24 Biological Fungicides and Plant Strengtheners in Thuringia: Use and Research

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1 24 Biological Fungicides and Plant Strengtheners in Thuringia: Use and Research W. DERCKS 1 and R. SCHMATZ 2 1 Fachhochschule Erfurt - University of Applied Sciences, Department of Horticulture, Leipziger Straße 77, 9985 Erfurt, Germany 2 Thüringer Landesanstalt für Landwirtschaft, Referat Pflanzenschutz, Kühnhäuser Straße 11, Erfurt - Kühnhausen, Germany Abstract. Biocontrol is not widespread in Thuringia and only a few biological fungicides and plant strengtheners have been used by growers. There are no supportive measures or financial aids for growers to promote biocontrol strategies and no biocontrol company is based in the state of Thuringia. Biocontrol projects are only run at Erfurt. The Biocontrol Technology Transfer Project was initiated by the FH Erfurt - University of Applied Sciences. It is carried out in close collaboration with various cooperators. The objective of the project is to promote use of biocontrol agents in horticultural crops. Two model test systems were developed for a standardized check of the efficacy of biocontrol agents: Fusarium oxysporum f. sp. cyclaminis - cyclamen and Sclerotinia sclerotiorum - sunflower. In cyclamens, the effect of different inoculum densities and inoculation methods (substrate inoculation, poured spore suspension) on development of Fusarium wilt was investigated. Disease incidence increased with inoculum density. Substrate inoculation caused faster, less variable, and stronger disease development than poured spore suspension. Thus, the former method is better suited for trials. The non - pathogenic Fusarium strain FO 47 (Fusaclean G) delayed the onset and development of the disease but was not able to prevent infection or reduce final disease levels. At the end of the trial, disease levels were in the same order of magnitude in non - treated and in Fusaclean G - treated plants inoculated with Fusarium oxysporum f. sp. cyclaminis. In sunflowers, Contans WG (Coniothyrium minitans) exhibited good activity against S. sclerotiorum if it had been applied to the soil early. Under wet conditions, efficacy was better than that of Basamid - Granulate (dazomet), lime - nitrogen (calcium cyanamide), and ROVRAL (iprodione). Presumably, the latter compounds drained from the upper soil layers quickly. The combination of Contans WG before sowing and ROVRAL at occurrence of the first symptoms is a promising strategy for integrated control of soft rot. Modern Fungicides and Antifungal Compounds IV BCPC, Alton, UK,

2 W. DERCKS AND R. SCHMATZ Background and Objectives Soil-borne plant diseases are a major threat to many horticultural crops in Germany. Some companies offer formulations of microbial antagonists (bacteria or fungi) for prevention or biological control of soil-borne plant pathogens. Some of the microorganisms can promote plant growth or flowering and enhance plant health. Such organisms can be registered as plant strengtheners provided they have no adverse effects on humans, animals, and the environment. A microorganism that has a direct effect on the pathogen (biocontrol agent; BCA) needs to be registered as a plant protection chemical. Whereas plant protection chemicals are checked for efficacy during long and cost-intensive trials, proof of efficacy is not required for plant strengtheners (Bode, 2). This has led to the market introduction of some products that show inadequate efficacy under practical conditions. Without critical testing, efficacious products will not be able to compete with the non-efficacious ones because the whole group has been suffering from a bad reputation. This is a regrettable situation, since the number of chemical or non - chemical alternative options for the control of many soil-borne plant diseases is limited. In Germany, only one chemical (Basamid Granulate ; dazomet) was registered for soil disinfestation. Registration expired on 3 September 24. Reregistration was not granted (Status quo: October 24), so the chemical can only be used until 31. December 26 if nothing changes. In order to develop sustainable solutions to deal with soil-borne plant diseases, the Biocontrol Technology Transfer Project (BTTP; Dercks et al., 21) was initiated. The objective of the project is to promote use of BCAs in horticultural crops by sound scientific market introduction. The goals are 1) identification of active BCAs in trials; 2) product development and optimization of protocols for use; 3) demonstration and advice to growers by extension. Two