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What is it?
Fusarium basal rot in onion plants is the result of the soil-inhabiting fungus of the fusarium species. In addition to onions, fusarium basal rot also attacks other vegetables in the garden including garlic, shallots and chives. Unfortunately fungi of the fusarium species can exist indefinitely in a soil base, so susceptible plants may need to be relocated in future years plantings.
What does it look like?
Fusarium basal rot often first appears as a white fungal growth which shows up at the bottom or base of onion bulbs. Other visible signs of fusarium basal rot infection in onion plants are bulbs that are slightly squishy on the outside, and are brown and very mushy on the inside. Leaftips of onion plants may die off or die back and wilt. The neck of the onion bulb may be very soft and squish in your hand if you pick it up. However, unless you look at the onion bulb itself you will most likely think that the wilting of your onion plant leaves and thier dieback may have another cause. That’s why it’s important to recognize the signs of fusarium basal rot which can dmage your crop progresively for many years if you are not aware of it and continue to plant in the same space.
How does it manifest?
Fusarium basal rot manifests in onion plants through contaminated bulbs, soil and equipment. Fusarium basal rot enters the bulb through small wounds in the surface of the onion bulb. These wounds can be caused by cultivating tools, sand or soil abrasion, old entry points of onion maggots or old root scars. Once there is a wound in the onion bulb, fusarium basal rot can enter and begin to spread up into the leaf system. This spread of the fungi causes the onion plant leaves to yellow, wilt and die back or die off. The most susceptible onion bulbs to fusarium basal rot invasion are those which are approaching maturity. Unfortunately, if infection occurs just prior to harvest, or sometimes after harvest infections will occur, then the fusarium basal rot may not show up in your onions until they are already in storage. Fusarium basal rot infections tend to set up in onion bulbs when they are in storage in moist areas with a temperature that is regularly above 70° F, which is prime conditions for quick spread of the fusarium fungi.
What can you do about it?
Unfortunately there is no chemical control for fusarium basal rot and all infected onion plants and onion bulbs must be destroyed. The only way to remove fusarium from the soil is through extensive fumigation techniques, therefore unless you want to engage in this process, it is best not to replant any plants susceptible to fusarium species fungi in that area the following planting season. Additionally, by controlling onion maggots you can help reduce chances of infection becuase your onion bulbs are less likely to have open wounds which the fusarium basal rot can invade. Another way to prevent fusarium basal rot is to store your onion plants in a cool, dry place after you have harvested the onion plants at maturity.
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