Florida tomato growers have observed an increase in crop losses associated with soilborne pathogens, such as Fusarium wilt, weeds, such as Cyperus spp., and nematodes such as Meloidogyne spp, since the transition from the use of methyl bromide to alternative fumigant systems. Our research indicates that the observed increases in soilborne pests and pathogens is linked to the lower vapor pressure and higher boiling point of the alternative fumigants compared to those associated with methyl bromide. These two factors limit the movement of the alternative fumigants through the raised bed. Two strategies were tested to improve fumigant distribution within raised beds. First, experiments were conducted to evaluate the performance of drip-applied fumigants, with the use of the surfactant Integrate® 20 to improve lateral movement. The results of this experiment indicated that the application of Integrate® 20 the day prior to fumigant application, did little to improve lateral fumigant movement of AIT, Dazitol, Inline, or metam potassium.
Second, we conducted experiments to define the effective zone of fumigation in a standard 1,3-dichloropropene + chloropicrin (1,3-D:Pic) fumigated raised bed system, and also the effect of supplemental fumigation with chloropicrin along bed edges, immediately beneath the plastic extending into the row middle (the “tuck”). Two weeks after fumigation, we collected soil samples from specific locations within the raised bed in all three seasons to enumerate population densities of total Fusarium spp. Fusarium wilt incidence was collected each season and used as a major indicator of supplemental fumigation effectiveness. The grower standard, 1,3-D:Pic, was effective at reducing levels of total Fusarium spp. at all sampling locations within the bed in all three seasons. Supplemental chloropicrin applied with the Avenger coulter significantly reduced population densities of total Fusarium spp. as determined from soil samples, and Fusarium oxysporum f.sp. lycopersici (FOL) race 3 from recovered buried bags. Buried bag results revealed that population densities of FOL were significantly reduced at all locations with the treatment of supplemental chloropicrin.
We conducted additional experiments on commercial farms, with a known history of high Fusarium wilt incidence, to evaluate the effects of using supplemental applications of chloropicrin along the bed edges of 1,3-D:Pic-fumigated, raised beds on the incidence of Fusarium wilt and on marketable tomato yields. The second objective of these experiments was to investigate the minimum rate of supplemental chloropicrin required to reduce the impact of Fusarium wilt. The results from these studies revealed that 168 kg/ha-1 of supplemental Pic is needed to effectively reduce the incidence of Fusarium wilt. Supplemental chloropicrin application also improved marketable tomato yields in all three seasons by as much as 26%.
|Advisor:||Vallad, Gary, Boyd, Nathan|
|School:||University of Florida|
|School Location:||United States -- Florida|
|Source:||DAI-B 78/05(E), Dissertation Abstracts International|
|Keywords:||Allyl-isothincynate, Chloropicrin, Fumigation, Plasticulture, Surfactant, Vegetable production|
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