Biological control of weeds by using phytophagous mites may help to contain infestations and reduce their spread in time. Although, eradication is not the goal due to the vastness of the areas, the most desirable scenario is achieved when weeds are no longer a concern and no other control is necessary. However, biological control should not be considered the unique strategy to face weed problems, thus commonly; other methods are still required to attain the desired level of control.

There is an increasingly interest in using mites for biological control of weeds, primarily those belonging to Eriophyidae because of they are host-specific and often weaken the host plant affecting plant growth and reproduction. Although eriophyid mite species impact the fitness of their host plant, it is not clear how much they have contributed to reduction of the population of the target weed. In some cases, natural enemies, resistant plant genotypes, and adverse abiotic conditions have reduced the ability of eriophyid mites to control target weed populations. Besides, susceptibility of eriophyids to predators and pathogens may also prevent them from achieving population densities necessary to reduce host plant populations.

In addition to eriophyid mites, tetranychid mites are also being considered as an alternative for weed control. The gorse spider mite, Tetranychus lintearius Dufour, has shown to reduce shoot growth on gorse (Ulex europaeus L.) by around 36% in impact studies conducted over 2.5 years in Tasmania. New colonies expand rapidly and cause severe damage to gorse plants, but often do not persist in large numbers.

Since the use of phytophagous mite species is a safe alternative for controlling weeds, in this chapter we will review some examples of biological control programs using eriophyid and tetranychid mites worldwide.