Location: Subtropical Plant Pathology Research
2012 Annual Report
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.