Location: Subtropical Plant Pathology Research
2012 Annual Report
The field trial conducted in 2009-2010 was repeated on a commercial flower production farm in 2010-2011. Treatments included standard methyl bromide, and an untreated check, solarization alone, steam treatment after solarization using standard 3” perforated plastic drain pipe (steam 1), and steam treatment following solarization using custom-drilled plastic drain tile with 1/16” holes spaced every 1.5”(steam 2). Drain tile buried at 14” deep in the previous year was used again in the repetition of the experiment. There were four tiles per 6’ by 100’ plot. Before application and plastic installation, soil samples were collected from each plot and analyzed for baseline nematode and fungal propagules. Steam application followed the four week solarization period in late-October. All steam was again generated using the Sioux propane boiler system. Plots were steamed for sufficient time to reach the target temperature of 158°Fahrenheit for 20 min. Solarization plastic was retained on the plots during steaming and these were also covered with a layer of carpet padding to provide additional insulation. At the completion of the steam application, soil sampling was repeated. At the grower’s request, the field was divided into three sub-sections and planted to three different flower crops. In each planting area, two sub-plots were established for data collection. Midseason and late season soil sampling was performed for snapdragon (1 Jan 2011, 14 Feb 2011) and sunflower (13 Dec 2010, 7 Feb 2011), and late season on delphinium (12 April 2011) and analysis was conducted for nematode and fungal propagules. Weed emergence was quantified in the data collection areas during the same time periods and the weeds were removed. In addition, yield of marketable stems was recorded by the grower cooperator for snapdragons and delphiniums. Due to a significant freeze event, sunflowers were not harvested. In addition, roots and soil were analyzed for the presence of potentially deleterious rhizobacteria. Total fungal propagules per gram of soil followed similar trends throughout the trial with minor differences between crops, most likely due to differences in duration of the crop between planting and harvest. Soil solarization had the greatest number of fungal propagules when compared to all other treatments though the mid-season sample of sunflowers and snapdragons. By the mid-season sampling of snapdragons, there was no longer an interaction between depth and treatment for total soil fungal propagules, although solarization remained the highest. There was no significant treatment effect on the total number of nutsedges by the time the first crop was established. This was not the case for crab grass, which was the dominant weed at this location for this year and was poorly controlled by the solarization treatment. A total marketable sunflower and delphinium stem cut was greatest in the steam treatments and were significantly higher than solarization alone. There were no significant differences found between treatments regarding the isolation of potentially deleterious rhizobacteria. Following steam treatments, root-knot nematode juveniles in soil were very effectively reduced compared to solarization which appeared to increase their numbers. This is consistent with other solarization data regarding effects on juvenile nematodes (J2) in soil. Root-knot nematode J2 in soil from sunflower and snapdragon plots were characteristically low for Dec. and Jan. although numbers from snapdragon soil were numerically highest for solarization.