RESUMO
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.
RESUMO
A binomial sampling method for the potato aphid, Macrosiphum euphorbiae (Thomas), on processing tomato plants, Lycopersicon esculentum (Mill), is proposed. Relationships between mean number of M. euphorbiae per leaf and proportion of leaves infested [P(I)] with M. euphorbiae for both upper and interior leaves of the processing tomato varieties 'Alta' and 'Halley' are presented. A split-plot design was used with variety, position in the plant canopy, and block as the factors examined through linear regression and analysis of variance (ANOVA). Results supported the hypotheses that M. euphorbiae densities on upper canopy leaves are predictive of densities on inner canopy leaves and that proportion of M. euphorbiae infested leaves are predictive of mean densities per leaf. Mean M. euphorbiae density was greater on 'Alta' than 'Halley' tomato plants, supporting the assumption that 'Alta' is the more susceptible variety. Taylor's Power Law coefficients, a and b, were similar for proportion of M. euphorbiae-infested upper and inner leaves of both 'Alta' and 'Halley'. Taylor's b coefficients ranged from 1.57 to 1.74, indicating a highly clumped distribution for M. euphorbiae.