model test systems were developed for a standardized check of the efficacy of biocontrol agents: Fusarium oxysporum f. sp. cyclaminis (FOC) - cyclamen and Sclerotinia sclerotiorum - sunflower. These pathogens are of great economical importance. Whereas FOC is specific for cyclamens, S. sclerotiorum can attack a whole range of different crops. In cyclamens, Fusaclean G (FO 47; non-pathogenic strain of Fusarium oxysporum) has been evaluated for prevention of FOC. In sunflowers, Contans WG (strain of Coniothyrium minitans) has been tested for control of soft rot. Sunflowers were chosen as a model crop of an annual host plant for S. sclerotiorum. During the mid- to late nineties, FO 47 had been on the German market for a limited time under the trade name Fusaclean with inconsistent results in trials from different crops, most notably cyclamens. In Thuringia, it was used on only.3 ha (Anonymous, 21). The product vanished from the market for various reasons outlined by Dreßler (1999) and Soubabère (22). It is intended to reintroduce it with a new and optimized formulation under the trade name Fusaclean G as a plant strengthener by the French company Natural Plant Protection in Nogueres and Pau (N.P.P.; Soubabère, 22). This was the reason to re-evaluate FO 47 s performance. Contans WG has a registration in several crops, most notably oilseed rape but also lettuce and other vegetables. In 22, it was used on 55ha of rape in Thuringia (Dercks and Schmatz, 23). Mycelium of the fungus Coniothyrium minitans grows from the granules in soil and parasitizes the sclerotia (survival bodies) of 236

3 Biological Fungicides S. sclerotiorum thus killing them. This is not the only way to fight the soft rot fungus. It is also possible to use Basamid - Granulate (dazomet), lime - nitrogen (calcium cyanamide), or ROVRAL (iprodione). Dazomet is a chemical that has been used for soil disinfection for decades. It has general biocidal activity on fungi, bacteria, insects, nematodes, and weeds. However, it is expensive and it s metabolites may be toxic to the crop if time between application and sowing (or planting, respectively) has not been sufficiently long for wetness and temperature dependent degradation. This makes timing of soil management and crop production schemes difficult. Similar logic applies to lime - nitrogen, a traditional fertilizer, the active breakdown product of which is calcium cyanamide. All products (Contans WG, Basamid - Granulate, and lime - nitrogen) are applied to the soil and act on the sclerotia. ROVRAL is a dicarboximide fungicide that can be applied to the stem and leaves of a plant and acts on the mycelium of S. sclerotiorum. Use recommendations state the compound should be sprayed or poured when first symptoms of wilt appear in the crop. This may prevent further spread of the disease; but it is not possible to cure plants that are already diseased. To the best of the authors knowledge, no trials have been carried out in which all of these options have been tested for comparison. This was the reason for the experimental design and the treatments chosen. The results and conclusion of the trials may firstly be instrumental in delivering solutions for control of important soil-borne pathogens. Secondly, if BCAs stand the test against chemical standards or can be integrated with them, the project may help to promote biocontrol and integrated pest management schemes. With regard to the poor availability of fungicides in many minor horticultural crops the project might be helpful to develop sustainable production schemes. It is worthy to note that biocontrol is not as advanced in Thuringia as in most other German states (Anonymous, 21). Only a few biological fungicides and plant strengtheners have been used by growers. There are no supportive measures or financial aids for growers to promote biocontrol strategies. No biocontrol company is based in the state of Thuringia and the projects in Erfurt are the only ones in the state directed at taking biocontrol out into the field and greenhouse. Biocontrol needs sound education, research, and extension at all levels of teaching, training, and work in the horticultural industry. Understanding the Biocontrol Agent and the Pathogen / Reasons for the Pathosystems Chosen To achieve satisfactory results when using BCAs it is essential to perceive how they live and act on the target organism. It is also important to fully understand the life cycle of the pathogen in order to target the BCA and place it properly into the production system. BCAs have different mechanisms of action (Koch, 1996). They may compete with pathogens for binding sites at the roots and for nutrients in the rhizosphere (indirect action). Or they may act directly on the pathogen by secreting antibiotics or parasitizing them. Some do also cause reactions of induced resistance in the plant (another example for an indirect action). In many cases, more than one mechanism is at work. An overriding feature to be aware of is that all BCAs are only able to work if they are applied before infection of the plant by the pathogenic organism has taken place. This calls for preventive treatments. In other words, it is not possible to use BCAs in connection with economic threshhold levels in the way of 237

