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Brewing up solutions to pest problems
By Lisa Wickland, Todd Murray & Joyce Jimerson
BioCycle
March 2001 |
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Washington State University Extension staff work with growers to evaluate compost tea to suppress plant diseases.
Lisa Wickland, Todd Murray and Joyce Jimerson
THERE is a rising interest among growers in compost tea as a natural disease inhibitor due to its concentration of beneficial microbial organisms. It contains many microbial components that enhance plant growth and aid disease suppression, including bacteria (Bacillus), yeasts (Sporobolomyces and Cryptococcus), and fungi (Trichoderma), as well as chemical antagonists such as phenols and amino acids.
In theory, by introducing a diverse microbial community to agricultural systems, beneficial microorganisms in compost tea out-compete destructive microorganisms for nutrients. This biological control practice is common in plant pathogen suppression. However, there is very little scientific data useful for growers, and few facts published about aerated compost tea.
Grower Research
University researchers traditionally provide reliable recommendations for pest problems. However, in a time when growers are inundated by new management strategies, the plethora of snake oils and silver bullets challenge individual growers to judge useful management practices for themselves. For an additional challenge, many preferred Integrated Pest Management (IPM) strategies, such as biological control, are still in their early developmental stages and are not yet fully understood by the academic community. Growers have limited reliable information on which to base decisions. This is why on-farm research is paramount.
Maturity, composition and the environment of compost are major factors for determining the fate of the microbial community in compost tea. Temperature, brewing length, method, timing and frequency of application, and weather conditions all play a large part in the final tea results. It is important to keep these factors as consistent as possible. Although no one has control over sunshine, the type of compost used, brewing and application methods can be monitored.
Teas can be brewed in various ways and with different ingredients. Some mechanical tea brewer manufacturers suggest vermicompost, kelp and molasses be added with water. These additional components offer food and nutrients for microbes in the tea and may benefit plants. Vermicompost is specified to encourage an aerobic mesophilic environment.
Building A Hypothesis
In April, 2000, Whatcom County greenhouse grower Alison Kutz-Troutman of Cascade Cuts gave the Washington State University Cooperative Extension an opportunity to test the efficacy of compost tea as a valuable IPM strategy. The previous winter when she was considering a compost tea brewer purchase, Kutz-Troutman contacted the Cooperative Extension for information and advice. All that we could offer was personal anecdotal experience dating back 25 years, when it was a fad for gardeners in New England to make compost tea in five-gallon buckets. There were also a few interesting research trials, but they involved various bucket methods without emphasis on aeration of the tea.
Kutz-Troutman bought a brewer and began conducting informal trials on her crops, seeing positive trends that she attributed to tea use. Kutz-Troutman noted that when it was applied to Cyclamen, she observed “a clear suppression of Fusarium (crown rot) in the crop.” The control group was treated with two conventional applications of fungicide, and there was some incidence of Fusarium. In the tea group, which was not treated with fungicide, there was no Fusarium. The tea group also had suppression of Botrytis (gray mold) throughout the crop of French Lace scented geraniums. “This is the best crop of scented geraniums I’ve ever seen!,” one of the growers exclaimed.
While Kutz-Troutman showed optimism concerning the compost tea brewer’s role in her operation, we were not as confident. Todd Murray, the IPM coordinator for Whatcom County Cooperative Extension, rolled his eyes and turned up his ivory-towered nose: “Where’s your data? How do you know you have control of your plant pathogens?” Joyce Jimerson, Whatcom County Master Composter program manager, added cantankerously, “In my day, we just soaked compost in water. We didn’t need to add air. It worked fine… and we liked it.”
But the idea of using oxygenating brewers to make tea was intriguing, and merited further research. Watching Kutz-Troutman’s enthusiasm over her experiences with the brewer encouraged us to offer help to conduct standardized trials to see what, if any, difference compost tea could make on specific crops for specific diseases. Our hypothesis stated: “There is no difference in the suppression of diseases that cause damping off in seedlings between weekly treatments of water, aerobic and anaerobic tea.”
Kutz-Troutman explained her problems and walked us through the day-to-day life of her crops from seed to sale. She taught us the limitations and problems she faces to control her disease pressures. For her farm, ornamental basil crops sown in spring have difficulty battling “damping off” diseases caused by Fusarium, Pythium and Rhizoctonia organisms. On her farm, Siam Queen is the most susceptible variety. This is the perfect problem to test. Many conditions and organisms cause damping off, so we periodically sent the plants off to have pathogens identified.
