ABSTRACT
Tomato spotted wilt virus (TSWV; species Tomato spotted wilt orthotospovirus; genus Orthotospovirus; family Tospoviridae) is a thrips-transmitted virus that can cause substantial economic losses to many crops, including tomato (Solanum lycopersicum). Since 2005, TSWV emerged as an economically important virus of processing tomatoes in the Central Valley of California, in part due to increased populations of the primary thrips vector, western flower thrips (WFT; Frankliniella occidentalis). To develop an understanding of the epidemiology of TSWV in this region, population densities of WFT and incidence of TSWV were monitored in California's processing tomato transplant-producing greenhouses and associated open fields from 2007 to 2013. Thrips were monitored with yellow sticky cards and in tomato flowers, whereas TSWV incidence was assessed with indicator plants and field surveys for virus symptoms. All thrips identified from processing tomato fields were WFT, and females were three-fold more abundant on sticky cards than males. Symptoms of TSWV infection were observed in all monitored processing tomato fields. Incidences of TSWV ranged from 1 to 20%, with highest incidence found in late-planted fields. There was no single primary inoculum source, and inoculum sources for thrips/TSWV varied depending on the production region. These results allowed us to develop a model for TSWV infection of processing tomatoes in the Central Valley of California. The model predicts that low levels of primary TSWV inoculum are amplified in early-planted tomatoes and other susceptible crops leading to highest levels of infection in later-planted fields, especially those with high thrips populations. Based upon these findings, an integrated pest management (IPM) strategy for TSWV in processing tomatoes in California was devised. This IPM strategy focuses on strategic field placement (identification of high-risk situations), planting TSWV- and thrips-free transplants, planting resistant varieties, monitoring for TSWV symptoms and thrips, roguing infected plants, thrips management targeting early generations, extensive sanitation after harvest, and strategic cropping to avoid overlap with winter bridge crops.
ABSTRACT
In California, sweetpotato is mostly grown on light sandy soils in Merced County. Root-knot nematodes (Meloidogyne spp.) can reduce sweetpotato yields and quality. Fluensulfone is the active ingredient of the new non-fumigant nematicide Nimitz. Unlike fumigant nematicides, toxicity toward non-target organisms is low, and it does not emit volatile organic compounds which negatively impact air quality. In two field trials, the effect of fluensulfone on M. incognita levels, and on the yield and quality of sweetpotato was determined. Fluensulfone was applied as a pre-plant soil incorporated drench or as a drench followed by post-plant sprays. Fluensulfone treatments more than doubled the marketable yields over an untreated control and a metam-sodium treatment in both trials. It strongly reduced nematode symptoms on the harvested roots and nematode infestation of these roots. The lowest rate of fluensulfone was as effective as the higher rates, and post-plant sprays following a pre-plant soil incorporated drench did not result in any additional benefits. Fluensulfone did not reduce soil nematode levels at harvest. It was concluded that a pre-plant incorporated fluensulfone drench at a rate of 1.96 kg/ha could provide a viable alternative for currently used nematicides to mitigate root-knot nematode damage in sweetpotato.In California, sweetpotato is mostly grown on light sandy soils in Merced County. Root-knot nematodes (Meloidogyne spp.) can reduce sweetpotato yields and quality. Fluensulfone is the active ingredient of the new non-fumigant nematicide Nimitz. Unlike fumigant nematicides, toxicity toward non-target organisms is low, and it does not emit volatile organic compounds which negatively impact air quality. In two field trials, the effect of fluensulfone on M. incognita levels, and on the yield and quality of sweetpotato was determined. Fluensulfone was applied as a pre-plant soil incorporated drench or as a drench followed by post-plant sprays. Fluensulfone treatments more than doubled the marketable yields over an untreated control and a metam-sodium treatment in both trials. It strongly reduced nematode symptoms on the harvested roots and nematode infestation of these roots. The lowest rate of fluensulfone was as effective as the higher rates, and post-plant sprays following a pre-plant soil incorporated drench did not result in any additional benefits. Fluensulfone did not reduce soil nematode levels at harvest. It was concluded that a pre-plant incorporated fluensulfone drench at a rate of 1.96 kg/ha could provide a viable alternative for currently used nematicides to mitigate root-knot nematode damage in sweetpotato.