4 W. DERCKS AND R. SCHMATZ systemic fungicides (Dercks, 24). They should be looked at as a means of sanitation and seen as an integrated part of the production system (Koch et al., 1999). FO 47 is a non-pathogenic strain of Fusarium oxysporum. It was discovered in France and developed as a BCA by I.N.R.A Dijon (Alabouvette et al., 1998). The company N.P.P. now owns the marketing rights for a new formulation of FO 47 (Fusaclean G) containing spores of the fungus (Soubabère, 22). This formulation is mixed into the substrate of potted ornamental plants and some vegetables before use. If applied early enough the mycelium of the fungus grows throughout the substrate and completely covers the roots. It colonizes the epidermis but is not able to penetrate into the inner tissue layers. Thus, potential penetration sites for pathogenic strains of Fusarium oxysporum are blocked (Alabouvette et al., 1998; Benhamou and Garand, 21; Soubabère, 22), at least in theory. It has also been demonstrated that FO 47 is able to induce resistance towards soil-borne pathogens, for instance in tomatoes against Fusarium oxysporum f. sp. lycopersici (Fuchs et al., 1997). Fusaclean G has been tested in cyclamens within the framework of the BTTP. Cyclamens are the most important greenhouse ornamental crop in Thuringia with Fusarium wilt being the most important disease (Tischer, 1999). However, this is also true for all of Germany (Stock, 1999) and for many parts of the world (Elmer, 22). Detailed information on Fusarium wilt and FOC is presented by Koch (1993) and Elmer (22). Chlamydospores as well as micro- and macroconidia of FOC survive in soil and plant debris. Their germination is stimulated by the presence of cyclamen roots. The mycelium penetrates the roots into the deeper layers. The fungus is able to colonize the root system, the tuber, and the petioles of the whole plant. Most of the colonization takes place within the xylem; here, conidia are distributed by the transpiration stream. Sooner or later, wilt symptoms become apparent. Primary symptoms (yellowing) can be seen where the petioles enter the leaves. Under disease conducive conditions (e.g. at high temperatures, usually in summer) leaves may wither and wilt until the whole plant is affected; then, mycelium and spore formation may occur on the petioles. The disease can spread by dissemination of spores, especially in ebb - and - flow systems. There are no possibilities for chemical control with registered products at legal concentrations. (In the past, some products were allowed, but their effect was marginal, if there was one.) Most important for prevention are sanitation measures; e.g. removal of diseased plants. In addition to this, BCAs may be applied to the substrate. When using BCAs, they need to be mixed into the substrate at every stage of production: at seeding, at pricking-out, and at potting. No BCA is able to work when applied, for instance, at potting if infection by FOC has already occurred at an earlier stage. Coniothyrium minitans is a fungus antagonistic to S. sclerotiorum. It was discovered in 1947 but subsequently found to be present in many parts of the world (Whipps and Gerlagh, 1992). It parasitizes the sclerotia of S. sclerotiorum in soil. The fungus is a soil-borne pathogen causing soft and stem rots in many plants (Purdy, 1997). In Thuringia, it has become one of the major soil-borne diseases causing severe problems over the last decade. This can be attributed to the expansion of the area of production of oilseed rape, one of the most important crops in Thuringia and the rest of Germany. S. sclerotiorum survives in soil by sclerotia, aggregations of compressed mycelium which form inside diseased plant tissue and remain in the field with plant 238

