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 Table of Contents
 Asian soybean rust
 Corn nutrient uptake throughout...
 Corn planting in June
 Timing nitrogen on cotton
 Kill date of bahiagrass and soil...
 Micronutrients on peanuts
 Cadre + select tank-mixes
 Limpograss and herbicides


FLAG IFAS PALMM UF



Agronomy notes
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Permanent Link: http://ufdc.ufl.edu/UF00066352/00069
 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: June 2006
 Subjects
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 )
 Notes
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.
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 000956365
notis - AER9014
System ID: UF00066352:00069

Table of Contents
    Table of Contents
        Page 1
    Asian soybean rust
        Page 2
    Corn nutrient uptake throughout the season
        Page 2
    Corn planting in June
        Page 2
    Timing nitrogen on cotton
        Page 3
    Kill date of bahiagrass and soil compaction
        Page 3
    Micronutrients on peanuts
        Page 4
    Cadre + select tank-mixes
        Page 4
    Limpograss and herbicides
        Page 5
        Page 6
Full Text






AGRONOMY
UNIVERSITY OF
FLORIDA NOTES
IFAS EXTENSION


Vol. 30:6


IN THIS ISSUE


CORN
Asian Soybean Rust .................. ..
Corn Nutrient Uptake Throughout the Season
Corn Planting in June ....................

COTTON
Timing Nitrogen on Cotton ...............

PEANUTS
Kill Date of Bahiagrass and Soil Compaction
Micronutrients on Peanuts ................


WEED CONTROL
Cadre + Select Tank-Mixes ..............
Limpograss and Herbicides ..............


. . . . . . . 4


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, Interim
Dean.


June 2006


DATES TO REMEMBER

June 3 Perennial peanut field day Milton, FL
June 10 Perennial peanut producers field day Moultrie, GA









Asian Soybean Rust


Asian soybean rust did not spread rapidly
during the months of March and April in
Florida due to the dry weather. However,
with recent rains in late May, we are
beginning to see rust on kudzu with greater
frequency. It is expected that rust will be
worse in 2006 due to the amount of
inoculum that survived on kudzu over the
winter. It appears that rust survived the
winter in North Florida and has been
observed as far north as Montgomery,
Alabama (sheltered underneath a highway
overpass). Researchers and graduate
students from universities throughout the
Corn Belt states will be working at the
NFREC on this problem.

David Wright

Corn Nutrient Uptake Throughout the
Season

Corn grows slowly during the first few
weeks of growth. It normally takes 6 weeks
for corn to reach the point of rapid nutrient
uptake. From planting (March) to 6 weeks
old, corn will assimilate approximately a
third of a pound of N per day per acre
(Table 1). From 6 weeks to 9 weeks of age,
demand becomes much greater and corn will
use 3 lbs of N per day per acre. This can go
as high as 5 lbs per day in ideal growing
conditions. Eight to nine weeks is normally
the start of tasseling. From tasseling to 12
weeks, corn will continue to use about 3 lbs
of N per day. Corn will continue to take up
2-3 lbs of N per acre per day after tasseling
with most of this going into grain since
vegetative growth is almost complete by this
time.

About 45-50% of the weight of a corn crop
is grain, so most of the biomass in the corn


crop after tasseling is due to the developing
ear.

Late N uptake is not critically important for
yield, but can make some difference in
protein content of the grain. However, a
late-season application of N is a fairly
expensive way to raise the protein content.
The key to good yields is to do a good job of
N management during the first 9-10 weeks
of growth (from planting to mid May).

Table 1. Macro nutrients removed per acre
by 30-ton corn-silage crop are shown in the
table below.


Total Nutrient Uptakes of corn plants at
Several Stages of growth and age (Quincy).

Stage of Days After
Growth Planting N P K

lbs uptake/A

20 inches 41 14 2 27

48 inches 60 72 8 116

tassel 82 122 18 191

maturity 132 280 45 296

David Wright

Corn Planting in June

There are very few corn hybrids that can be
planted in June without major damage from
insects and disease. Therefore, growing a Bt
corn is critical for late planting. Although
Bt hybrids will manage many common
insects, these hybrids are still sensitive to
diseases such as southern corn rust and corn
leaf blight. However, we have had good
success with tropical Bt hybrids which have
both insect and disease tolerance.









Asian Soybean Rust


Asian soybean rust did not spread rapidly
during the months of March and April in
Florida due to the dry weather. However,
with recent rains in late May, we are
beginning to see rust on kudzu with greater
frequency. It is expected that rust will be
worse in 2006 due to the amount of
inoculum that survived on kudzu over the
winter. It appears that rust survived the
winter in North Florida and has been
observed as far north as Montgomery,
Alabama (sheltered underneath a highway
overpass). Researchers and graduate
students from universities throughout the
Corn Belt states will be working at the
NFREC on this problem.

