Dieback and Leaf Miner
Birch are beautiful ornamental trees. They have nice white bark and rich yellow fall colour. In their native habitat birches grow in moist locations near streams, rivers and lakes. Therefore it is not surprising that many birch trees under go moisture stress at some point in the course of their life. This condition leads to dieback and leaves the tree vulnerable to attack by birch leaf miner.
- sparse foliage and dead branches
- generally begins at the top of the tree and tips of the branches
What to watch for:
- in mid-summer leaves will turn yellow and start dropping pre-maturely
- in the following spring there may be dead branches, sparse unhealthy foliage
- caused by lack of water—moisture stress
- rainfall does not provide enough water—supplemental water is necessary
- plants growing around the base of the tree may compete with tree for available moisture
- it is extremely important to water your birch tree on a regular basis
- water, water, water……
- birch require a lot of water especially in the spring, fall and during hot spells in the summer
- when watering move hose / sprinkler around the entire tree to ensure even distribution of moisture
- the area to be watered is from the trunk to the drip line and beyond the drip line (drip line: the ground directly beneath the outermost tips of the tree’s branches)
- if there is no rain, water the tree at 1-2 week intervals. The soil should be soaked to at least 20cm (8 inch) depth.
- reduce the amount of watering in late August-September to allow tree to harden off. In early to late October trees should be watered well in preparation for winter.
- if grass does not surround the tree it is a good idea to mulch area to prevent moisture loss
*** It is important to set up a fertilizing schedule starting in May and ending at the end of July. Use of an evergreen fertilizer will help prevent iron chlorosis which is common on birch.
BIRCH LEAF MINER
Characterized by unsightly, brown blotched leaves. Cause by the tunneling and feeding of larvae between the two surfaces of the leaves.
Distribution & Hosts:
- three species of leaf miner attack birch in the Northwest Region (Fenusa pusilla, Profenusa thomsoni and Heterarthrus nemoratus)
- all three were accidentally introduced from Europe and are now widely distributed in Canada and the Northern United States
- all native and ornamental birches are susceptible to at least one species of birch leaf miner
confined to the leaves
- first signs of damage can be seen in June. Small light green or gray spots appear on the leaves around the areas where eggs were deposited. As these spots develop they turn into brown blotches, usually more then one on each leaf.
- as the larvae feed between the leaf’s surfaces, the blotches increase in size and merge, eventually covering the entire leaf.
- larvae can be seem by holding leaf up to a light or by peeling back the surface layer of the leaf.
- birch leaf miner is caused by a sawfly
- larvae are whitish and slightly flattened, 6-7 mm long when fully grown
- larvae mature into small black flies
Fenusa pusilla-attacks trees in the spring, preferring newly formed leaves in the exposed crown of the plant. In mid-May females lay eggs in slits near the midribs on the upper surfaces of the young leaves. Larvae hatch from eggs in early June and feed on the tissue between the leaf surfaces. Mature larvae emerge from the leaves in late June-early July and drop to the ground to pupate. 2-3 weeks later they emerge as adults and the life cycle is repeated with a new generation of larvae dropping to the ground to pupate in late August and another in early September. Usually two generations and sometimes a smaller third occur in the prairie provinces.
The two other leaf miner species are similar in appearance and biology. They attack trees later in the year (July) when the leaves are mature and only produce one generation per year. Feeding by these two species continues during the fall. Profensu thomsoni over winters and pupates in the soil, Heterarthrus nemoratus pupates in fallen leaves.
Most damage to ornamental birches in the prairie provinces is caused by Prodensu Thomsoni.
Prevention & Control:
- keep trees healthy
- well watered (in fall, spring and during summer heat)
- well fertilized (set up a schedule from May-August)
- prune out dead and diseased branches
- certain species of birch leaf miner pupate in fallen leaves—clean up leaves in the fall reduces the numbers of pupae
- Use an insecticide:
- Using a contact, foliar insecticide- spray on the leaves as the adults are emerging from the soil. This ensures that the adults will be killed when they crawl onto the leaves to lay eggs.