5 Biological Fungicides debris. These sclerotia are induced to germinate via mycelial hyphae in the presence of host plant roots. The germinating mycelium may directly infect roots of certain plants. It is also possible that sexually differentiated mycelia meet in soil to mate and generate fruiting bodies, the so-called apothecia. These rise above the soil surface to release ascospores from the asci formed inside the fruiting body. The ascospores are distributed by wind and can cause airborne infections of plant tissue. The main infection cycle is not understood for all host plants of S. sclerotiorum. However, in rape it is taken for sure that the infection is airborne. In this case, applications of ROVRAL may give acceptable results for control. However, a lot of benefits could be expected if sclerotia were distroyed in soil by Contans WG, Basamid - Granulate, or lime - nitrogen since the disease pressure by airborne ascospores would be reduced. In crops the roots of which are infected by mycelium of S. sclerotiorum in soil (e.g. in sunflowers), little effect can be expected from ROVRAL applied when symptoms are already present. It makes much more sense to attack the sclerotia in soil. When using Contans WG it is very important to apply the BCA several weeks before seeding or planting, respectively, in order to give it a good head start. The granules need time for germination and the spreading mycelium of Coniothyrium minitans needs time to find and parasitize the sclerotia of S. sclerotiorum present in soil. If Contans WG is applied too late S. sclerotiorum may outrun the BCA and infect the plant before Coniothyrium minitans comes into action. Contans WG was developed and is marketed by the company Prophyta in Malchow / Poel. Material and Methods Trials in Cyclamen (Fusarium oxysporum f. sp. cyclaminis; FOC) Two trials were carried out to check the influence of inoculum density and inoculation method of FOC on the development of Fusarium wilt in cyclamens: the first one in absence, the second one in presence of Fusaclean G. The treatments were: 1. Substrate inoculation spores FOC / pot Poured spore suspension spores FOC / pot Most trials described in the literature for FOC and FO 47 (e.g. Schmilewski, 21; Krebs, 21) were carried out with a spore suspension of FOC that was poured into the pot after potting. However, it is very likely that these spores do not disseminate evenly but rather concentrate in a certain compartment of the substrate. This may over - challenge the BCA at one part of the plant s root, thus rendering this plant a victim to infection by FOC. Most results presented in the literature were very variable. In Schmilewski s (21) work, low inoculum densities (5 and 5 spores per pot) 239

6 W. DERCKS AND R. SCHMATZ resulted in only little attack, whereas very high densities (5. spores per pot) killed almost 1 % of the plants, even in the presence of FO 47. Intermediate densities (5. and 12.5 spores per pot) resulted in sufficient disease, but already overpowered FO 47. By contrast, inoculum mixed evenly into the substrate would probably better represent natural infection situations. The first objective of the first trial was to check whether or not substrate inoculation leads to a more even infection and better disease development than inoculation by poured spore suspension. The second objective of the first trial was to check whether increasing inoculum densities result in differentiation of attack. The objective of the second trial was to determine, whether or not FO 47 can prevent, delay, or reduce disease development and final disease levels of FOC in cyclamens. Substrate inoculation (treatments 1 to 4) was carried out by spraying a spore suspension of equivalent density into the substrate when this was being rotated in a concrete mixer. Cyclamen persicum Mill. plants of the variety `Leuchtfeuer Bob` were planted in this substrate. For treatments 5 to 8, a spore suspension of equivalent density was poured into each pot after potting. The FOC strain used for inoculation was strain No of the Biologische Bundesanstalt für Land- und Forstwirtschaft. The plants were assessed for disease development weekly until the end of the trial. The trials were each carried out with 98 plants per treatment in fully randomised blocks, each with 7 replicates of 14 plants in the greenhouse at 18 C. All experimentally and horticulturally relevant data are presented in more detail elsewhere (Dercks and Schmatz, 23; Dercks et al., 23). Trials in Sunflowers (S. sclerotiorum) The trial was carried out from 21 to 23 on the same field in a fully randomised block design with every plot being physically identical every year. The sunflower cultivar used was Helianthus annuus Valentin. Each treatment was tested in six replicates (1 