I grow about 1000 roses in zone 5 northern Ohio. I do not spray and I am not bothered by (much) blackspot. Is this because all (most) of my roses are immune to blackspot? I do not think so. I feel that it is because my garden has reached an equilibrium. The general term is called “biocontrol”.
The following may be useful in putting the concept of biocontrol into layman terms:
"Disease-suppressive soil microorganisms have been found in many places. In monoculture wheat the severity of “take all” disease often decreases within three to five years. This phenomenon is known as “take all decline,” and is considered an effective natural control. Although the mechanisms are not completely understood, the decline is associated with changes in soil microorganisms that compete with and prey on the fungus. Melon plants grown in the Chateaurenard region of France do not show Fusarium wilt symptoms even though the fungus is present in the soil. Soils with suppressive characteristics tend to develop slowly and are usually found in fields where perennial crops or monocultures have been grown for many years.
Suppressiveness may be lost if the monoculture is interrupted even for one year, or if pesticides are applied. For example, researchers first recognized soils suppressive to cereal-cyst nematode when nematode numbers increased after application of a broad-spectrum biocide. Many species of fungi and bacteria in the genera Trichoderma, Streptomyces, Bacillus and Pseudomonas suppress diseases, but at this time only a few strains are commercially available. Additional commercial products may be available soon, however, as this is currently an active research area."
The quote was taken from:
Http://www.cals.ncsu.edu/sustainable/peet/IPM/diseases/org_cert.html
The following article from the Maine Rose Society web page ( Maine Rose Society | Things To Do Outdoors in Maine ) was written by by DR. LAKSHMI SRIDHARAN, who should be familar with those of you that are members of the American Rose Society.
He is a Member of the American Rose Society Research Committee, see:
Http://www.ars.org/d5web/1001124/explore.cfm?M=264&SM=&SC=100050101&W=M&P=N&S=1001124&U=1&SS=1
Examples that friendly fungi do exist (but of course probably not in gardens after their biweekly chemical spraying):
Http://taylorandfrancis.metapress.com/app/home/contribution.asp?wasp=59ghxnlylp03feg2dr2p&referrer=parent&backto=issue,1,10;journal,2,54;linkingpublicationresults,1:100635,1
Http://taylorandfrancis.metapress.com/app/home/contribution.asp?wasp=4g1ltlxhtr3ya223recn&referrer=parent&backto=issue,8,10;journal,4,54;linkingpublicationresults,1:100635,1;
Http://taylorandfrancis.metapress.com/app/home/contribution.asp?wasp=8000375kwm5qnk5e7y47&referrer=parent&backto=issue,1,10;journal,6,54;linkingpublicationresults,1:100635,1;
Http://taylorandfrancis.metapress.com/app/home/contribution.asp?wasp=07wckmqrxr3jqg6kducy&referrer=parent&backto=issue,9,10;journal,7,54;linkingpublicationresults,1:100635,1;
Blackspot on roses is scientifically called “diplocarpon rosae”. The link below reports that trichoderma harzianum is a promising control - see their exact wording (the document is a PDF document. The applicable section is easily found by typing diplocarpon into the PDF find command - the binoculars).
Http://www.gtz.de/ecosan/download/Bangalore03-Ramanujam.PDF
Title: The Abundance and Structure of the Root-Associated Microbial Complexes of Two Greenhouse Rose Cultivars.
Authors: Polyanskaya, L. M.; Ozerskaya, S. M.; Kochkina, G. A.; Ivanushkina, N. E.; Golovchenko, A. V.; Zvyagintsev, D. G.
Authors affiliation: Faculty of Soil Science, Moscow State University, Vorob’evy gory, Moscow, Russia.
Published in: Microbiology (Moscow, Russian Federation)(Translation of Mikrobiologiya), volumn 72, pages 496-502, (2003).
Abstract: “The study of the root-assocd. microbial complexes of affected and healthy rose plants of two cultivars (Grand gala and Royal velvet) grown in a greenhouse showed that the biomass of eukaryotic microorganisms in the rhizoplane and rhizosphere of healthy rose plants and in the surrounding soil was considerably lower than in the same loci of affected plants. In contrast, the biomass of root-assocd. prokaryotic microorganisms was higher in the case of healthy than in the case of affected rose plants. The root-assocd. bacterial complexes of both affected and healthy rose plants were dominated by the genera Arthrobacter, Rhodococcus, and Myxobacterium and did not contain phytopathogenic bacteria. The root-assocd. fungal complex of healthy roses was dominated by fungi of the genus Trichoderma, whereas that of the affected rose plants was dominated by the species Aureobasidium microstictum. The affected cane cuttings and cankers occurring on affected canes were found to contain Coniothyrium fu-ckelii (the causal fungus of rose stem canker) and sclerotia of Botrytis cinerea (the causal fungus of gray rot). The micromycete complex of healthy rose plants was not so diverse as was the micromycete complex of affected rose plants.”
