Problem type: Disease
Name of problem: Fusarium basal rot
Plant name(s): Onion, garlic, chives, shallot, leek
Symptoms / Characteristics:
Foliar symptoms begin with yellowing and tip dieback. Eventually the entire aerial potion of the plant collapses. Infected plants can be easily pulled from the soil due to the deterioration of the root system. Decay often appears on one side of the bulb base, causing bulbs to appear irregularly shaped. A pinkish-brown discolouration begins at the base of the bulb and moves upward as the disease develops and the decay progresses. White fungal growth may be visible on the decayed portions of the bulb. Bulbs usually become soft, particularly at the neck. Sometimes, however, the outside scales may appear perfectly normal, making it necessary to examine the inside of the bulb for discolouration and decay. Symptoms of late season infections may not become obvious until after the bulbs are in storage. Fusarium basal rot has also been known to affect ornamental bulbs, such as lily, iris and narcissus, causing similar foliar symptoms and bulb decay.
Fusarium basal rot is caused by the soil-borne fungus, Fusarium oxysporum. The fungus may penetrate the crown or root system but typically gains entry through wounded, cracked or diseased bulbs. Onion maggot damage, for example, often precedes fusarium basal rot. The fungus thrives in warm, wet soils and may be spread by water, soil, air, insects, equipment, and contaminated bulbs.
Control / Preventions:
Implement a three-year crop rotation that includes non-host plants. Planting onions or other susceptible crops in succession will increase the disease incidence in soils that harbor the pathogen. Plant only disease-free sets and restrict onion plantings to light, well-drained soil. Disease severity tends to increase in high-temperature, poorly drained soils. Avoid excess irrigation and apply a layer of mulch around the plants to lower the temperature of the soil. Throughout the growing season, keep plants as healthy and vigorous as possible. This involves effective water management and a balanced fertilizer program. Avoid causing unnecessary damage or stress to the plants (particularly the roots and bulbs) that may facilitate the entry of Fusarium oxysporum. Avoid digging around the plants and do not apply excess fertilizer. Fertilizer burn is detrimental to plant health and will render the plants especially susceptible to fusarium basal rot. Controlling onion maggots will effectively reduce the number of wounding sites available for fungal invasion. Remove and destroy symptomatic plants on a regular basis in order to reduce the amount of inoculum present in the garden and, therefore, reduce subsequent infections. At harvest, remove and destroy all injured and diseased bulbs. Advance only healthy, intact bulbs to storage and ensure cool, dry storage conditions. Soil fumigation may be warranted in heavily infested soils. There are several onion varieties available with varying levels of tolerance to fusarium basal rot