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Agronomy notes
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Permanent Link: http://ufdc.ufl.edu/UF00066352/00097
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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: February 2008
Subjects / Keywords: Crops and soils -- Florida   ( lcsh )
Crop yields -- Florida   ( lcsh )
Agriculture -- Florida   ( lcsh )
Agronomy -- Florida   ( lcsh )
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Full Text

IFAS Extension

Agronomny /otes

Volume 32:2 FerQuary 2008


Update on Bahiagrass pH Target and
Fertilization Recommendations ......... Page 2

Soybean Prices, Seed Availability
and Varieties..................................... Page 2

Wood eontrot
Soft Rush Biology and Control
in Pastures......................................... Page 3
Drift Perspective and Factors One
Can and Cannot Control .................. Page 4
Early Burnout for Collon ....................... Page 5
Roundup Original Max replaced by
Roundup PowerMax......................... Page 7
Topdressing Wheat with Nitrogen .......... Page 7
Wheat Plant Population and
Tillering ........................................ Page 7

Calendolr .................................................. Page 3

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity-
Affirmative Action Employer authorized to provide research educational information and other
.ser ice' only to individuals and institutions that function without regard to race, color, sex, age,
Ihndicap 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.

The updated recommendation and target pH for
bahiagrass production is now 5.5 or higher.

Liming should be recommended if soil pH test is at
5,.3 or lower, in which case a lime test should be
conducted. If the lime test calls for a lime application
apply it 3 to 6 months before the growing season
comes into play. Soils should be tested for pH every
"- 2-3 years.

gt/ sOur wchsite now has a video on the bahiagrass
fertilization updates. Access it at the link below:
hlit tp:/.'./a grono my. i fas. u fIl .Cd u./S t ate P 1.1, 11 t11 I

Limin Dr. Yoana New man,
Hahingrass Liming
Photo: Yoana Netsnan Extension Forage Specialist

Soybean Prices, Seed Availabieity and Varieties

In 2007 corn prices rose dramatically in relationship to soybean and about 9 million more acres of corn
were planted in the U.S. than has been the tradition, displacing soybeans in the Midwest and cotton in the
south. During the last half of 2007 soybean prices rose and are now at historic highs. The mix in soybean
prices will result in more soybeans being grown and displacing some corn and some cotton.

In any case, all commodity prices have advanced and will give growers an option to rotate and still make
a profit with almost any of the commodities. The dilemma for southern growers is that soybean seed for
planting will be in short supply due to poor germination from seed harvested in 2007 and allocations
from the seed companies will be based on past acreages. Therefore, it is very importantfor growers to
get seed set up early for the 2008 season. Get varieties in the maturity group range 5-7. White flies were
bad on late planted and late maturing soybeans in 2007 due to the dry weather.

Dr. David Wright. Extension Agronomist
North Florida REC, Quincy
wright.u fl.cdu

IAgronomyy Notes P

Update on Baiaagrass pH Target and

Fertilization RecoIammendations

"Agronimnv Notes" is prepared by: J.M. Benneil, Chainnan and Yoana Newman, Extension For-
age Specialist (yvene (tull.edu): J.A. Ferrell, Extension Agronomist (_iaterrellih'ilhs.utl.edu);
F.M, Fishel, Pesticide Cxordinator (.wecddrQ( i ias.ul l.e ul, Brent Sellers, Extension Weed Scien-
tist (bsc llIr- i,. ull.du): and D.L. Wright, Extension Agronomist (dl ItAiirtas.ull.edul. Designed by
Cinihia Hight (cighigli ull.clu.) The use of trade names does not constitute a guarantee or war-
rant of products named and does not %ignil' approval to the exclusion of similar products.

I Soft Rwus Bioeogy and Controe in Pastures

"!-" '.JV" The bad thing about a drought is that it is "dry." The good thing about a
,'I .'... i. F C drought is that you can control weeds in areas of pastures that are often too
i- wet to spray in a 'normal' year.

:'"' Soft rush (Juncus effitsus), often called bull rush by many ranchers, is one
0 3;, '-"u' of those weeds that could be controlled. Soft rush is a native plant that of-
ten colonizes wet, low-lying areas within a pasture.
It is a perennial bunch-type rush with green cylindrical stems and a white
So.ft Rush (Bull Rus.li pith. Although the individual clumps become larger in time, the main mode
Photo: Brent Sellers of spread is through seed production. Information from the literature sug-
gests that as many as 25 million soft rush seeds/acre can be produced in a
highly infested pasture. Therefore, soft rush should be controlled before seed production occurs to
limit the amount of new seedlings in the pasture.

Control of soft rush can be obtained with 2,4-D in the spring. Research conducted at the Range
Cattle REC during 2006 and 2007 found that 4 pints/acre of 2,4-D amine applied in mid to late
April provided over 90% control of soft rush 365 days after treatment. Both non-mowed and
mowed soft rush were compared (2,4-D was applied the same day after mowing) however, no
differences were detected. The result from the comparison imply that soft rush does not need to
be mowed prior to 2,4-D application. However, the soft rush clumps will remain standing after
2,4-D application, so a mowing operation may be performed just prior to spraying for aesthetic
reasons and to allow desirable forages to increase groundcover.

