Watch out for bacterial blight in hazelnuts

From Erica De Jong, OMAFRA Summer Student and Melanie Filotas, Specialty Crops IPM Specialist, OMAFRA

While most members of Ontario’s emerging hazelnut industry recognize the importance of managing eastern filbert blight, other pests can also affect this crop and will require attention.  Following two harsh winters, we have seen an increased incidence of bacterial blight in many Ontario hazelnut orchards.  While not quite as devastating as filbert blight, this disease can still significantly affect the health of hazelnut trees, particularly newly established ones.

Bacterial blight is caused by the bacterial pathogen Xanthomonas arboricola pv. corylina, and most commonly causes losses in young, establishing trees less than 6 years of age, or in very stressed older tress.  Bacteria enter the tree through natural openings or wounds on buds, branches or trunks.   Bacteria spread between trees and orchards by rain splash, infected nursery stock or contaminated pruning tools.  The freezing weather experienced in recent winters not only weakens the trees and makes them more susceptible to infection, but also increases wounds and cracks providing entry points for the bacteria, which may be why we have seen an increased incidence of the disease in Ontario hazelnuts.

The best way to recognize bacterial blight is on the leaves, where it causes angular, reddish brown spots that may be surrounded by a yellow halo, which may eventually coalesce at the tip of the leaf.

HM Bacterial Blight Fig 1Bacterial blight lesions on hazelnut leaf

Spotting lesions on branches or trunks can be challenging, as they are easily confused with winter injury, sunscald or normal bark splitting.  Lesions are typically vertical sunken splits in the bark, which may ooze a sticky liquid in humid conditions.

HM Bacterial Blight Fig 2Cracking of hazelnut bark due to bacterial blight

If you remove the outer layer of bark near a bacterial blight lesion, the underlying tissue will be brown.

P1090241Browning of tissue under bark lesion

Infected buds can turn brown and fail to leaf out.  Although not as common, spotting can also be found on the nut husks.

HM Bacterial Blight Fig 3Bacterial blight lesions on hazelnut husk

Lesions girdling branches and trunks initially cause premature wilting of leaves under hot, sunny conditions, followed often by dieback of small branches.   These symptoms can be a cue to start looking for lesions by following the dead branches back into and down the tree.

HM Bacterial Blight Fig 4Wilting and dieback due to bacterial blight

It has also been reported that buds can be infected for over 200 days before symptoms appear -meaning infected trees can look healthy.  If you find bacterial blight symptoms, prune out diseased material 60-100cm below the infected branch and burn or remove it from the orchard.  Because of the difficulties in diagnosing, it is a good idea to sterilize pruning tools following every cut in order to minimize the further spread of the bacteria within the orchard.   Commercial hazelnut growers can refer to OMAFRA’s Fruit Production Guide for treatment options for this disease.

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