Introduction
The blueberry leaftier, Croesia curvalana (Kearfott),
found in low numbers throughout the blueberry growing area
of Nova Scotia, can be a serious problem in commercial fields.
In the past, damage has been restricted to certain areas
of Cumberland County. This fact sheet outlines the description
and biology of the various stages of the blueberry leaftier.
Ways to monitor and control this insect are suggested. |
Blueberry
Leaftier adult
Click picture to enlarge
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Description
The adult is a small moth, about 6 mm long, with a wingspan
1.4 to 1.6 cm. The thorax and margins of the wings are yellow;
the central portion of the front wing is reddish brown,
with a small kidney-shaped yellow spot on each forewing.
The hind wings are gray with a fringe of white.
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| The
eggs are small, approximately 0.3 mm in diameter, and
oval. The eggs are white in colour when they are first
laid, but turn brown after three days. The first to third
instar larvaeare cream coloured with a dark thorax and
black head. The fourth instar larvae are yellowish with
a cinnamon brown head and thorax. The pupae are dark brown
and about 5 to 7 mm in length. |
Leaftier
larva
Click picture to enlarge
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Biology
The eggs, the overwintering stage of the blueberry leaftier,
are laid singly on leaf litter around the base of blueberry
plants in late July and early August. The eggs hatch over
a three week period beginning in late April and early May.
Newly hatched larvae climb up blueberry stems and burrow
into flower buds where they begin to feed. |
Flower bud
showing
larval activity
Click picture to enlarge
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| Second
and third instar larvae feed on expanding leaf buds and
young leaves. Leaves are fastened together with silk to
form a protective shelter around the larvae. Older third
instar larvae and fourth instar larvae often move about
and feed on the flowers as well as leaves.
Pupation takes place during the first three weeks of
June, usually within the shelters. |
Leaftier
leaf shelters
Click picture to enlarge
|
| The
adults begin to emerge during the first week of July, reaching
peak numbers in late July. Males begin to emerge a few days
before the females. |
Damage
This insect causes damage solely in its the larval stage.
First instar
larvae feed on developing flower buds. This is the most
serious damage caused by leaftier and can affect up to 20
percent of buds.
Older larvae feed on leaves and also flowers. In severe
outbreaks defoliation can be close to 100%.
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Monitoring
Technique
To determine if a field will need a spray to control larvae
the following spring, adult moths can be monitored using
pheromone traps. Green Unitraps® baited with blueberry
leaftier pheromone are recommended. The traps are available
from Phero Tech Inc., 7572 Progress Way, Delta, B.C. V4G
1E9.
Traps to monitor adult emergence should be placed in
the field by the third week of June. Traps should be set
at least 40 m apart and at least 25 m from the edge of
the field.
|
Number of Monitoring Traps Required per Field | |
| Field
Size |
Traps
Required |
| Less
than 10 acres |
3 |
| 11 -
50 acres |
6 |
| 51 -
100 acres |
9-10
|
| 101-200
acres |
12-15 |
Traps should
be checked every two to three weeks from mid-June until
mid-August. The number of leaftier moths in each trap
should be recorded each time the trap is checked. The
average number of moths caught per trap is determined
at the end of the season. This number will be used to
determine if it will be necessary to control the larvae
in the following year.
Action
Threshold
The action threshold for applying a spray to control larvae
the following spring is an average of 750 moths per trap
for the trapping season.
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Control
Control of the larval stage can be obtained by applying
Deltamethrin (Decis) when the flower buds have begun to
swell and there is some green colour showing. This corresponds
to a 10% egg hatch and the Fl stage of flower bud development.
Application rates can be found in the Lowbush Blueberry
Protection Guide, ACC No.1011.
|
Flower bud,
F1 stage
Click picture to enlarge
|
References
Delbridge, R. and P. Hildebrand. 1993. Control of Monilinia
blight of lowbush blueberries. Nova Scotia Department of
Agriculture and Marketing fact sheet. 4pp.
Polavarapu,
S. and W.D.Seabrook.1995. Use of pheromone traps for monitoring
blueberry leaftier, Croesia curvalana (Tortricidae)
populations. In: The Management of Blueberry Insect Pest
Workshop Report. Pest Management Alternatives Office,
Ottawa. pp. 27-34.
Ponder, B.M.
and W.D. Seabrook. 1988. Biology of the blueberry leaftier
Croesia curvalana (Kearfott) (Tortricidae) a
field and laboratory study. Journal of the Lepidopterists'
Society. 42(2) pp. 120-131.
Seabrook,
W.D. 1995. A first instar spray for control of the blueberry
leaftier Croesia curvalana. In: The Management
of Blueberry Insect Pest Workshop Report. Pest Management
Alternatives Office, Ottawa. pp. 35-40.
Acknowledgements
I would like to acknowledge Agriculture and Agri-Food
Canada Research Centre, Kentville, Nova Scotia for the
second, third and fourth slides, and R. Delbridge for
the fifth slide. I would also like to thank Dr. Kenna
Mackenzie for reviewing this fact sheet.
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Prepared by: Lorne Crozier, Entomologist 
