Location: Subtropical Plant Pathology Research2012 Annual Report
1a. Objectives (from AD-416):
To establish the effective rates of a novel, chemical, non-fumigant methyl bromide alternative, establish crop sensitivity to the material, determine optimal application method, and potential worker safety requirements.
1b. Approach (from AD-416):
Research sites in Florida will be established at two locations that have adequate pest pressure to evaluate the spectrum of activity of the experimental material applied under a typical production system for each selected crop. The first two studies to be implemented will be in the raised-bed vegetable and strawberry production system. The strawberry trial will include seven treatments: Untreated Check, four rates of the experimental material, MeBr (as the standard), and the best non-chemical standard developed in a recently completed project. In the vegetable trial, to be conducted at the USDA, ARS Research Farm in Fort Pierce, FL, the experiment will be conducted as split plot design with all treatments consisting of 100’ of treated bed with the split consisting of application method. Treatments will be replicated four times and main plots will be arranged as a randomized complete block design. The MeBr application for the vegetable trial will be shank applied at bed formation. All treatments will be covered with Canslit brand metalized film to assist with whitefly control. In the strawberry trial, to be conducted at the strawberry research farm in Dover, FL experimental treatments will be applied in paired plots with the MeBr treatment. In the second year of the project, both of the previous trials will be repeated. Also in the second year of the project, extension personnel and growers will be invited to field day presentations to share the current progress. Nematode, weed, and fungal populations at each field site and for each year will be assessed prior to treatment, immediately following treatment prior to crop establishment, at mid-season of the crop, and at the initiation of harvest.
3. Progress Report:
This research relates to inhouse project objectives: 1.A. Evaluate new and alternative chemistries singly and in combinations for their efficacy, spectrum of activity, and feasibility under controlled and field conditions, and 2. Develop and test novel application technologies and methods for chemical fumigants that improve their effectiveness and reduce their environmental impacts. Two strawberry field trials have been conducted. The data collected during this period included weed incidence, composition and weight, root-knot nematode and sting nematode soil density, crop growth parameters, incidence of soil borne disease, soil quality parameters, crop yields, and generation of volatile organic compounds. In addition, pathogen packets, containing inoculum of Fusarium oxysporum and Macrophomina phaseolina were placed in beds either under the drip tape or in the bed middle. Two packets were inserted in each replicated plot. These were recovered, plated onto selective media, and survival was quantified. The strawberry trials included five treatments: Untreated Check, two rates of ASI-261, InLine (as the commercial standard), and the best non-chemical standard developed in a recently completed project. Treatments were replicated four times. The In-Line and ASI-261 applications were performed using a standard drip application system. Nematode, weed, and fungal populations were assessed prior to treatment, immediately following treatment prior to crop establishment, at mid-season of the crop, and at the initiation of harvest. Ten soil cores were taken in each plot using a 2.5-centimeter (cm)-diam soil probe. Soil cores were combined, and a 100-cm3 subsample used to extract nematodes using the Baermann funnel or centrifugation technique. Nematodes from the subsample were identified as either root-knot or sting, other parasitic, or free-living nematodes and counted using an inverted microscope. Survival of fungal propagules was assessed by dilution plating of soil samples onto general media. In-field disease ratings were performed throughout the season beginning with seedling damping off and continuing through root condition ratings following the final harvest. Weeds were identified to species for quantification and weed biomass was measured at crop completion. Plots were harvested based on the commercial standard. After the final harvest, plants were removed from the soil and plant growth measurements, including top weight, root weight, and stem caliper at crown were recorded. At the end of the season, nematodes were extracted from plant root tissue, counted, and identified as described above. Generation of volatile organic compounds was monitored immediately after treatment, 24 hours, and one week after treatment. None were detected in any of the ASI-261-treated plots. There was a significant interaction between treatment and packet placement with regard to the fungal inoculum that was placed in the beds prior to treatment. For the M. phaseolina introduced inoculum, the higher rate of ASI-261 was more effective than the lower rate and the lowest number of colony forming units survived in the bed center with ASI-261 rate 2 and In-Line. Parasitic nematode populations were much lower at this location than was anticipated. A site with a higher population of sting nematode has been identified for the repeat of this trial. Although the overall numbers were low, there was a statistically significant difference between the number of sting nematodes in the untreated check and the treated plots immediately after treatment. At harvest, the population had dropped again and few, if any sting nematodes were found in any of the plots. Strawberry fruit was harvested based on commercial standard. There was a total of 23 picks. Total weight of fruit was numerically lowest in the untreated check; however there were no statistically significant differences among any treatments. Soil populations of Fusarium spp. Fusarium oxysporum, and Trichoderma were monitored throughout the trial. Immediately following treatment application, populations of Trichoderma spp., a potentially beneficial fungus, were significantly increased in plots treated with ASI-261. Late season populations of Trichoderma remained high in both ASI-261 treatments. The implications of this finding are extremely important for the use of this material as a methyl bromide replacement in the production of tree liners in the southeast, which require a Trichoderma population to prevent transplant failure. Also of significance is the increase in the native soil population of total Fusarium spp. in the untreated, which did not occur in any of the other treatments. This resulted in an increase in disease incidence in the untreated check, which was higher than all other treatments.