Title: Biological control of black spot of rose caused by Dipocarpon rosae .
Authors: Prasad, R. D.; Rangeshwaran, R.; Sunanda, C. R.; Vinita, J.
Authors affiliation: Project Directorate of Biological Control, Post Bag No. 2491, H.A. Farm Post, Bellary Road, Hebbal, Bangalore 560 024, India.
Published in: Annals of Plant Protection Sciences,volumn 10, pages 256-259, (2002).
Abstract: “Fungal biological control agents (Trichoderma harzianum , T. viride and Chaetomium globosum ) were used either alone or in combination with fungicides (chlorothalonil and mancozeb) to manage black spot of rose caused by D. rosae under greenhouse conditions. Black spot incidence in biological control agent and/or fungicide treatments was significantly low (disease ratings from 0.33 to 3.33) compared to the control at all observation dates. After 100 days of spraying, defoliation was lowest with chiorothalonil, Trichoderma harzianum +chlorothalonil, C. globosum +chlorothalonil and T. harzianum +mancozeb treatments. The highest mean vigour index was recorded in T. harzianum treatment. The highest flower production was recorded in C. globosum +chlorothalonil treatment (4.33) followed by T. harzianum alone and T. harzianum +chlorothalonil treatment (4.00).”
Cornmeal is considered to be a good food for the friendly fungus “trichoderma harzianum”. The fungus is available commercially, see:
http://www.ipmofalaska.com/files/trichoderma.html
There may be another benefit to this fungus as there is a report that it helps root growth:
Title: Effect of Trichoderma Colonization on Auxin-Mediated Regulation of Root Elongation.
Author: Bjoerkman, Thomas.
Department of Horticultural Sciences, Cornell University, Geneva, NY, USA.
Published in: Plant Growth Regulation, volumn 43, pages 89-92, (2004).
Abstract: “The biocontrol fungus Trichoderma harzianum 1295-22 increases root growth in addn. to roles in suppressing disease. Its agricultural use could be expanded if the mechanism of growth enhancement were known. Among the proposed mechanisms of growth enhancement is that the fungus counteracts auxin inhibition of root-cell elongation. We tested whether there was evidence for a secreted auxin inhibitor, for enhanced auxin degrdn., or for altered auxin sensitivity. Our results provide no support for any of these mechanisms. Trichoderma secretions inhibited growth, whereas an auxin inhibitor would increase growth. Auxin inhibited growth to the same extent in colonized and uncolonized roots, indicating no change in auxin sensitivity. Endogenous auxin levels maintained growth closer to the max. in uncolonized roots, indicating stronger auxin limitation of growth in colonized roots. These tests indicated that Trichoderma-colonized roots had a faster max. growth rate, but an unchanged response to auxin.”
Even if naturally occurring trichoderma harzianum only reduces the amount of blackspot fungus by 10 to 20 % (the numbers are just a guess), there are probably going to be a number of different “friendly” fungi in an organic garden.
For example, the following paper reports that 2 fungi that are now recognized as biocontrol potential have increased levels on blackspot infected leaves:
Title: PHYLLOPLANE MICROORGANISMS OF ROSA CULTIVAR PICADILLY FOLLOWING INFECTION BY DIPLOCARPON-ROSAE
Author: HAYES A J
Author Affiliation: DEP OF FORESTRY AND NATURAL RESOURCES, UNIV OF EDINBURGH, UK.
Published in: Transactions of the British Mycological Society, volumn 79, pages 311-320, (1982).
Abstract: “The phylloplane microflora of the hybrid tea rose cultivar Picadilly was studied for 2 growing seasons on healthy leaves and on leaves infected by D. rosae. Large increases in numbers of yeasts and bacteria on healthy leaves were noted from the end of July until the beginning of Oct. Late in the growing season numbers of all types of microbes increased dramatically. Following infection by D. rosae numbers of microbes generally showed a marked increase, but this was not always sustained. Cryptococcus laurentii and Micrococcus sp. populations on infected leaves were 3-4 times those on correspondingly healthy leaves. The species composition and changes in numbers of phylloplane microbes are compared with descriptions of microflora isolated from leaves of other plants and possible reasons for the observed differences are discussed.”
The following two links are Google searches for the two fungi listed and the word biocontrol.
Http://www.google.com/search?hl=en&lr=&q=%22cryptococcus+laurentii%22+biocontrol&btnG=Search
Http://www.google.com/search?hl=en&lr=&q=micrococcus+biocontrol&btnG=Search
The science of biocontrol is still in its infancy. The use of Chitosan is one of the early results of this area of research.
