Plant Health Problems
Garlic belongs to the same family as onion and leek and may be susceptible to many of the same diseases. See Onion for a more detailed discussion of these diseases.
Diseases caused by Fungi:
Root and bulb rot, Pythium spp., Fusarium spp.
Symptoms appear as wilting and a slow or rapid collapse of the plant. The bulb can appear brown and water-soaked instead of white and firm.
Control can be achieved by using a two-year rotation with nonsusceptible plants, such as corn, to prevent the buildup of pathogenic organisms.
Garlic is susceptible to onion insects, except onion maggot.
This little springtail may occasionally damage young seedling garlic.
Lesser bulb fly, Eumerus tuberculatus.
This insect may injure garlic, but it most severely injures narcissus. The flies appear in May and June and lay eggs at the base of the leaves. The larvae find their way to the tip of the bulb and then go downward into the interior. When fully grown, these maggots are between 1/3 and 1/2" long, wrinkled and grayish yellow. They pupate in August in the bulb or in the soil near it. Certain larvae overwinter in the bulbs, but these are thought to be the second generation, from which flies emerge the following spring. The fly is about 1/3" long, and has gray wings and a black abdomen marked with three white crescent-shaped bands. Destroy any infested bulbs after harvesting.
Onion thrips, Thrips tabaci.
Thrips injury is called "white blast" because seriously injured plants turn white due to the feeding on the outer chlorophyll-containing tissue. Thrips are very small insects with narrow fringed wings that are lacking in the nymphs. In feeding, a thrips leaves a whitish chain-like mark on the surface. They hide in the sheaths of the leaves and are difficult to reach with an insecticide. Hot, dry weather increases thrips damage.