Group Title: Agronomy Notes
Title: Agronomy notes
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 Material Information
Title: Agronomy notes
Uniform Title: Agronomy notes (Gainesville, Fl.)
Physical Description: v. : ill. ; 28 cm.
Language: English
Creator: Agronomy Department
Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Place of Publication: Gainesville
Publication Date: January 2010
Subject: 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 )
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
Bibliographic ID: UF00066352
Volume ID: VID00119
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000956365
notis - AER9014


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IFAS Extension

Agronomy / notes

Volume 34:01


Timing Is Everything ........................ Page 2
Cotton And Corn As Influenced By Foliar Disease............ Page 2

Soil Testing For Forage Production............... Page 3
Grass Te tany ............................. ................... Page 4

Small Grain For Grain ............................ ................... Page 2

Weed Control
FQPA 's Effect On Pesticide Use Trends .................... Page 4
Control Of Winter Weeds In Hayfields............................ Page 5

Calendar .........................................................................Page 4

"Agronomy Notes" is prepared by: Maria Gallo, Interim Chair and Y. Newman, Extension Forage Specialist
(; J. Ferrell, Weed Specialist (; F. Fishel, Pesticide Information Officer
( 1 ....I..I ,, ,i1l i..lI B. Sellers, Extension Weed ". i. i I d il I i.,i i1 c....l i and D. Wright, Extension Agronomist
( Designed by Cynthia Hight ( 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.

January 2010


Timing Is Everything

In most areas of life we find that timing is
everything. Nitrogen fertilization is no
exception. Peak uptake by most crops starts
around 6 weeks after planting. Cotton starts
Sa squaring at 5-6 weeks after planting and this
Starts a peak uptake period for N uptake. Yield
of cotton is highest from N applied about 42
days after planting but was not significantly
different from N applied earlier in the season.
Nitrogen applied after the 3rd week of bloom did
not increase yield above the control with no N.
These data indicate that it is better to apply N
early than too late for top yield. Applications
made too early may leach out in times of heavy
rain or on sandy soils so applying N from 5-6
weeks after planting for cotton is the best timing
when cotton is squaring to early bloom.
Dr. David Wright

There are articles in most farm magazines about fungicides on both cotton and corn which have
typically not had fungicides applied. Are they necessary and will they increase yield? The answer to
this is that it depends on environmental conditions and that there are locations that have diseases
routinely and other areas that do not. In fields that are known to have had disease problems in the past,
there may be a good likelihood that there
will be again. Some of our data (shown
below) with cotton has shown that there
is a good correlation to yield with leaf
area. In other words, if we can keep the
plants healthy and retain leaves, we have
a better chance of making higher yields.
Fungicides should not be used routinely
on cotton or corn unless there are fields
that are known to have a history of
getting leaf diseases and in the case of
cotton defoliates early. Early defoliation
on cotton has also been associated with
potassium deficiency so that should be
checked out and necessary management
included to eliminate that if possible.

Dr. David Wright

Agrnoy Notes Pa

Small Grain For Grain

Small grain can be a very
Fertility Fall & Spring profitable crop in a wheat/
Fall N (Ibs/a): soybean rotation. Proper planting
+ Behind peanuts: 10-20; soybeans: 10-20; corn and fallow:25-30; cotton: 35-40 date and variety selection is
important to obtain high yields.
+ Should provide growth till January. Plan to count tillers and possibly tissue important to obtain high yields.
analysis. Red color often a response to cold temperatures, Sugar accumulation. Timing of nitrogen (N)
applications is important on
wheat and other small grain and
Spring N (Ibs/a): rate depends on crop rotation and
+ < 80 tillers/sq ft apply 30 lbs early January and remainder @ stem elongation. tillering. Suggested rates of N
+ > 80 tillers/sq ft apply all N at late January to early February. are shown below when grown
after other crops and timing. On
Very sandy soils, N applications
may be split into two applications in the spring similar to applications made with lower tiller numbers.

