Southern stem blight is a fungus present in many soils across the Southeast. This fungus is responsible for the loss of many valuable vegetable crops including tomatoes, peppers, and beans. The effects of this blight occur during summer where temperatures are between 77-92 degrees. On our farm, losses are often so rapid that any action taken is too late. With crop loss comes loss of income, which is something any farmer wants to minimize as much as possible.
Many organic farmers use compost as a soil building block on the farm. On our farm we work hard on our compost creation, treating it like we would a crop. We use the compost on our farm as a way to increase sustainability, build up carbon in the soil, develop the soil’s moisture holding capacity, as a mild fertilizer, and to inoculate our fields with beneficial microbes. To maximize this resource the compost is also brewed into a tea. We create the compost tea through an aerated process with a purchased compost tea brewing machine that constantly circulates oxygen with an air pump. The aerated compost tea can be used as a foliar spray or run through our drip irrigation. Our research focuses on testing the efficacy of using compost tea as a competitive biostimulant to increase the beneficial microbial activity, which could suppress the negative activity of Southern stem blight. We believe that creating a significant competition for access to the rhizosphere of our plants will slow, and potentially inhibit, the quick spread of Southern stem blight. Research from Bulluck et al. in Organic and Synthetic Fertility Amendments (2002) and Liu et al. in Long Term Effects of Organic and Synthetic Soil (1997) has suggested that organic amendments such as compost and organic inputs, and the presence of soil microbes, such as Trichoderma spp., Bacillus subtilis, and Pencillium spp., can help suppress the infection and spread of Southern stem blight.
- A creation of a preventative practice that reduces the spread of Southern stem blight with on-farm resources
- Reduce the crop loss to Southern stem blight
- A possible increase in yield through the applications of compost tea
We proposed to run the experiment in fields we have seen damage from the blight in previous years. To make sure we would see the effects of the blight we planted Bright Lights chard in Block 1 and Red Ace beets in block 5; the locations of our two trials for the test. Both of these crops are known to be affected by Southern stem blight, if conditions are present. The Bright Lights chard saw more damage than the Red Ace beets. For an early spring planting we were surprised to see as much damage as we did. The beets saw damage only later into the season as temperatures began to warm up. Each area was 2,500 sq ft with three beds and equally divided into nine sections; however, we did not maintain our goal of no edge effects.
These locations were managed in a no-till manner; the process of turning over the area went in the order of: removing all crop residue by hand, raking any smaller material out of the field, broad forking the beds the entire length, hoeing the bed to even soil particles, then raking the bed smooth. This was a common practice on the farm. To accomplish this we only needed strip hoes, rakes, and broadforks. After preparation, we took soil samples of the area and submitted them to the county extension.
We selected the ‘EZ pick’ variety of bush beans to plant. Jade was not available as planned and EZ pick is a variety we chose because of heat resistance and ability to obtain years to come.
To plant these beds we used an Earthway seeder, equipped with the bush bean seed plate, and direct seeded 2 rows per bed for the 3 beds. The same seeder and plate were used for both plots to make sure similar seeding was achieved. The same day as seeding we installed new drip tape and fittings, one drip per row, and connected the system. The beans were not divided into nine subplots until after the true leaf stage in block 1 and at germination for block 5. In block 1, we did not expect to see stem blight so early, so we adjusted the dividing to subplot time to a more proper time for block 5. Once divided, the nine plots were assigned an application method in the area. To do this we placed 4 T-posts in each bed, separated every 90 feet, and strung string, tomato twine, at the top the entire length. Based on the plot, a color piece of tape was hung the length of the plot on that string; control, yellow; single treatment, pink; double treatment, orange. Once germination occurred we looked out for infected plants. We began counting once a week when signs of blight were found. Counting included two buckets to collect plants, one note pad to record the number found, and a pen. Two people usually were involved in counting the infected plants. Counting concluded the day crop residue was removed from the field, which was after the final harvest.
Applications of our farm-made compost tea occurred after the first true leaf was present on the plant. The tea was made by aerating potable water for 24 hours, placing 4 lbs of farm compost in 4 layers of 2’x1 1/2’ cheese cloth that was tied into a ball, then submerging that ball of compost into the water while tied in place with string and was allowed to brew for 24 hours. After 24 hours, we measured out the correct amount of compost tea into back sprayers, one gallon for single treatment and two gallons for double, and applied the compost tea at soil level while drip was on. The original proposal was to apply the compost tea through the drip line. This was not possible because the pressure needed to properly inject into the system was not obtainable in the 90 foot sections. The drip irrigation stayed on the entire time of treatment to make sure compost tea was worked into soil, drip was always turned on prior. The three divided plots per bed were control, single treatment, and double treatment. The control section of each bed received zero applications of compost teat throughout the entire trial. The single treatment got one gallon of compost tea applied to the 90 foot section. The double treatment had two gallons of compost tea applied to the 90 foot section. These areas were marked and remained the same throughout the trial.
The process of treatments and recording infected plants happened once a week on separate days. The data for weather was collected via National Center for Environmental Information (NCEI). Data was then entered into computer documents. A brewed batch of tea and soil samples at the end of the trials were taken to test to microbial activity.
