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Tentiform Leafminer (Phyllonorycter mispilella)
Hosts
Apple, pear, cherry.
Damage
Leaves - Young larvae (sap-feeders) cause blotch-shaped mines that are
visible only from the underside of the leaf. Older larvae (tissue-feeders)
produce speckled tent-shaped mines on the upper side of the leaf. Premature
leaf drop can occur when third-generation larvae are present in August,
especially if the trees are under stress due to some other factor(s). Most
premature leaf drop has been reported with nursery stock and young trees.
Fruit - Larvae do not attack the fruit but can affect the fruit
through their damage to the leaves. Only very high infestations of leafminers
have the potential to reduce fruit quality and size. Early fruit drop,
increased sunburn, reduced soluble solids and stunted shoot growth are other
reported effects of severe leafminer infestations. Because certain tree
management practices can also cause the same type of losses, care must be taken
in blaming such effects on leafminers.
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Leafminer damage
Photo courtesy of Agriculture & Agri-Food Canada |
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Leafminer sap feeder larval damage |
Identification
Sap-feeding larva - White, flattened, wedge-shaped, legless, 1-2.25 mm
long.
Tissue-feeding larva - White or yellow, cylindrical, with legs, 2.5 -
4.5 mm long.
Pupa - Yellow to dark brown, cylindrical, pointed at one end.
Adult - 3- to 5-mm long moths with gold-bronze forewings streaked with
white held roof-like over the body.
Life History
Pupae overwinter in leaves on the orchard floor, and adults emerge before apple
bloom. Eggs are laid on the underside of leaves. Upon hatching, larvae enter
the leaves and feed within leaf mines until they pupate in the mines. There are
2-3 complete generations per year.
Monitoring
Monitoring can determine the average number of mines per leaf and the
percentage of leafminers killed by parasites (see Control -Biological below).
Instructions on how to sample for leafminers and parasites are described in the
fact sheet Sampling Procedures for Tentiform Leafminer
and its Parasites available from BCMAFF and field service offices. If you
need assistance in determining the level of parasitism, contact your crop
management advisor.
Control
Biological - Parasitic wasps, which kill by feeding on and stinging
leafminer larvae, have spread along with the leafminer. It usually takes 1-2
years after the first appearance of the leafminer before the parasites
effectively control the pest. Thirty percent parasitism of the first-generation
tissue-feeder larvae in the spring should provide biological control for the
rest of the season.
Chemical - Parasites prevent leafminers from causing economic damage
during normal growing seasons. However, when third-generation leafminer larvae
appear in August, some damage can occur as described above. The tentiform
leafminer and its major parasite is resistant to organophosphate insecticides
(Diazinon, Imidan, Guthion, and Sniper). Attempts to control tentiform
leafminers in other fruit-growing regions with pyrethroids and carbamates have
destroyed predators and parasites, induced further resistance development in
the leafminer and led to outbreaks of leafminers, mites and woolly apple
aphids. When tentiform leafminer abundance reaches the action level, apply
Admire, Assail or Agri-Mek (plus 0.25% summer oil) when the leafminer
population is mainly in the sap-feeder stage. A second application may be
required 10 days later if severe pressure continues or generations are
overlapping. Alternatively, apply Confirm or Intrepid at first egg hatch of the
first generation only. Admire and Assail are in the same chemical class so
rotate their use with Agri-Mek to reduce the risk of pesticide resistance
development. Do not apply more than two applications of Assail or Admire either
alone or alternately per season regardless of target pest (codling moth,
aphids, leafhoppers, leafminers) to avoid mite flare-up. Assail applied when
codling moth is laying eggs will aid in control of codling moth.
March 2006
Sampling Procedures for Tentiform Leafminer and its Parasites
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