replicate = 1 plot = 15 m²). The treatments were: 1. Untreated control (check) 2. Contans WG 6 kg / ha before sowing 3. Basamid - Granulate 5 kg / ha before sowing 4. Lime - nitrogen 6 kg / ha before sowing 5. ROVRAL.1% at occurrence of first symptoms and again 14 days later 6. Contans WG 6 kg / ha before sowing + ROVRAL.5% at occurrence of first symptoms and again 14 days later All compounds were applied according to the producers use instructions. Contans WG was worked into the soil up to a deep of 15 cm (recommendation by the company Prophyta). Each plot was inoculated with 4 sclerotia of S. sclerotiorum (8 little bags each containing 5 sclerotia). The idea to reduce the concentration of ROVRAL from 24

7 Biological Fungicides.1% to.5% in the combined treatment of Contans WG and ROVRAL (treatment 6) had been taken from the work of Budge and Whipps (21). The combination of biological and chemical fungicides might be a key element of future integrated management schemes (Brückner, 22). The plants were assessed for disease development weekly until the end of the trial. Results Effect of inoculation method on development of symptoms of Fusarium wilt in cyclamen leaves Substrate inoculation (Figure 1) caused a more rapid, more even (less variation between replicates) and more intense development of symptoms than poured spore suspension (Figure 2). With both inoculation methods, first symptoms occurred in the fourth week following inoculation. However, with the substrate inoculation, a continuously increasing disease level could be observed from the fifth week after inoculation until the end of the trial. With poured spore suspension, a distinct increase occurred only from week 13 following inoculation. At the end of the trial, levels of disease were higher for every tested inoculum density in the substrate inoculation method as compared to the poured spore suspension treatments. % diseased plants weeks following inoculation spores / pot Figure 1. Effect of different inoculum densities of Fusarium oxysporum f. sp. cyclaminis on development of wilt symptoms in cyclamen leaves following substrate inoculation (total of 98 plants in 7 replicates, each with 14 plants). 241

8 W. DERCKS AND R. SCHMATZ % diseased plants weeks following inoculation spores / pot Figure 2. Effect of different inoculum densities of Fusarium oxysporum f. sp. cyclaminis on development of wilt symptoms in cyclamen leaves following inoculation by poured spore suspension (total of 98 plants in 7 replicates, each with 14 plants). Effect of inoculum density on development of symptoms of Fusarium wilt in cyclamen leaves Figures 1 and 2 also demonstrate the influence of inoculum density on development of the disease. Levels of disease at the end of the trial were dependent on inoculum density. With the poured spore suspension, levels increased proportionately to inoculum density. In principle, this was also true for the substrate inoculation. However, there was no difference between 1. and 2. spores FOC per pot. Statistically, all inoculum levels were different from one another and from the control in the poured spore suspension treatments. They were not statistically different from one another but all different from the control in the substrate inoculation treatments. Effect of Fusaclean G on the occurrence of first symptoms of Fusarium wilt in cyclamen leaves dependent on different inoculation methods and inoculum densities Symptoms occurred earlier in the substrate inoculated treatments than in the treatments inoculated by spore suspensions (Table 1). Effect of Fusaclean G on the development of Fusarium wilt and the final levels of disease In the substrate inoculation, a distinct increase of disease levels was seen only from approximately the twentieth week following inoculation onwards (Figure 3). In the poured spore suspension treatments, a continuous increase was noticed after occurrence of the first treatments (Figure 4). Levels of disease at the end of the trial 242

9 Biological Fungicides Table 1. Occurrence of first symptoms of Fusarium wilt in leaves of cyclamen treated with Fusaclean G 1 Inoculation method Inoculum density FOC (number of spores / pot) Point in time (weeks following inoculation) Substrate inoculation Poured spore suspension all treatments received 2 g Fusaclean G per m² substrate at seeding, pricking out, and potting were in the same order of magnitude (mid fifties to lower seventies percent). At flowering (approximately 18 th / 19 th week following inoculation) they were, 4, 2, and 1 % (, 1., 2., and 3. spores per pot) in the substrate inoculated treatments and, 13, 16, and 2 %, respectively, in the treatments inoculated with spore suspensions. % diseased plants weeks following inoculation spores / pot Figure 3. Effect of different inoculum densities of Fusarium oxysporum f. sp. cyclaminis on development of wilt symptoms in cyclamen leaves following substrate inoculation in the presence of Fusaclean G (total of 98 plants in 7 replicates, each with 14 plants; all treatments received 2 g Fusaclean G per m² substrate at seeding, pricking out, and potting). 243