- Stirrup hoes
- Compost tea Brewer
- Cheese cloth
- Farm compost
- Clean water
- 2 Five gallon buckets
- Tomato Twine
- Drip tape
- Drip header
- Drip connectors
- Note Pad
- 24 Tpost
- Color tape (yellow, orange, and pink)
- Earthway seeder and bush bean plate
- EZ pick beans
- Red Ace beets
- Bright Lights Chard
In the first trial of beans planted, we saw 5,643 beans germinate starting on 5/27/2017. We divided and began counting the total number of infected plants on 6/6/2017 and ended on 7/25/17, which gave a total of five counts of the life span of the crop. Of the 5,643 beans, 1,493 were identified as infected with Southern stem blight, which is 26% of the entire crop. This statistic alone supported the hypothesis of how impactful Southern stem blight, when in a mild year, could be to crop loss. Of the total number of infected, 372 were in the control sections (25%), 732 in the single treatment sections (49%), and 389 in the double treatment sections (26%). It was shocking to see that the control saw the least amount of loss throughout the trial. The double treatment was at control levels, but no improvement on suppressing the spread of Southern stem blight. Because of the high number of infected plants on the single treated section we looked closer into the data collected. We found that single treated group 1 bed 1 had the highest total number of infected plants every week. This bed was also located on the edge of the field. While this may have had some factor into the increased numbers, overall bed 2 (38.2% of infected plants) had the most infected plants over the lifespan of the crop. This was followed by bed 1 (31% of infected plants) and lastly bed 3 (30.8% of infected plants). This data did not support the theory of the increased competition in the root zone decreases the spread of Southern stem blight.
The weather plays a key role in the conditions which stem blight spreads. Over trial the average high temperature was 86 degrees Fahrenheit and the low was 70 degrees Fahrenheit. Over the total nine week trial 11.26 inches of rain fell, giving us an average of 1.25 inches a week. These conditions did present challenges or watering in the compost tea when soils were already moist. We did not see or count any losses from water related loss.
Only one harvest was taken from this crop of beans. The quality after first harvest was determined not economically justifiable to repeat. On that harvest we got a total of 183 pounds of beans. Of those beans 62 pounds came from control sections, 59 pounds single treated sections, and 62 pounds double treated sections. Since single treated sections saw the most loss to Southern stem blight, it was not unusual to see the least come from that section. Double treated sections, which had 26% of the total infected plants, were even in harvest totals from the control. This did not support enough that compost tea could possibly increase yield totals. The harvest by row did show negative affects of the beds being on the edge of the field. Beds were numbered from the edge to the center of the field and bed one yielded 33 pounds, bed 2 69 pounds, and bed 3 81 pounds.
Trial one did not show any data supporting our hypothesis that compost tea would reduce the amount of plants infected with Southern stem blight or increase yields.
Trial 2 was conducted from 6/23/2017 to 8/18/2017. This trial only had 3,564 bean germinate. We got six infected plant counts of the life span of this crop. Of the 3,564 beans, 1,125 were identified as infected with Southern stem blight, which is 32% of the entire crop. Of the total number of infected, 394 were in the control sections (35%), 323 in the single treatment sections (28.71%), and 408 in the double treatment sections (36.27%). The data collected for this trial was somewhat similar to that of trial one. Overall, we know that as the temperature increases the spread of Southern stem blight does also. This is supported by the 32% crop loss compared to 26% in the first trial. The biggest change was single treatment sections had a dramatic decrease in infected plants. There was a 20% change in the share of infected plants and 409 plant difference. The double treated sections saw a 10% increase in share of infected plants, but on 18 plant difference. This makes the data for double treatment consistent. The control infected increased by 10% also and only had a 22 plant increase of infected from Trial 1. The control and double treated plots saw very little change in number of infected, the increases can be contributed to the parallel slight increase in temperature, which was more significant to soil temperature at this point in the growing year. Since the beds were not on the edge of the field the data did not seem significant, but numbers did show a significant difference. This is because the habit of Southern stem blight is to travel plant to plant through the root-zone. Bed 1 had 304 (27.02%) infected, bed 2 487 (43.29%), and bed 3 334 (29.69%).
The weather data collected over this trial had only a slight increase in air temperature at average high of 87 degrees Fahrenheit and average low of 71 degrees Fahrenheit. The rain fall over this period was very similar also with 11.45 inches total and an average of 1.27 inches per week.
A total of three harvest occurred for this trial. A total of 204 pounds were harvested from the field; 68.75 the first harvest, 52 pounds the second harvest, and 83.25 the third harvest. Of the beans harvested 67 pound came fro control sections, 72.25 from single treated sections, and 64.75 double treated sections. The total number of beans harvested averaged over three harvest is 68 pounds per harvest. This is less that the 183 single harvest yielded in trial one. The total number of bean plants certainly influences this decreased number for trial two.
The data collected in trial two showed very similar results for trial one. Both did not support clearly a direct correlation between the spraying of compost tea to decrease infected plants or increased yields. The single treated plants in Trial 2, however did show promise for 2018 if the trend continues.
In our conventional beds, we’ve seen similar losses in the past to summer bean crops. We never took record to compare data. The harvest from spring to summer beans we could quantify. The spring crop of beans had a harvest of 315 pounds, compared to 183 pounds in Trial 1 and 204 in Trial 2. Spring beans saw a gross income of $1,302.75, where as summer no summer trial matched that total. The crop loss does affect farm profits, which continues to motivate us towards an on-farm solution.