Dr. David Wright, Extension Agronomist, North Florida REC, Quincy

Periodic soil testing, followed by liming and fertilization according to soil test recommendations, is
critically important to achieving good forage production and maintaining forage stands.

Soil testing is the most effective way to determine the nutrient status and pH of the soil in a pasture or area
where forages are to be planted. Soil test results are useful to determine whether fertilizer or lime
applications are needed. It is recommended to do the testing well before it is time to plant because in the
case of lime it is recommended that you allow sufficient time for the soil to react with the lime.

Soil samples should be analyzed at the University of Florida/IFAS Extension Soil Testing Laboratory
(ESTL; or other reputable laboratory. The ESTL uses soil test methods that were
developed specifically for Florida soils. The lab determines soil pH, lime requirement, and the available soil
nutrients in the sample. These test methods have been calibrated across Florida and other Southeastern states
for many years to guarantee that the results are valid under Florida conditions. Private laboratories may or
may not use soil tests that are calibrated for our region; therefore, if you choose to have your sample
analyzed by a private laboratory, it is important that you know which tests are offered. Additionally, UF/
IFAS fertilizer recommendations are specific to the soil tests offered through the ESTL, which is important
when interpreting the results.

Next is the link to the nutrient testing for bahiagrass pastures: files/BahiaProtocalForm.pdf

Dr. Yoana Newman
Extension Forage Specialist

Agronomy Notes Pa


Grass Tetany

Grass tetany or grass staggers is a disorder in cattle associated with low levels of magnesium in the
blood of the ruminants grazing ryegrass, or small grains in late winter and early spring. In Florida,
grass tetany tends to occur when cattle graze plants grown on soils low in available magnesium, or
when grazing the first flush of growth from cool-season forages when forage is at a young stage. Once
the forage is more mature the likelihood of the problem is reduced. It can also occur when cattle graze
areas right after a frost or very low quality pastures causing them to be deficient in magnesium at a
time when lactation requires a substantial quantity of this element. Wet soils, low in oxygen, may also
prevent plants from taking up sufficient magnesium regardless of the soil magnesium level.

Grass tetany is more likely to occur on soils low in phosphorus but high in potassium and nitrogen
because this combination tends to inhibit magnesium uptake by the plant. This can be a problem with
cool season grass forage fertilized with high rates of N or broiler litter. Generally, forage containing 0.2
percent magnesium or more is unlikely to cause tetany.

To avoid grass tetany, if pastures are deficient in magnesium, they need to be limed with dolomite or
dolomitic limestone. Dolomite is a mineral composed of calcium and magnesium carbonates; pure
dolomite contains 40 to 45% MgCO3 and 54 to 58% CaCO3. Dolomitic limestone has a lower
concentration of MgCO3 usually 15 to 20%.

Pastures containing sufficient legume forage will normally offset the problem because legumes have a
high concentration of magnesium in their tissues. However, legume growth is often limited in winter,
so most of the early season forage may be grass. The most dependable control is supplemental feeding
of a mineral mix fortified with magnesium during the potentially dangerous tetany season.

Dr. Yoana Newman
Extension Forage Specialist

Feb. 4-15 Florida State Fair, Tampa

Feb. 7-8 American Society of Agronomy Southern Branch, Orlando

Feb. 24-26, 2010 UF Water Institute Symposium, Gainesville

May 3-6 Aquatic Weed Control Short Course, Coral Springs

May 5-7 Florida Beef Cattle Short Course, UF Gainesville, Hilton UF

July 12-16 Greater Everglades Ecosystem Restoration Meeting, Naples

Aug. 1-5 Ecosytem Restoration Conference (NCER) Baltimore, MD

Agronomy Notes

Winter weeds are always a problem early in the spring, but the lifecycle is over soon after the first hay cutting.
The first hay cutting often serves to remove these winter weeds to aid in
sts w r e increasing the quality of subsequent harvests. Since winter weeds don't linger,
we have come to accept that hay bales from the first cutting are typically weed
infested and low in quality. With the frequent rain that the state has received
this fall, winter weeds will be more prevalent than normal. Taking steps now to
reduce the winter weed infestations will result in better quality hay. There are
many herbicide options that will effectively control these winter weeds and
increase the quality of the hay from the first cutting. Below is a short list of
products that I have found to be valuable for control of winter weeds.

