Problem type: Insect
Name of problem: Leaf roller
Plant name(s): Deciduous ornamentals and fruit trees
Symptoms / Characteristics:
Moth larvae form feeding shelters by spinning silk webs around young leaves and rolling them together. Single leaves may also be rolled into tight cylinders. The larvae may skeletonize the leaves, (only the veins remain intact) or consume them whole. Severed leaf segments remain within the silk webbing and become bleached or brown.
When disturbed, the larvae become extremely agitated and wiggle vigorously. They often fall to the ground or dangle on silk strands. A species of leaf roller common to Manitoba, Archips purpurana, attacks basswood, birch, aspen and willow. The worm-like larvae is light green with a dark brown head, and is about 1 inch in length. Leaf rollers also feed on fruit species such as saskatoon, apple, plum and cherry.
Control / Preventions:
Leaf roller damage does not usually have an adverse effect on plant vigour, as foliage loss is relatively low. However, aesthetic value is reduced due to leaf disfigurement. To eliminate unsightly appearance, rolled leaves can be removed and heavily infested areas can be pruned.
Chemical insecticides are often ineffective, as the larvae are protected within the rolled leaves, and direct contact is inhibited. A registered spray (such as carbaryl) may be applied in late May or early June when the larvae are still exposed. Systemic insecticides can be used on selected plants only, as per manufacturer instructions. Biological insecticides, such as Btk, are effective when the larvae are exposed. A dormant oil application before bud break can effectively destroy overwintering egg masses. Use according to manufacturer directions and use precaution as dormant oil may be harmful to certain plants such as maple and walnut.