The twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and the hawthorn spider mite, T. viennensis Zacher, are two of the most important pest mites of apple trees (Rosaceae) in China. Because garlic straw, Allium sativum L. (Amaryllidaceae), is normally dumped on farmland, it potentially represents a cheap and readily available resource for pest management. The contact toxicity and repellent effects of garlic-straw extracts (20, 10, 5, 2.5, and 1.25 g/L) were tested against female adults of T. urticae and T. viennensis in the laboratory. The 20 g/L concentration caused 76.5% and 54.9% mortality 48 h after treatment on T. urticae and T. viennensis, respectively. The toxicity regression equations for garlic-straw extract on T. urticae and T. viennensis 48 h after treatment were y  =  1.3 x 3.9 and y  =  0.8 x 4.1, and the LC₅₀ values were 7.2 g/L and 13.8 g/L, respectively. Repellency of T. urticae was 95.6% and 65.2% after 24 h at extract concentrations of 10 g/L and 20 g/L, respectively. The other concentrations of the garlic-straw extract had no significant repellent effects. However, each concentration of the garlic-straw extract had significant repellent effects on T. viennensis, and the repellent rates were higher than 90% for each concentration. Garlic straw or extracts from it may have potential uses for the sustainable management of T. urticae and T. viennensis.