Prepare your scouting plan for your Christmas trees

Spring has sprung and it is time to start scouting your Christmas trees and prepare your integrated pest management (IPM) plan for the year.

A hand shaking a branch with needles falling out of it onto a white piece of paper.
Shaking branches over a white piece of paper will help identify smaller insect pests such as aphids and mites. Photo by Jill O’Donnell, MSU Extension.

Now that spring has arrived, it is time to begin scouting your Christmas trees and prepare your integrated pest management (IPM) plan for the year. First, what is IPM? IPM is managing pests by not only using chemical control but also using cultural and biological tools in order to protect plant health and reduce environmental impacts. By implementing IPM, growers no longer spray for a certain pest based on a calendar date but seek to spray for pest insects when control will be most effective.

In addition, IPM programs can reduce the use of broad-spectrum pesticides that might also kill beneficial insects. When beneficial insects are also killed after a pesticide application, a grower can get into a continuous cycle of spraying for insects that would have been otherwise controlled with natural enemies present naturally in the environment.

What do I need to scout Christmas trees?

Regularly checking your fields throughout the growing season will help you detect any problems early and help avoid damage. The equipment you will need to scout Christmas trees are a hand lens (10x to 15x), scouting board, a clipboard and paper, pest ID materials, colored flagging tape, knife, bags or bottles, and a pair of hand pruners.

Another handy tool used to scout the bottom of branches is a mirror attached to a pole to reduce the amount of bending when scouting (Photo 2). The “IPM Basics for Christmas Trees” guide from PennState Extension provides an excellent overview of these tools.

A long pole with a mirror at the end of it.
Photo 2. Using a mirror on a pole can be helpful when scouting the undersides of branches in conifers. Photo by Heidi Lindberg, MSU Extension.

Why am I scouting?

Scout your Christmas trees in order to look potential insect, disease, weed and nutritional problems along with beneficial insects. Scouting enables you to catch problems more quickly so that you can take action to correct or remediate the problem more quickly. You will also be able to see if previous treatments in an affected area were effective.

What am I scouting for?

First, it is essential to know the tree species that are present in your field as some insects or diseases affect some species and not others. For example, cooley spruce gall adelgid is an insect pest of Douglas-fir and spruces but is not a pest on true firs (Fraser, balsam and concolor) or pines. In contrast, spruce spider mite is a pest of spruces and true firs but not Douglas-fir or pines. With respect to diseases, Douglas-fir are susceptible to Rhabdocline or Swiss needlecast while spruces are susceptible to Rhizosphaera and Stigmina needlecasts. Learn more about which pests affect which plant species by accessing the “Michigan Christmas Tree Pest Management Guide.”

While an IPM program doesn’t promote calendar-based spray programs, you can use a calendar as a general rule of thumb to know when to be on the lookout for certain pests. For Michigan Christmas tree growers, there is a seasonal pest calendar in the “Michigan Christmas Tree Pest Management Guide” based on the time of year and tree species. For example, growers should be on the lookout for the following pests and diseases in their fields in early April:

  • Douglas-fir: Cooley spruce gall adelgid
  • Pine: Pales weevil, white pine weevil and Zimmerman pine moth
  • Spruce: Admes mite, Cooley spruce gall adelgid, Eastern spruce gall adelgid, spruce spider mite, spruce gall midge, Diplodia tip blight and Phomopsis tip blight
  • True fir (Fraser, balsam and concolor): Balsam twig aphid, eriophyid mites, spruce spider mite and fir needle rust

Instead of relying on a calendar, Michigan State University Extension has several helpful tools. The first is the IPM for Christmas Trees website. Here you can find growing degree day information for conifer pests. In addition, there are average growing degree base 50 maps for Michigan. The second tools is MSU Enviroweather, which is a network of weather stations across the state that monitors air temperature, calculates growing degree days (GDD) and rainfall. GDD is calculated based on the amount of heat accumulated over time (based on 50 degrees Fahrenheit). For example, in Allegan as of March 28, 2021, there was a total of 65 GDD accumulated. According to the map produced by the Enviroweather system, we are currently ahead of normal for 2021 so far.