David Wright

Corn Nutrient Uptake Throughout the
Season

Corn grows slowly during the first few
weeks of growth. It normally takes 6 weeks
for corn to reach the point of rapid nutrient
uptake. From planting (March) to 6 weeks
old, corn will assimilate approximately a
third of a pound of N per day per acre
(Table 1). From 6 weeks to 9 weeks of age,
demand becomes much greater and corn will
use 3 lbs of N per day per acre. This can go
as high as 5 lbs per day in ideal growing
conditions. Eight to nine weeks is normally
the start of tasseling. From tasseling to 12
weeks, corn will continue to use about 3 lbs
of N per day. Corn will continue to take up
2-3 lbs of N per acre per day after tasseling
with most of this going into grain since
vegetative growth is almost complete by this
time.

About 45-50% of the weight of a corn crop
is grain, so most of the biomass in the corn


crop after tasseling is due to the developing
ear.

Late N uptake is not critically important for
yield, but can make some difference in
protein content of the grain. However, a
late-season application of N is a fairly
expensive way to raise the protein content.
The key to good yields is to do a good job of
N management during the first 9-10 weeks
of growth (from planting to mid May).

Table 1. Macro nutrients removed per acre
by 30-ton corn-silage crop are shown in the
table below.


Total Nutrient Uptakes of corn plants at
Several Stages of growth and age (Quincy).

Stage of Days After
Growth Planting N P K

lbs uptake/A

20 inches 41 14 2 27

48 inches 60 72 8 116

tassel 82 122 18 191

maturity 132 280 45 296

David Wright

Corn Planting in June

There are very few corn hybrids that can be
planted in June without major damage from
insects and disease. Therefore, growing a Bt
corn is critical for late planting. Although
Bt hybrids will manage many common
insects, these hybrids are still sensitive to
diseases such as southern corn rust and corn
leaf blight. However, we have had good
success with tropical Bt hybrids which have
both insect and disease tolerance.









Asian Soybean Rust


Asian soybean rust did not spread rapidly
during the months of March and April in
Florida due to the dry weather. However,
with recent rains in late May, we are
beginning to see rust on kudzu with greater
frequency. It is expected that rust will be
worse in 2006 due to the amount of
inoculum that survived on kudzu over the
winter. It appears that rust survived the
winter in North Florida and has been
observed as far north as Montgomery,
Alabama (sheltered underneath a highway
overpass). Researchers and graduate
students from universities throughout the
Corn Belt states will be working at the
NFREC on this problem.

David Wright

Corn Nutrient Uptake Throughout the
Season

Corn grows slowly during the first few
weeks of growth. It normally takes 6 weeks
for corn to reach the point of rapid nutrient
uptake. From planting (March) to 6 weeks
old, corn will assimilate approximately a
third of a pound of N per day per acre
(Table 1). From 6 weeks to 9 weeks of age,
demand becomes much greater and corn will
use 3 lbs of N per day per acre. This can go
as high as 5 lbs per day in ideal growing
conditions. Eight to nine weeks is normally
the start of tasseling. From tasseling to 12
weeks, corn will continue to use about 3 lbs
of N per day. Corn will continue to take up
2-3 lbs of N per acre per day after tasseling
with most of this going into grain since
vegetative growth is almost complete by this
time.

About 45-50% of the weight of a corn crop
is grain, so most of the biomass in the corn


crop after tasseling is due to the developing
ear.

Late N uptake is not critically important for
yield, but can make some difference in
protein content of the grain. However, a
late-season application of N is a fairly
expensive way to raise the protein content.
The key to good yields is to do a good job of
N management during the first 9-10 weeks
of growth (from planting to mid May).

Table 1. Macro nutrients removed per acre
by 30-ton corn-silage crop are shown in the
table below.


Total Nutrient Uptakes of corn plants at
Several Stages of growth and age (Quincy).

Stage of Days After
Growth Planting N P K

lbs uptake/A

20 inches 41 14 2 27

48 inches 60 72 8 116

tassel 82 122 18 191

maturity 132 280 45 296

David Wright

Corn Planting in June

There are very few corn hybrids that can be
planted in June without major damage from
insects and disease. Therefore, growing a Bt
corn is critical for late planting. Although
Bt hybrids will manage many common
insects, these hybrids are still sensitive to
diseases such as southern corn rust and corn
leaf blight. However, we have had good
success with tropical Bt hybrids which have
both insect and disease tolerance.









