Thursday, July 21, 2011

Tree Deaths from Herbicide Use

This spring as usual I prepared my garden for summer, deadheaded some of perennials (which I promise to do more aggressively this year in early winter), cleanup the dead leaves and remove any dead plants. The incredibly harsh winter of 2009-2010 followed by the heat wave last summer killed off four shrubs and 6 evergreens. It was a sad and expensive loss. In preparation for planting the six replacements and one additional tree I purchased seven Treegator Pro Jr. watering bags to ensure that my hollies and Crytomeria would be watered for their first season. For extra insurance I planted them with seaweed and fish heads. Even after the 100 degree days in May and June and the return of heat in July my new trees are looking good.

However, I can not say that about my Japanese dogwood. It is withering. After four years of surviving the hot summers of Virginia it is withering and so I began my investigation when I noticed one more odd thing in my garden. In the stone garden around my septic controls the weeds had withered. In no other place in my garden had the weeds withered. I do not use herbicides or pesticides in my garden. The beds are weeded by hand. Weeding is the work of gardeners. So what had caused the weeds to die off in this little spot and was that related to my Dogwood? Despite my asking my septic service company and the company that cuts my lawn there seems to be no source of herbicides on my garden. However, while I was investigating my problem I came across the suspected Imprelis caused tree deaths.

University Extension websites from Kansas to Pennsylvania have reported injury to evergreens on lawns and golf courses treated with Imprelis. Homeowners, lawn service operators and others have observed browning of shoots and needles and twisting and stunting of shoots, especially near tops of trees. Symptoms are usually most severe on current year growth on tree tops and outer branches. Unlike insect and disease problems, Imprelis damage occurs quickly, within two to three weeks of application. The most commonly affected trees are Norway spruce, Colorado blue spruce and eastern white pine. Firs and yews may also be affected. My dogwood is a Cornus species and not reported to be impacted.

Imprelis is a new herbicide from DuPont, approved for use in 48 states last fall. The U.S. Environmental Protection Agency approved Imprelis (aminocyclopyrochlor) last year for commercial use in controlling dandelions, ground ivy, violets, clover and other weeds in lawns. It’s not available for use by homeowners, so it is unlikely that my neighbors used it. In addition, the damage from Imprelis appears unlikely to be from pesticide drift. Imprelis was developed and marketed to control weeds in lawns and works by both direct uptake through the leaves as well as root uptake by interfering with a plant’s normal hormonal balance. It was designed to be long lasting and does not break down easily. Imprelis is not approved for use in New York and California because both states have separate review procedures for new herbicides. New York State officials identified a problem: the herbicide does not bind with soil, and may leach into groundwater. California has not completed its review.

Reportedly, Imprelis went through about 400 trials, including tests on conifers, and reportedly performed without problems. The U.S. Environmental Protection Agency reviewed the herbicide for 23 months before granting its conditional approval, though all of the safety data was not yet in, the agency believed Imprelis to be a good product. Now, however, The EPA will begin an "expedited review" by the end of July into whether the weed-killer Imprelis is harming or killing some species of evergreens. Most Imprelis applications have not reported damage to spruce or pine, but cases of damage cause alarm when dealing with a newly released herbicide.

The reported cases from Indiana indicate that this may not be a simple herbicide drift issue, but rather from root uptake. Clippings from lawns treated with Imprelis should not be composted because the chemical survives the process and can kill flowers and vegetables that are treated with the compost. That warning is included on the Imprelis product label. The types of trees that are reported to be most commonly affected typically grow vigorously and are therefore good candidates for recovery from minor injury. Reduce drought stress by watering during dry periods. Avoid over-watering that causes water-logging. This is the same advice that the forest service and nursery gave me to try and save my dogwood.

I am reminded of my neighbor’s comment about how bad the dandelions were this spring. My own reaction was to embrace dandelions as pretty and anything green growing in what passes for a lawn around here is considered good- crab grass, clover and other weeds. We need to rethink the use of herbicides in ornamental gardens. Unintended consequences.

1 comment:

  1. Hi Elizabeth,
    Great blog! I'm a reporter with Michigan Radio and wondered if you would be interested in sharing your expertise for a story today. You can tweet @ameliabell44 to get in contact with me or reply to this comment.

    Amelia Carpenter