Experimental Design
The center of Kutz-Troutman’s greenhouse is well suited for testing because there is little variability in temperature, airflow, and watering conditions. For our experiment, we chose this site and a completely randomized design that selects plots from a larger population and randomly assigns treatments to selected samples. It is a simple yet precise design used for research with uniformity throughout the test plots.
In these experiments, we planted two 288-cell starter flats with four to six basil seeds per cell. These flats were randomly separated into the different treatments and then different replications, and flagged with bright tape to distinguish them as trial starts. We started with 192 cells per treatment with four replications (48 cells for each replication). These were treated and placed in a controlled germination chamber for five days, then moved to a warm greenhouse for further development. They were monitored closely for disease every week starting with the second treatment, seven days after planting.
Two to three weeks later, we transplanted them into 3.5-inch pots with four to six plants/pot, totaling about 100 pots/treatment, with at least 24 pots/replication. Each pot was color coded with a sterilized toothpick, and each replication flat of 24 pots was marked with flagging tape and randomly placed on the floor of the greenhouse. After the plants were put into place, the entire site was flagged with bright tape and markers to ensure the trial plants were set apart from the rest.
To remain consistent, we randomly assigned treatments to basil plants, applying at the same time and same day every week, and the same person collected data. We kept the biases and unwanted variation at a minimum.
Applying The Treatments
Our treatments consisted of a control (straight tap water), anaerobic tea and aerobic tea. Anaerobic and aerobic tea shared the same ingredients, differing only in the brewing process. For the anaerobic tea, we soaked vermicomposted separated dairy solids, soluble kelp and molasses in a bag for 48 hours. The solution was strained and mixed with water to a dilution of 1:10. The aerobic tea was brewed in a large aerated container developed by Growing Solutions. This extract also was diluted to the same ratio with water. The tea treatments began upon germination, and continued until the plants were ready for sale. Applications were made early in the morning to avoid damage to organisms sensitive to UV sunlight. A hand held atomizer was used to apply a “sprench” (combined foliar and drench application) of tea, penetrating about one-quarter inch into the soil. A plastic shield was put up between treatment plants to prevent drift of tea to other plants during applications.
Armed with hand lenses, wax pencil and data sheets, we examined plants each week for signs of damping off. Indications included a split stem, wilted foliage, visible dark brown rot at the soil line, and sometimes spore production. Three trials and seven months later, it was time to analyze the results.
Overall, the data were inconsistent. In two of the three trials, we found a significant difference between weekly treatments of water, aerobic tea, and anaerobic tea in the suppression of damping off in seedlings. Although there was a greater incidence of disease in the control plants than both aerobic and anaerobic teas, statistical differences did not occur until six to eight weeks after germination. Thus, when compost tea works, it takes some time to see the results. We found no statistical difference between the bucket-type and the new oxygenated brewing method of tea.
To Tea Or Not To Tea?
Even though some of our results are statistically significant, the practical benefits of using compost tea to suppress root diseases may be marginal. In our research, we did not see an extreme amount of disease suppression as we observe when experimenting with traditional pesticides. Using tea as a reliable amendment is difficult since benefits are contributed through many factors other than known active ingredients. Unlike many other types of cultural amendments or pest treatments, compost is comprised of a very large and diverse community. The dynamics of compost tea are not understood or currently controllable.
Despite these results, Cascade Cuts is “absolutely” satisfied with integrating compost tea in its IPM program. “Growers need to determine what is economically feasible for them in their particular setting, whether evaluating a chemical product or natural supplements such as compost teas,” said Kutz-Troutman. “It (the experiment) enabled us as growers to evaluate crops in a subjective manner… We had some really obvious successes with the tea.”
She was philosophical about the on-farm trial and recognizes the need for growers to do more research: “The basil studies raised more questions than gave answers. That is alright and understandable. The whole field of microbiology seems to be in its infancy — we need more testing methods and much more information about what we are actually looking at.”
Lisa Wickland is a technician for the IPM Project at Washington State University Cooperative Extension in Whatcom County, Bellingham, Washington. Todd Murray is the IPM project manager and Joyce Jimerson is the Master Composter program manager, WSU Whatcom County. For more information, visit http://whatcom.wsu.edu.
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