Yellow, distorted and disappearing leaves?


Late instar gypsy moth (Lymantria dispar) larva showing large size (J. Lemay)

Gypsy moth larvae are finally finishing up their foliar munching and are pupating across Southern Ontario.  Female larvae can measure up to 3 inches long, they need to be bigger than males since it takes so much energy to produce all those eggs.  Now’s the time to order your sticky tree bands.  Wrapping bands coated in tanglefoot around trunks near pupa will help trap flightless females, which means they will be forced to lay their eggs on the sticky bands for you to remove later at your convenience.  Females will also be sending out pheromones, chemical signals that attract the male moths.  They in turn will get stuck to the sticky band surface and the mating cycle will be (unhappily) interrupted.


Tiny green nymphs of the potato leafhopper feeding on maple. The white one on the left is a cast skin after molting to a larger nymph size. (J. Lemay)


Injury to the petiole (blackening and malformation) of hornbeam from feeding of the Potato leafhopper

Nymphs and adults of Potato leafhopper are feeding on leaf undersides and tender leaf stems (petioles) of several deciduous trees (including, Norway, Freemanii, and sugar maple; hackberry, hornbeam) this year.  Adults will fly away quickly but these tiny, green, wingless, nymphs scuttle SIDEWAYS, rather quickly, across the leaf and to the other side.  Older, hardened off foliage is not usually as susceptible.  Leafhoppers (and aphids) suck plant sap from soft, expanding foliage and cause foliage and stems/petioles to wilt, turn brown/black (‘Hopper Burn”) and become stunted and malformed. Registered insecticides in the nursery include Tristar and Sevin XLR.  Leafhoppers are attracted to yellow sticky cards for monitoring purposes.


New Woolly beech aphids on tri-colour European beech (with a predatory syrphid larva to the right)

Often misidentified as a pest, this is a larva of a ladybird beetle.  Ladybird beetle larvae are awesome predators of plant pests!  Here this ladybird beetle larvae is feasting on soft-bodied woolly beech aphids....delicious :) (J. Llewellyn)

 Larva of a ladybird beetle (black and orange larva) feasting on soft-bodied woolly beech aphids….delicious.

Woolly beech aphid (Phyllaphis fagi) are still actively feeding on the undersides of leaves of European beech at this time.  We saw several young nymphs, completely exposed with no way filamentous covering to them….leaving them exposed to predators.  We saw both Syrphid fly larvae (the little green maggot to the right) and Ladybird beetle larvae feeding actively on the aphids.  Large trees can withstand a large infestation of woolly beech aphids without doing any harm to the tree.  Young nursery stock may sustain damage, try dislodging aphids with a strong stream of water or a good spray of insecticidal soap.

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Look for diffuse-margin leaf spots on apple and crabapple as a symptom of Apple Scab (Venturia inaequalis).  This leaf spot can always be found along the veins (and never in between the veins, like Frog-eye leafspot a.k.a. black rot) (photo on the left).  Hopefully you are seeing very little apple scab, but many areas received frequent rains during leaf emergence and so apple scab can be quite bad in some areas.  Unfortunately, apple trees can respond quite defiantly to apple scab infection as it causes early senescence and leaf drop (photo on the right).  What can you do to limit disease next year?  Try mowing fallen leaves this summer and fall to accelerate leaf break down and reduce the number of leaves with fruiting structure poised to release spores for next spring.

What are some cultivars of Crabapple that are more tolerant of apple scab?

Malus baccata (Siberian crabapple) (Photo: TreesOnline)

Malus ‘Calocarpa’ (photo: Red Butte Garden)

Malus ‘Sutyzam’ (Sugar Tyme) (photo: Blerick tree farm)

Malus ‘Prairifire’ (photo: Hedgerow Rose)

Malus ‘Lanzam’ (Lancelot) (photo: Fiore Nursery & Landscape Supply)

Malus sargentii ‘Tina’ (photo: Centre Jardin Barbe)

Malus ‘White Angel’ (photo: Visit My Garden)

Plus a lot of the weeping selections are quite disease resistant!

Malus 'Moonstone' - Tipei Crab Apple

Malus ‘Moonstone’ (selected in Ontario by the late Horst Dickert) (photo: Connon Nurseries NVK Holdings)


About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
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