Final Report for GNC03-019
Field and greenhouse studies were conducted to evaluate the potential for use of a vermicompost-based aerated compost tea to control septoria leaf spot disease in tomato. In each of four trials conducted during 2003 and 2004, plants treated with weekly sprays of compost tea were healthier than plants sprayed with water, and as healthy as those treated with mancozeb at recommended rates. In the trial conducted at Wichita. Kansas, during the summer of 2003, yield of number 1 tomatoes was significantly higher from compost tea treated plants than from other treatments. Vermicompost-based compost tea may prove useful to organic tomato growers.
Compost tea (CT) is getting increased attention and is being used as an alternative plant disease control measure in organic horticulture (NOSB, 2004). An increasing body of experimental evidence indicates that plant disease can be suppressed by treating plant surfaces with a variety of water-based compost preparations (Scheuerell and Mahaffee, 2002). CT differs from compost extracts, compost leachates, or manure teas in the methods of production (Diver, 2002).
CTs are aqueous extracts of compost that are prepared using various processes, which may include specialized brewers and added ingredients that may also culture the organisms being extracted from the compost, including bacteria, fungi, protozoa and nematodes (Ingham, 2002). CTs may be produced by methods that include active aerating during the brewing process (ACT) or with more passive methods that do not include active aeration after initial mixing (NCT). Both ACT and NCT methods rely on specific recipes, well-characterized (high quality) compost, and aqueous extraction for defined periods of time.
CT applied to foliage has been demonstrated to suppress a range of foliar diseases (Scheuerell and Mahaffee, 2002); however most of the studies reported on CT to date, have used NCT (Hoitink, 1990) and much of the research on microbial communities involved in compost-induced suppressiveness of plant diseases has focused on compost or compost-amended soil; and not on aerated compost tea (Scheuerell and Mahaffee, 2002).
Inconsistent results have been a hallmark of efforts to use aerated compost tea for disease suppression. Many factors likely contribute to this inconsistency, including compost quality, added nutrients, brewing time, temperature, and water quality, sufficient levels of aeration during brewing, specific disease being controlled, and local environmental condition.
Diseases are a limiting factor in tomato production in many parts of the world and can be particularly challenging for organic growers. Septoria leaf spot caused by the fungus Septoria lycopersici and early blight caused by Alternaria solani are often severe in Kansas (Marr et al, 1995). These diseases may occur anytime during the growing season, but septoria leaf spot generally becomes more severe after fruit-set, affecting older foliage, while early blight can attack leaves, stems and fruits. Recommended control practices for these diseases include use of wilt resistant varieties, a 3 to 4 year rotation with unrelated crops, and fungicide sprays (Egel et al., 2004). Organic producers have fewer options for disease control on tomatoes and other vegetables and may suffer significant yield losses.
The objective of this study was to evaluate the potential of ACT made from vermicompost to suppress septoria leaf spot and early blight of tomato in Kansas. Experiments were conducted in the field and greenhouse to compare the disease suppressiveness of CTs with fungicide-treated and untreated controls. Experiments also included application of CT to root and leaf surfaces, and the use of various recipes in order to test hypotheses related to modes of compost tea action and to evaluate parameters related to compost tea quality.
A short-term outcome of this project will be enhanced knowledge by cooperating farmers and researchers about compost and compost tea quality, related to disease suppression on vegetable crops, particularly tomato. Intermediate outcomes may include expanded use of compost tea by organic and conventional growers for improved vegetable crop health. Intermediate outcomes may also include a continuation of researcher/grower cooperation to design and implement studies on the use of compost tea to improve vegetable crop health. Longer term outcomes of a successful compost tea research project will include widespread adoption of appropriate use of compost and compost tea, leading to improvements of yields and quality of vegetable and other crops, and to reductions in the use of synthetic pesticides by conventional growers. If successful this project will contribute directly to the overall desired outcomes of SARE, including a) improving the profitability of producers and associated businesses and b) sustaining and improving the environmental quality and natural resources base on which agriculture depends (through reduction in pesticide use and enhancement of soil biological activity).
