Cause Fusarium proliferatum, a fungus. This fungus can persist in soil and plant debris. Other crop plants can be hosts to this fungus, including garlic and sweet corn. Fusarium species are good saprophytes, which enables F. proliferatum to persist more than several years in soil in spite of not producing chlamydospores (durable survival structures). Fusarium species in general can potentially increase their population on plant debris as well as in the rhizosphere of asymptomatic plants. Affected fields can lose half or more of the normal yield. This fungi can produce mycotoxins, which may be present in affected onion bulbs.
Symptoms This rot of onion bulbs in storage shows symptoms similar to the neck rot. Symptoms usually start at the neck and progress down along the fleshy scales, but the basal plate is not affected. Infected scale appears faint yellow, water-soaked, and translucent, later turning tan-brown and soft. Occasionally, a white mold grows between rotten scales. Frequently, the rot appears to progress along a single fleshy scale in the bulb, although rotting of all the scales in a bulb also has been observed. Usually, infected bulbs do not show any pronounced external symptoms or signs of the fungus.
Cultural control At present, few control measures are recommnended because the mode of infection and conditions that favor disease development are not well understood.
- Rotate out of alliums and avoid sweet corn, wheat, potato, and sunflower for four years.
- Ensure that seed cloves are free from Fusarium species.
- Use aerial bulbils that are produced on the scapes rather than seed cloves.
- Avoid injuring bulbs during harvest and post-harvest handling.
- Clean equipment after working in infested fields; power washing to remove soil and plant debris will aid in reducing the spread on-farm.
- Examine harvested bulbs closely and cull any bulbs with evidence of disease before storage.
- Maintain ideal environmental conditions while garlic is in storage, with relative humidity maintained at 60-70% under cold conditions.
Biological control Efficacy unknown in the Pacific Northwest.
- Bexfond at 7 to 28 fl oz/A for soil applications at planting via drenches, in-furrow applications, drip irrigation, or sprays, followed by irrigation, and reapply at 4-week intervals. 4-hr reentry. O
- Prestop WG at 1.4 to 14 oz/10 gal water (0.1% to 1.0% suspension) as a soil drench or incorporation into growing medium. 4-hr reentry. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, or 3 to 4 quarts/A as a soil drench (drip or chemigation) on 10- to 21-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
References Gálvez, L., and Palmero, D. Fusarium dry rot of garlic bulbs caused by Fusarium proliferatum: A review. 2022. Horticulturae 8:628. https://doi.org/10.3390/horticulturae8070628.
Kalman, B., Abraham, D., Graph, S., Perl-Treves, R., Meller Harel, Y., and Degani, O. 2020. Isolation and identification of Fusarium spp., the causal agents of onion (Allium cepa) basal rot in Northeastern Israel. Biology 9(4):69. https://doi.org/10.3390/biology9040069.
Schwartz, H.F., and Mohan, S.K. Compendium of Onion and Garlic Diseases and Pests; APS Press: St. Paul, MN, USA, 2008.