Herbicide damage on Spruce and Pine

The Plant and Pest Diagnostic Lab (PPDL) has recently received several samples of Norway spruce and white pine with symptoms that appear to be associated with injury caused by synthetic auxin (growth regulator type) herbicides. Typical off-target symptoms caused by these herbicides can include epinasty (twisting and curling) of the shoot and tips (Fig. 1) of branches. On conifers, affected new growth may turn brown and die (Fig. 2). On broadleaf plants, leaf cupping (upward or downward), bending or twisting may occur on new growth and in extreme cases, new leaves may appear irregular in size and shape (usually smaller than normal) and have abnormal leaf margins. These symptoms are similar regardless if it is an ornamental broadleaf plant or a weed. The new growth on the conifers submitted to the lab appeared to be brown and dying. Samples of Norway spruce and white pine submitted to the PPDL and injury reported in other areas of the country appear to be linked back to the common denominator of the herbicide aminocyclopyrachlor applied to nearby lawns for broadleaf weed control. The damage appears to be from root uptake rather than drift or volatilization.

Fig. 1. Epinasty (twisting and curling) of the shoot and tips on white pine caused by an auxin herbicide. Photo by Gary Crum.

Fig. 2. New growth on Norway spruce is dying due to injury from a synthetic auxin herbicide. Photo by Gary Crum.

Herbicides with good soil activity may cause problems on nearby broadleaf ornamentals through root uptake if they are applied within root zones of non–target plants or if drainage patterns funnel run-off to trees. Many herbicide labels have statements that say “Do not apply this product directly to, or allow to be under, ornamental ground covers, foliage plants, flowers, nearby crops or other desirable plants; or to the soil where potentially sensitive plants…” or “…care should be taken within the dripline of trees or shrubs.” It is unclear if the samples received this spring were from misapplications (within dripline or directly to foliage) but it appears that spruce and pine injury may also be occurring due to the expansive root system of these trees beyond the dripline of the tree. It is important to read all labels thoroughly to avoid applications that are not recommended on the label. A list of synthetic auxin herbicides commonly used on turf is shown in Table 1.

Table 1. Synthetic auxin herbicides labeled for use in turf in Indiana.

Other spruce maladies such as conifer dieback from abiotic stress, Rhizosphaera and Stigmina needle cast, spider mites, and frost damage are also common on spruce in Indiana. Drought injury is especially common right now on spruce after the drought experienced last July-November in Indiana.

For evergreens injured by auxin herbicides, we are recommending the following management based upon recommendations from Bruce R. Fraedrich, Ph. D., Bartlett Tree Research Laboratories:

1. Trees usually recover from light herbicide injury. Irrigating the plant during dry periods will help recovery and minimize moisture stress. Irrigation also will help leach root active herbicides from the root zone of the plant.

2. Fertilization should be avoided for a minimum of one growing season following injury, because stimulating excess growth can compound injury from certain herbicides.

3. Similarly, if branch dieback results, pruning should be delayed for at least a year to fully assess the extent of the injury. This will avoid additional pruning of dead branches that may result from continued decline. However, immediate pruning is necessary if dead branches pose a danger to life or property.

For additional information on herbicide injury to plants see “Diagnosing Herbicide Injury on Garden and Landscape Plants”, ID-184-W.

The Office of Indiana State Chemist (OISC) is aware of the issue concerning the application of Imprelis herbicide. Lawn care operators (LCO) and homeowners have reported growth regulator type injury (twisting and curling of new growth) to their evergreens including Norway spruce and white pine. DuPont, the manufacturer of Imprelis, is also aware of the issue and has released a letter to turf professionals and turf distributors (read here). As DuPont collects more information, further written communication regarding Imprelis will be coming in the near future.

If you or your clients want the OISC to investigate injury to evergreens that may have been caused by an application of Imprelis, you should contact George Saxton at (765)494-1582 or at saxtong@purdue.edu. As with any OISC investigation, lawn care operators will routinely be asked for information regarding their applications.

Lawn care operators may have affected clients contact OISC on their own or the LCO may contact OISC for their clients. If the lawn care operator decides to contact OISC for their clients, please make sure the clients are aware that the OISC will need access to the client’s property. If you have questions or require more information on this issue please contact the OISC pesticide section at (765)494-1492.

Aaron Patton, Assistant Professor of Agronomy, Turfgrass Extension Specialist
Gail Ruhl, Plant Disease Diagnostician, Purdue Plant and Pest Diagnostic Lab
Steve Weller, Professor of Horticulture and Landscape Architecture
Joe Becovitz, Pesticide Program Specialist, Office of Indiana State Chemist