Onion Disease Control

Onion Disease Control - Solution Guide

  • Rotate onion crops. Onions should be rotated every season. However, if you have had issues with fungal diseases in the past don't replant in that same spot for at least 3 years is the recommendation. Many fungal diseases can affect onion plants, all with similar symptoms, which makes them diagnosable only through a pathology test by a certified lab. Fungal pathogens can build up in soils year after year to become a major problem for Allium crops, with few options for recovery other than time.
  • Avoid high-nitrogen fertilizers. This is true, especially after mid-season. Soils with high nitrate levels keep plants in a vegetative and potentially weakened state. High nitrogen can also contribute to poor or delayed bulb formation, which growers don't want. Have a soil test done to identify nutrient levels.
  • Avoid damaging onion bulbs. Hand-pull weeds or cultivate carefully to prevent physical damage to bulbs while in the field. Onion bulbs are easily cut or nicked by weeding tools and wounds are welcomed entry points for disease pathogens.
  • Practice proper sanitation. Clean gardens well at season's end. Thoroughly clean and discard leaf and bulb debris (cull the piles) after harvest. Don't till old onion debris into the soil as that old leaf material can harbor fungal pathogens that overwinter to reinfect a field next season. This is another good reason to rotate properly.

Always plant-certified disease-free onions. We only ship certified disease-free onion seeds, sets & plants.

Fungicide Use for Onion Fungal Diseases

Fungicides with the active ingredient chlorothalonil, such as Fung-onil® by Bonide® OR a bio-fungicide like Zonix™ Biofungicide can be applied as a preventative measure. However, fungicide product effectiveness is dependent on following all the above-mentioned management and avoidance measures as well.

On their own, fungicides cannot protect crops from infection or re-infection when a high disease hazard exists.

Fungicide applications for onion disease control are complex and specific.

Read and follow all product label instructions and precautions