By Dwight Lingenfelter
William S. Curran
Herbicides in new grass and legume seedings: Herbicide selection for new forage grass and/or legume seedings are limited. Most herbicide labels for grasses like orchardgrass, timothy, etc. state that the grasses should be well established with at least 4-5 inches of growth. Some labels are more restrictive than this. The metsulfuron label states that grasses should be established for at least 6 months prior to an application. This ensures that they are developing a solid root system that could tolerate potential stress from the herbicide. Herbicide selection, formulation (ester vs. amine) rate, and environmental conditions at application will all impact the potential for injury. Herbicide use in new legume seedings has similar concerns. In general, legumes should have several trifoliate leaves and be 2 to 3 inches tall before making an application. The Pursuit and Raptor labels state that alfalfa should have 2 trifoliates or larger at application; two of the most lenient products for new alfalfa seedings. Also, keep in mind that at the same time that we want our crop to have sufficient growth, our targets are generally “small” annual weeds which are easier to kill – a bit of a paradox. Finally, products are even more limited with mixed seedings. Pursuit is labeled for established alfalfa-grass mixtures as is metribuzin (Dimetric, Glory, TriCor, etc.); MCPA and Maestro (Buctril) are labeled on legume/small grain companion seedings, and several other products have labels for CREP mixtures.
Established hay and pasture: The flowering stage is an excellent time to attempt some control of poisonous perennial plants. A number of common plants can be poisonous when eaten in sufficient quantity by livestock, so monitor those pasture and hay fields closely. Remember that perennial weeds are most sensitive to control with a systemic herbicide when they are in the bud to bloom stage and in late summer. Biennials including musk and plumless thistle, burdock, wild carrot, etc. should be treated before they begin to bolt (they are bolting now or very soon) and the smaller the better. Late fall or early spring is even a better time to treat them. And finally, control summer annual weeds as soon after they emerge as possible when they are most sensitive to chemical control. Below are some guidelines to provide a quick management summary for some common weeds of pasture.
Management guidelines for some problem weeds of pastures.
Annuals
Winter annuals (Mustard species, common chickweed, etc.)
- Mow after bolting to prevent seed production.
- Apply an effective herbicide in fall or spring prior to bolting.
- Most winter annuals emerge by late fall – a smaller percentage will emerge in early spring.
- Prevent seed production to prevent spread.
Summer annuals (Pigweed species, common lambsquarters, common ragweed, etc.
- Keep pasture full and competitive.
- Mow after bolting to prevent seed production.
- Apply an effective herbicide in early summer.
- Prevent seed production to prevent spread.
Biennials
Biennials (common burdock, bull and musk thistle, poison hemlock, etc.
- Mow after plants have bolted but before seed set to prevent seed production.
- Remove or dig individual plants by hand.
- Apply an effective herbicide to rosettes in the spring or fall.
- Prevent seed production to prevent spread.
- Several insect biocontrol tools may help with thistles in the future.
Perennials
Creeping perennials (Canada thistle, horsenettle, etc.)
- Mow to suppress vegetative growth and prevent seed production.
- Spray with an effective systemic herbicide at bud to bloom stage or in early fall prior to frost.
- Most perennials spread by both seed and vegetative structures.
Woody perennials (multiflora rose, autumn olive, etc.)
- Mow to suppress and prevent seed production – remove roots by hand or with heavy equipment.
- Spray with an effective systemic herbicide at bud to bloom stage or in early fall.
- Rose rosette disease has spread as far North as Central PA and may impact this weed in the future.
Multiflora rose control in pastures: As spring progresses, multiflora rose begins its growth and eventually will bloom in late May/early June. Certain herbicides can provide good control of multiflora rose, especially when applied during the bud to bloom growth stages. Several foliar applied herbicides are suggested for late-spring/summer including Cimarron Plus/metsulfuron, Crossbow/Remedy Ultra, GrazonNext HL, and glyphosate.