Wichita – summer 2003
Trial layout. A study was conducted to evaluate the potential of pre-plant compost, and vermicompost CT, applied as a foliar spray or through drip fertigation, to control septoria leaf spot of tomato. Treatments were randomized in a split-plot design with three factors: pre-plant application of NPK (13-13-13) or vermicompost; fertigation with calcium nitrate (CaNO3) or CT; and foliar spray with CT, fungicide (mancozeb) or water. Fertigation treatments were main plots and preplant fertilizer as sub-plots and the foliar sprays as sub-subplots. The trial was replicated four times. The trial was laid out on 8 rows of red plastic mulch with drip irrigation line beneath the plastic. Individual plots consisted of 5 plants with 0.61 m (2 ft) spacing between plants, and 1.52m (5 ft) between adjacent plots. 13:13:13 fertilizer at the rate of 560 kg/ha (500 lb/acre) and vermicompost at the rate of 6567 kg/ha (5862 lb/acre) were applied to previously designated plots. Seeds of tomato cultivar Merced were sown on April 15th in flats with Jiffy Mix (Jiffy products, Batavia, IL) as the medium and plants were watered as needed. At transplant (May 21st, 2003) plants were watered in with Miracle-Gro 10:52:10 (Marysville, Ohio) at the rate of 4.92 mL (1 tsp) per gallon of water, with each plant receiving about 500 mL (2 cups) of solution. Plots were irrigated twice a week and fertigated with compost tea or calcium nitrate once a week or more often as needed throughout the summer.
CT recipe. Fifty gallons (189 L) of CT were brewed weekly using an Alaska Giant tea brewer (Alaska Bounty, Palmer, Alaska) using the following recipe: 2.27 kg (5 lb) vermicompost, 0.45 kg (1 lb) alfalfa pellets, 120 mL (1/2 cup) unsulfured molasses, ½ cup fish emulsion (Neptune’s Harvest, Gloucester, Massachusetts) and 4 tsp (20 mL) Humisolve TM7 (BioAg Corp, Carson City, Nevada). Brewing time was 24 hours with vigorous aeration. CT was filtered through 2 layers of nylon stocking before it was applied to plants.
Sprays and fertigation. Spray treatment of plots started 2 weeks after transplanting (June 4th 2003) and prior to inoculation of the trial with Septoria lycopersici. CT, fungicide, and water were sprayed weekly at the rate of up to 3.8 L (1 gal) per plot, Dithane DF (mancozeb) at the rate of 2.23 kg/ha (2 lb/acre) and water at the rate of 7.6L (2 gal) per plot, with the amount of spray varying with the size of tomato plants and increasing during the season. Four rows of the trial were fertigated with 38 L (10 gal) of CT and the remaining 4 rows with 37 kg/ha (33 lb/acre) of calcium nitrate, weekly when the CT was brewed.
Disease Inoculation. Dried leaves with Septoria leaf spot (Septoria lycopersici) were obtained from a previously infected greenhouse tomato crop and were crushed into fine pieces. Cotton mesh bags (2” x 2”) were packed with 2 grams of inoculum and were placed at the base of the central plant of each plot on 19th June 2003, 4 weeks after transplanting. Plots were then sprinkler irrigated to enhance infection.
Disease severity was recorded weekly (July 29th to August 13th) on individual leaflet and whole plot basis after the appearance of disease. Two terminal leaflets were selected randomly from lower leaves on opposite sides of each plant and were marked with tags. Disease severity on individual leaflets was rated as a percentage of leaf area affected. Whole plots were visually rated using a 1 to 9 scale, where 1 = 0%, 2 = 12.5%,3 = 25%,4 =37.5%,5 =50%, 6= 62.5%,7 =75%,8 =87.55 and 9 = 100% infection. Plots were harvested twice weekly from July 2nd till August 14th 2003, and data on tomato grades were recorded.
