Why Control Weeds? Good weed control is one of the most important operations if high quality Christmas trees are to be grown at minimum cost. The control of weeds in a Christmas tree plantation produces several important benefits:
It improves the survival and growth of the trees. Weeds compete with Christmas trees for the limited amounts of sunlight, water and nutrients available on the site (Fig. 18). Excessive weed competition significantly reduces the survival and growth of the trees (Fig. 29). Such competition is particularly detrimental when trees are young and during years when the spring and summer are dry. Benefits are most pronounced on sites having heavy weed cover and with the more demanding spruces, firs and Douglas-fir, but any species of Christmas tree planted on any site benefits from good weed control (Figs. 30, 31).
Fig. 29: Effects of weed control on growth of 7 to 8 year old Christmas trees. Trees on left have had annual mowing and chemical weed control, while those on right have had annual mowing only.
Fig. 30: Fraser fir seedlings grown for three years on areas having different methods of weed control or types of herbaceous weed competition. L. to R., 1) site scalped and kept bare with mechanical cultivation; 2) vegetation controlled with herbicide; 3) site having broadleaf weed competition and 4) site having grass sod competition.
Fig. 31: Scotch pi ne seedlings grown for three years on areas having different methods of weed control or types of herbaceous weed competition. L. to R., 1) site scalped and kept bare with mechanical cultivation; 2) vegetation controlled with herbicide; 3) site having broadleaf weed competition and 4) site having grass sod competition.
It results in better formed trees. Physical abrasion and shading by tall weeds growing near Christmas trees destroy needles and branches on the lower portion of trees (Fig. 32). Unless these limbs are removed, trees will be of lower value, and removal of limbs can add one to three years to the time needed to produce quality trees of the desired size.
Fig. 32: Effect of tall weed competition on Christmas tree form.
It makes it easier to work in plantations. It is much easier and quicker to walk and move equipment through weed free plantations. Activities such as spraying, shearing, inspecting for insect and/or disease problems, evaluating and grading trees and harvesting can be carried out quicker and at less expense. Ease of movement is essential in choose-and-cut operations.
It reduces the insect and disease potential. Tall weeds in Christmas tree plantations increase the risk of serious insect and/or disease problems. Weeds may act as an alternate host for diseases. They may provide an alternate source of food for insects, and they create a dark, damp environment ideal for many insects and diseases. For example, dew remains on weeds and lower branches of trees much later in the day, providing a good environment for fungus diseases and resulting in greater damage from needlecasts such as Lophodermium.
It reduces animal damage potential. Weeds around young Christmas trees provide cover and nesting material for mice and other animals that may kill or deform trees.
It reduces fire hazard. Standing or fallen dry weeds can be highly flammable fire hazards in late fall, winter and early spring.
It produces more attractive plantations. Plantations without adequate weed control may look ragged and ill kept. They can give the impression that the grower is less competent than others with better kept plantations. This can be especially important in choose-and-cut operations.
Because of these benefits, most Christmas tree growers perform some type of weed control throughout the entire life of a plantation with three important objectives in mind:
Fig. 33: Strip application of herbicides to control vegetation around base of trees.