Editor’s Note: Two University of Florida weed researchers offer answers to some frequently asked questions regarding yellow herbicide applications, timing and crop injury. Use these answers to guide your weed management early on.
Q. Can I apply a yellow herbicide (Prowl, Sonalan) with Valor?
A. Yes, but you need irrigation to make
this work at peak performance.
The yellow herbicides are prone to
degradation from sunlight if it lays on
the soil surface for more than a few days.
Both the Prowl H2O (pendimethalin)
and Sonalan (ethalfluralin) labels suggest
that incorporation should occur within
48 hours of application.
Tillage has traditionally been used to
incorporate these herbicides into the soil
with excellent results. However, the Valor
(flumioxazin) label clearly states that mechanical
incorporation will reduce the activity
of this herbicide.
Considering these conflicting scenarios,
there are two options: One option is to incorporate
with irrigation or rainfall. Applying
one-half to one inch of water will
incorporate all of these herbicides, and
no further activities would be required
for optimum performance.
The second option is to apply them
separately. If irrigation is not available
and rainfall is not eminent, apply the yellow
herbicide followed with mechanical
incorporation. Then, apply Valor within
three days after peanut planting. Rainfall
is needed to activate the Valor, but it does
not require immediate incorporation.
Q. Do I lose efficacy if Valor is applied
prior to planting?
A. Yes, you might lose residual control
during the growing season and allow weed
emergence within the planting row.
Depending on how long before planting
you spray Valor, you might be losing
late-season residual weed control. Besides
the good control Valor provides of important
weed species, such as Palmer amaranth,
that emerge early during the season,
you will want to take advantage of the
potential this herbicide has for controlling
late-emerging species such as Florida beggarweed
Valor is a herbicide with very low mobility
within the soil, so once you apply
it, it is important to avoid soil disturbance.
If Valor is applied before planting,
and then the soil is disturbed for planting
the seed, the herbicide layer on the
ground will not be as uniform in this area
where it is needed most. This is exactly the
situation to avoid in the planting row so
that weeds do not grow and compete right
next to peanut plants.
Plant peanuts first and then spray the
herbicide (PRE application). Make sure that Valor is applied no later than three
days after planting and before cracking,
otherwise peanut injury is likely. Remember,
if the application is made at the
right time, you will be taking full advantage
of the benefits Valor can give you as
a weed control tool.
Q. How much Basagran should I mix
with paraquat for the “at cracking”
A. Basagran may not be required at all.
Basagran has traditionally been used
with paraquat to reduce peanut injury.
However, numerous experiments have
shown that this early season paraquat injury
rarely translates into peanut yield
loss. Furthermore, the addition of
Basagran has not been shown to improve
peanut yield and commonly adds minor
weed control benefits.
If you do not wish to spray paraquat
alone, adding Storm might be a better
option. Storm, which contains the active
ingredients of both Basagran and Ultra
Blazer, can help reduce the paraquat burn
while improving both morningglory and
pigweed control over paraquat alone.
Q. Is applying Cobra with crop oilconcentrate
A. No, Cobra (lactofen) plus crop oil
concentrate will cause visible leaf injury
(pictured above, left), but peanut plants
will quickly recover (above, right) and no
yield reductions should be observed.
Cobra can cause severe peanut injury
when applied with crop oil concentrate.
The most common symptoms of injury
are mainly speckles of dead tissue on the
Our studies have shown that applying
Cobra with crop oil concentrate at 15,
30 or 45 days after planting (DAP) can
cause up to 30 percent injury seven days
after treatment. However, despite this level
of injury, which might make growers
nervous, peanut plants will quickly produce
new leaves, and usually a week later
the injury is minimal. Very soon the plants
are fully recovered, and by the end of the
season, yields are not reduced.
An important detail is that the earlier
you spray, the higher the injury, but this
does not mean that you have to delay
your application. Proper application timing
in relation to the weed size is critical.
You need to spray early enough so the
weeds will have no more than four true
leaves ensuring proper control.