Factors That Affect Ryegrass Control This Spring
PRINCETON, KY.
Fall is the preferred time to
control Italian ryegrass in
Kentucky; however, the
conditions last fall were not
favorable for the development
of wheat or ryegrass. Although
planting was ahead of
schedule, both wheat and ryegrass
plants did not begin to
emerge until late October or early November due
to the extremely dry conditions. The fact that
December’s statewide temperature was nearly 9
degrees cooler than normal also limited the developme-
nt of wheat and ryegrass plants.
The good news is the cold temperatures during
December and January enhanced the likelihood
of winter kill of small seedling ryegrass.
However, growers should not take it for granted
that the freezing temperatures eliminated all the
ryegrass. Some plants will survive and additional
seedlings could emerge as we transition
from winter to spring. Fields with a history of
ryegrass could still be a problem.
The following are some factors growers need
to consider if they determine there is a need to
make a spring application for controlling ryegrass:
Weather Conditions: Ideally ryegrass and
wheat plants need to be actively growing in
order to achieve optimum control and avoid
crop injury. Be aware it may take several days,
if not weeks, to control ryegrass, especially if
temperatures are cool. Large fluctuations between
daytime high and nighttime low temperatures
can result in crop injury with some
herbicides. Frost the night before or within two
days following application can also enhance the
likelihood of wheat injury.
Competition: Wheat is somewhat behind in
its development, therefore it is important to control
competitive weeds, especially ryegrass, in
order to give wheat a better chance to finish
tillering and develop a competitive canopy.
Growth Stage: Crop growth stage can impact
when certain herbicides can be applied. Spring
treatments with Hoelon need to be applied prior
to jointing of wheat; whereas, Osprey and PowerFlex
can be applied up to jointing. Axial XL
may be applied up to pre-boot stage. Ideally
spring applications should be applied before
ryegrass exceeds the maximum growth stage of
2 tillers. The delay in emergence and development
of ryegrass will increase the likelihood that
most plants will be within the 2- tiller growth
stage this spring. Even if plants exceed the 2-
tiller stage, a spring application may control or
suppress plants enough to limit ryegrass competition
to wheat.
Timing of Nitrogen Fertilizer: Osprey and
PowerFlex are acetolactate synthase (ALS) inhibitor
herbicides that can injure wheat if applied
near the time of topdressing nitrogen.
Stunting and leaf chlorosis are typical injury
symptoms that can occur when these herbicides
are applied near the time of topdressing nitrogen.
The PowerFlex label cautions against making
applications within seven days of
topdressing ammonium nitrogen fertilizer, while
the Osprey label suggests waiting 14 days between
application and topdressing. Visual injury
can occasionally occur even when following
these directions, yet UK data show that it is unlikely
this will result in a reduction of wheat
yield.
Rotation Restrictions: The rotational crop
restrictions can impact which option to consider
when applying herbicides in the spring for ryegrass
control. The Hoelon label does not prohibit
planting to double crop soybeans;
whereas, Osprey and PowerFlex require a minimum
of 3 months between application and
planting double-crop soybeans. The rotation intervals
for Finesse Grass & Broadleaf and Olympus
Flex are much longer which prohibits their
use for spring applications.
Tankmixing: The use of Harmony Extra, 2,4-
D or dicamba as tankmix partners with Holeon
may limit ryegrass control. However, Harmony
Extra is an approved tank mix partner with
Axial XL or Osprey. Consult product label directions
for approved tank mix partners and use
of additives. Δ
DR. JIM MARTIN: Extension Weed Control Specialist,
University of Kentucky