Garlic PestsGarlic is generally very resistant to pests. In fact it is often grown spefically to protect neighbouring plants - see the page on garlic co-planting.
However there are a few pests to which garlic is itself succeptible. Many of these also attack onions, to which garlic is closely related. I can't cover everything here, nor can we diagnose individual cases, however I can give some idea of the sort of problems to look out for.
Some of these pests can be dealt with via commercially available pesticides. For those who favour a more natural, organic approach crop rotation and careful selection of clean seed is the usual recommendation.
Bulb MitesBulb mites can grow up to 1mm long. They are slightly off-white and shiny, with a bulbous shape. They are usually found clustered together under the roots of the plant.
Bulb mites stunt plant growth and result in a smaller crop. They can also result in the garlic rotting during storage. Bulb mites can live from one season to the next so it is best to rotate crops with a non-allium variety.
Pea LeafminerLiriomyza huidobrensis
Leafminers appear on garlic plants first as eggs layed within the leaf tissue. They hatch to form small off-white larvae that tunnel inside the leaves, causing a pattern of damage that is visible to the eye.
Leafminers leave the garlic leaves when full grown. Adults are small black and yellow flies.
Damage to garlic from leafminers is mainly cosmetic and they don't usually pose a serious threat to the plant itself or the bulbs. However leafminers can cause very serious damage other crops where the leaves are of more importance and this might be a factor if you grow such crops near your garlic.
Wheat Curl MiteEriophyes tulipae
The wheat curl mite doesn't usually cause much damage to the growing garlic plant unless the infestation is severe. In this case, the garlic leaves will be streaked and twisted and growth stunted.
The main damage from wheat curl mite occurs in the harvested and stored bulb. Its presence can cause the cloves to dry out and crumble. If the affected garlic is planted the crop will probably be infected by Yellow Streak virus which will damage the leaves.
The mite is only about 0.25mm long so is unfortunately difficult to spot. Possible infestation can be reduced by hot water treatment of seed garlic before planting, but be careful. Too high a temperature could kill the garlic itself.