Statistical analysis. Data were analyzed using the PROC MIXED procedure of SAS version 6.12 (SAS Institute Inc., Cary, NC). Significance was evaluated at P<0.05 for all tests. Mean separation was accomplished using Fisher’s protected least significant difference test. Pearson correlation coefficients were calculated between the two types of disease severity data.
Greenhouse – winter 2003 and 2004
Two greenhouse trials conducted at Manhattan, Kansas, during the fall/winter of 2003 and spring 2004, assessed effects of CT sprays on development of Septoria leaf spot disease on tomato. The winter-2003 experiment started on 3rd October 2003 and was completed on 5th December and the spring-2004 experiment from 12th April to 14th June.
Plant production Seedlings were produced as for the Wichita trial except the tomato (cv. Beefsteak) seeds were sown on October 3rd 2003(experiment 1) and April 12th (2nd experiment). After 3 weeks, seedlings were transplanted on October 23rd (experiment 1) and May 4th (2nd experiment) into 6-inch plastic pots (one plant per pot, five pots per treatment) containing Jiffy Mix and were fertilized with slow- release fertilizer (3.0 g of Osmocote 17:6:12 plus trace elements) per pot and watered daily or more often, as needed.
Experimental design. Pots were arranged in a randomized complete block design (RCBD) on the greenhouse bench, with 5 different spray treatments for the first experiment and 7 spray treatments for the second experiment.
CT recipes. The same recipe used in the Wichita field trial (see above) was used to make CT in the greenhouse, except that a smaller brewer of 5 gallons capacity (Alaska Bounty, Palmer, Alaska) was used, and proportions were scaled down. CT was made using 0.22kg (0.5 lb) of vermicompost, 100g (0.25 lb) of alfalfa pellets, 10 mL of unsulfphured molasses, 10ml of fish emulsion (Neptune’s Harvest, Gloucester, Massachusetts) and 1 tsp of Humisolve powder. Activated CT(CT-A) was made using the same recipe used in CT but adding 50g (0.11lb) soy flour to compost 24 hours prior to brewing the tea. In the 2nd experiment additional spray treatments were made using CT and CT-A, which were autoclaved before application.
Spray applications started one week after transplanting for first experiment starting on November 2nd. CT, CT-A, fungicide, foliar fertilizer, and water were sprayed weekly at the rate of up to 1 L (0.26gal) of CT per 5 plants, mancozeb at the rate of 1/4 tsp per L (0.26gal) of water per 5 plants, Miracle Gro 10:52:10 at the rate of 1 tsp per 1 L (0.26 gal) of water per 5 plants, and water at the rate of 1 L (0.26 gal) per 5 pants. Separate garden and greenhouse plant sprayers (Gardener’s supply Co, Burlington, VT) were used for spraying CT, fertilizer and fungicide. Spray treatments in second experiment started on May 11th using the same treatments and application rates as the first experiment, and autoclaved CT and CT-A at the rate of 1L (0.26gal) per 5 plants.
Disease inoculation. Conidia of Septoria lycopersici were harvested from cultures grown on ¼ strength potato dextrose agar (PDA) in Petri plates for 2 weeks by vigorously washing the plate surface with autoclaved tap water to dislodge spores. The suspension was collected, adjusted to a concentration of 1 x 10³ spores/ml, and immediately sprayed on the tomato plants on 16th November for experiment 1 and May 22nd for experiment 2 using a garden and greenhouse plant sprayer. Plants were incubated for 48 hours in a mist chamber (24° C, relative humidity >95%) and then returned to the greenhouse bench in a RCBD. Symptoms were first observed 5-7 days after inoculation and the spray treatments were not applied during the week when the plants were inoculated.
Disease assessment. Two leaflets from the lower to middle portion of each plant were randomly selected and were tagged. Nectrotic lesions were counted for each leaf and the data were recorded on 5th of December for experiment 1 and from June 14th for experiment2.
