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Basal rot of onion and garlic

Basal rot is a common disease of onion and garlic in Minnesota. Growers should monitor garlic and onion crops for symptoms of basal rot when the crop is in the field and at harvest.

Caused by the fungus Fusarium oxysporum f. sp. cepae, basal rot can occur in all Alliums but causes most significant damage on garlic and onion. Bulb rot begins in the field and can spread post-harvest.
several small purple onion plants with brown rot at the base of the bulb
Tip dieback of leaves and brown rot extending up from the base of the bulb are symptoms of Fusarium basal rot.
M. Grabowski, UMN Extension

What to look for when scouting in the field

  • Stunted plants with yellow foliage and poor bulb development 
  • Plants with tip burn, yellow and collapsed foliage 
  • Plants pull up easily from the soil, few to no roots remain attached 
  • Firm brown rot begins at the basal plate and moves up the bulb 
  • White fluffy fungal growth may be present in humid conditions
close up of purple onion bulb with brown rot and white fungal growth
Fluffy white growth of the fungus can be seen on this infected onion.
M. Grabowski, UMN Extension

How to inspect the harvest

Press on the base of the bulb where the roots attach. Infected bulbs will feel soft and give slightly under pressure. Infection can be confirmed by pulling back the wrapper layers and looking for rot in the bulb or cutting the bulb in half to look for internal rot.
shallot bulb cut in half to reveal soft rot extending up from the base
Rot can be seen progressing up the bulb in this shallot post harvest
M. Grabowski, UMN Extension 

Management options

If only a few plants are infected, pull the plants and compost them in a compost pile that heats up to a minimum of 148℉ and results in the complete breakdown of all plant material. If disease is widespread, plant debris can be tilled under after harvest. Do not plant Alliums in fields where disease has been identified for 3 to 4 years.

Inspect all bulbs at harvest and discard any bulbs with symptoms of rot. Store bulbs at 0℃ and relative humidity of 65-70%. Inspect stored onions and garlic regularly and discard any infected bulbs.

Onion varieties with resistance to Fusarium bulb rot are available and can be used in combination with rotation on farms where disease has occurred. Purchase disease free sets or start plants from seed.

M. Grabowski, UMN Extension educator

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