Here are more common problems you might encounter in your summer-grown garlic.
This is a common problem, caused by a soil-borne fungus, Fusarium. The heads are attacked while the plants are still growing in the field or garden. If found, it is best not to compost the diseased garlic, as the fungi can persist in plant debris and in the soil. For more on this disease, see the PNW Plant Disease Management Handbook sections on garlic-basal rot and fusarium bulb rot of garlic.
Blue mold (which sometimes looks green) is caused by at least 9 Penicillium species. This post-harvest decay fungus often enters from air-borne spores through wounds, especially when leaves are removed before they are fully dry. Affected cloves should be discarded. For more on this disease, see the PNW Plant Disease Management Handbook.
This is a newly emerging problem here in Oregon. Typically found in warmer states, it has been showing up in recent years on various crops. The soil-borne fungus that causes this disease, Macrophomina, is a generalist and isn’t picky about which plants it will infect. Discard any affected heads and do not compost!
This is caused by the common mold fungus, Rhizopus. This fungus is a hard-working decomposer that will affect any vegetable matter that is old, injured, moist, or otherwise not in the best of shape. This is one problem you shouldn’t see if your garlic was properly dried and stored dry. This one is OK to compost, as it is probably already in your compost pile!