A new disease of celery: Leaf curl (Anthracnose)
Leaf curl is a serious disease on celery caused by the fungus Colletotrichum acutatum that was observed for the first time in several locations throughout Ontario during 2012. In Australia, the disease caused significant crop losses during the 1990s. The disease has recently been observed in celery fields for the first time in Michigan and Pennsylvania during 2010 and 2011. Infected celery plants are unmarketable due to leaf malformation and lesion development on the stalks (petiole). The recent discovery of celery leaf curl could have a serious negative impact on celery production in Ontario. The Ontario Ministry of Agriculture and Food and the Minisry of Rural Affairs together with the University of Guelph will be conducting a survey for leaf curl in celery fields during 2012.
Growers should become familiar with the symptoms of this disease. Celery leaf curl is sometimes mistaken for early symptoms of Aster yellows however the two diseases look quite different. Celery plants can be infected at any age with the leaf curl pathogen.
Infected plants appear stunted with small malformed cupped leaves but remain green unlike the bleached or yellow plants infected with Aster yellows. Older leaves on infected plants often appear fan-like and curl downward (Figure 1). Brown lesions may develop on the leaf margins of infected plants and occasionally yellow translucent spots appear scattered on the upper leaf surface. Symptomatic leaves eventually become brittle and crack along their length which may extends into the stalk. The stalks of infected plants eventually become twisted with reddish to light brown lesions that candevelop on either the outside or inside of the stalks or inside the crown at the base of the infected plants (Figure 2). Spores of the fungus are produced in the lesions that develop along the stalk and in the crowns and are easily disseminated by water splashing during overhead irrigation or rainy and windy weather. The fungus has been isolated from many non-celery host plants including strawberry, pepper, apple and numerous weeds. It is not known if strains of the fungus infecting the different alternative hosts can infect celery and visa versa.
Figure 1. Leaf curl on infected celery plants appear stunted with small malformed cupped leaves. Older leaves on infected plants often appear fan-like and curl downward.
Figure 2. Twisted stalks of celery plants develop reddish to light brown lesions that contain spores of the leaf curl pathogen.
Currently there are no fungicides registered for the control of leaf curl on celery in Ontario, however, it is probable that some fungicides registered for the control of early and late blight of celery may have activity on Leaf curl but more research is required to identify which ones are most efficacious as well as their timing and rate of application prior to obtaining registration for use for Leaf curl control. Since the pathogen can overwinter in un-decomposed plant residue of infected celery, growers should not plant celery in fields that have infested plant residue and a 3-4 year crop rotation with non-host crops should be followed. Deep ploughing or cultivating of infested residue of infected plants immediately after harvest will encourage decomposition of the residue and lower the population of the pathogen in the field. A few resistant cultivars have been identified in Australia but may not be suitable for Ontario growing conditions. Regardless, growers should grow resistant varieties when identified that are suitable for the region. If possible and practical, disease plants should be rogued, place in plastic garbage bag and remove from field or bury before the disease can spread.
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