Metsulfuron and Cimarron Plus 63WG: (metsulfuron + chlorsulfurfon) can be used as a broadcast or spot treatment. Apply Cimarron Plus at a rate of 0.625 to 1.25 oz/A plus a surfactant for broadcast treatments or 1.25 oz/100 gallons water plus surfactant for spot treatments. (Metsulfuron-methyl 60DF is sold as a single active ingredient in products such as Accurate, Ciramet, Plotter, PureStand, Rometsol, and others and can be applied at a rate of 0.5 to 1 oz/A.) Applications should be made in the spring, soon after plants are fully leafed-out. There is no application to grazing interval for Cimarron Plus or metsulfuron herbicides. Make sure grass forages are well established (6 months for orchard, brome, bluegrass, 12 months for timothy, and 24 months for fescue) before a metsulfuron application.
Foliar applications of Crossbow: Can be effective on multiflora rose. For spot treatments, use 4 to 6 oz of Crossbow/3 gallons water and spray until foliage is uniformly wet. For broadcast applications, use 1.5 to 4 gallons of Crossbow in enough water to deliver 10 to 30 gallons of spray per acre. Early to mid-June is an excellent time to make these applications. Follow-up treatments may be necessary. An interval of 14 days is required for lactating dairy if using 2 gallons/A or less. On a side note, technically, Crossbow (and other similar triclopyr+2,4-D premix products) may not be used on forage that is to be cut and sold for commercial purposes. Remedy Ultra (triclopyr only) can be tank-mixed with 2,4-D ester and used on forages for hay production.
To spot spray individual rose bushes, GrazonNext HL: Can be used at 34 fl oz in 100 gallon of water with 32 fl oz of non-ionic surfactant. If tank mixing GrazonNext HL with Remedy Ultra, use 32 fl oz of each herbicide in 100 gallons of water plus the surfactant. Apply from full leaf through flowering. There is no application to grazing interval for GrazonNext HL herbicide. If Remedy Ultra is tank-mixed, except for lactating dairy, there are no grazing restrictions; for lactating dairy, do not graze until next season. Keep in mind that GrazonNext HL can only be used in permanent grass pasture settings in Pennsylvania, it cannot be used in hay production. Also be cautious of manure management issues when using GrazonNext HL.
Glyphosate: Can be used as spot treatments on isolated patches of multiflora rose. Apply a 1 percent solution (about 1 qt/25 gallons water) of glyphosate with a hand-held sprayer. Uniformly wet leaves and green stems, but avoid runoff. Application should be made in late summer or early fall when plants are actively growing (after fruit formation). Glyphosate has been more effective at controlling multiflora rose in PSU research at fall application time. A 14 day interval is required for grazing animals.
No matter which control tactic is used, follow-up maintenance practices are a must for long-term control. Removal of dead brush, annual mowing and adequate soil fertility are examples of practices that should be used to maintain control of multiflora rose and in turn, will encourage pasture growth.
On a side note, rose rosette disease (RRD) on multiflora rose (Rosa multiflora) is a very common sight in central Pennsylvania these days. RRD is a suspected virus transmitted by an eriophyid mite that is a generally fatal to multiflora rose as well as some other rose species. We first identified this disease in the central region back in 2002. RRD has been commonplace in W. Virginia and in parts of the Midwest and scattered throughout numerous other states including Pennsylvania. It has long existed in the southwestern part of PA and has been slowly moving North and eastward. Farmers and land managers plagued with multiflora rose have happily anticipated the arrival of RRD in the hope that it will reduce or even eliminate multiflora rose. Unfortunately, some ornamental roses are also susceptible, so rose enthusiasts are equally concerned about the spread of RRD. Although many farmers and other landowners may welcome RRD, don’t expect it to solve the multiflora rose problem any time soon. Our experience has been that for every plant that dies from the disease, two or three new ones become established over that period of time. Unless you’ve heard differently, we think multiflora rose is still alive and well in Pennsylvania and other parts of the Northeast.