The cause of unusual and unsightly damage, the couch mite may be tiny but can present a big problem to those caring for couch grass lawns.
Couch mites are, not surprisingly, only a problem in couch turf (Cynodon dactylon). They represent a fairly unique problem and although small and difficult to detect, the damage they cause (pictured above) is a tell-tale sign of their presence.
Couch mites are an eriophyid mite and being a mite they are an arachnid rather than an insect. The mites spend most of their lives beneath the leaf sheath, which is the paper-like casing around the stem. Eggs (0.07 mm) are laid in the leaf sheath and the larvae that hatch are worm-like in shape with two pairs of legs and up to 0.13 mm in length. The nymph passes through two instars before developing into an adult, with an elongated body shape that is yellow-white in colour, and around 0.2 mm in length. They are very small!
Although the adult female only lays around ten eggs in her lifetime, with a life-cycle as short as seven days, numbers can build up very rapidly. There may be as many as 200 mites in a single leaf sheath. The mites suck juices from the plant and the initial signs of damage may be a yellowing and distortion of the leaf tip. The mites also inject a toxic saliva into the plant that causes the shortening of the internodes and swelling of the leaf sheaths, which results in the classic ‘witches’ brooms’ appearance. Damage will first appear in spring, with dieback and browning often following in the summer months.
Couch mites are pretty tough and survive weather conditions of up to 50ªC. Reduced mowing heights and collection of clippings to avoid spread can help reduce the problem, but chemical treatment will be required to eliminate the problem. There are limited products available, but perhaps the best options for residential treatments would be abamectin-based miticides such as Thumper Miticide, although the label must be read thoroughly before application and no re-entry is permitted until the product has dried on the leaf surface.