If corn is to be planted after corn, a soil
insecticide should be used. Coincidentally,
anytime that you plant into a green mat of
weeds or previous crop roots, a soil
insecticide is critical. Considering that it
takes about 4 of weed-free conditions or
between crops for the insect population to be
reduce to non-harmful levels. Unless you
intend to wait 4 weeks between harvest and
replanting, a soil insecticide is needed to
provide protection during this time.

David Wright

Timing Nitrogen on Cotton

Cotton should have a low rate of N as a
starter for early growth. Nitrogen should
also be applied to cotton at first-square to
early bloom for good yields. However,
timing is very critical on cotton since it will
continue in the vegetative stage of growth if
it has ample N and moisture, often at the
expense of boll set. Nitrogen studies in
Florida have shown that the critical period
for N application is usually about 40-60
days after planting. N applied more than 12


weeks after planting generally shows no
benefit, or decreases yield. Other problems
associated with late applications of N are
increased boll rot and hard lock, as well as
increased usage of growth regulators to
control excessive growth.

David Wright

Kill Date of Bahiagrass and Soil
Compaction

Data from recent studies have shown that
killing bahiagrass in the fall vs. the spring
can have a big impact on root growth of
peanut (Image 1). Fall killing of the
bahiagrass allows for decomposition and
heavy tillage does not have to be performed.
Peanuts may then be strip tilled directly into
fall killed bahiagrass with excellent results.
If bahiagrass is spring killed, some tillage is
required to achieve similar yields to fall kill.
Fall killing of bahiagrass can result in as
many as 4-8 less trips across the field,
having a major impact on fuel consumption
and cost of production. Fall killing also
results in less compact than spring kill at
planting (Figure 2).


Figure 2. Soil compaction, measured in kPa resistance, in fall vs spring killed bahiagrass.


Cone Index Value (kPa)
0 500 1000 1500 2000 2500 3000 3500


n


S2:0
E ':'


5:


S--Fall Killed
-u-Spring Killed


'* y 3
Penetometer readings in May *


r

"
I.









If corn is to be planted after corn, a soil
insecticide should be used. Coincidentally,
anytime that you plant into a green mat of
weeds or previous crop roots, a soil
insecticide is critical. Considering that it
takes about 4 of weed-free conditions or
between crops for the insect population to be
reduce to non-harmful levels. Unless you
intend to wait 4 weeks between harvest and
replanting, a soil insecticide is needed to
provide protection during this time.

David Wright

Timing Nitrogen on Cotton

Cotton should have a low rate of N as a
starter for early growth. Nitrogen should
also be applied to cotton at first-square to
early bloom for good yields. However,
timing is very critical on cotton since it will
continue in the vegetative stage of growth if
it has ample N and moisture, often at the
expense of boll set. Nitrogen studies in
Florida have shown that the critical period
for N application is usually about 40-60
days after planting. N applied more than 12


weeks after planting generally shows no
benefit, or decreases yield. Other problems
associated with late applications of N are
increased boll rot and hard lock, as well as
increased usage of growth regulators to
control excessive growth.

David Wright

Kill Date of Bahiagrass and Soil
Compaction

Data from recent studies have shown that
killing bahiagrass in the fall vs. the spring
can have a big impact on root growth of
peanut (Image 1). Fall killing of the
bahiagrass allows for decomposition and
heavy tillage does not have to be performed.
Peanuts may then be strip tilled directly into
fall killed bahiagrass with excellent results.
If bahiagrass is spring killed, some tillage is
required to achieve similar yields to fall kill.
Fall killing of bahiagrass can result in as
many as 4-8 less trips across the field,
having a major impact on fuel consumption
and cost of production. Fall killing also
results in less compact than spring kill at
planting (Figure 2).


Figure 2. Soil compaction, measured in kPa resistance, in fall vs spring killed bahiagrass.


Cone Index Value (kPa)
0 500 1000 1500 2000 2500 3000 3500


n


S2:0
E ':'


5:


S--Fall Killed
-u-Spring Killed


'* y 3
Penetometer readings in May *


r

"
I.









Image 1. Impact of soil compaction on
peanut root development.


David Wright


Micronutrients on Peanuts

Peanuts do not require a large amount of
fertilizer when compared to many crops.
However, peanuts do need some nutrients in
higher amounts than other crops.

