Control of Bacterial Blight of Hazelnut
Introduction
Bacterial blight can cause serious damage to hazelnut trees in B.C., especially young ones.
It is caused by the bacterium Xanthomonas campestris pv. corylina which infects Corylus
species. Bacterial blight should not be confused with eastern filbert blight
which is caused by a fungus.Description of Bacterial Blight
Bacterial blight is easiest to detect during the spring. Leaves can develop small spots
(usually less than 3 mm in diameter) that are reddish-brown and surrounded by a yellowish-green zone. The disease can also cause small, dark brown or black spots on the green
nut, although this is quite rare.
![](/web/20061229053437im_/http://www.agf.gov.bc.ca/cropprot/images/hazelnt_bl1.jpg)
Leaf buds and pistillate-flower bearing buds are also susceptible. The outer bud scales are
infected first and then the bacteria moves into the bud itself. Buds may be completely
killed or only partially damaged. Shoots emerging from buds generally become infected
from infected bud scales.
Bacterial blight can cause lesions which encircle the trunk of young trees and cause them
to die. These lesions can be difficult to detect, but close examination shows the bark to be
slightly sunken and reddish-purple in colouration. If you remove the bark at the crown
with a knife, the tissue beneath is brown. A sticky liquid containing many bacterial cells
may ooze out of the lesions during periods of high humidity, and dead leaves will generally
cling to the girdled trunks for some time.
![](/web/20061229053437im_/http://www.agf.gov.bc.ca/cropprot/images/hazelnt_bl2.jpg)
Branch dieback can occur on trees of any age. This dieback results in reduced yields.
Process of Infection
The bacterial pathogen enters through open stomata (on leaves) and wounds on the plant.
It survives from one season to another in cankers and infected buds, surviving better in the
large branch and trunk lesions than in the smaller twig lesions (less than 8 mm in diameter).
It generally does not attack and kill branches that are more than 3 years old.
Trunk lesions develop from pruning wounds or migration of the bacteria from adjacent
infected buds or shoots. Pruning and suckering young trees with unsterilized pruners will
spread the disease.
Susceptibility
Buds appear to be most susceptible from when they are three quarters grown, until they
open in the spring.
Twigs and branches are also most susceptible during the same time period. Twigs become
tolerant to stomatal infections after they have stopped growing and become woody. Any
infections that occur after this stage are from wounds or infections from adjacent buds.
Leaves are susceptible until they have reached their maximum size.
It is not known if the disease infects the plant systemically but the bacterium does not seem
to move into the roots.1
Weather Factors
Temperatures above 20 oC favour infection, although
infection can occur at lower temperatures if the period
of wetness is long enough.
Wet weather is an important factor in the spread of
bacterial blight. The pathogen can be picked up from
cankers and carried by water droplets onto branches
below the cankered branch. Moisture must be present
on the plant tissue for infection to occur, but the
infection time can be as short as one hour for leaf
infections if the leaf is wet during that period.
Disease incidence also seems to increase following
freezing weather. This may be because the trees are
weakened, or because there may be more entry sites
through wounds.
Other Factors
Researchers could not isolate the pathogen from soil
under severely infected tress in Oregon trials. This
suggests that the pathogen does not survive in soil.
It does not appear that insects have an important role
in disease spread.
Disease Management
Although bacterial blight is widespread in the Pacific
Northwest, it can be managed. Identification is the first
step in controlling this disease. Sometimes bacterial
blight can be confused with other diseases such as
sunscald and winter damage, but lab tests can confirm
the presence of the bacterial pathogen. It is easiest to
test for the bacterium during the spring.
Buds can be infected but not show symptoms for over
200 days. This means that healthy looking trees can be
infected. All young trees (planting stock) should be
handled as though they were infected.
Healthy trees are less susceptible than weakened trees
so growers should encourage good growing conditions.
Trials conducted in Oregon showed that the removal
of infected plant material helped reduce the spread of
disease but did not eliminate it. Sprays of Bordeaux
mixtures (6-3-100) in late summer (August) were
sufficient to control the disease. However, in exceptionally
rainy years, three sprays - in late summer, late
fall when leaves were about three-quarters off the tree,
and early spring when the buds were opening - were
necessary to control the disease.
The Oregon trials showed that fixed copper with a
spreader sticker was also an effective deterrent.
Guardsman copper oxychloride 50% (PCP No. 13245)
and UAP Copper Spray (copper oxychloride 50%, PCP No. 19146) are registered in Canada.
Use 3-9 kg of copper oxychloride per hectare. Make the first
application in August/September before fall rains,
the second application when 3/4 of leaves have
fallen, and the third in early spring before bud set.
Use the low rate on small trees and the high rate
on large trees. Apply in 1000 L water/ha by
ground spray only. There is a maximum of three
applications per year.
Disinfect pruners between cuts.
Disinfectant Treatments for Cutting Knives |
Best Disinfectants | Treatment Time |
5% Virkon | Quick Dip |
10% Bleach* | Quick Dip |
DCD Floralife (16 mL/L) | Quick Dip |
Ethanol 70% | 20 seconds |
* Household Strength (5.25% sodium hypochlorite)
Prune out infected branches, making cuts 60 to 100 cm
below the infected branches. Burn the branches or
dispose of them off site.
BC Ministry of Agriculture, Food & Fisheries
Plant Health Program
Abbotsford Agriculture Centre
1767 Angus Campbell Road
Abbotsford, B.C. V3G 2M3
Phone: 604 556-3001
Fax: 604 556-3030
September, 2004
1 Miller, P.W., Bollen, W.B. and Simmons, J.E. (1940) Filbert bacteriosis and its control. Oregon Agricultural Station Technical Bulletin 16.
Return to Pest Management Home
|