The following is the EPA summary:
( Http://www.epa.gov/pesticides/biopesticides/ingredients/factsheets/factsheet_128930.htm )
"SUMMARY
Chitosan is used primarily as a plant growth enhancer, and as a substance that boosts the ability of plants to defend against fungal infections. It is approved for use outdoors and indoors on many plants grown commercially and by consumers. The active ingredient is found in the shells of crustaceans, such as lobsters, crabs, and shrimp, and in certain other organisms. Given its low potential for toxicity and its abundance in the natural environment, chitosan is not expected to harm people, pets, wildlife, or the environment when used according to label directions."
There is a scientific literature report of 10 - 20 % effectiveness against blackspot.
Title: Chitosan as the biocontrol agent of fungal pathogens; activity and mode of action.
Authors: Wojdyla, Adam T.
Authors affiliation: Research Institute of Pomology and Floriculture, Skierniewice, Pol.
Published in: Bulletin of the Polish Academy of Sciences: Biological Sciences, volumn 51, pages 159-165, (2003).
Abstract: “In in vivo expts. showed that chitosan added to potato dextrose agar at 3 mg/cm3 in 50% suppressed radial growth of Colletotrichum gloeosporioides and Phytophthora cryptogea. Another tested fungi were less sensitive to chitosan. ED50 for Cylindrocladium scoparium and Myrothecium roridum was more than 5 mg/cm3. In vivo expts. showed that only 10-20% effectiveness of the compds. against Diplocarpon rosae was found, when chitosan at 0.2-0.4 mg/cm3 was used for rose spraying. Also spraying of willow 2 times at weekly intervals against Melampsora epitea decreased the mean no. of rust pustules per leaf. Spraying of dieffenbachia 24 h before inoculation with M. roridum resulted in significant decrease of necrosis spread on leaves. Five days after inoculation the compds. inhibited the development of leaf spot about 94%. Chitosan applied preventively before inoculation of leaves gave significantly better results in the control of M. roridum than used 24 h after inoculation. Spraying of chrysanthemum, naturally infected with Puccinia horiana decreased the mean no. of pustules per leaf about 95%.”
New research regarding how trichoderma spreads.
Http://www.publish.csiro.au/nid/39/paper/AP03070.htm
Title: Monitoring the survival and spread of the biocontrol fungus Trichoderma atroviride (C65) on kiwifruit using a molecular marker
Authors: S. L. Dodd, R. A. Hill and A. Stewart
Published in: Australasian Plant Pathology, volumn 33, pages 189 - 196, (2004).
Abstract: “An isolate-specific restriction fragment length polymorphism (RFLP) marker previously found for the Trichoderma atroviride (formerly T. harzianum) isolate C65, an isolate with biological control activity against the kiwifruit stem-end rot pathogen Botrytis cinerea, was modified into a dot blot assay to facilitate the screening of large numbers of leaf and flower/fruit samples for the presence of C65. To increase sensitivity, the dot-blot assay was used in conjunction with a Trichoderma semi-selective medium. This modified diagnostic assay was used to track the survival and spread of C65 on kiwifruit leaves in the shadehouse and flowers/fruit in the orchard over two consecutive growing seasons in the Canterbury region of New Zealand. Results showed that isolate C65 could survive on both leaves and flowers/fruit over an entire growing season. The fungus, applied once in early summer (late November/early December) to coincide with bud burst, was detected on both leaves and fruit through to harvest in late summer (March). In addition to its ability to survive, isolate C65 was shown to spread to uninoculated leaves and fruit on the same plant and plants at least 3 m away. It is postulated that the high population of thrips present in the orchard at flowering was responsible for spread of the fungus within the orchard and that resident insects or wind currents could be responsible for spread in the shadehouse. The ability of C65 to survive and spread in the phylloplane and fructoplane of kiwifruit vines over an entire growing season makes it an ideal candidate biological control agent for reducing B. cinerea inoculum in the orchard at harvest and, consequently, post-harvest fruit rot.”
Question: Are there any studies to support the concept that roses produce defensive chemicals against blackspot when infected?
Title: Elevation of extracellular beta-1,3-glucanase and chitinase activities in rose in response to treatment with acibenzolar-S-methyl and infection by D. rosae
Authors: Suo, Yuying; Leung, David W. M.
Authors affiliation: Department of Plant and Microbial Sciences, University of Canterbury, Christchurch, 1, New Zealand.
Published in: Journal of Plant Physiology, volumn 158, pages 971-976, (August 2001).