Statistical analysis. ANOVA was performed using the mean numbers of lesions counted of 10 leaflets per spray treatment. The PROC MIXED procedure of SAS version of 6.12 was used for analysis.
Olathe - summer 2004
Trial layout. A field trial was conducted at the K-State Research and Extension Center, Olathe, to examine effects of treatments on foliar fungal diseases of tomato. The trial was laid out as a RCBD with four replications on 3 rows of black plastic mulch with spacing of 5 ft between rows and with drip tape laid under the plastic. Plots consisted of 5 plants with 0.61 m (2 ft) spacing between plants, and 1.52 m (5 ft) between plots. Treatments were foliar sprays of two CTs, EM/bokashi (Sustainable Community Development Co, Kansas City, Missouri), mancozeb, foliar fertilizer (Miracle-Gro), and water. Plots receiving spray treatments with EM also received soil applications of Happy Farmer Bokashi (Sustainable Community Development, Kansas City, Missouri) at a rate of 1.7 oz per plant on July 25th 2004. Seedling production and procedures and tomato cultivar were similar to those used in the Wichita trial. Seeds were sown on May 15th and transplanted on June 18th, 2004.
CT recipe. Two CTs were made simultaneously in 30 gallon (113.5L) batches, using Alaska Giant extractors with a split air stream running from one air pump. Except where noted, the recipe was similar to that used in Wichita, with the proportions reduced. Four lb (1.82 Kg) vermicompost (Windswept Worm Farm, Blue Spring, MO) was either used straight (CT) or after addition of 250 mL (1 cup) fungal activator (Alaska Giant Co., Alaska) 72 hours prior to brewing the tea (CT-A). Fish emulsion (FertiLome, VPG, Inc., Bonham, Texas) was used in place of fish hydrolysate used in earlier recipes.
Spray treatments started 3 weeks after transplanting (from July 9th) and prior to inoculation of plants with Septoria leaf spot. Plots were sprayed weekly at the rate of 1.9 L (0.5 gal) of CT or CT-A per plot, mancozeb at the rate of 2lb/acre, Miracle-Gro fertilizer at the rate of 2tsp/gal, with 0.5 gal applied per plot, EM at 3.7 mL (0.25 Tsp)in 1.9 L(0.5 gal) of water per plot, and 1.9 L water per plot.
Disease inoculation. Septoria lycopersici inoculum was prepared as previously described for the greenhouse experiment and sprayed on the tomato plants using a garden sprayer on August 6th, 2004. Disease ratings were first initiated 11 days after inoculation. The trial was also naturally infected with early blight.
Data collection. The methods of data collection were same as in the previous Wichita trials except the disease severity ratings for whole plots were recorded using % scale. Data were collected weekly from August 17th till September 28th. Plots were harvested from September 3rd to October 1st and yield was recorded for each plot by grade.
Statistical analysis. Data were analyzed using PROC MIXED procedure of SAS (SAS Institute Inc., Cary, NC) version 6.12. Significance was evaluated at P<0.05 for all tests. Mean separation was accomplished using Fisher’s protected least significant difference test. Pearson correlation coefficients were calculated between the two types of disease severity data. To compute the area under disease progress curve (AUDPC), the mean values of weekly severity for each plot were summed using the trapezoidal method. The disease severity estimates for each plot were averaged and summed to compute the final disease severity per treatment. The area under disease progress curves (AUDPC) were calculated for individual leaflet and whole plot measures of disease severity.
In the first field trial, there were no effects of pre-plant or fertigation treatments on tomato yield or Septoria leaf spot disease severity, but there were significant effects due to foliar sprays on counts of number 1 and cull fruit grades, and on disease severity rating at each rating date. Disease severity by both individual leaflet and whole plot measures, increased during the three weeks of evaluation, and was significantly lower on CT and fungicide-sprayed plots than on the water-sprayed plots at trial termination 9 weeks after inoculation. Disease progress was more rapid on the basis of individual leaf than whole plot ratings. Plots sprayed with CT and fungicide yielded significantly more US No.1 tomatoes than water sprayed plots which yielded more culls. There were significant positive correlations (P<0.005) between individual leaflet and whole plot ratings (0.71, 0.68, 0.98) at each rating date.
