Extension Bulletin E3237 • Updated • May 2018. Weed Control in Christmas Trees. Bernard Zandstra and Jill O’Donnell. Department of Horticulture, MSU Extension. Michigan State University. Weeds can interfere with tree growth at any stage of East Lansing, Michigan. Christmas tree production. eed control is an important cultural practice in even kill trees. Young trees that grow with minimal transplanting to keep weeds from germinating and WChristmas tree production throughout the year. weed competition develop healthy root systems, competing with the small seedlings. Small trees also Preemergence and postemergence herbicides are which allow them to withstand drought and adverse may be sensitive to postemergence herbicides, and it needed to minimize weed competition in Christmas conditions later. The rate of growth in the second is important to follow label instructions regarding tree tree plantings. The tree species, age, growth stage, and third years is related directly to the amount of age, size and herbicide timing. Established perennial size, time of year and soil type must be considered weed competition. On sandy soils, weeds may use up plants such as Christmas trees usually tolerate most when formulating a herbicide program. An effective available moisture, and young trees may succumb to preemergence herbicides because the herbicides stay weed control program controls most weeds drought. As trees become larger, weeds interfere with on or near the soil surface and the roots of the trees without stunting or injuring the trees. A successful production practices such as pruning and spraying. It are deep in the soil where they do not absorb the program may include mowing and hand weeding is difficult to spray pesticides and prune trees in fields herbicides. If the tree roots come into contact with along with applying residual preemergence and/or infested with Canada thistle, horsenettle, poison ivy, the herbicides due to light/sandy soils, heavy rain or postemergence herbicides with different modes of horseweed, ragweed, pokeweed, sumac and other other reasons, they may absorb the herbicides, which action. Fall or spring-applied preemergence herbicides large or poisonous weeds. Weeds growing under and can result in tree injury. Using very low-solubility control most annual weeds for 6-8 weeks. However, near Christmas trees should be controlled for two herbicides and rotating modes of action reduces residual herbicides do not last throughout the season. to three years before tree harvest. The seedheads of the potential for herbicide buildup in the soil and Postemergence herbicides are often needed to control some grasses – such as fall panicum, giant foxtail and percolation down into the tree root zone. perennial weeds, annuals that germinate during the witchgrass – as well as broadleaves, such as common Postemergence herbicides target specific season, and weeds that escape due to herbicide and giant ragweed, hoary alyssum, field bindweed, biological activities in plants. All plants have similar tolerance or resistance. hairy vetch and wild carrot, may grow into the tree physiological and biochemical processes – for branches and be difficult to remove. Weeds interfere with tree growth at any stage of example, photosynthesis, respiration and cell division production or time of year. Effective weed control is Young trees may be sensitive to some preemergence – so herbicides may injure crop trees under some essential in seedling beds and in the first three years herbicides the year of planting in the field. After circumstances. Tree safety is based on the degree after transplanting in the field, to obtain a good stand roots have become established and soil is packed of tree tolerance to herbicides. Growers may apply and vigorous growth. Weed competition during the around the seedlings, there is less potential for tree some postemergence herbicides safely over the tops year of establishment may suppress tree growth and injury. Apply preemergence herbicides soon after of conifers at any stage of growth. In other situations, 1 the level of herbicide selectivity is narrower, and the most effective method of control of these woody Christmas trees are only moderately tolerant of low weeds. Treating the stumps of woody weeds with Abbreviations used in tables. doses of herbicides. Various tree species may have concentrated herbicides after cutting the stems and different levels of herbicide tolerance. If a herbicide branches may reduce regrowth. ACCase inhibitor = Acetyl CoA Carboxylase is marginally safe on Christmas trees, avoid herbicide inhibitor. Use of appropriate equipment for herbicide contact with the trees during periods of active tree applications is important to obtain maximum weed ALS inhibitor = Acetolactate Synthase inhibitor. growth, and apply the herbicides at less sensitive control and avoid tree injury. A boom sprayer works PPO inhibitor = Protoporphyrinogen Oxidase growth stages, such as before budbreak in spring and well during the first three years after transplanting inhibitor. after new growth has hardened in the fall. Directing seedlings in the field for broadcast or directed the spray to avoid tree contact helps to minimize PS II inhibitor = Photosystem II inhibitor. (with drop nozzles) applications. Growers can use a tree injury. highboy sprayer to straddle trees on level ground for RUP = restricted use pesticide. When making postemergence applications during two to three more years. As trees expand vertically VLCFA synthesis inhibitor = very long chain fatty the summer, select herbicides that have good foliar and horizontally, driving through the plantings acid synthesis inhibitor. activity and that are safe on the trees, as indicated by becomes more difficult, and growers may be tempted information on the herbicide labels. In general, avoid to use air-blast sprayers to apply preemergence and broadcast applications over the tops of trees between postemergence herbicides. Air-blast sprayers are To protect yourself, others and the environment, always bud break and Sept. 1, by which time most new not effective for herbicide applications and normally read the label before applying any pesticide. Although growth has hardened. If applications must be made should not be used for weed control. After trees are efforts have been made to check the accuracy of during the summer, direct the herbicides toward the too tall for a boom sprayer, back-pack sprayers may information presented, it is the responsibility of the person using this information to verify that it is correct soil between the rows of the trees. Postemergence be the most effective application method. Applicators by reading the corresponding pesticide label in its herbicides need to contact actively growing weeds must wear personal protective equipment to avoid entirety before using the product. Labels can and do to be effective. Some winter annuals, biennials and self-contamination. A few herbicides are registered change — greenbook.net, cdms.com, and agrian.com perennials – including horseweed, wild mustards, and safe for airplane or helicopter application to are free online databases for looking up label and MSDS goldenrod, quackgrass, spotted knapweed and Christmas trees. Check labels before making aerial information. wild carrot – are susceptible to preemergence and applications. postemergence herbicides applied in the fall. When applying glyphosate (Roundup) post- Some perennial and woody weeds are difficult to emergence in Christmas trees, use a formulation control in Christmas tree plantations. Seedling trees that does not contain a surfactant or other adjuvant. such as poplar, maple, mulberry and sumac often Roundup Ultra, with 4 pounds of the isopropylamine become established in spite of the use of residual (IPA) salt of glyphosate (3 pounds of acid equivalent herbicides. Vining plants such as field bindweed, [ae] per gallon), is a good example. Many generic poison ivy, Virginia creeper and wild grape often grow formulations of original glyphosate are available. in and through the Christmas trees. They cannot be The herbicides included in the following tables treated with herbicides without risk of injury to the Trade names and formulations of herbicides are given are labeled for use in Christmas trees. Many of trees. Other weeds such as wild brambles, multiflora for the convenience of the user. Other formulations of the the herbicides are available in other commercial rose and pokeweed are tenacious and tolerant of same herbicides or other herbicides with the same active formulations with the same active ingredients. Check most herbicides. These weeds may be controlled ingredients also may be labeled for use on certain species. labels to determine use instructions for Christmas The mention of trade names does not imply that they are with spot treatments of glyphosate or triclopyr trees. Always have labels of all pesticides in your endorsed or recommended over those of similar nature while avoiding direct spray on the Christmas trees. possession before application. not listed. In many situations, hand weeding is the safest and 2 Table 1. Annual broadleaves and grass response to Christmas tree herbicides. *E=Excellent, G=Good, F=Fair, P=Poor, N=No Control. Annual broadleaves Annual grasses Foxtails; Giant, Green, Yellow Green, Giant, Foxtails; Sandbur; Field, Longspine Nightshade, Eastern Black Eastern Nightshade, Smartweeds, Ladysthumb Smartweeds, Common Lambsquarters Common Horseweed (Marestail) Horseweed Mustards, Wild radish Wild Mustards,