The addition of boron is essential to prevent
hollow heart and is especially critical on
sandy soils. Spring of 2005 was wet and
several fields were identified with boron
deficiencies. Boron can be applied with
herbicide and/or fungicide applications at
low rates (1/4 lb a.i.) in 2-3 applications.
Although total uptake of boron will often
not exceed about one tenth pound per acre
by maturity, the need for boron is still
critical. The most common form of boron is
Solubor, (sodium borate). This material has
a high pH and may influence the efficacy of
pesticides if applied as a tank mix. Be sure
to check pesticides labels to see if it has an
influence on pesticide efficacy if tank
mixed.

One micronutrient that is often found at
toxic levels in peanuts is zinc. Peanuts are
much more susceptible to zinc than


soybeans, corn, or cotton. High zinc levels
will result in split stems and increased
incidence of disease. The only solution to
growing peanuts on high zinc soils is to
maintain a high pH to make zinc less
available to the plants. Some soils may be
high enough in zinc that peanuts can never
be grown without some damage. Since crop
removal for zinc is about 1 pound per acre
per year, it may take many years to reduce
the amount in soils by crop removal.

David Wright


Cadre + Select Tank-Mixes


In the next few weeks, Cadre herbicide will
be sprayed on several thousand acres of
peanuts. Cadre is a highly effective
herbicide that controls numerous broadleaf
and grass weeds. Although Cadre provides
good control of crabgrass, it will not
consistently control other grasses such as
goosegrass or Texas panicum. If these
weeds are present, growers will commonly
tank-mix Select or Poast Plus to improve
control.

However, Select is easily antagonized by
other herbicides. In a study conducted last
year, Select was applied alone and with
Cadre to control goosegrass, crowfootgrass,
and crabgrass. Select applied alone (8 oz/A)
provided 100% control of all grass weeds
present. However, when Select (8 oz) +
Cadre (1.44 oz) were applied together,
goosegrass and crowfootgrass control
dropped to 60% (Figure 2).

If grass weeds, that Cadre does not easily
control, are present in peanuts, it is best to
apply Cadre and grass herbicides separately.
Although this requires an extra trip across
the field, weed control will be greatly









Image 1. Impact of soil compaction on
peanut root development.


David Wright


Micronutrients on Peanuts

Peanuts do not require a large amount of
fertilizer when compared to many crops.
However, peanuts do need some nutrients in
higher amounts than other crops.

The addition of boron is essential to prevent
hollow heart and is especially critical on
sandy soils. Spring of 2005 was wet and
several fields were identified with boron
deficiencies. Boron can be applied with
herbicide and/or fungicide applications at
low rates (1/4 lb a.i.) in 2-3 applications.
Although total uptake of boron will often
not exceed about one tenth pound per acre
by maturity, the need for boron is still
critical. The most common form of boron is
Solubor, (sodium borate). This material has
a high pH and may influence the efficacy of
pesticides if applied as a tank mix. Be sure
to check pesticides labels to see if it has an
influence on pesticide efficacy if tank
mixed.

One micronutrient that is often found at
toxic levels in peanuts is zinc. Peanuts are
much more susceptible to zinc than


soybeans, corn, or cotton. High zinc levels
will result in split stems and increased
incidence of disease. The only solution to
growing peanuts on high zinc soils is to
maintain a high pH to make zinc less
available to the plants. Some soils may be
high enough in zinc that peanuts can never
be grown without some damage. Since crop
removal for zinc is about 1 pound per acre
per year, it may take many years to reduce
the amount in soils by crop removal.

David Wright


Cadre + Select Tank-Mixes


In the next few weeks, Cadre herbicide will
be sprayed on several thousand acres of
peanuts. Cadre is a highly effective
herbicide that controls numerous broadleaf
and grass weeds. Although Cadre provides
good control of crabgrass, it will not
consistently control other grasses such as
goosegrass or Texas panicum. If these
weeds are present, growers will commonly
tank-mix Select or Poast Plus to improve
control.

However, Select is easily antagonized by
other herbicides. In a study conducted last
year, Select was applied alone and with
Cadre to control goosegrass, crowfootgrass,
and crabgrass. Select applied alone (8 oz/A)
provided 100% control of all grass weeds
present. However, when Select (8 oz) +
Cadre (1.44 oz) were applied together,
goosegrass and crowfootgrass control
dropped to 60% (Figure 2).

If grass weeds, that Cadre does not easily
control, are present in peanuts, it is best to
apply Cadre and grass herbicides separately.
Although this requires an extra trip across
the field, weed control will be greatly










improved. Additionally, retreating with
Select because the first application was
ineffective is more expensive than initially
planning to make two applications.

Figure 2. Antagonism of Cadre + Select on
annual grasses.