Greenhouse trials, winter 2003 and spring 2004. There were significant differences among spray treatments in both greenhouse trials. In the first experiment, disease severity was significantly lower on plants sprayed with CT or CT-A or fungicide than the plants sprayed with foliar fertilizer or water. In the second greenhouse study three significantly different levels of disease severity were observed, with lowest disease severity on plants sprayed with CT or fungicide, intermediate severity on plants sprayed with CT-A or autoclaved CTs, and highest on those treated with water or foliar fertilizer.
Field trial, Olathe, summer 2004. There were significant effects due to spray treatments on disease severity, but not on yield in the trial conducted at Olathe. The total produce harvested per acre was 55,780 lbs during the course of experiment. Weekly disease (early blight and septoria leaf spot) disease severity ratings based on individual leaflet and whole plot were taken over a seven week period. Water, foliar fertilizer and EM/bokashi treated plots were significantly more severely affected than fungicide and CT-A treated plots at the later stages of evaluation. AUDPC results for individual leaflet and whole plot disease severity ratings show similar result by both methods, though higher AUDPC values for the individual leaflet rating method. Plots sprayed with fungicide or CT-A were least affected, followed by plots sprayed with CT, plots sprayed with foliar fertilizer or EM, and plot sprayed with water were most severely affected. There were significant positive correlations (P<0.005) between individual leaflet and whole plot ratings (ranging from 0.5 to 0.72) at each rating date.
Discussion. In each one of four trials conducted in Kansas, two in the field, and two in the greenhouse, foliar sprays of vermicompost CTs were as effective as mancozeb at suppressing the foliar fungal tomato diseases septoria leaf spot and/or early blight. Both CT and mancozeb sprays were consistently superior to water control sprays in our experiments, indicating real effects of CT in suppressing these tomato diseases. Furthermore, in the field trial at Wichita, both CT and mancozeb sprayed plots yielded more US No. 1 grade fruits (58% and 47% respectively) than did water sprayed plots, indicating the potential for CT as an economical control measure for tomato producers. In none of our trials was disease suppression by the fungicide as effective as might be expected with a commercial fungicide used according to the label, so it would be premature to conclude the vermicompost CT can provide a comparable biological alternative to conventional fungicides for tomato commercial growers. Nevertheless it appears that vermicompost CTs may have the potential to provide organic tomato producers with a tool for significant suppression of foliar fungal diseases.
Over the course of trials, we used 2 basic vermicompost CT recipes, with based on vermicompost to which a fungal “activator” had been added some time prior to brewing, or which used non-activated vermicompost. Additionally there were minor variations between the recipes used over the experiments, with variations based on brewer type and batch size (CT was made in 50 gallon batches, CT and CT-A were made in 3 or 30 gallon batches), addition of fungal activators (CT-A was made using vermicompost to which soy flour had been added 24 hours prior to brewing at greenhouse trials, or using vermicompost to which fungal activator had been added 72 hours prior to brewing at Olathe trials) or variation in fish emulsion type (cold-processed fish hydrolysate at Wichita and greenhouse trials, whereas heat processed fish emulsion at Olathe trials). While the CTs evaluated consistently resulted in lower disease severity than water controls, there were significant but inconsistent differences in suppressiveness between CT and CT-A (soy activated) in the two greenhouse studies, and with CT-A (fungally activated) performing better than CT in the Olathe field trial. Because CTs made in different batch sizes or with different fish emulsions and activators were not compared in the same trials, it is not possible to draw conclusions about the effects of these recipe variations on efficacy of CT for disease suppression. The fungal activation method used in the greenhouse trials was probably insufficient in length (24 hours) to have allowed growth of fungal populations in the vermicompost prior to tea making, and the differences in suppressiveness of CT and CT-A on septoria leaf spot in the two greenhouse trials are difficult to interpret. However, the fungal activation of vermicompost used to brew CT-A at Olathe consistently resulted in luxuriant growth of fungal mycelium, and CT-A sprayed plots were significantly less diseased than plots sprayed with CT, possibly indicating an effect of fungal populations in CT on suppression of disease. These results support recommendations of Ingham (2000 and 2002) that high quality compost tea should contain a good fungal population. On the other hand, CT, used at Wichita, had low fungal populations (Soil Foodweb report), and was effective at suppression of Septoria leaf spot. EM/bokashi was not as effective as vermicompost CT for suppression of tomato early blight in the single field trial in which we evaluated it.
