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Agronomy notes
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066352/00087
 Material Information
Title: Agronomy notes
Uniform Title: Agronomy notes (Gainesville, Fl.)
Physical Description: v. : ill. ; 28 cm.
Language: English
Creator: Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Place of Publication: Gainesville
Creation Date: April 2007
Subjects / Keywords: Crops and soils -- Florida   ( lcsh )
Crop yields -- Florida   ( lcsh )
Agriculture -- Florida   ( lcsh )
Agronomy -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
periodical   ( marcgt )
serial   ( sobekcm )
Statement of Responsibility: Florida Cooperative Extension Service, University of Florida, Institute of Food and Agricultural Sciences.
General Note: Description based on: January 1971; title from caption.
 Record Information
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000956365
notis - AER9014
System ID: UF00066352:00087


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Vol. 31:4 April 2007

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Projected Dry Spring and Corn Planting Date.............. ......... ...............2

Consider April Planted Cotton............... ............ ............... .....2

Spring G razing M anagem ent ............................ ........................... ...................3

Soybean Sentinel P lots.......... ............................................ ........................

D brought and W eed Control ........ ............................................... ............... 3
Spring B lackberry C control ........................................................ ........... ...... 4

Row Applied or Starter Fertilizer ............................................. ............... 5

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity _Affirmative Action Employer authorized to
provide research, educational information and other services only to individuals and institutions that function without regard to race, color,
sex, age, handicap or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension
Office. Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Larry Arrington, Dean.

Projected Dry Spring and Corn Planting

The projected cool, wet winter did not occur
as predicted this winter. This may mean a
dry spring as occurred in 2006. Dryland
corn producers were hit hard in 2006 by the
drought with early planted corn starting to
silk and tassel in mid May. The ear fill
period is a critical stage that needs good
moisture for grain yield. The grain also
contributes about 50% to silage yield.
Therefore, it may be better to plant dryland
corn later if the spring is dry and to catch
afternoon summer showers during the ear
fill period in late June and July. Higher fall
armyworm and corn earworm damage
occurs with late planting (May-July). Less
insect damage occurs on the Bt than the non
Bt hybrids, and it is very apparent in both
silage and grain yield. Therefore, if one is
to plant dryland corn late (mid-April to mid-
May) consider using a Bt hybrid. If
adequate water is available, little difference
is noted in corn planted in February through
early April There are differences in
hybrid's responses to southern corn rust.
Tropical corn hybrids recommended for
Florida have less rust than temperate hybrids
in variety trials. This becomes more
apparent with late planting. However, there
are differences in the rust tolerance of
temperate hybrids and some temperate
hybrids do much better against southern rust
than others with late planting (late April-
June). Check variety trial information from
as many nearby locations as possible to
compare hybrids.

David Wright

Consider April Planted Cotton

April is the key month for cotton growers in
the Deep South. Will adequate moisture be
available for planting or will it be too cold

and wet? In the past few years, growers
have had dry weather conditions to contend
with at planting. A target of killing cover
crops 5 weeks in advance of planting is a
good idea for moisture conservation as well
as reduction of insect pests that could
damage young cotton seedlings. Many
growers strip rows off several weeks ahead
of planting to spread the workload and to
allow a smaller tractor with planters to come
in for the planting operation. All of these
practices can work for growers, but extra
care will be needed to insure that new weed
growth does not occur between the time of
killing cover crops and planting, or strip
tilling and planting. Generally, 2,4-D type
herbicides can be applied in January or
February followed by glyphosate five weeks
ahead of planting which will control many
of the broad leaf weeds on which glyphosate
is weak. Many growers are using some
residual herbicides in the burn down
herbicide application to keep weed growth
from coming on before planting. If moisture
is conserved from a late March killing of the
cover crop, cotton can be planted at almost
any time in mid to late April with good
results. Starter fertilizer is not used as often
with cotton as with corn but has been proven
to be more efficient than broadcast
applications and should be considered if
high amounts of P or K are required. Care
should be taken with N to keep it 1 inch
away from the row for each 10 lbs/A of N
applied as a starter. Phosphorus has been
shown to be more effective (use 2/3rds the
rate or less) when applied as a starter in a
band near the row, or 2"X2"as compared to
broadcast applications. Therefore, consider
starter applications if high amounts of P are
required for the cotton crop.

David Wright and Jason Ferrell

Spring Grazing Management or
Balancing the Energy Reserve

Grazing management is about managing the
energy reserves of a plant that is
continuously 'drawing' energy through
grazing or haying. What happens when you
overgraze a pasture? When you graze or
stock beyond the critical stubble height, the
plant is left without enough leaves and stems
from which to re-grow. Because it can not
take or 'draw' energy from the leaves, it
starts using the energy from the roots.
Gradually the root systems shrinks, and you
start seeing the common thinning of
pastures. During drought years, like this
one, keeping the energy reserve is critical
because you want the root system to be as
large and deep as possible to explore and
take as much of the limited soil moisture.
Stubble height is the most important grazing
management tool and allowing the pastures
to rest will aid in the recuperation of the
pasture and allow the resumption of grazing
in the spring.

Pastures grasses like bahiagrass have a
prostrate growth habit and are adapted to
close grazing. These pastures are able to
tolerate close grazing better than those
grasses with more upright growth (such as
limpograss) because of the large rhizomes or
underground stems. These rhizomes store
and provide the energy for regrowth after
grazing. Bahiagrass pastures, while needing
a rest period as well, will recuperate faster.
Indeed, grazing of bahiagrass pastures is
recommended in early spring to allow
limpograss pastures to recover from winter
stress. However, caution is advised: too
closely grazed bahiagrass will eventually
run out of reserves in the rhizomes and thin
out as well, opening 'spaces' and
opportunities for smutgrass or other
troublesome weed to encroach. It is
recommended to rest limpograss pastures
from grazing and allow them to accumulate
at least 10 to 12 inches of growth before
grazing is resumed. Stock or graze

rotationally taking no more than 12 of the top
growth. During the warm season, it is
important to always leave sufficient leaf area
on the plants after grazing. This will help to
maintain a healthy productive stand.

Yoana Newman

Soybean Sentinel Plots

Florida is a key state in the detection and
spread of Asian soybean rust for the rest of
the soybean states. Sentinel plots have been
planted all across the state in about 20
locations in MG III, V, and VII soybeans.
Locations include several south Florida
counties, the research center at Citra in
central Florida and counties across the
panhandle of Florida. These plots are
checked weekly for the occurrence of
soybean rust and results are posted on the
national website, http://sbrusa.net. Each of
the soybean producing states has these plots
and spread of rust can be checked weekly.
Several kudzu sites are monitored year
round in Florida and throughout the winter
months. Soybean rust has been found each
month at kudzu sites in north Florida. The
website and commentary is updated weekly
and can be helpful information for growers
to determine whether to spray their crop for
soybean rust.

David Wright and James Marois

Drought and Weed Control

Weed control under dry conditions can be
problematic, and the reason is two-fold.
Weed competition with crops and forages is
more detrimental to yield than under normal
or wet conditions. Additionally, weeds are
less affected by herbicide applications under
dry conditions.

Preemergence herbicides. Preemergence
herbicides require rainfall for incorporation
into the soil. Without rain, the herbicide
will be less active and will result in more

weed escapes. Additionally, many of our
soil applied herbicides are degraded by
sunlight. So, without incorporation by
rainfall, less herbicide will be available for
uptake by weedy species and will be lost
through degradation from sunlight.

Postemergence herbicides. Postemergence
herbicides are also affected by drought.
This is due to decreased growth of the weeds
we are trying to kill. Under dry conditions,
weeds have more wax on their leaf surfaces,
which restricts movement of the herbicides
into leaf tissue. Also, drought-stressed
plants often grow slower due to decreased
metabolism and less air exchange as plant
close their stomates to conserve water.

For postemergence applications, the addition
of the correct adjuvant system can help
weed control operations under dry
conditions. Some herbicide labels
specifically list which adjuvant should be
used under such conditions. In any case, it
is best to be familiar with the label to
optimize herbicide activity under any
environmental condition.

Some believe that plant growth regulators
(2,4-D, etc.) are not affected by drought
conditions. Unfortunately, this is not the
case. Under normal conditions 3 pt/acre of
Pasturegard provides >95% control of
dogfennel. In research plots last year, this
same rate of Pasturegard provided <80%
control under drought conditions. Once
rainfall occurred and plants resumed normal
growth, control returned to >95%.

The shortage of rainfall this year is similar
to that of last year. However, we are already
short of rainfall for the year, further
complicating the drought condition
compared to last year. Therefore, I expect
that any herbicide applications in pastures
will result in less than satisfactory results,
especially compared to "normal" years.

If weeds are actively growing, herbicide
applications will continue to work
adequately. However, if weeds are wilting
during the day and recovering overnight, an
herbicide application should be delayed until
rainfall has been received and weeds are
actively growing.

Brent Sellers

Spring Blackberry Control

Blackberry often remains green throughout
the winter and begins its new growth very
early in the spring. In order to maximize
early-season grazing, control of blackberry
in the spring can be desirable. However,
spring applications can be tricky and can fail
if not done properly.

Blackberry is most sensitive to herbicides
when blooming or late in the fall. This is
because the plant is actively loading
carbohydrate into the root system at these
times. Therefore, the herbicide will enter
the leaf and immediately be transported with
the carbohydrate into the roots, where the
herbicide control is most effective.
However, blooming is a relatively short
process that soon leads to fruiting. During
fruit development, energy transport is
shifted away from the root and is targeted at
the fruit. Applying a herbicide at this stage
will result in the product staying in the
leaves and buds with very little of it ever
finding its way to the root. An herbicide
applied at fruiting will generally cause rapid
leaf brown-out, but respouting from the
root-stock will begin to occur within 2 or 3

Another factor to be aware of is the overall
weather condition during blooming. Dry
weather causes the plant to grow more
slowly. Therefore, drought will reduce the
amount of carbohydrate flow into the root.
If herbicides are applied during drought,
they will not be quickly transported and the

leaf will die before the herbicide has time to
move to the root system.

As stated previously, blackberry control in
the spring can be tricky. It is important that
you spray at bloom when there is adequate
soil moisture. If conditions are dry, or
plants are fruiting when you are prepared to
spray, it is best to delay the application until
the fall or poor control will result.

Jason Ferrell

Row Applied or Starter Fertilizer

Fertilizer applications were historically
made in row for many years. Larger acreage
and bigger equipment with many operations
occurring at planting led farmers to do more
broadcast applications of fertilizer which
speeded up the planting operation.
However, root systems of many of the crops
that have been planted in wide rows never
reach to the middles of rows and may never
encounter the applied fertilizer. In many

cases, if applied in row, as much as 1/3 less
fertilizer than in broadcast application can
be applied with better results than
broadcasting the full rate. Growers need to
consider the acreage and the cost difference
of banding vs. broadcasting fertilizers and
may be surprised at how much could be
saved by row application of fertilizers.
There are other studies that indicate that
band applications may be even more
effective than mentioned above. Equipment
has gotten better for growers to band
fertilizers and buggies are available to bring
fertilizer to the field to auger it into banding
units to keep labor to a minimum. Growers
who want to try reducing rates should split
fields where they broadcast normal rates of
fertilizer and compare it to 1/2 to 2/3 rates
applied in a band near the row. This would
be the most cost effective on wide row crops
that have a high fertilizer requirement (corn,

David Wright

The use of trade names does not constitute a guarantee or warrant of products named and does not signify approval to the exclusion of similar
Prepared by: J.M. Bennett, Chairman i1.1, ,,11l ... ; J.A. Ferrell, Extension Agronomist I i n II, ., ,,l ...Ih J. Marois, Plant Pathology
i .11' ... ill i.i Y.C. Newman, Extension Forage Specialisti ..-, i il ..I i B.A. Sellers, E 11 ..1.. r ._..1..11 1 1 I I., I, ,,1 l .h,,
D.L. Wright, Extension Agronomist idJl a if,.utf.edIu