How to Tell Foxtail from Timothy and Control It

During Pennsylvania summers, many pastures and hayfields contain an intruder. At first glance, it looks like the popular timothy grass, but a close inspection can tell you that it's really foxtail.

Foxtail is a summer annual grass, meaning it grows from seed in the spring and dies in the fall. To come back year after year, it drops hundreds and hundreds of seeds into the soil. Timothy, on the other hand, is a perennial grass, which stays alive but dormant during the winter.

Timothy is a beloved favorite of horses and their owners for its palatability and the great hay it produces. While the immature foxtail plant has no ill effect on horses, the seed heads are troublesome. Each individual seed contains spikes with barbs called "awns," which can lodge in horses' mouths and gums, or even scratch an eye. These awns can work their way through the tissue, causing lesions and infections. It is not recommended to feed foxtail with seed heads to horses.

Identification

So how do we tell these similar looking plants apart? There are a few features you can check.

The seed head

This will only be obvious when the grasses are going to seed and aren't mowed. The foxtail seed head may droop over, which is a dead giveaway that it isn't timothy. However, there are several different varieties of foxtail, and some seed heads remain upright. Next, check for the awns, which look like hairs coming off each tiny seed on the head. These are what gives foxtail its illustrative name. Some varieties may have very long and obvious awns, but others may have shorter awns that you need to look for. Timothy has no awns.

Left image: Timothy seed head. Photo: Ohio State University. Right image: Green foxtail seed head. Photo: North Carolina State University.

The collar region

Pull a leaf away from the stem and examine the area where they meet (this is called the collar region). You may want to use a magnifying glass or hand lens. On a timothy plant, you will see a tall membrane come away from the stem and stand upright. On a foxtail plant, you will see a fringe of hairs instead of a tall membrane. The leaves of a foxtail plant may have some hairs as well.

Left image: Timothy: Tall membrane (ligule) at collar. Photo: Ohio State University. Right image: Foxtail: Fringe of fine hairs at collar. Photo: Cornell University.

The plant crown

If you can pull or dig up the plant, take a look at the crown, where the shoots meet the roots. Timothy has bulb-like structures called "corms" and they may resemble the bulbs of onion grass. Foxtail does not have corms.

Timothy corm. Photo: Ohio State University.

Control

Now that you can tell the difference between timothy and foxtail, what can you do about the foxtail in your pasture or hayfield? Because it's a grass, it is nearly impossible to eradicate with herbicides that won't also damage your desirable grass. You have 3 options:

Renovate your pastures

If the foxtail infestation is minor, you can overseed with desirable cool-season grasses in the late summer (mid-August to mid-September in Pennsylvania) so that by springtime, the new grass can shade out the foxtail seedlings. If the infestation is widespread and there isn't much desirable grass left in the pasture, you may want to plow everything under and reestablish the field. This will bury the seeds too deep for them to germinate. Remember to take soil tests and correct pH or nutrient deficiencies before you seed, and to avoid grazing the pastures for at least 6 months after seeding to allow the new grasses to establish healthy root systems.

Let it grow up and begin producing seed heads, then mow it

If you keep an eye on these plants, you can tell when the seed heads start developing within the sheath (the boot stage). You will need to be able to identify the grasses without the seed head present! If you mow between this stage and full seed set, then the plant will not be able to drop seeds for next year, and it won't grow another seed head during this year. There are three important things to remember with this method:

• Regular mowing will not fulfill this task. Like desirable forage grasses, foxtail is not deterred by mowing. In fact, if you regularly mow it to a short height, you will end up with very short foxtail seed heads that are below your mower height. To use this method, you must let the grass grow tall before producing seed heads.
• The foxtail seeds in your pasture may have germinated at different times in the spring. Therefore, they will not all set seed at the same time. You will need to watch them to know when to mow.
• There may be a considerable seed bank in the soil. You will need to do this for several years in a row before you achieve control. Letting the foxtail drop seeds just once will replenish the seed bank.

Apply a pre-emergent herbicide

There is one pre-emergent herbicide approved for pasture use in Pennsylvania called pendimethalin (trade names Prowl H2O or Satellite HydroCap) that you apply in the early spring, before foxtail seedlings emerge, that will prevent them from growing. It is also effective on other summer annual grasses like crabgrass and some broadleaf weeds. This method has a few drawbacks. First, it is relatively expensive and should be sprayed twice for maximum effectiveness. Second, the herbicide has a planting restriction of 10 months for grasses. Therefore, if your field had a lot of foxtail last year and you use this herbicide in the spring, you will have bare ground in its place and no way to fill it in with desirable grass until the following spring. Other weeds may pop up in the bare areas, and bare ground is at higher risk for soil erosion. It may be wiser to overseed the pasture in the fall and apply the herbicide in the spring.

Any time you use an herbicide, read the label carefully and follow all instructions; the label is the law. If you have questions, reach out to the manufacturer or an ag professional for assistance.

Conclusion

In conclusion, horse owners and hay producers should learn how to tell the difference between foxtail and timothy grasses. In a severe infestation, eradicating the foxtail may be difficult and can take several years.