Treatments and controls in our experiments may provide some insights into modes of action of compost tea on suppression of Septoria leaf spot of tomato. In the Wichita field trial we did not see evidence of a systemic response by plants to the soil applications of vermicompost or CT, but was effective as a foliar spray. Under the greenhouse conditions there were no difference between foliar fertilizer and water controls, but in the Olathe field trial, there was a significant mild reduction in disease due to foliar fertilization with Miracle-Gro, indicating a possible minor contribution of foliar fertilization to disease suppression by CT. In the second greenhouse trial, autoclaved CTs resulted in intermediate Septoria leaf spot severity to water and unheated CTs, possibly indicating an antibiotic effect of non-heat-labile metabolites or recipe ingredients present in the CT. Greater disease suppression in unheated CTs (CT in the second greenhouse trial) appears to indicate an additional disease suppressive effect due to the living component of CT.
Various methods have been used to evaluate plants for disease severity under field conditions (Barksdale, 1969). In both Wichita and Olathe trials, individual leaflet and whole plot rating assessment was used to evaluate disease severity. Disease severity rating based on individual leaflets (10 per plot) were much more time consuming to determine than whole plot ratings, but gave similar results for comparison of spray treatments in our trials. The rapid progress of disease on individual leaflets from the lower or middle parts of the plants, might also lead to a failure to detect differences between treatments, if leaflets of all treatments become fully affected. For practical purposes, assessment of disease severity in future trials could probably rely on careful whole plot assessments and on evaluation of treatment effects on fruit yield. The use of the AUDPC method was very useful for combining the results of multiple evaluations over time.
We found consistent disease suppression by vermicompost CTs over four trials, but reports of CT efficacy are inconsistent (Scheuerell and Mahaffee, 2002). Joslin et al., (2004) used the same source of vermicompost as us in 2003, without suppression of foliar tomato diseases in Iowa. However, the trial was severely affected by bacterial speck/spot complex. Further work is required to evaluate potential efficacy of our CT recipes against diseases of tomato. Small plots and multiple treatments in our experiments might have contributed to overall severity of disease development in our field trials. Further work should perhaps evaluate treatment effects on larger plots or on replicated individual farms.
Barksdale, T.H. 1969.Resistance of tomato seedling to early blight. Phytopathology, 59:443-446.
Diver, S.2002. Notes on Compost Teas: A 2002 supplement to the ATTRA publication
Compost Teas for Plant Disease Control Pest Management Technical Note. ATTRA publication, Fayetteville, Arkansas.
Hoitink.H.A and Chung, Y.R.1990. Interactions between thermophillic fungi and Tricderma hamatum in suppression of Rhizoctonia damping-off in a bark compost-amended container medium.Phytopath. 80:73-77.
Ingham, E.R. 2000 and 2002 .The Compost Tea Brewing Manual. Soil Foodweb, Inc., Corvallis, OR
Joslin et al.,2004.Control of Foliar Disease,Septoria lycopersici,in Organic Tomato Production,HortSceince,Vol.39(4),July 2004.
