I have a customer that has planted garlic for a few years with good results. this year when he pulled the plants the bulb was slimy and rotten. He had planted over 100 cloves and all were rotten except one plant. It also has affected his onions. He planted some of them in a different spot as well but got the same results. I am not sure what answer to give him so I need your help.
Garlic can be a very easy-to-grow herb in the garden, however it is also prone to several diseases. One of the nastiest of garlic problems is the stem and bulb nematode Ditylenchus dipsaci. Nematodes are soil-borne microscopic worms which are often introduced to an area from soil movement due to human activity or by the planting of infected cloves . The nematode lives and reproduces inside garlic plants, eating parts of the stems, leaves and bulbs. It is capable of living without water and can survive for several years in the surrounding soil. The nasty part of garlic nematodes is that the populations of this pest usually build up for several seasons without visible damage. Healthy garlic plants can tolerate moderately large densities of these nematodes without a significant drop in production, and then all at once, populations can reach a level in which the entire crop can be destroyed in a single year.
Infested garlic bulbs tend to be soft, shriveled, discoloured and lighter in weight. Often bacteria, fungi, maggots and mites will invade severely infested bulbs causing them to become mushy with soft rot and decay. This pest attacks all allium crops which includes onions.
From your description it sounds as if your client inadvertently planted cloves that were infected with this nasty pest. The following articles from OMFRA: Managing stem and bulb nematodes in garlic starts in the fall and Stem and bulb nematode management in garlic gives detailed instructions on how to manage this pest.