Open, landscaped or yard-like environment

If your hemlocks are growing in a very open, yard-like or landscaped environment you may approach treating them a bit differently than you would if they were in a forested setting.

Trees in your landscape or near your house may be considered ‘high value’ trees for several reasons. For example, the trees may be growing very near your home or driveway and it is important that they do not decline in health and become a hazard. Perhaps the trees act as a hedge or important privacy barrier or perhaps they are very large and would be extremely costly to remove were they to decline, etc. These type of ‘high value’ trees’ may warrant special care, attention or resources. In order to minimize risk and ensure the highest degree of treatment efficacy it may be worthwhile to have a professional arborist assess and treat these trees.

First, assess your trees if possible (see Hemlock Health Assessment Guide). There are a few reasons why open grown trees may be slightly healthier than trees growing in the shade of the forest (less adelgid pressure, more water and nutrients, innate resistance in exotic landscape varieties). It is best to confirm the presence of HWA before pursuing treatment.

The following organizations can all provide assistance with pest ID and hemlock health assessment:

Your county’s NC Cooperative Extension Office

Your County Forest Ranger

the Hemlock Restoration Initiative: info@savehemlocksnc.org

For smaller landscape trees that are very easy to monitor alternative treatments such as foliar sprays of insecticidal soap or horticultural oil may be appropriate. It is important to note that the efficacy of these products depends entirely on the applicators ability to thoroughly coat all of the tree’s foliage using a high-pressure sprayer. Foliar application of soaps and oil must be repeated regularly (at least twice per year) and are not recommended for large tress or trees growing in the forest.

Finally, before beginning treatment it is useful to know if, when and how the tree was previously treated. Depending on treatment method and product, hemlock treatments can be effective anywhere from a few months (horticultural soaps and oils) to several years (5-7 years for imidacloprid). Over application of imidacloprid can cause other pest outbreaks and so it is important to treat trees only when necessary (see HWA Identification Guide).

 Forested, closed canopy

Sometimes trees in a forested setting can be considered ‘low value’ trees. This does not mean that they do not have ecological value. In a forest, the value lies not in each individual tree but in the forest as a whole. This means that you may make different treatment decisions in a forested setting than you would in a landscape setting. It is not necessary to have the same solution for every tree.

It is common in forested settings for large trees to be in more advanced states of decline and for there to be many potentially unnoticed, healthy seedlings regenerating in the understory. In general forested settings tend to have more trees of different size classes and differing states of health. In these situations you may pick and choose which trees you want to treat and how. Some reasons you may choose to treat only some of your trees:

1.      Cost: If treating every tree is too expensive you may choose to treat only some trees

2.      Acreage limits for chemical application: There are legal limits to how much chemical you can apply to an acre of land in one year. It is important to understand and follow these limits closely. If treating every tree would cause you to exceed these limits it is best to treat only some of the trees and return the following year to treat the remaining trees.

In these circumstances it is recommended that you treat a subset of trees representing all size classes with special attention to treating the largest, sickest or most valuable trees first.

Keep in mind that it can be more difficult to identify and assess a hemlock in a forested setting (see Hemlock Health Assessment Guide). Hemlock ID and assessment can be easier when deciduous trees are bare. It is best to look at the tree from some distance and from multiple vantage points to get a good sense of its overall health.

Be careful that the tree you intend to treat is indeed a hemlock. See Is it a hemlock for help with hemlock ID. Accurate tree ID is important when treating in forested settings. Be very careful not to apply chemical to a tree which blooms and attracts pollinators (tulip poplar, sourwood, basswood and other blooming trees are common in mixed hardwood/ hemlock forests). If you find that the roots of the hemlock to be treated are intertwined with the roots of a flowering tree, a soil-based application may be inappropriate. In these cases you may choose not to treat the tree or to use a trunk-based treatment (basal bark spray or stem injection).

Steep slopes

When performing soil drench applications on steep slopes, liquid chemical can run downhill and away from the hemlock roots to be treated. To prevent run-off on steep slopes it is best to pour chemical to the upslope side of the tree only and to pour very slowly, making sure that all of the chemical is being absorbed into the soil at the application site.

Wet, seepy areas with saturated soils

It is not advisable to perform a soil based application in continuously wet areas, seeps or saturated soils. If soil moisture is high due to a rain event, wait to apply chemical until soil had dried. Soil should be moist but not saturated.

If soil is continuously wet and saturated because the tree to be treated is growing in a seep, drainage, pond or other water; a soil based application is likely not appropriate. In these situations it is best to use a trunk-based application (a basal bark spray or trunk injection) or to avoid treating the tree all together.

Sandy soils

If the tree to be treated is growing in very sandy or rocky soil, a soil based application may not be appropriate. The insecticides that are used to treat HWA bind tightly to organic matter in the soil and become immobile. If the soil is low in organic matter, the insecticide may move more freely through the environment posing increased risk to waterways and off-target organisms like beneficial insects. In these situations, it is best to use a trunk-based application (a basal bark spray or trunk injection) or to avoid treating the tree all together.

In immediate proximity to flowering plants

If used improperly, neonicotinoid insecticides do pose a risk to pollinators and other beneficial insects. When using these chemicals for hemlock treatment, application methods are key to managing risk.

Before treating, inspect the area around the base of the tree. Are the root systems of other plants growing in the immediate area where you will apply your treatment? Are these flowering plants or trees? If so you can further minimize risk by: cutting back the flowering plant or removing the plant all together, choosing to perform a trunk-based treatment (basal bark spray or trunk injection), or choosing not to treat the hemlock at all.

Please keep in mind: when properly used, the ecological benefits of hemlock treatment far outweigh the risks to off-target organisms. Put another way: if hemlock communities are lost, numerous species (birds, animals, fish, insects and plants) will be permanently impacted and may disappear, whereas the proper use of neonicotinoid insecticides for hemlock treatment will present minimal impacts to invertebrate species on a short-term basis and substantial benefit to invertebrate communities on a long-term basis. It is up to each applicator to decide what they are comfortable with.