10 W. DERCKS AND R. SCHMATZ % diseased plants weeks following inoculation spores / pot Figure 4. Effect of different inoculum densities of Fusarium oxysporum f. sp. cyclaminis on development of wilt symptoms in cyclamen leaves following inoculation by poured spore suspension in the presence of Fusaclean G (total of 98 plants in 7 replicates, each with 14 plants; all treatments received 2 g Fusaclean G per m² substrate at seeding, pricking out, and potting). Effect of different treatments on the level of disease caused by Sclerotinia sclerotiorum in sunflowers Disease levels in the untreated control were highest in 21 and lowest in 23 with 22 lying in-between. The treatments had different effects (Table 2). The best treatments in the respective years were: 21: Lime - nitrogen and Contans WG / ROVRAL 22: Contans WG / ROVRAL and Contans WG 23: Contans WG and Contans WG / ROVRAL Table 2. Control of Sclerotinia sclerotiorum in sunflowers (% diseased plants of a total of approximately 2.5 per treatment at the end of the trial). Treatment Untreated control (check) 17,8 11,6 6,3 Contans WG 13,3 8,3 1 3,9 Basamid - Granulate 8,6 1,6 5,4 Lime - nitrogen 6,2 1 14,4 5,8 ROVRAL 2 1,7 11,7 7,4 Contans WG / ROVRAL ³ 8,4 1 8,1 1 4,9 1 statistically significant different from control ².1 % ³.5 % 244

11 Biological Fungicides Discussion Trials in Cyclamens Inoculation method with FOC. It was demonstrated that substrate inoculation caused a more rapid, more even and more intense development of symptoms than poured spore suspension. This emphasizes that is it better suited for trials because the results are less variable than with poured spore suspension. It can also be expected to be closer to the natural situation of inoculation and should be used in trials wherever possible. However, it is also very tedious and time consuming. Where poured spore suspensions need to be used for technical reasons the number of replicates and the number of plants per replicate should be as high as possible. Inoculum density of FOC. With increasing inoculum density higher levels of disease were attained. On one hand, in order to assure that disease pressure is high enough to differentiate between the effect of BCAs on FOC, inoculum levels should not be too low. One of the key demands for a good test system is the necessity of high levels of disease in the untreated control under disease conducive conditions. On the other hand, high inoculum levels may over challenge BCAs. From the results described here the tentative conclusion might be drawn that 1. spores per pot may be recommended for trials with BCAs, especially if the substrate inoculation method is used. However, since disease pressure is dependent on so many different factors (especially temperature) which can never be exactly predicted, it would be wise to work generally with two different inoculum densities. Occurrence of disease in the untreated controls. Regrettably, there were also diseased plants in the checks of both trials, especially in the first trial that had been carried out over summer. This happened although all thinkable precautions to avoid contamination had been taken (e.g. placing the pots on an elevation, so that draining water was only able to flow downwards). Fusarium wilt is a very difficult and tricky disease to work with, one reason being the long duration of a trial, primarily dependent on the plant s long life span and the long latent period of the pathogen. The diseased plants can almost certainly be attributed to secondary infections happening in later stages of the trials when high levels of inoculum had built up in the inoculated treatments. However, it should be pointed out that this undesired effect did not have any influence on the conclusions concerning inoculation method and inoculum density. Effect of Fusaclean G on the development of Fusarium wilt in cyclamens and the final levels of disease. It was established that, under the experimental conditions chosen, Fusaclean G clearly delayed the onset of disease. This effect was more pronounced in the substrate inoculated treatments than