Struggling river birch - Ask Extension
A three-year old river birch in my backyard is struggling this spring. Many branches are totally barren, some have leafed out and quickly gone brown, ...
Knowledgebase
Struggling river birch #793079
Asked May 28, 2022, 12:47 PM EDT
A three-year old river birch in my backyard is struggling this spring. Many branches are totally barren, some have leafed out and quickly gone brown, and other leaves appear to have been devoured by pests. Photos of each condition are attached. Thoughts? I have lost a maple in the yard to verticilium several years ago.
Baltimore City County Maryland
Expert Response
Fortunately, River Birch is listed as resistant or immune to Verticillium Wilt, so it's unlikely that is a factor. Unfortunately, we don't see any clear symptoms that point to a particular cause. Did the tree sustain significant cicada egg-laying injury on the thin branches/twigs last year? Perhaps branch tips that didn't succumb to damage then are succumbing now if the wounds are not sealing-over well or if storm damage caused further tissue injury. Do any of the stems with wilted and browned foliage have cicada scars further down the stem?
Have you seen any caterpillars on the tree? We can't tell for certain, but it appears there may be shed caterpillar skins clinging to the chewed leaf in your close-up. Although it's a valued plant for several native insects, few caterpillars are considered pests on birch, though sawflies (wasp relatives whose larvae look very similar to, and feed like, caterpillars) are a possibility. An established tree with healthy roots should be able to grow out of minor defoliation like this, though it may take a few weeks. Caterpillars tend to leave their host plant when they are mature and ready to pupate, which is why they seem to disappear after the damage becomes prominent, though many are also eaten by birds and other predators before they can complete their life cycle. Naturally-occurring insect-specific diseases can also wipe-out a population of caterpillars if the weather is conducive, which can be another reason an outbreak seems to disappear after initially causing damage.
Does the new growth at the branch tips look ok? If so, that's probably an encouraging sign the tree will recover. Birch does grow fairly rapidly, at least. For now, just monitor the tree for new or worsening symptoms, and you can trim off any twigs that are completely leafless. As you have probably already been doing since planting, check the root zone for watering needs as we move into hot weather with less-regular rains. Birches can shed foliage when drought-stressed in summer. Feel free to send us additional images for assessment if you notice a decline in the tree.
Miri
Have you seen any caterpillars on the tree? We can't tell for certain, but it appears there may be shed caterpillar skins clinging to the chewed leaf in your close-up. Although it's a valued plant for several native insects, few caterpillars are considered pests on birch, though sawflies (wasp relatives whose larvae look very similar to, and feed like, caterpillars) are a possibility. An established tree with healthy roots should be able to grow out of minor defoliation like this, though it may take a few weeks. Caterpillars tend to leave their host plant when they are mature and ready to pupate, which is why they seem to disappear after the damage becomes prominent, though many are also eaten by birds and other predators before they can complete their life cycle. Naturally-occurring insect-specific diseases can also wipe-out a population of caterpillars if the weather is conducive, which can be another reason an outbreak seems to disappear after initially causing damage.
Does the new growth at the branch tips look ok? If so, that's probably an encouraging sign the tree will recover. Birch does grow fairly rapidly, at least. For now, just monitor the tree for new or worsening symptoms, and you can trim off any twigs that are completely leafless. As you have probably already been doing since planting, check the root zone for watering needs as we move into hot weather with less-regular rains. Birches can shed foliage when drought-stressed in summer. Feel free to send us additional images for assessment if you notice a decline in the tree.
Miri