There are helpful tools on the Enviroweather website for Christmas tree growers, which include:

For example, based on a GDD accumulation of 65 GDD accumulated in Allegan, Christmas tree growers should be on the lookout for cooley spruce gall adelgid because the first adults are active on spruce between 25 and 120 GDD and this is the time to apply treatments for them. On Douglas-fir, the control window for the first nymphs should be between 90 and 150 GDD.

How much pest damage is acceptable?

Every farm manager has a tolerance or a threshold for damage for pests on their Christmas trees, but in general, the tolerance for damage decreases as the Christmas trees get closer to their harvest date. For example, you might be able to accept damage from spruce spider mites when trees are not close to harvest, but it will be imperative to find and treat trees as they are nearing harvest. The acceptable level of damage or aesthetic appearance of your Christmas trees will also depend on your market and price point.

How do I scout Christmas trees?

Based on age and size

Scouts should pay attention to different potential problems of trees at different ages. For example, during the first growing season the transplants should be evaluated for color, root rots and weeds. It is essential to determine what caused the death of seedlings and try to address the issue early. A Christmas tree nearing harvest should be frequently scouted (i.e., weekly) and be assed for issues that will affect needles and retention such as needlecasts, spider mites and aphids. Growers should examine 40 to 50 trees per acre.

Scouting path

When scouting, you can scout the block in a few different ways:

  • Block scouting: Scout trees all within the same row, and once you reach the end you can move six to eight rows away (depending on the size of the trees) and continue.
  • Random walk scouting: Pick trees randomly throughout the field in a zig zag pattern and always scout trees that look to be a problem from a distance.
  • Hot spot scouting: Perform scouting in specific areas where problems have been observed and keep readdressing that area repeatedly throughout the season. Pay specific attention to low lying or shaded areas of the field that are prone to stay damp longer in the spring, making the trees in those areas more prone to root rots and diseases.

Treatment thresholds

The treatment threshold depends on the pest, tree species, age of the tree and if the pest in question is a quarantine pest. For example, pests that require preventative treatment include white pine weevil, gypsy moth and Pales weevil. You should be scouting and only spray as needed for mites, aphids and bagworms.

Michigan Department of Agriculture and Rural Development has a Christmas Tree Inspection and Quarantine Program. Quarantines regulate the movement of host species into and out of areas to prevent the spread of pests, such as gypsy moth, that could be very damaging to the local ecosystem. Michigan is under one U.S. Department of Agriculture (USDA) federal quarantine for gypsy moth quarantine. There is a zero tolerance for the presence of gypsy moth and all trees must be treated during the appropriate treatment window in order to be shipped or sold. Michigan used to be subject to the federal pine shoot beetle quarantine program but it was deregulated by the USDA in 2020.

Symptoms

Scouts should be looking for a variety of things when scouting fields: crooked tops, galls, stunted growth, missing branches, dead trees, browning/bronzing, curled or lost needles. Scouts should use a scouting board to shake shoots and observe any pests or predators that fall onto the board; this method is especially useful for small pests such as mites and aphids.

Those that are new to scouting Christmas trees should watch “Scouting for insects and disease.” For example, scouts should look at 15 to 30 shoots per acre for spruce spider mites. There are guides such as the “Scouting Fraser Fir Christmas Tree Guide” (Publication AG-573) from North Carolina (NC) State University that provide excellent recommendations on scouting method, frequency and treatment thresholds for individual pests. This guide should be available again soon on the NC State Extension IPM of Christmas Trees website.

Soil sampling

Fertility is important for trees of any size. Fertility issues will become more apparent as trees become larger and have more needles. Fertility should be addressed before planting a new field with Christmas trees and readdressed yearly in order to plan fertilizer applications. Standard labs check pH, cation-exchange capacity (CEC), micronutrients and provide generic recommendations. The Soil Testing and Interpretation of Results for Christmas Tree Plantations from NC State Extension is an excellent resource to understand soil sampling in Christmas trees.

Trapping

Traps can be used to monitor insect emergence or determine populations. Two common trapping systems used in Christmas trees include tether traps for white pine weevil and yellow sticky cards for Douglas-fir and spruce gall midge.

Resources

There are numerous excellent recourses to use when scouting Christmas trees:

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