Managing the top five toughest weeds in Michigan hay fields

Phil Kaatz and Erin Burns

When hay producers go to the field this summer to harvest forage crops, one of the challenges they face is how to address the weeds that creep in over time. Michigan State University Extension surveyed past participants of the Great Lakes Forage and Grazing Conference on what are the five toughest to control weeds in their hay fields. Many weeds were identified, but five rose to the top of the list: Queen Anne’s lace (wild carrot), horsenettle, hoary alyssum, curly dock and Canada thistle.

Starting with a vigorous forage stand is the best way to prevent weeds from getting established. In general, as forage stands decline, weeds find places to establish and continue to be problematic unless the management problem that caused the forage stand decline is corrected.

The first step in controlling any pest should be to have the weed properly identified. Secondly, if control methods include using pesticides, always follow label recommendations since the label is the law. Additionally, many herbicides outlined below have long residual activity or restrictions on forage and manure management. Take time to read and consider these restrictions seriously before making applications.

What are the toughest weeds to control in Michigan hay fields?

Each weed species may have unique control methods, however knowledge of weed biology and using it to target weeds when most vulnerable is key to long-term success.

Wild carrot (Queen Anne’s lace)

Reported the most troublesome weed in hay fields is wild carrot. This biennial is a deep-rooted plant that emerges in year one as a rosette, bolts in year two and forms flowers as early as June. Each flower can produce up to 1,000 seeds and can stay viable in the soil for up to seven years.

  • Mechanical control of wild carrot is an effective way to cut off flowers and stop seed production. Clipping/mowing in July has been shown to stop seed production.
  • Chemical control is limited. Wild carrot cannot be controlled in non-Roundup Ready (RR) alfalfa. The use of 2,4-D is effective in grassy hay fields, however, continued use leads to resistance in as few as two or three years, and resistant populations are already present in Michigan. Crossbow is the best option in grass hay fields.
  • Few herbicide options are available in legumes like alfalfa or legume/grass mixed fields. When infestations are too severe, renovating the field should be considered.


Horsenettle comes in second place as the most troublesome weed. Horsenettle is a perennial weed that reproduces by seed and vegetatively via new shoots from creeping roots called rhizomes. Spines on plants reduce livestock palatability. Horsenettle thrives in sandy or gravelly soils but will grow on a wide range of soils. The plants flower in late spring to early summer forming yellow berries. Vegetative parts of this weed and its fruit can poison livestock. Toxicity is reduced (not eliminated) when the plants are dried and is usually higher in late summer to fall than in the spring.

  • Mechanical control is difficult. Tillage at any depth can spread horsenettle. Mowing early in the season encourages growth whereas mowing later decreases some growth.
  • Very few herbicides are effective at controlling horsenettle. Herbicides will only “suppress” horsenettle and keep it from spreading. Multiple applications over several years are necessary for control. Possible options include glyphosate (RR alfalfa), Milestone, Crossbow and GrazonNext HL. Herbicide applications at the flowering stage prior to berry formation is the optimal time for application.
  • Alfalfa (non-RR) and alfalfa/grass mixed fields do not have good options for chemical control.

Hoary alyssum

Hoary alyssum was the third most popular (or unpopular in this case) weed in the survey. This is an annual to short-lived perennial weed with a long taproot that spreads by seed. Hoary alyssum is toxic when horses graze the fresh plant or eat it in dried hay. Hoary alyssum can remain toxic for up to nine months. This weed will thrive in low fertility, well-drained, coarse-textured soils. Nutrient management is important to maintain competitiveness of the desired forage over hoary alyssum. Controlling hoary alyssum is critical prior to the initial seeding of the hay field.

  • Conventional tillage when preparing the seedbed is an effective control method.
  • A burndown herbicide can be used in no-till systems.
  • Control in a legume/grass mixture is limited to a dormant application of metribuzin. If found in grass hay fields, treatment by a 2,4-D or dicamba will provide good control.

Curly dock

Another tough to control weed coming in at fourth place is curly dock. This is a perennial weed with a large, thick taproot that often shows up in older stands of alfalfa, alfalfa and grass, or all grass hayfields. Reproduction is by seed. Curly dock thrives in moist soils and has seeds that can remain viable in soil for up to 80 years. This plant can be toxic when consumed in large amounts.

  • Mowing can help reduce populations. Tillage will control curly dock or by using a shovel to remove the crown two inches below the soil surface.
  • Chemical control in grass hayfields is effective with Cimarron Plus, 2,4-D, dicamba, GrazonNext HL and Crossbow.
  • Established alfalfa and legume/grass mixtures have few options for chemical control. Raptor or Pursuit can be effective when applied on curly dock seedlings in pure alfalfa.

Canada thistle

Canada thistle rounds out the end of the top five toughest to control weeds in forages. This perennial spreads by seed and rhizomes. Emergence occurs in the spring and plants flower when days are the longest. Seeds have an attached pappus ‘feather-like structure’ that allows for long distance transport in the wind. Canada thistle’s creeping roots allows for the formation of large colonies that spread over the field (see photo).

  • Mechanical control of Canada thistle with infrequent mowing is not highly effective. Repeated mowing will stress the plant and force it to deplete root nutrients. Tillage can increase the problem by cutting roots thereby making new plants.
  • Canada thistle is most susceptible to herbicides between the bud and early flower stages or in the early fall prior to frost.
  • Most herbicides will only “suppress” Canada thistle and keep it from spreading. Yearly herbicide applications will be needed to get Canada thistle infestations under control. Possible herbicide options include Cimarron Plus, Crossbow, Milestone, GrazonNext HL and Stinger in grass hay fields.
  • Non-RR alfalfa and legume/grass mixtures have very few effective Canada thistle control options.

Mixed legume/grass stands present special challenges

Legume-grass mixtures have potential to provide agronomic and livestock feeding benefits such as plant diversity, increased persistence and livestock nutrition. However, there are no easy herbicide options for controlling weeds in mixed grass/legume stands. When considering planting legume grass mixtures, select fields with low weed pressure.