Celery Anthracnose: A New Disease For Michigan Growers

 

Each year since 2010, Michigan growers have encountered unusual symptoms on celery in the field that have resulted in large economic losses for some growers. The pathogen responsible for the symptoms was identified by the authors as Colletotrichum acutatum. C. acutatum has a broad host range from cultivated plants such as fruits, ornamentals and vegetables, infecting a variety of tissues, but it had never been associated with celery in Michigan prior to 2010. In other crops, sources of inoculum include seed, soil, plant debris and weeds. C. acutatum survives for up to nine months in the soil.

 

Since 2010, Michigan State University Extension has surveyed celery fields in different Michigan counties for celery anthracnose and found plants with severe and moderate symptoms. Disease and symptom development are favored by periods of warm temperatures (greater than 68 degrees Fahrenheit) combined with high humidity (Rodriguez unpublished data).

 

Anthracnose can be clearly distinguished from celery common blights (early, late and bacterial) based on the visual symptoms. Celery leaf cupping and petiole twisting are the most common symptoms along with oval lesions on petioles, adventitious roots and small galls. Thin elliptical lesions are confined to the petioles. Some lesions resemble cracks with brown edges and occasionally adventitious roots may be observed along the lesions. Lesions were commonly observed on the celery heart as leaf cupping that progressed into heart rot, similar to black heart. Occasionally, brown spots were observed on cupped leaf margins. Plants with severe disease were stunted and not marketable.

 

 

In our first field trial, the fungicides Quadris, Cabrio, Manzate and Bravo significantly reduced disease incidence compared with the untreated control. In our second trial, anthracnose was so severe that no fungicide program was able to limit the disease compared to the untreated control (see figures above). When harvesting, the diseased tissue was separated and considered to be trimmings. Although the rest of the healthy tissue is referred to as marketable, it was a poor quality product that would not meet the industry standards as marketable. Plots sprayed with Quadris and Endura showed higher yields compared to the untreated control, but most of the yield was not marketable.

 

In order to control celery anthracnose and diminish the risk of strobirulin resistance, a rotation of strobirulin fungicides – Quadris, Cabrio – with protectant fungicides – Bravo, Manzate – is recommended. Field and cultural practices include appropriate sanitation and avoidance of the pathogen. Transplant trays and flats need to be treated appropriately with commercial disinfestants if reused. The disease can be carried on infected celery transplants from the greenhouse to the field. Inoculum sources should be further investigated in order to determine if seed carry C. acutatum inoculum.