Herbicide Damage to a Dawn Redwood

Turfgrass herbicides sold under the trade name Imprelis can damage dawn redwoods.

Dawn redwoods (Metasequoia glyptostroboides) are deciduous coniferous trees with a narrow pyramidal form and a large, thick trunk. Their soft, feathery, light green leaves turn reddish-brown in the fall. Seen only in fossil records until 1941, dawn redwoods were thought to be extinct until a forester in China discovered a living example shortly before World War I. They are among the trees susceptible to herbicide damage, which is often first evident on new growth in the spring.

Symptoms

Symptoms of herbicide damage vary according to the local environment, the type of herbicide and the type of tree. Dawn redwoods often first exhibit herbicidal damage in their needles, or leaves, particularly when the herbicide is absorbed via their roots. These needles yellow and brown and then drop off altogether. They can also twist and curl, as can the tips of branches.

Turfgrass Herbicides and Dawn Redwoods

Dawn redwoods are among the trees believed by scientists to sustain damage from turfgrass herbicides with the active ingredient aminocyclopyrachlor, sold under the trade name Imprelis. Once applied to the grass, the herbicide is absorbed into the soil, which is then absorbed by nearby tree roots and foliage. The chemical accumulates in the growing regions of the shoots and roots, damaging new growth. At time of publication, the long-term affects of the herbicide are unknown, but damage can extend beyond the first year of exposure.

Treatment

Helping a dawn redwood recover from herbicide damage is almost entirely about properly timing support tactics and minimizing further exposure. Moderately irrigate the tree, particularly during drought, to eliminate water stress. Do not, however, flood the surrounding soil, as this might only spread herbicides. Do not fertilize the tree; if the chemical is targeting new growth, fertilizers will only promote the growth and make the problem worse. Prune out dead branch tips but avoid pruning out branch dieback until the extent of the problem can be better evaluated when the buds mature in late summer or early fall. If you can not rule out a soil-borne pesticide as the culprit, do not use the mulch or grass clippings from the area and do not plant new trees or shrubs in the soil.

Similar Conditions

Some conditions can mimic the symptoms of herbicide damage, such as insect or disease damage, drought or seasonal loss of leaves. Dawn redwoods are among the few conifers, along with the bald cypress and the larch, that lose all their needles in the fall. For these particular conifers, this is not a sign of herbicidal damage. Drought, insects and disease can also produce discolored, twisted and curled leaves. Be sure to evaluate the circumstances before concluding the problem is herbicidal damage. If necessary, take samples from the new growth, wood and soil and submit them to a local lab for testing.

References

• University of Arkansas Cooperative Extension Service; Plant of the Week: Dawn Redwood; Gerald Klingaman; 1999
• Nebraska Statewide Arboretum; "Botanical Bits"; From Acorns to Oaks; Kristina Jensen
• University of Wisconsin Extension Cooperative Service; Potential Imprelis® Herbicide Damage on Conifers; Laura Jull; 2011