100
90.
80.
70.
60-
50 Mgoosegrass
40 Ocrowfootgrass
30 Ocrabgrass
20
10
Select Select + Cadre


Jason Ferrell

Limpograss and Herbicides

Can I apply Pasturegard on my limpograss
pasture? What about that new Dow product,
Milestone will it hurt my limpograss?
These are a sample of the many questions
we recieve when a rancher wants to control
weeds in limpograss. Dicamba (Banvel) has
been the standard recommendation for weed
control in limpograss, because 2,4-D has
been reported to cause significant
limpograss injury. Over the past couple of
years, we have had several herbicides
labeled in the pasture market. These
herbicides include Cimarron, Telar,
Pasturegard, Overdrive, and Milestone, and
little information regarding the tolerance of
limpograss to these herbicides has been
recorded.

In a study initiated on 12 April, 2005, 2,4-D
amine at 2, 4, and 8 pints/acre, Remedy at 1,
2, and 4 pints/acre, and Milestone at 3, 5,
and 7 fluid ounces/acre were applied to


mowed (10 inches of regrowth) and non-
mowed limpograss. All three herbicides
caused some visual injury one month after
treatment. By 3 months after treatment,
there were no visual injury symptoms
present on either mowed or non-mowed
limpograss. When not mowed prior to
herbicide application, these herbicide
treatments did not impact limpograss
production 6 months after treatment.
However, if mowed prior to herbicide
treatment, a 20% yield reduction was
observed from 4 and 8 pints of 2,4-D amine
as well as 2 and 4 pints of Remedy.
Milestone caused a 15%-30% yield
reduction when limpograss was mowed
prior to application. This indicates that 2,4-
D amine is safe on limpograss when no
more than 2 pints/acre is applied.

The lack of limpograss injury from applying
2 pints of 2,4-D was surprising. Therefore,
a second study was initiated 16 September,
2005. In this study, Cimarron at 0.1-0.4
ounces/acre, Telar at 0.5 and 1.0
ounces/acre, Pasturegard at 2, 3, and 4
pints/acre, Banvel at 0.25, 0.50, and 1
pint/acre, 2,4-D at 0.75, 1.5, and 3
pints/acre, WeedMaster at 1, 2, and 4
pints/acre, and Overdrive at 4 and 8
ounces/acre was applied to 10 inch
limpograss. Applications of Cimarron,
Telar, Pasturegard at 2 and 3 pints, Banvel,
2,4-D at 0.75 pints, and WeedMaster at 1
and 2 pints caused less than 15% injury
chlorosiss and necrosis) 1 month after
treatment. By 2 months after treatment, no
chlorosis or necrosis was present from any
herbicide application. Although chlorosis
was not present, limpograss height was
reduced by at least 15% from applications
of Pasturegard at 4 pints, 2,4-D at 3 pints,
WeedMaster at 4 pints, and Overdrive.
Biomass was not recorded in this study.










At this point in time, Overdrive should not
be applied to limpograss as injury was too
severe. However, Cimarron and Telar are
additional options that can be considered.
Pasturegard (<3 pints/acre) and Remedy (<2
pints/acre) may also be applied to
limpograss if some initial injury can be
tolerated. At this point in time, Milestone
can be applied up to 7 fluid ounces/acre
when limpograss growth is mature.

Limpograss appears to be more tolerant than
previously thought to 2,4-D amine, but the
effects of 2,4-D amine appear to vary under
different environmental conditions.
Therefore, 2,4-D-containing products should
not be applied to limpograss until the effects
of 2,4-D on limpograss are fully understood.
Also, keep in mind that


new limpograss growth may be more
susceptible to herbicide injury than more
mature stands.

Herbicides often cause injury to desirable
species. How much injury can be tolerated
is usually up to the grower. However,
removing weeds in a pasture will often
outweigh the effects of an herbicide on
desirable species, especially when injury is
less than 15%. We will continue
investigating the effect of herbicide
applications at different times of the year to
gain a better understanding how herbicides
affect limpograss production.

Brent Sellers


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
products.
Preparedby: J.M. Bennett, Chairman; M.B. Adjei, Forage Agronomist I. ...1 ., I ,,ii ..., J.A. Ferrell, Extension Agronomist
I ,II. I, .i ,IIl .I.. F.M Fishel, Pesticide C......I....li ..l. .i .1.;l ..i C.R. Rainbolt, Extension Agronomist
.11 ....h.11, .I ,,l ..i, B.A. Sellers, Extension Agronomist .II. I., .I. ,l .I1..I E.B. Whitty, Extension Agronomist
.h .I .11 ,l ... I D.L. Wright, Extension Agronomist (dlw@ifas.ufl.edu).