Tree Facts: Weed control in shelterbelts can be a challenge

Planting and maintaining shelterbelts in the northern Great Plains is a real challenge. Weeds compete with trees and shrubs for moisture, sunlight, space, and nutrients. Weed control is a very important factor in survival, establishment and growth of shelterbelts. Timely weed control can increase survival and improve vigor of shelterbelts.

A weed is any plant growing where it is not wanted. There are three main types of weeds, annual, biennial and perennial. Annual weeds are plants that germinate from seed in the spring, grow and set seed in one growing season. Biennial weeds are plants that grow from seed but take two years to set seed. Perennial weeds are plants that grow from roots, rhizomes, stolons, tubers, tillers or seeds in the spring. Perennials do not die, they continue to grow and spread each year.

Plan one or two years ahead to control weeds before planting a shelterbelt. Do not use herbicides that may leave residues that may be harmful to tree and shrub species. The year before planting, control annual weeds with tillage and perennial weeds with systemic herbicides such as glyphosate. At planting time eliminate emerged weeds either with tillage or glyphosate. Another option is to incorporate trifluralin (treflan) in the top 2-3 inches of the soil to control annual grasses.

Tillage is very effective for control of annual weeds. However, tillage brings other weed seeds close to the soil surface where they germinate and grow. Repeated tillage is needed until the weed seed bank is exhausted. Tillage can actually spread weeds by dragging stolons, rhizomes, tillers, tubers and roots to other locations.

Herbicides alone are widely used for perennial weed control in shelterbelts. Effective weed control depends on matching herbicides to specific weeds and timing application to the weeds most vulnerable stage of growth. Preemergence herbicides for shelterbelts are best applied in the fall to prevent weeds from getting started. Simazine (Princep 4L), diuron (Karmex DF) and Dichobenil (Casoran 4G) are examples of preemergence herbicides. Post emergence herbicides for shelterbelts are used to control weeds during the growing season. Glyphosate (Roundup), Sethoxydim (Poast or Vantage) and Fluazifop-P (Fusilade DX) are examples of post emergence herbicides.

The above herbicides are available as granules, liquids or both. Rotary type spreaders can be used to apply granular products and ground sprayers, backpack sprayers or hand sprayers can be used to apply liquids. Proper calibration is very important regardless of the application method.

Herbicides can be used to compliment other weed control methods. Use an in-row treatment with tillage between the rows by applying herbicide to spray a 2-3 foot band on each side of the tree row. Use a between row treatment with weed control fabric by applying herbicide directed between the rows.

Tree and shrub species vary in their tolerance to specific types of herbicides. Care needs to be taken to ensure that herbicides are labeled for use around the tree and shrub species planted in the shelterbelt. Some herbicides cannot be used on soils that are sandy, gravelly, high pH or low organic matter or severe tree injury may occur. Check herbicide labels for directions and lists of tree and shrub species on which it can be used, weeds controlled, application rates and timing.

My sources for this news release were the USDA Natural Resources Conservation Service and North Dakota Cooperative Extension Service. If you would like more information about “Weed Control in Shelterbelts” contact Bob Drown at 605-244-5222 Extension 109 or by e-mail at robert.drown@sd.nacdnet.net.