Effect of Tetranychus urticae (Acari: Tetranychidae) on yield,quality, and economics of tomato production

The twospotted spider mite, Tetranychus urticae Koch, is an important and consistent pest of vegetables in central and western North Carolina, particularly on tomatoes, Solanum lycopersicum L. Small plot experiments were conducted in 2007, 2008 and 2009 in which acaricides were applied to early and late-planted staked tomatoes based on threshold levels ranging from 0 to 50 mites per leaflet, with a non-treated control included. Vine ripe fruit were harvested at weekly intervals from all plots, and fruit were weighed and graded for size and quality. A partial budget analysis was conducted to compare net profitability among treatments. Results from 2007 to 2008 showed that total and marketable yield was higher in plots with low versus high densities of T. urticae, and that yield differences were mostly due to number of fruit harvested rather than size of fruit. In 2009 there were no differences in yields among treatments. Gold fleck caused by T. urticae feeding directly on the fruit was another factor that influenced marketability, with more fruit affected and a higher percentage of surface area affected in higher densities versus lower densities of T. urticae. Net profitability varied considerably among planting dates and years, but an action threshold level to avoid yield losses by T. urticae injury on staked tomatoes appeared to be about eight mites per leaflet on a second or third recently expanded leaf.     

Effects of the invasive tomato red spider mite (Acari: Tetranychidae) on growth and leaf yield of African nightshades

The tomato red spider mite, Tetranychus evansi Baker and Pritchard, is one of the most serious pests of solanaceous crops in Africa. Field experiments were conducted to investigate its effects on the growth and leaf yield of five African nightshade species viz. Solanum americanum, S. sarrachoides, S. scabrum, S. tarderemotum and S. villosum during the 2008 and 2009 growing seasons. Plants were infested with 2–4 day-old female spider mites which were allowed to multiply. The number of mite motiles increased throughout the growing season in unsprayed plots and this number varied significantly between the African nightshade species. Except for S. sarrachoides, leaf damage was high on the other four Solanum species irrespective of the spraying regime during both seasons. However, S. scabrum had a significantly greater leaf area ratio (ratio of leaf area to total plant weight) and specific leaf area (ratio of leaf area to total leaf dry weight) during both seasons. Overall yields were 1.5 times more in S. scabrum and S. sarrachoides compared to S. americanum, S. tarderemotum and S. villosum. Our results show that T. evansi infestation affects the leaf area ratio and specific leaf area of African nightshade species differentially which eventually determines the plant's overall leaf yield. These findings present an opportunity for evaluation and selection of African nightshade species that can withstand spider mite infestation in small holder farms for increased vegetable production in Africa.