in the treatments inoculated by poured spore suspension. This can probably be explained by the more homogenous inoculation not over challenging the BCA in places of spore aggregations that inadvertently happen with poured spore suspensions. However, Fusaclean G was not able to prevent infections or reduce disease levels. The final levels of disease at the end of the trial were of the same order of magnitude as for plants not treated with Fusaclean G. A common problem in the literature is that many results (e.g. Krebs, 21) are presented as final data at the stage of flowering which is when cyclamen are usually sold. Disease levels at this point in time may be quite acceptable to the 245

12 W. DERCKS AND R. SCHMATZ grower. However, such results are meaningless if the disease is just withheld until after selling but then strikes on the buyer s window ledge. It would neither be good ethics nor a brilliant business idea to use Fusaclean G this way. At the moment, Fusaclean G cannot be recommended in cyclamen for situations of high disease pressure of FOC. The question remains whether or not the effect is different at lower inoculum levels representing lower disease pressure of FOC. Investigations to tackle this issue are planned for the future. It should also be stated that the findings described here do not necessarily allow conclusions about the effectiveness of FO 47 against other strains of Fusarium oxysporum in other crops. Every pathosystem needs specific evaluation. Trials in Sunflowers Firstly, the results must be interpreted with regard to the weather. The year 21 was pretty dry at the beginning but towards the end of the growing season there were a fair number of significant rainfalls. 22 was very wet, 23 was extremely dry, both the whole growing season over. The level of disease seen in the untreated controls can be judged as above average in 21, average in 22, and below average in 23 reflecting equivalent disease pressures from practical experience. Secondly, in order to name the main reasons for the performance of the treatments, it must be taken into account when the treatments were carried out in relation to the time of inoculation. In every year, time between treatment and seeding was long enough for all treatments to work (21: 72 days; 22: 7 days; 23: 99 days). Thus the results can be explained almost exclusively by the weather conditions. These heavily favoured Basamid - Granulate and lime nitrogen in 21 but Contans WG in 22. Under the initial conditions of little wetness in 21 Basamid - Granulate and lime nitrogen performed much better. In 22, Contans WG was favoured by excessive rains and the subsequently persistent wetness in soil; this resulted in much better performance. ROVRAL alone always came too late to prevent infections, but obviously, the combination Contans WG / ROVRAL provided a chance for the chemical to work even at a reduced rate of application. Under the wet conditions of 22, both Contans WG and Contans WG / ROVRAL gave satisfactory control outperforming Basamid - Granulate and lime nitrogen. These compounds probably drained from the soil quickly. In 23, disease pressure was so low that none of the effects should be over interpreted. Differentiation between treatments was marginal but there was a clear tendency to support the results of 22. Analysis revealed statistical significance from the untreated controls only for lime - nitrogen and Contans WG / ROVRAL in 21, as well as for Contans WG and Contans WG / ROVRAL in 22. Statistical significance is one thing to bear in mind when interpreting results (especially in field trials); a pattern that can be repeatedly seen over the years is something a grower takes confidence in. It is intended to carry on with the trials for another two to three years in order to generate recommendations for growers. In this regard, Contans WG alone or in combination with ROVRAL provides interesting prospects for sustainable management of soft rot expanding the traditional solutions of Basamid - Granulate, lime - nitrogen, and ROVRAL alone. 246

