Controlling Perennial Weeds on Hay and PastureLand

Before tearing up an old pasture or hayfield, consider improving what is already there. Frost action may have brought large rocks to the surface, interfering with futuremowing operations. Without additions of limestone over the years, soils in neglected fields become more acidic. This favors numerous weed populations, including bedstraw, milkweed, dandelions, as well as woody species if the fields were not mowed. Bluegrass begins to dominate the grass population. However, desirable grasses such as timothy or orchardgrass may have been well adapted to your site and will still give adequate yields if serious weed and fertilitiy problems are eliminated. If too much open ground exists after the weeds are killed, it may be necessary to introduce seeds of a desired species through no-till or minimum tillage techniques. And if too many surface rocks and stumps will interfere with desired seeding, mowing or clipping, then tillage operations will be necessary. This can be expensive. Large bulldozers with rock rakes can remove large rocks and stumps without removing too much soil. Often, these rocks and stumps are then buried in the field or left in a windrow to decompose. After these steps towards improvement are completed, future care of the forage crop is needed or your fields will soon revert back to the same weedy, infertile condition and your dollars will have been wasted.

Proper rest periods and timely mowing (three times per season) will tend to keep most weeds under control, by promoting healthy forage species able to compete with weeds. When in the bud stage, weeds should be cut 3 to 4” above the ground. Some pasture farmers clip each paddock after every grazing period. This weakens existing weeds by depleting root reserves and prevents further spread by preventing seed production. Even the toughest-to-control weeds such as Canada thistle will succumb to a monthly mowing, four times per season. Forcing livestock to browse heavily (10,000 pounds animal weight per acre) will help in the control of many species (goats love multiflora roses). This regular mowing or grazing, with fertilizer and lime additions, will produce a good field in three to four years. Mowing encourages tillering of grasses, which enables them to out-compete broad-leaved weeds. The soil becomes closed to migrating weed seed. The grass species composition will improve and various clover species will come back into the field.

Repeated mowings, clippings, and hand weeding, however, will not normally correct serious preexisting weed problems. Plants such as thistles, brush, and poisonous plants, may continue to be a problem even after you have intensified your system. Many weeds regenerate from deep underground storage organs. It is often impossible to deplete all of these underground structures to prevent re-sprouting. Multiflora rose, a noxious pest in New England, can be kept in check on flat land, smooth enough for a mower or on steep land with heavy grazing. But if not kept in check, multiflora rose will quickly convert pastures and hayland to brush and eventually to forest. Successful control of some preexisting weed problems may only be achieved with the use of herbicides. Herbicide treatments can be made in various ways. Dormant, cut stem, and foliar treatments are effective for eliminating brush, and foliar spraying is used for control of weeds such as thistles. Seeds from some weeds remain alive in the soil for many years, and are not affected by herbicide applications. These weed seedlings must be suppressed by the desired species’ canopy or by subsequent mowings.

Some herbicides are selective in that they kill certain types of plants and not others. Keep in mind, however, that most hay and pasture herbicides will remove desirable legumes from the stand. Before deciding which herbicide to use, be sure problem weeds have been accurately identified. Bring samples to your local CooperativeExtensionCenter for help in identification and for current herbicides recommended for control of those specific weeds. Time the herbicide application according to the label restrictions for the optimum stage of weed growth and any waiting periods required before haying or grazing the fields. Pesticides are registered for such use by the U.S. Environmental Protection Agency (EPA) and have been judged to be safe for humans, animals, and the environment when handled and used as directed on the label. Therefore the user must carefully read and follow label directions for herbicide use.

Foliar application of herbicides can be made when the plants are actively growing with full foliar canopy. The ideal time for treating them is after they have reached the bud stage in mid to late summer. During this period they have their maximum leaf area and are storing food reserves for the winter. Translocated herbicides applied during this period are absorbed by the leaves and moved into the underground reproductive and storage organs with the food reserves. When treating dense infestations, re-sprouting may occur and therefore may require additional follow-up treatment.

Drift of spray particles and vapors can damage trees, shrubs, flowers, and vegetable plants. To avoid drift to non-target areas, spray only on calm days and maintain large spray droplets by minimizing pressure. High temperatures can cause some herbicides to form vapors, easily carried by the wind away from the target weed. To maximize efficacy with foliar-absorbed herbicides, spray on dry foliage at times when rain is not expected for several hours.

If the weed problem occurs over the entire field, herbicides can be broadcast sprayed. Contact the local farm supply outlet to determine rates to custom spray your fields. Density of brush and presence of surface boulders will influence the ability of equipment to apply herbicides properly. A high gallons per acre rate is needed for brush control to provide thorough coverage of leaves, stems and crowns. It may be necessary to bush-hog fields to create a sprayable height, with subsequent re-growth to the full leaf stage, before spraying for maximum effectiveness.

More frequently, weeds are patchy, making spot spraying the preferred method of control. Spot spraying is less costly than broadcasting, but requires farm labor to apply the herbicide using a hand sprayer. A selection of herbicides is available to farmers who are not licensed applicators and who usually wish to purchase only small amounts. Handsprayers place the operator near the nozzles and discharge point of the sprayer. Therefore, all operators should wear a hat, a long-sleeved shirt and trousers, or a spray suit. Depending on the toxicity of the chemical, other protective wear may be required by the label. Spray when winds are less than 5 mph, which is a very mild breeze, so the chemical is not blown on the operator.

A dormant treatment involves spraying the basal stem region of completely dormant brush to a height of 12 to 18 inches above the ground line. Avoid application when snow or water prevents spraying to the ground line. The selected herbicide is mixed with fuel oil, diesel oil, or kerosene. Freshly cut stumps can be sprayed with several products to control re-sprouting of unwanted trees and shrubs. This will not control root suckering species such as sumac.

Prepared by Joyce E. Meader, Assistant Extension Educator (8/99)

References:

Ahrens, J.F. et al. 1993 New England Guide to Chemical Control of Problem Weeds and Brush Around Homes and on Non-Cropland, New England Cooperative Extension Publication.

1998 Cornell Recommends for Integrated Field Crop Management. Cornell Cooperative Extension. p.66

Daum, Donald. Sprayers for Christmas Trees, Agricultural Engineering Department, Penn StateU

Kersbergen, Rick. This Old Hayfield: A Fact Sheet on Hayfield Renovation, Cooperative Ext, U of Maine

Wisconsin Pastures for Profit. p.12-13