Blight of Walnuts

Xanthomonas campestris pv. juglandis

Names:

Walnut Black Spot.

Description:

A bacterial disease that initially causes small water soaked spots on leaves and catkins. These enlarge to 2-3 mm wide, turn brown and become angular with time. Dark sunken spots may occur on the leaf veins, midribs and petioles. On young shoots, sunken black areas may develop. Catkin infection can interfere with pollen production and fruit set. Symptoms on nuts depend on the age of infection and include stained, shrivelled and rotten kernels, adherence of the husk to the nut, and premature falling of nuts.

Species Affected:

Walnut.
Seedling trees appear to be the most susceptible.

Biology:

Favoured by spring rains, frost and hail damage.
Over winters in infected buds and twigs.
Spores spread by raindrop splash.
Only young shoots are susceptible and they are resistant to infection by their second season.

Life Cycle:

Over winters in buds and twigs and is splashed onto new growth in spring.

Origin and History:

Distribution:

Significance:

Difficult to control and very damaging.

Management and Control:

Plant tolerant varieties.
Remove and destroy infected shoots in winter.
Apply fungicides.

Related and Similar Species:

References:

1291

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.