by Jesse Bussard
Weeds can be a pose a major problem for many forage producers. Weeds can negatively impact forage yield, stand persistence, and forage quality. Forage yield is effected because weeds will ultimately contribute to the total yield of the forage crop and can drastically reduce the total amount of desired forage in the hay crop.
Once established forages can out compete most weeds. The exception would be aggressive winter annual weeds such as chickweed. If a forage stand becomes invaded with weeds, the stand’s persistence will weaken. This can be caused by a number of factors including diseases, insects, low fertility, winter damage, and improper cutting management.
The largest affect weeds have on a forage crop is by reducing forage quality. Contrary to what you may think though, weeds are not necessarily always low in quality. Weeds such as barnyardgrass or giant foxtail are actually quite nutritious.
So if there are weeds high in quality, then why do we associate them with low forage quality? The reason lies in the fact that most forage quality tests do not include a palatability measurement. The crude protein content means nothing if animals won’t eat it. Another issue with weeds in forages include the fact that many weeds dry slower, which delays baling and increases exposure of forages. Weeds also tend to generally mature earlier than forage species.
When planting a new forage crop, the most critical weed control period is the first 60 days of forage emergence. Weeds that emerge along with the forage crop are generally the biggest issue.
To control or not to control? That’s the big question. When considering what weed control tactics to use it’s important to ask yourself the following questions:
- What is the intended use of the forage
- On farm use can generally tolerate some weeds.
- Forage to be marketed can not tolerate weeds.
- How old is the forage stand?
- Young stands (<2 yrs) can compensate and fill in better than old stands.
- Older forage stands (>4 yrs) may not compensate for yield loss when weeds are eliminated.
- How think is the forage stand?
- Non-spreading forage species (no rhizomes or stolons) have a stand density threshold below which production is not economical (alfalfa is 4-5 plants/sq ft).
- What is the weed species and how bad is the infestation?
- What is weed quality relative to time of harvest?
- Is it a noxious or poisonous weed?
There are many methods to control weeds in your forage crops. When establishing a new forage seeding it is important to buy certified (weed-free) seed. Be sure to control weeds in the proceeding crop. Another thing that isn’t always considered is animal manure. Feeding weed seeds to animals does not always kill the seeds. Many times manure is contaminated with weed seeds, so care must be taken to not spread manure that is loaded with weed seeds on a new seeding field.
To ensure a good stand it is important to maximize the competitive edge of forages. This can be done by selecting adaptable species and varieties and in return this reduces chances of diseases, insects, and winter damage. It is essential to also provide the optimum growing environment for forage growth with and ideal pH, soil fertility, and proper cutting management.
It is also important to minimize the competitive ability of your weeds. Depleting root carbohydrates by cutting them before they are mature, before seed production, through practices such as mowing will decrease weed competitiveness. A note for producers applying manure, adding manure to pure legume stands will encourage grass weed invasion.
In the end if a weed problem is still present, herbicides can be used. There are many herbicides available that will control broadleaf weeds in grasses and also grass/broadleaf control in legume forages. Unfortunately very little if any herbicides exist that offer control weeds in legume-grass mixtures or for grass weeds in forage grass crops.
For more information about weed control in forages, follow the links below to these extension publications: