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Fall Cropping Management Practices

Posted: January 21, 2008

Del Voight
Agronomy Extension Agent,
Lebanon, Pa.
October 18, 2002

Fall allows the producer many opportunities that will impact next year’s crops. Liming,
fertilizer applications and fall tillage will set up the right conditions for next years crop season. I
will discuss the fall decisions related to applications of herbicides to manage weeds and crop
rotation. Applications of an herbicide in the fall may mean better crops in future years for a
range of reasons, from killing a grass sod to get ready for next springs corn planting to
eliminating the toughest perennial weeds in the field.

Two falls ago Charlie Bomgardener a
producer near Annville had many green fields in the fall after silage harvest that contained both
perennial and annual weeds. After viewing the weeds we decided to apply Round Up™ to
eliminate the weeds this fall. Not all fields received the application and boy could you tell next
spring. The cleanest fields in the spring were the ones receiving a late fall herbicide treatment.
Not only were the weeds clean the usual chickweed and other winter annuals were eliminated
apparently they had germinated at the time of application in the fall. This is not a one-time
testimonial. Dr. Bill Curran PSU Weed Specialist has done along with other Universities many
studies documenting the tremendous impact fall applications of herbicides have on certain weed
species mostly perennials. In fact in his research Hemp dogbane was controlled 90% with fall
applications compared to 60% if the same product was applied in the spring.

In most cases one may suppress many perennials (hemp dogbane) during the growing
season using an array of products but those established plants will be there the next season to be
suppressed again. The only way to completely kill the established plant and have no recovery
the next year is to fall apply systemic herbicides such as Round UP, Touch Down, 2,4-D or
Banvel. Sure one might control seedlings during the growing season but I am referring to those
plants with large root systems that can compete much more than a few seedlings. What is the
best time? Penn States investigations show that shortly before a frost (Early October) is the best
time to apply in the fall if the weeds have green leaves in good condition.

Another fall herbicide application that makes sense is to kill orchard grass and alfalfa
stands in the fall. Gerald Hoffer a producer farming by Hershey picked up some rented land last
season that had some alfalfa. Since Gerald is mostly interested in grain he decided to let the
alfalfa go to first cutting in the spring harvested the first cutting and then killed the stand and no
tilled corn into the stand. Fortunately the alfalfa was thick and he received high quality and
tonnage followed by a decent stand and resulting yield of corn in that year. I can also point to
cases where producers not only got a weedy half crop of alfalfa in the spring followed by a
drought stricken almost complete loss for a corn crop. Alfalfa produces an enormous amount of
nitrogen (commonly 100-120lb/acre) released from its nodules on the roots that enables some of
the best corn crops to be grown after, if killed in the fall and planted early in the spring. There is
no question this is the best use of the alfalfa stand. There are ways to make better decisions to
either kill the alfalfa in the fall or to let it go to after first cutting. The decision to make is how
many plants are there right now this fall.

Make, buy or borrow a alfalfa square (simply a 1 foot
square wire or wood outline) throw it randomly in the field and count plants within the square.
If there are less than four plants per foot kill it this fall and plant full season corn in spring. If
however you find a decent stand over 4 plants per foot then consider leaving the stand for
another year or if you have to due to forage need plan to harvest first cutting and plan for silage
harvest using sorghum for drought prone areas and corn for others. Does it make any sense get a
poor quality crop of alfalfa and poor yield of corn? No, assess alfalfa in the fall and manage
accordingly. One final note related to weeds in alfalfa is that growers should be applying
residual herbicides now to eliminate chickweed in the field. Products like Pursuit or Raptor kill
both emerged plants and leave a barrier for plants that might emerge later in the winter time. A
quick look at the past years Five-acre corn club results shows the relation to high yielding corn
crops after legumes (soybean and alfalfa). In almost all cases the top producers rotated from a
legume.
Fall applied herbicide rates may be reduced due to the fact that the plants are more
susceptible in the fall while transporting nutrients along with the herbicide into the roots for
winter. For example, the labeled rate for fall application to kill alfalfa for the herbicide Round
Up is1 quart per acre while the spring application rate is 2 quarts. If dandelions are present
which many times is the case use 1pt of 2,4-D as a tank mix to eliminate this weed. For control
of perennials in fields to rotate to corn next year Round Up rates can be reduced to1 pint/acre in
most cases and the highest rate needed for fall applied would be 1 quart per acre. Touchdown is
another systemic herbicide similar in activity to Round Up but is applied at a lower rate. Check
the label for specifics.

Insects also seek over wintering sites this time of year. By eliminating vegetation this
fall populations of an array of insects will be eliminated simply by removing these over
wintering sites. Where fields have high enough residues to hold the soil in place the removal of
winter annuals like chickweed and henbit will ensure cutworms, armyworms and other moths
will not migrate to that field. Keep this in mind with cover crops as well for this will force them
to lay eggs into the cover crop and growers will need manage these fields by delaying planting at
least 14 days after the cover crop is harvested or killed with a herbicide.
By performing some key activities this fall such as fall applied herbicides and assessing
alfalfa fields and fertility levels producers may be better prepared to ensure next seasons yield
and profitability.