Weed Management
in Established Forages
Jerry
Doll
I. Good
crop management = 75-90 % of forage weed control program
A. Few
herbicides used in established forages: cost often exceeds
benefit
B. Follow
the basics of sound forage production to "prevent"
weeds
1. "EGG WAS FIRST": Weedy alfalfa due to thinning
stand; not the reverse
2. Crop rotation key component of forage/weed management
II.
Impact of Weeds on Forages: Returns on the Investment
A. Yield:
1. do
not expect total tonnage to increase
2. do expect
a higher percentage of legumes in the harvested forage
B. Quality: here is where the payoff (returns) must be
1. depends on
the species present (see Table 4-1 on page 116 of Pest
Management bulletin)
2. varies
with the stage of weed growth: older weeds have less feed value
3. depends on
weed density
4. some weeds
have low palatability, weed digestibility declines more rapidly
than legumes:
a. yellow rocket:
reduced protein content by 1-2% and is relatively low in
digestibility
b. quackgrass:
reduced protein content by 3-6% with lower digestibility
c. dandelion:
protein reduced only in first cutting; no impact on
digestibility
d. white cockle:
rarely a weed of economic importance in forages
C. Water content/drying time
1. weeds wetter than alfalfa at cutting time are
dandelion, curly dock and white cockle
2. weeds like dandelion can slow the forage
drying rate
3. can add an extra day to make dry hay
4. weed moisture content not as concern when
making silage
D. Nitrogen credits. Without quackgrass (or
other grasses) more nitroge credits could be given to the following corn crop
E. Forage
stand longevity: weeds alone are not likely to reduce stand
longevity
F. Weeds and
the two stress theory: forage legumes will stand one
abuse; two or more invite yield and stand loss
Ex: weeds + leaf hoppers or weeds + low K levels = stand loss
and low yields
BOTTOM
LINE:
 It
is difficult to put $ value on the impact of weeds in forages
Quality
will continue to be the criterion by which we judge success in
forage production
III.
Possible Herbicide Alternatives in Established Forages
A. For
quackgrass and annual grasses: Poast Plus or Select (fatty acid
synthesis inhibitor)
1. Treat
quackgrass 6 to 8" tall; will reinfest later in season
2. Also
excellent to control annual grasses (yellow foxtail;
barnyardgrass) in midsummer
3. Cost is
reasonable and treatment is often justified
B. Broad
spectrum, spring dormant treatments: all are photosynthesis
inhibitor
1. Sencor:
Only in stands at least 2-yr old
Spring "pre-greenup" treatment unless applied with dry
fertilizer as carrier
Good to excellent for several of our common perennial
broadleaves; suppresses quack
2. Velpar:
Can treat with up to 2" new growth and maybe year after
seeding
Good to excellent for several of our common perennial
broadleaves; suppresses quack
C. Herbicide
use strategy in established forages
1. Threshold
to justify herbicide use in forages is 4 to 5 alfalfa plants/sq.
foot or > 55 alfalfa stems/sq. foot
2. Monitor
forage stands and weed situation in spring and fall
3. When
stands thin and weeds appear, crop rotation best choice in most
cases
4. Do on-farm
evaluations, including forage quality comparisons
5. Should
never need broadleaf weeds more than once in the rotation
IV.
Idealized Weed Management Program in Forages |