=> Glyphosate. In north Florida, where bermudagrass goes completely dormant in the winter,
glyphosate can be highly effective and cost less than $5 per acre. Apply 11-16 oz/A (see product
label for specific use rate) for control of winter grasses (except ryegrass) and broadleaf weeds. If
wild radish or cutleaf evening primrose is present, the addition of 1-2 pt/A 2,4-D will be necessary.
Do not apply glyphosate if bermudagrass has any green tissue present. Glyphosate applied to
bermudagrass during transition will delay greenup and extend the first cutting. If the grass is starting
to transition, Gramoxone Inteon (40 day cutting restriction) can be substituted for glyphosate.
Broadcast applications of glyphosate are not recommended in hayfields in south Florida because
many of these fields never go totally dormant.

=> Metsulfuron. Metsulfuron, formerly sold as Cimarron, is now available under a variety of trade
names. This herbicide is fairly inexpensive and effective on a wide variety of broadleaf weeds. Wild
radish, chickweed, and red sorrel are very sensitive to this herbicide. Bermudagrass injury is not a
concern with this herbicide and it can be applied at any time since there are no grazing or haying

=> Chaparral. Chaparral is a relatively new herbicide that combines metsulfuron and aminopyralid
(the active ingredient in Milestone). Metsulfuron controls many winter weeds, as noted above, while
the aminopyralid component improves control of thistles, cudweed, Carolina geranium, and fireweed.
The combination of these herbicides will likely control a majority of the broadleaf weeds present on a
given hayfield.

=> 2,4-). 2,4-D is often the least expensive way to control a variety of troublesome broadleaf
weeds. This herbicide will be effective on pepperweed, wild radish, cutleaf eveningprimrose, and
small thistles. Application rates in excess of 1 qt/A will be necessary if the wild radish is blooming
or if thistles are greater than 12" in diameter. 2,4-D will not adequately control fireweed or red sorrel.
For optimum control of sensitive weeds, it is best to use the ester formulation when applying during
cooler temperatures.

Winter weed control can be relatively easy and inexpensive. Removing these weeds will allow the
bermudagrass to transition from dormancy more quickly, and greatly improve the quality of the first hay

Dr. Jason Ferrell, Weed Specialist

Dr. Brent Sellers, Extension Weed Specialist
Range Cattle REC, Ona Notes
sellers [--

A recent article in the IR-4 newsletter provided some interesting pesticide use trends since the passage of the Food
Quality Protection Act (FQPA). The FQPA of 1996 resulted in major regulatory changes in the registration of
pesticides with special focus on the older pesticides such as organophosphates and carbamate anticholinesterase
insecticides, and the B2 carcinogenic fungicides, including captain, chlorothalonil, iprodione, mancozeb and
maneb. Many of the uses of these pesticides were cancelled and/or restricted because of potential health hazards
and worker safety concerns. At the same time, the registration of newer Reduced-Risk (RR) pesticides was

The goal of the RR program is to quickly register commercially viable alternatives to riskier conventional
pesticides such as neurotoxins, carcinogens, reproductive and developmental toxicants, and groundwater
contaminants. This ensures that these RR pesticide uses get into the marketplace and are available to growers as
soon as possible. Expected participants in this program are the chemical companies and state or Federal agencies
that submit to the EPA initial registration and amended registration applications for pesticide products.

