90 to 100% on roses infected with Black Spot.
After the trial was finished and spraying discontinued, there was a significant increase in Black Spot on refoliated roses and on roses clean of infection. It appears that Bacillus subtilis QST Strain 713 moves through the environment at a very fast rate. We assume that sufficient populations of Bacillus subtilis were not present to control Black Spot.
The following pictures show the dramatic difference between the rose varieties used at the test site. Note that the spread of Black Spot was slowed between Lavaglut and Scentimental. Lavaglut was totally defoliated, while Scentimental stayed surprisingly clean. This is significant since the spacing between the two roses was less than one foot.
Site selection, planting disease resistant roses, good rose hygiene, and a spray program for managing pests and diseases are important considerations when planning a successful rose garden. The biofungicide Serenade® SolutionsTM may just be the answer for Black Spot control that rose growers are looking for.
Lavaglut, August 2004 Scentimental, August 2004 Scentimental, October 2004
(After the spray program ended)