Mandel, Q., and Baker, R.1991. Mechanisms involved in biological control of Fusarium wilt of cucumber with strains of nonpathogenic Fusarium oxysporum.Phytopathology. 79:361-366.
Marr, Charles W.Tisserat, Ned, Baurenfeind, Bob.1995. Commercial Vegetable Production. K-State Extension and Research publication, Pub.No.MF1124, January 1995.
National Organic Standards Board.2004.COMPOST Tea Task Force Report, April 6, 2004.Published online by the Agricultural Marketing Service/USDA at www.ams.usda.gov/nosb/meetings/CompostTeaTaskForceFinalReport.pdf.
Parker, S.K., Nutter, F.W. Jr., and Gleason, M.L. 1997. Directional spread of Septoria leaf spot of tomato rows. Plant Dis. 81:272-276.
Scheuerell, S.J., and Mahaffee, W. F. 2002. Compost Tea: Principles and Prospects for Plant Disease Control. Compost Science and Utilization, Vol.10, No.4, 313-338.
Educational & Outreach Activities
Results of this work were presented to an interested audience at the Great Plains Vegetable Growers Conference at St Joseph, MO on January 8, 2005. They were also presented in a poster presented at the annual conference of the American Society of Horticultural Science, held in Austin, Texas, in July 2004. The reference is:
Gangaiah, C., E.E. Carey and N.A. Tisserat. 2004. Suppression of septoria leaf spot disease of tomato using aerated compost tea. HortScience 39, 831 [Abstract only].
A manuscript reporting these results is in preparation for submission to a peer-reviewed journal, HortTechnology.
The work done under this project was primarily conducted on research stations. Initially a series of on-farm trials had been planned, but the burden of on-station and laboratory trials proved too great to allow for coordination and follow up of on-farm trials. Grower cooperators established observational plots for assessing effects of compost tea on tomato diseases during 2003, and did not see striking effects.
The results of the trials that we conducted are interesting, and indicate that compost tea may have the potential to play a role in tomato disease control programs. However, our results are still preliminary and will need to be further evaluated at the farm level to determine the potential of compost tea for providing effective control of foliar tomato diseases in commercial production systems. That we achieved consistent results over 4 consecutive trials, and that compost tea significantly increased yields of number 1 fruit in one trial is very encouraging, and provides a strong justification for further evaluation of compost tea in tomato production systems.
Assuming that CT is as efficacious as fungicide applications (this requires further study), and that yields of tomato crops sprayed with CT would be similar to those treated with mancozeb, the main costs to using CT compared to a conventional fungicide would be the cost of a brewer and labor. The cost of our brewer was roughly $350, which could be amortized over the course of a number of growing seasons. With care toward making bulk purchases of CT ingredients, the cost of ingredients to make 5 gallons of tea (to treat one acre) would be $0.8. When the cost of the brewer is spread over 60 applications (12/season for 5 seasons), the cost of treating one acre is $6.60. This compares with the cost of mancozeb (Dithane DF) of $3.00 per lb applied at a rate of 2 lb/acre.
It is premature to talk about farmer adoption of CT for disease control in tomatoes as a result of this study since further work is needed.
Areas needing additional study
Results of this study were promising, demonstrating a consistent effect of CT on septoria and possibly early blight of tomato. However, in all of our trials, disease built up to serious levels by the end of the trial. This might have been due to the high levels of inoculum present in our trials as a result of disease development in untreated control plots. A logical next step would be to evaluate the efficacy of CT in larger plots which are isolated from untreated control plots. This could be done on-station, and could also be done through collaborative on-farm trials, where large production plots could be split between conventional and CT treatments (conventional growers) and between CT and no treatments (organic growers).
A further area for investigation is to evaluate the efficacy of CT on other diseases, such as bacterial diseases, which are normally controlled through the use of products containing copper. Understanding the potential for using CT for tomato disease control, and the diseases and conditions for which it can be effective, would be a logical next step.