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United States Department of Agriculture

Agricultural Research Service

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Location: Subtropical Plant Pathology Research

2013 Annual Report

1a.Objectives (from AD-416):
Expand on-going efforts to determine the impacts of soil solarization and steam, and combinations of these treatments for effects on soilborne pests.

1b.Approach (from AD-416):
Field trials will be conducted with a grower cooperator to determine the optimal combination of soil solarization and soil heating through hot air or steam. Trials will be replicated experiments designed to evaluate the impacts of soil heating on efficacy of controlling numerous soilborne pests. These methods will be evaluated for their on-farm practicality, as well as efficacy for the control of native populations of root-knot nematodes, weeds and soilborne plant pathogens. All trials will be conducted using cut flower crops and yields will be collected based on the grower standards.

3.Progress Report:

This research is related to inhouse project objectives 1. Develop new management strategies for control of pests and pathogens currently or previously controlled by soil fumigants in vegetable and ornamental cropping systems; and 3. Identify impact of pest management tactics on biological and functional diversity of soil microflora, nematode, and weed populations, their competitive interactions, and effects on crop health and to develop genomic technologies to characterize changes in soil microbial populations in response to pest management tactics and the resulting effects on crop health.

Two years of cut flower field trials were focused on determining differences in efficacy of steam delivered through two different types of steam delivery tile. Experiments were conducted on a commercial cut flower farm. Treatments were arranged in randomized complete block design with four replications. Treatments included: 1)standard methyl bromide check under Canslit® metalized film,.
3)steam treatment after solarization using standard 3” perforated tile, and.
4)steam treatment following solarization using custom-drilled drain tile with 1/16” holes spaced every 1.5”, approximately 120 degrees from the green center line of the tile. Drain tile was buried at approximately 14” from the soil surface in order to adequately heat soil for optimal nematode control in a long-term flower crop. Each plot was approximately 100’ long and 6’ wide. Four tiles were laid in each plot. A solarization period of four weeks was followed by steam application over several days in mid-October. All steam was generated using the Sioux boiler system. Plots were steamed for approximately 3.5-4 hours in order to reach the target temperature of 70°C for 20 minutes. Solarization plastic was retained on the plots during steaming and these were also covered with a layer of carpet padding to provide additional insulation. Soil temperatures were monitored for the duration of active heating using compost thermometers at various depths and locations along the tile. The field was divided into three sub-sections and planted to three different cut flower crops. Soil temperatures during the solarization period ranged from a low of 25°C at night to a maximum temperature of 52°C with daytime temperatures ranging generally from 45-50°C during the period prior to steaming. At steam initiation, soil temperatures were between 26 and 30 C across the measured profile. The highest soil temperatures were reached at the depths closest to the drain tile. High soil temperatures were maintained for several hours after active steaming. Steam treatments killed all nutsedge that had emerged under the plastic, but differences between treatments were not statistically significant due to high variability in nutsedge distribution. Soon after treatment application, solarization plots had significantly more goosegrass and spurge remaining alive than either steam or methyl bromide treatments.In the snapdragon crop, Carolina geranium was a dominant weed and was most effectively controlled by the methyl bromide treatment and steam method 2. In the delphinium plots, white clover was most effectively controlled by steam method 2, the total of which was significantly lower than in solarization plots. Total weight of weeds collected from the delphinium subplots was significantly lower in the methyl bromide and steam plots than in those treated with solarization alone. There were no significant differences between the numbers of marketable stems taken from larkspur subplots with the order of treatments being methyl bromide (102 stems), steam method 2 (90), solarization (87), and steam method 1 (85). Snapdragons, the most nematode susceptible crop, had yields that were statistically similar, but in the order of steam 1 (175), steam 2 (174), methyl bromide (135), and solarization (131). Height of snapdragon plants followed the same trend, with the tallest and heaviest plants occurring in the steam treatments, which were significantly higher than the other two treatments. Snapdragon and delphinium stem diameter differences were not significant, but larkspur stems were significantly larger in methyl bromide and both steam treatments than in solarization alone. The overall conclusion of the series of experiments is that the efficacy of steam is acceptable for production of root-knot nematode cut flower species, but the duration of an effective treatment is not commercially feasible with the current technology.

Last Modified: 4/17/2014
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