Abstract: “Changes in activities of beta-1,3-glucanase and chitinase were determined in intercellular fluids of leaves of in vitro rose shoots at various times after treatment with acibenzolar-S-methyl (BTH, a benzothiadiazole derivative; trade name Bion 50WG) or inoculation with Diplocarpon rosae. The results indicate that BTH treatment led to enhanced activities of beta-1,3-glucanase and chitinase in the intercellular spaces of rose leaves. An increase in extracellular beta-1,3-glucanase and chitinase activities was also found in D. rosae-infected leaves. However, the increase in enzyme activities occurred much more rapidly and was more strongly enhanced in D. rosae-infected leaves that were previously treated with BTH, suggesting that the increased beta-1,3-glucanase and chitinase may play a role in restricting the development of disease symptoms on the rose leaves infected with D. rosae. The expression patterns of rose beta-1,3-glucanase and chitinase isoforms were investigated on native PAGE with specific staining techniques. A similar induction pattern of these enzymes was observed in both treatments. The increased beta-1,3-glucanase and chitinase activities are mainly due to the enhanced expression of beta-1,3-glucanase isoform G2 and chitinase isoforms C1 and C2. These isoforms are likely to be a part of rose defense responses to pathogen attack.”
Title: Induction of resistance to Diplocarpon rosae and Agrobacterium tumefaciens by acibenzolar-S-methyl (BTH) in rose
Authors: Suo, Y.; Leung, D. W. M.
Authors affiliation: Department of Plant and Microbial Sciences, University of Canterbury, Christchurch 1, New Zealand.
Published in: Zeitschrift fuer Pflanzenkrankheiten und Pflanzenschutz, volumn 108, pages 382-391, (July 2001).
Abstract: “Acquired disease resistance can be induced in rose by acibenzolar-S-methyl (BTH), a novel synthetic chemical which has been shown to induce a broad-spectrum disease resistance in many plant species. BTH was applied by dipping whole in vitro rose shoots into the chemical at different concentrations for a few seconds before returning them to a shoot growth medium. Four days later, the shoots were challenge inoculated in vitro with D. rosae or A. tumefaciens under otherwise aseptic conditions. Pretreatment of rose shoots with 50 muM BTH led to resistance to Diplocarpon rosae and Agrobacterium tumefaciens by significantly reducing the disease severity of blackspots, percentage and mean size of crown galls formed, respectively.”
Title: BTH-induced accumulation of extracellular proteins and blackspot disease in rose
Authors: Suo, Y.; Leung, D. W. M.
Authors affiliation: Department of Plant and Microbial Sciences, University of Canterbury, Christchurch, 1, New Zealand.
Published in: Biologia Plantarum (Prague), volumn 45, pages 273-279, (2002).
Abstract: “Treatment of rose shoots with 50 muM acibenzolar-S-methyl (BTH) resulted in increased protection against Diplocarpon rosae. This was accompanied by the induction and accumulation of a set of extracellular proteins as shown by SDS-PAGE and 2D-PAGE. Some of these proteins have been identified as PR-1, PR-2, PR-3 and PR-5 proteins by immunoblot analysis probed with tobacco antisera against PR-1c, PR-N, PR-Q and PR-S protein. Most of the extracellular proteins activated by BTH were also induced and found to accumulate in leaves upon infection with Diplocarpon rosae. However, their accumulation was much more pronounced in BTH-pretreated leaves than in water-pretreated leaves upon a challenge inoculation with D. rosae, particularly, the 15 kD PR-1, 36 and 37 kD PR-2 proteins. They may be more important in the expression of disease resistance.”
Title: Accumulation of extracellular pathogenesis-related proteins in rose leaves following inoculation of in vitro shoots with Diplocarpon rosae
Authors: Suo, Y.; Leung, D. W. M.
Authors affiliation: Department of Plant and Microbial Sciences, University of Canterbury, Christchurch 1, New Zealand.
Title: Accumulation of extracellular pathogenesis-related proteins in rose leaves following inoculation of in vitro shoots with Diplocarpon rosae
Published in: Scientia Horticulturae (Amsterdam), volumn 93, pages 167-178, (March 2002).
Abstract: “Rose shoots var. ‘Iris Gee’ grown in vitro infected with Diplocarpon rosae (blackspot causal agent) led to the accumulation of the pathogenesis-related (PR) proteins in the intercellular space of leaves. Electrophoresis of intercellular fluids by SDS-PAGE and 2D-PAGE revealed that extracellular PR proteins accumulated strongly in infected leaves starting at day 3 after inoculation and increased in abundance with disease development. Sixteen proteins, which were absent or present at a low level in the healthy leaves, have been detected in the intercellular fluid extracted from the infected rose leaves 7 days after inoculation with D. rosae. Western-blot analysis showed that rose PR proteins are serologically related to tobacco PR proteins. Infection of D. rosae resulted not only in strong accumulation of PR-2, PR-3, and PR-5 proteins in the intercellular spaces of rose leaves but also induction of PR-1 protein at a later stage of infection. However, no systemic induction of PR-1 protein was detected in upper newly expanded and uninfected leaves.”
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