Stem and bulb nematode symptoms and their cultural management in Onion

Causal Agent: Ditylenchus dipsaci

Symptoms:

• Infected young seedlings are stunted, pale and have swollen areas along the cotyledons.
• Leaves can develop yellowish-brown spots, can be short and thickened and stem swelling (bloating) can occur.
• As the disease progresses, the foliage collapses and the stems and necks of bulbs soften.
• The bulb scales become soft and light gray.
• Infected bulbs are light in weight, may be malformed or produce sprouts and double bulbs.
• Fungal and bacterial secondary infections are common and often give off a foul odor.

Control:

• To avoid introducing the nematode, check onion sets to verify they are disease free prior to planting.
• If the nematode is present in the soil, fumigation can give good control.
• Complete removal and destruction of cull piles, volunteer onions and host weeds are important for reducing this disease.
• Also, a four year crop rotation to non-hosts such as spinach, carrots, beets, crucifers, lettuce or grains has proven effective.