FARMINGTON — Two destructive diseases that can decimate a garlic crop and are spread through infected seeds, or cloves, has reached Maine, according to agricultural experts with the University of Maine Cooperative Extension.

The stem-bloat nematode has been confirmed on one farm and allium white rot appeared last year and has now spread to three farms, according to a letter sent this week to Maine garlic growers by Dr. Steven Johnson, the Extension’s crops specialist.

The pathogens are both widespread problems in New York state, Canada, and on the West Coast and were likely spread when stock was ordered from out-of-state companies, he said.

With this year’s garlic harvest under way in about two weeks, infected crops will already be showing signs of disease.

The plants will be stunted with prematurely yellowing leaves. If the attack is from stem bloat, the bulb will be discolored, will darken and become shrunken, soft and eventually decay. It infects garlic, onions, leeks, chives, celery, parsley, salsify, some varieties of peas and lettuce, and high-value bulb crops such as tulips, gladiolus, and daffodils among others. It can live in the soil for four to five years.

Allium white rot has been described as the AIDS of alliums because it can result in the total loss of a crop and take the affected land completely out of production for garlic, onions, leeks for 20 to 30 years.

Signs are early yellowing of leaves and a white, fluffy, thread-like growth around the base of the stem and bulb. There will also be small, poppy seed-sized bodies containing the pathogen scattered through the threads and decaying garlic tissue.

Garlic infected with allium white rot can be safely eaten but the cloves cannot be used for seed.

“With garlic-growing gaining momentum in the home garden and commercially in Maine, people really need to know where their seed stock is coming from,” David Fuller, the Extension’s agriculture specialist from the Franklin County office, said.

He and Johnson work together on the Maine Garlic Project that educates growers about the crop and the latest diseases and pests. Together, they are developing a certification system that would guarantee clean stock.

Amy LeBlanc of Whitehill Farm, a certified organic farm in Wilton, said the 20 raised beds she used to grow about 2,500 plants in 2004 became infected after she planted a portion with seed stock she bought from a company in Oregon.

“Our attempts to confine the fungus have failed. In fact, as the disease can be easily moved on plant material, shoes, tools, in compost and by rainwater or irrigation, we have very likely moved it around ourselves,” she said.

“Now I have new beds, new soil, new tools, a new location and new sanitation protocols,” LeBlanc said.

But she no longer sells seed garlic that had been a mainstay offering in her specialty catalog, Tomato Lovers Paradise. She also sold garlic bulbs for seed and food through farmers markets.

“I’ve lost major money. Where I used to grow my own garlic for seed, now I buy it,” she said.

“I would discourage anyone from growing garlic unless they have seen the garlic in the field or know the person who grew it,” she said.

“Both diseases are on the loose in Maine and people need to know what they are buying. Local is usually OK but — sometimes it isn’t,” she said.

Most of the garlic grown in Maine is from small farms, both organic and conventional, and the crop represents a significant percentage of farm income, LeBlanc said.

Determined to find a solution, she has been awarded a grant from the U.S. Department of Agriculture’s Sustainable Agriculture Research & Education program.

Her multi-year project involves researching the potential of using an aggressive program of biostimulation by using garlic juice and ground garlic greens from healthy plants introduced into infected beds.

The aim is to trick the dormant fungal spores into germinating without an actual host crop. Since there is no crop, the fungus will not be able to complete its life cycle and will die, she said.

In her project summary, LeBlanc wrote that repeated biostimulation and sanitation have been found to “achieve results similar to the use of chemical fungicides, especially when coupled with a four-year rotation plan.”

For information, contact Johnson at the Maine Garlic Project at 764-3361; Fuller at 778-4650; or visit http://extension.umaine.edu/gardening/maine-garlic-project.