Grow Trees Not Weeds! Weed Control Strategies in Christmas Tree Plantings

Weeds in Christmas tree plantings are often the most difficult pests to control. They can reduce growth rates in young trees and affect the shape of older ones. They can provide a refuge for insects and create microclimates that diseases love. And they just get in the way of shearing, spraying and harvesting.

White clover ground cover in Christmas tree plantation. Photo by Elizabeth Lamb

Planning before planting is always the best strategy. Map the planting area for differences in soil type, drainage, and elevation (for temperature differences). At the same time, map the area for the major weeds present. Take particular note of whether you have summer annuals, winter annuals or perennial weeds, as that information will help you plan your weed control practices.

Cultivation is most practical and effective before planting. Use a labeled post-emergence herbicide to kill weeds before cultivation. Especially target any weeds that are likely to be problems once the trees are planted. Vines and woody perennials are weeds to look out for!

Improving fertility levels is also easiest when preparing the field before planting. Have your soil tested to determine what you need to apply. Applying nutrients in the rows rather than broadcast will make them more available to the trees and less available to the weeds between the rows. Your trees will reward you with faster growth and better weed competition.

Even species selection can help in your fight against damage due to weeds. Choose tree species best adapted to the site and environment, as well as desirable to the consumer. Trees grown under stressful conditions are more likely to have pest problems of all sorts, and those slower growing trees are more likely to be out grown by weeds.

Keep weed control in mind when you plant your trees. Any equipment you use for mowing or spraying needs to fit between the rows and perhaps between trees in the row when they are mature.

If you are renovating an area or replanting in between existing trees, you can still do some weed control in advance. A summer mowing will result in actively growing weeds for a fall spot treatment of herbicide. Check to make sure the herbicide is labeled in your location for the weeds and the surrounding tree species, and is appropriate for the site and soil conditions. Even labeled pesticides can cause damage, especially on young trees, so be sure to shield them if you are not sure.

Specifics on herbicides for New York State can be found in the annual Pest Management Guide for Commercial Production and Maintenance of Trees and Shrubs or through the NYS Pesticide Product, Ingredient and Manufacturer System.

Not too many growers are still growing their own transplants in seed or transplant beds. If you do, weed control is essential. Even though the high density of planting would seem to help crowd out weeds, seedling evergreens don’t offer much ground cover and may be slower growing than the weeds. Younger trees are more susceptible to herbicide damage so seed/transplant beds are the one place in Christmas tree production where mulches to exclude weeds are practical.

Once you are in the full swing of production, weed control is based on scouting — just like disease and insect control. Scout before tree budbreak in the spring and again in July/August to identify weed problems. Spring, early summer and late summer mowings are the backbone of the weed management program. Where needed, spring pre-emergent herbicide and fall post-emergence herbicides are used for problem weeds based on the results of your scouting. Being especially vigilant during the first few years of tree growth will pay off in faster growth rates and fewer losses to other pests.

Ground cover management is of growing interest as a weed management tool. In effect, if you are promoting low growing weeds, like chickweed, between rows with mowing and suppressive rates of herbicides, you have a ground cover. You can also plant low-growing fescues or clover between the rows when you plant the trees or overseed them in an existing field. Ground covers suppress the growth of less desirable weeds, keep soil temperatures cooler, and reduce the need for mowing. Bear in mind that a groundcover can also compete with the trees so a weed free area at the base of very young trees is advisable.