Battling Weeds With Herbicides
By: David Jessee, Agronomist for Southern States
When weeds encroach into weakened stands of forage crops, they not only reduce the yield but also affect its quality and hurt your pasture’s appearance. Once established, weeds reproduce by seed and extensive root systems to take over weakened areas of the pasture. The fact is, horses don’t like weeds. They will preferentially graze away from weeds, further weakening your stand. Getting rid of weeds allows new establishment of forages in the voids. Prevention can be accomplished with good agronomic practices such as paying attention to pH and fertility, managing harvest and grazing, and controlling weeds early before they get a foothold.
Knock Out the WeedsChemical herbicides are the most common way of controlling weeds. Integrated Pest Management methods also include non-chemical means of cultural control (e.g. rotation, species selection) or mechanical control (e.g. mowing at critical stages, plowing). Non-chemical means can be combined with herbicides for a one-two punch, but this discussion focuses on chemical herbicides.
Choosing the right herbicide requires knowing what kind of weeds are growing so that the application can be timed to the most susceptible growth stage. Spraying early is best for annuals like spiny pigweed that survive by making seed. Conversely, the perennial horse nettle relies upon fleshy carbohydrate storage in the roots, so they must be sprayed later when the carbohydrate reserve weakens for the herbicide to be more effective. Biennials like thistle grow in a vegetative rosette for the first year, followed by flowering, so the best way to control them is in the first year’s rosette before they go to seed.
A Fresh StartHerbicidal weed control will usually require successive applications into grass stands over a few years. Any desired legumes will have to be sacrificed and reintroduced after the weeds have been eliminated, since most herbicides will kill or severely stunt clovers. In some cases, the grass stand may be so thin that a total kill of grasses and broadleaves is the best course of action, especially if undesirable grasses have encroached.
Following all chemical warnings is vital.
Here is a quick reference on available brand name herbicides and their susceptible weeds. Check with your local Southern States or Agway for more detailed information. Then give those weeds the old one, two punch, and knock ‘em out for good.
| Herbicide |
Weeds Susceptible |
|
Annual |
Biennial |
Perennial |
| Forefront |
|
cd, this |
pw, hn, bc |
| Grazon |
|
cd, this |
pw, hn, bc |
| Aim |
spw |
|
|
| Banvel |
spw |
|
mfr |
| Cimarron Plus |
spw, must, cw, bb |
cd, this |
mfr, bc |
| Crossbow |
|
|
mfr, db, bb |
| 2,4-D |
must |
this |
bc |
| Milestone |
|
cd, this |
hn, bc |
| Surmount |
|
|
db |
| 2,4-D+Banvel |
cw |
cd |
pw, mfr, db |
| Weed Key |
Time to Spray |
| bb (Blackberry) |
|
Early Bloom |
| bc (Buttercup) |
|
Spring |
| cd (Curly Dock) |
|
Rosette or Early Bloom |
| cw (Chickweeds) |
|
Late Fall / Early Spring |
| db (Dogbane) |
|
Early Bloom |
| hn (Horsenettle) |
|
Early Bloom |
| mfr (Multiflora Rose) |
|
Early Bloom |
| must (Mustards) |
|
Late Fall / Early Spring |
| pw (Pokeweed) |
|
Early Bloom |
| spw (Spiney Pigweed) |
|
Pre-bloom - Late Spring or Early Summer |
| this (Thistles Biennial) |
|
Rosette (Early Spring or Late Fall) |