Controlling vining weeds in Christmas trees
Wild buckwheat and field bindweed can entwine themselves in Christmas trees, making pruning and harvesting difficult.
Vining weeds in Christmas tree plantings are often the most difficult weeds to control. While vines may be moderately competitive for water and nutrients, their greatest effect is their physical presence. They grow up into the trees, distort growth and reduce air circulation, which adversely affects disease management and makes pruning and harvesting difficult. Their presence in harvested trees reduces quality. Wild buckwheat and field bindweed are commonly found in Christmas tree plantations, and may be confused with each other.
Wild buckwheat (Polygonum convolvulus L.) is in the smartweed family (Polygonaceae) and is a fast growing annual weed with a vining habit. It trails along the ground or twines around trees or other plants with which it comes into contact (Photo 1). The leaves are alternate, heart- or arrowhead-shaped, rounded at the tip, and have widely separated lobes at the base. Plants bloom throughout the summer.
Photo 1. Wild buckwheat.
The flowers are very small (less than 0.25 inches) and have no petals, but have five greenish or pinkish sepals. Flowers are located in short-stemmed clusters in the axils of the leaves or at the end of stems (Photo 2).
Photo 2. Wild buckwheat entwined in the leader of small concolor
Wild buckwheat can be controlled somewhat preemergence with Westar, Goal and Sureguard. It can be controlled post-emergence with glyphosate (Roundup) and Garlon. For glyphosate, use the original formula (4 lb/gallon of the IPA salt). It may take two applications to obtain control. Goal also has good post-emergence activity against wild buckwheat. 2,4-D (Turret) and clopyralid (Stinger, Lontrel) also have activity against emerged wild buckwheat.
Field bindweed (Convolvulus arvensis L) is in the morning glory family (Convolvulaceae). The plants send out twining vines from deep, perennialroots. Early leaves are round and about 1 inch in diameter. Later leaves are arrowhead- or heart-shaped and about 2 inches long. Flowers are funnel-shaped, white to pinkish and about an inch wide and there are two bracts on the stem below the flower (Photo 3). Bindweed reproduces from seed and from roots. Hedge bindweed [Calystegia sepium (L.)] is a closely related species that has larger flowers and more pointed leaves.
Photo 3. Field bindweed leaves and flowers.
Bindweed is very difficult to control under any conditions. Most herbicides are not effective against it. Since it is very deeply rooted, few preemergence herbicides have any effect on it. Hexazinone (Velpar or Westar) has moderate activity against established bindweed and will control seedling bindweed. Garlon 3A at 3 to 4 pints per acre and 2,4-D (Turret)at 2 to 3 qt/acre will suppress field bindweed. Glyphosate (Roundup Original and generics - IPA salt) gives fair control. It should be applied in late July or later, when the bindweed is in full bloom. Apply 2 to 3 qt of glyphosate per acre. A second application three to four weeks later will improve control. It will take several applications of herbicides over two to three years to substantially reduce bindweed stand. Keep Christmas tree contact with herbicides to a minimum.
When using Roundup, Garlon or 2,4-D, wait to apply these products until the new tree growth has hardened off in late summer or early fall. To help reduce injury, direct sprays to weeds at the base of the trees to minimize contact with tree foliage. Christmas growers should use only Garlon 3A. Garlon 4 is not labeled for Christmas trees and has an ester formulation, which is more volatile and dangerous to surrounding trees. Garlon 3A should only be applied to trees that have been planted at least one full year prior to application. When using any pesticide, read and follow all label directions.
Dr. Zandstra’s work is funded in part by MSU‘s AgBioResearch.