Anticholinesterase and RR Insecticide Groups Use Trend

990 1992 1994 1996 1998

2000 2002 2004 2006 2008

--OPs(Ibs) -* -OPs (acres)
--- Carbamates (Ibs) --- Carbamates (acres)
I RR Insecticides (Ibs) RR Insecticides (acres)

The IR-4 program has focused on supporting the registration
of RRs and organophosphate replacements by conducting 70
- 80% of food use studies on such compounds since the
passage of the FQPA. Despite the initiative to substitute RR
pesticides for these older, toxicologically suspect compounds,
there has been little public analysis of changes in pesticide
use and residue levels or of changes in risk resulting from
FQPA. In this study, several pesticide use databases such as
the California Department of Pesticide Regulation (CA-DPR)
and the CropLife Foundation (CLF) that are publicly-
available were used to determine how pesticide usage has
changed in the United States since FQPA. The data presented
are for usage in California from CA-DPR but they reasonably
represent the less comprehensive data on national use trends
from the CLF database. The most commonly used
organophosphate and carbamate insecticides showed an
overall decline in use of about 50% and 70%, respectively,
from 1994 to 2006 (Figure 1). The B2 fungicides showed
much less decline in use, about 10-20% (Figure 2).

Conversely, the RR insecticide and fungicide groups showed
a steady increase in use over this time such that they are now
key components in pest management programs for fruits and

Agronomy Notes Pc






Fig. 1

B2 and RR Fungicide Groups Use Trend

3,000,000 --- ---
2,000,000 -
1,000,000 -
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008
B2s (lbs) B2s (acres)
Fig. 2 RR Fungicides (Ibs) RR Fungicides (acres)

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/Millie Ferrer-Chancy, Interim Dean.

Environmental load

S0.80 -
0.00 .
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008
-4-Carbamates ---OPs RR Insecticides

Environ mental load
1.50 -- ------ -
a 1.00
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008
ig. 3 B2s RR Fungicides

OP and Cbartnmae InsectIdes
SAcutle Toxicty Category

- ILDS0=0 o S

SII LO50=50 to i

III ILD 50 SH to

Rekdued*tsk Insecifcide
Acute To

_1.80 Environmental load
1.80 & =4

I 0.90 -
1992 1994 1996 1998 2000 2002 2004 2006 2008
-i.-Lbs/acre (OPs, Carbamrnates & RR insecticides)
Fig. 4 -I-Lbs/acre (B2 Carcinogenic and RR fungicides)

The environmental load is the rate of application (lbs/acre) of
chemicals to the environment. Figure 3 (on the left) shows the
environmental loads (calculated as the ratio of the total lbs of
pesticide applied and the total acres treated based on the CA-DPR
data) for the anticholinesterase and RR insecticides, and for the B2
carcinogenic and RR fungicide groups. The RR pesticides are
generally used at significantly lower application rates than the
conventional compounds they are replacing, which has the effect
of decreasing the amount of chemical applied to the environment.

Figure 4 (above) shows the combined environmental
loads of the new and the old pesticides grouped into
insecticides and fungicides. This demonstrates the
impact of the increasing use of RR compounds on the
overall environmental loads of the insecticide and
migkg) fungicide groups. The RR pesticides have substantially
decreased the overall loads in these groups from 1994 to
DoMngg) 2006 by 45% for the insecticides and by 54% for the
S5000mg ngg

W V 5LOfO SIOOm1'k gI

II ILD50( to 50 mgPgi

1n IL.o= S01o 50Q J

*IV ILD50>500 mgmhg

- -

The main concern with the anticholinesterase
insecticides is acute toxicity. As shown on the left in
Figure 5, 73% of these compounds most widely used in
the U.S. fall into the highest toxicity class of EPA and
none are in the safest class. By contrast, 64% of the RR
insecticides fall into the highest safety class and the rest
are in the next safest group III. On the other hand the
major concern with B2 fungicides is potential
carcinogenicity rather than acute toxicity. All of the RR
fungicides included here were classified as "not likely
to be carcinogenic" and they introduced no appreciable
acute risk. While formal risk assessment requires
knowledge of exposure levels as well as toxicity, the
radical change in toxicity properties of the RR
compounds coupled with their lower use rates suggests
that the replacement of the older groups by the RR
compounds has significantly lowered or eliminated risks
ners, applicators and the environment.

Dr. Fred Fishel
Pesticide Information Director

Agronomy Notes Pc

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