Onion Smudge

Onion Smudge

Onion smudge is a disease described as early as 1851 by Berkeley in England. He then confirmed the disease in America in 1874. The causal fungus is Colletotrichum circinans. Colletotrichum circinans overseasons as mycelia or stroma in infected onion sets or in the soil. Infected sets planted in the spring serve as inoculum for the crop. Moist weather conditions allow acervuli present in diseased lesions to produce crème-colored conidia and black setae in the centers of them. The conidia are wind-blown or rain-splashed to new plants. Transfer can also occur via tools. Conidia can penetrate plants directly creating new infections on the outer scales of the onions. Inner infection occurs with increased moisture and temperature.

Disease Cycle

Symptoms

Dark green to black 'smudges' appear on the outer scales and necks of bulbs. These smudges can be irregular to circular in shape and up to 2 cm in diameter, often forming in groups. This disease primarily affects white onions and rarely the necks of colored bulbs. These smudges reduce the aesthetic value of the onions and can lead to bulb shrinking and premature sprouting.

Plant Health Management

Crop Rotations: for at least three years
Good drainage
Fungicides
Clean seed and transplants
Dry onions before storage
Store onions at 32F at less than 70% relative humidity

References

Useful Links

Oregon State University

Highlighted Area

This disease is associated with the 'red and white onion phenomenon'. It was observed that red onions (and colored ones in general) did not develop onion smudge while white ones did. For many years it was thought that the red pigment of the colored onion gave it resistance. After careful studies, J.C. Walker determined that resistance was due to a plant produced chemical. These chemicals are the phenolic compounds protocatechuic acid and catechol

Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched and drafted by: Jennifer Fleer, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

E-Mail Home Page