13 Biological Fungicides Overriding conclusions Independently of the effectiveness or non-effectiveness of any given BCA, it is the authors firm believe that the main value of the work described here lies in the establishment of reliable and reproducible test systems which can be used for purposes of research, extension, and education. This is a valuable asset for promotion of BCAs and an important prerequesite for taking biocontrol out into the field and greenhouse. However, the all important goal continues to be the development of solutions for the grower. Biocontrol will not be readily accepted as such if it does not offer distinct benefits with regard to disease control, economic considerations, user and environmental safety, or other important aspects of horticulture. It has to be successful. Acknowledgements The authors wish to thank the Bundesministerium für Bildung und Forschung (BMBF; FK ) and the Thüringer Ministerium für Wissenschaft, Forschung und Kunst (TMWFK) for financial support of the Biocontrol Technology Transfer Project. The technical support by Ms. A. Keuck, the gardeners, students, technical personnel and faculty members of the Fachbereich Gartenbau, as well as the help and materials provided by several cooperators is gratefully acknowledged. References Alabouvette, C.; Schippers, B.; Lemenceau, P.; Bakker, P.A.H.M. (1998), Biocontrol of Fusarium wilts: toward development of commercial products. In: Boland, G.J.; Kuykendall, K.L.D. (eds), Plant - microbe interactions and biological control. Marcel Dekker, Inc., New York Basel Hong-Kong, 2, Anonymous (21), Statusbericht Biologischer Pflanzenschutz. Bundesministerium für Verbraucherschutz, Ernährung und Landwirtschaft, Bonn. Benhamou, N.; Garand, C. (21), Cytological analysis of defense-related mechanisms induced in pea root tissues in response to colonization by nonpathogenic Fusarium oxysporum FO 47. Phytopathology 91, Bode, E. (2), Entwicklung und Marktzugang mikrobieller Antagonisten von Pflanzenkrankheiten. Nachrichtenblatt deut. Pflanzenschutzd. 52, Brückner, S. (22), Erfahrungen über den Praxiseinsatz von Contans WG zur Bekämpfung von S. sclerotiorum und Entwicklung einer integrierten Strategie zur nachhaltigen Bekämpfung des Erregers. Mitt. Biol. Bundesanst. Landw. Forstw., Berlin - Dahlem 39, Budge, S.P.; Whipps, J.M. (21), Potential for integrated control of Sclerotinia sclerotiorum in greenhouse lettuce using Coniothyrium minitans and reduced fungicide applications. Phytopathology 91, Dercks, W. (24), Ist das Konzept der wirtschaftlichen Schadensschwelle neu zu überdenken? - Ein Diskussionsbeitrag. Proceedings 8 th Thüringer Agrarökologie - Kolloquium: Agrarproduktion und Biodiversität, Jena, 18 May 24. Thüringer Ministerium für Landwirtschaft, Naturschutz und Umwelt, Erfurt, Germany, in press. Dercks, W.; Keuck, A.; Schmatz, R.; Orlicz-Luthardt, A.; Hennig, F. (21), The biocontrol technology transfer project. Phytopathology 91 (6 ; Supplement),

14 W. DERCKS AND R. SCHMATZ Dercks, W.; Keuck, A.; Kreller, M.-L.; Seyler, C.; Hennig, F. (23), Fusaclean G als Mittel gegen die Cyclamenwelke geprüft. Gärtnerbörse 24, Dercks, W.; Schmatz, R. (23), Biologischer Pflanzenschutz in Thüringen. Proceedings 7 th Thüringer Agrarökologie - Kolloquium: Pflanzenschutz und Umweltschutz, Jena, 15 May 23. Thüringer Ministerium für Landwirtschaft, Naturschutz und Umwelt, Erfurt, Germany, Dreßler, H. (1999), Versorgungslücke bei Fusarium - Antagonist. Gärtnerbörse 5, 8. Elmer, W.E. (22), Influence of inoculum density of Fusarium oxysporum f. sp. cyclaminis and sodium chloride on cyclamen and the development of Fusarium wilt. Plant Dis. 86, Fuchs, J.-G.; Moenne-Loccoz, Y.; Défago, G. (1997), Nonpathogenic Fusarium oxysporum strain FO 47 induces resistance to Fusarium wilt in tomato. Plant Dis. 81, Koch, E. (1996), Wirkungsweise und Anwendungsmöglichkeiten mikrobieller Antagonisten von Pflanzenkrankheiten. Gesunde Pflanzen 48, Koch, E.; Ganze, M.; Dercks, W. (1999), Biologische Krankheitsbekämpfung. Deutscher Gartenbau 47, Koch, M. (1993), Untersuchungen zur Latenz der Fusarium-Welke an Cyclamen persicum und zum Frühnachweis des Erregers in der Pflanze und im Kultursubstrat. Dissertation, Fachbereich Gartenbau, Universität Hannover. Krebs, E.-K. (21), Möglich oder unmöglich? Biologische Bekämpfung der Cyclamenwelke: Gb - Das Magazin für Zierpflanzenbau 9, Purdy, L.H. (1979), Sclerotinia sclerotiorum: history, diseases and symptomatology, host range, geographic distribution, and impact. Phytopathology 69, Schmilewski, G. (21), Wirkt FO 47 in Substraten? Deutscher Gartenbau 4, Soubabère, O. (22), Pflanzenschutz: Mittel gegen die Cyclamenwelke. Deutscher Gartenbau 2, Stock, M. (1999), Cyclamenwelke mit Schäden von unbekanntem Ausmaß. Monatsschrift, Magazin für den Gartenbau-Profi 2, 251. Tischer, T. (1999), Auftreten und Häufigkeit von bodenbürtigen Pflanzenkrankheiten im Thüringer Zierpflanzenbau unter Glas. I.: Ergebnisse einer Umfrage. Studienarbeit, Fachbereich Gartenbau, Fachhochschule Erfurt. Whipps, J.M.; Gerlagh, M. (1992), Biology of Coniothyrium minitans and its potential for use in disease biocontrol. Mycol. Res. 96,