Brent A. Sellers, Extension Weed Scientist
Range Cattle REC, Ona

oIae a Dates

January 26-31 American Forage and Grassland Council (AFGC)
Louisville, Kentucky

January 29-30 19th Annual Florida Ruminant Nutritional Symposium
at the Best Western Gateway Grand in Gainesville, FL
http://conference.ifas.ufl.edu/rumin ant

February 3-5 Southern Association of Agricultural Scientists (SAAS)
Dallas, Texas

July 13-17 Caribbean Food Crops Society Meeting
Miami, FL Hosted by UF/IFAS

July 13-15 Southern Peanut Growers Conference
Edgewater Beach Resort, Panama City Beach, FL

Agronomy Notes Pt

Drift Perspective and Factors One Can and Cannot Control

> The UF/IFAS Pesticide Information Office receives
S- correspondence from FDACS regarding all misuse
investigations that occur in Florida involving agricultural
use of pesticides. One of the most common, if not the most
common, report is alleged spray drift of crop protection
chemicals causing injury to desirable plants. Florida is not
alone; every state has issues with drift. (See inset photos.)

Spray droplet size should be considered when drift is a
concern. 'he rate at which particles fall through the air
and, subsequently, the distance pesticide spray particles
travel is affected by their size and gravity. Droplet size
refers to the size of the individual spray droplets that
comprise a nozzle's spray pattern. You measure the
Herbicide i(eim) to soybean. o diameter of spray droplets in microns a micron is
1/1,000 of a millimeter or 1/25,000 of an inch. The
Photo: Fred Fishel diameter of a human hair is between 50 and 100 microns.

Other diameter comparisons: a sewing thread is 150 microns; a toothbrush bristle is 300 micronts, and a
paper clip is 850 microns. To put droplet sizes in perspective with their relative drift hazard, the National
Coalition on Drift Minimization made the comparisons in the table.

Evaporation and deceleration of various size droplets.*
Droplet diameter Terminal Final drop diameter Time to evaporate Deceleration
(microns) velocity (ft/sec) (microns) (se) distance (in)
20 .04 7 0.3 <1
50 .25 17 1.8 3
100 .91 33 7 9
150 1.7 50 16 16
200 2.4 67 29 25
*Conditions assumed: 90 F, 36% R.H., 25 psi, 3.75% pesticide solution.

You may believe that small droplets coupled with high pressure will provide the best coverage. In
reality, it is almost impossible to force a small droplet to move more than a few inches. This table
shows the terminal velocity, the final drop diameter, time of evaporate ion, and the deceleration
distance (in inches) for spray droplets of various sizes. For instance, the fastest a 20 micron
droplet will fall is 4/100 of a foot per second. Due to evaporation the final droplet diameter will
be approximately 7 microns in diameter and it will fall (deceleration distance) less than one inch.
Therefore this droplet size is very susceptible to drift. In contrast, a 200 micron droplet falls at 2.4
feet per second, has a much larger final droplet size because it evaporates more slowly, and will
fall at least 25 inches.

A claims survey was conducted by Farmland Insurance during the 1990's to investigate drift
causes. The survey showed that 38% of the cases were caused by poor decision- making by the
applicator; 26% were due to incorrect or faulty nozzles: 23% were due to weather conditions, and
13% occurred for unknown reasons.

Drift Factors artilee continued on page 6A
=Agtomomy Notls P

Drift Perspective and Factors One Can and Cannot Contro$ (continued)

Herbicide injuy to ornamental tree.
Photo: Fred Fishel

Factors the applicator can't control:

=Wind (speed and direction)
=>Susceptible crops or other nearby sensitive areas on
someone else's property

Factors that an applicator can control include:

=Selection of the applicator/operator
->Equipment selection and setup (particularly nozzles
and boom height)
>The choice of product

The only New Year's resolution that I've made in the previous 25 years was to go fishing
more often, but that was broken 25 years ago as well. This year, as I'll see the FDACS
investigative reports come in, I can only hope that the number of drift incidents will de-
crease. Do your part to control those factors and keep crop protection chemicals where
they belong minimizing spray drift is in the best interests of everyone.

Dr. Fred Fishel
Pesticide Coordinator
weedd r@i fas.u fl.ed u

Wood Cottroe: earty 8urndowh for cotton

Although planting season is still several weeks away, it is time to start planning the spring burn-
down program. Wild radish and cutleaf evening primrose are two species that commonly escape
control from glyphosate applications. If not controlled, these weeds will compete with the crop
well into the summer and result in greater than expected yield loss.

Since these weeds are not controlled by glyphosate alone, other herbicides should be added to the
weed management program. The most effective way to control these weeds is to spray 2,4-D (16
or 32 fl oz/A) or Clarity (8-16 fl oz/A) in early March, then follow up with a glyphosate or
Gramoxone application near planting. This will allow plenty of time for these herbicides to dissi-
pate from the soil before cotton is planted. However, these herbicides can be tank-mixed with gly-
phosate or Gramoxone. Table 1 details the effectiveness of different herbicide combinations on
control of radish and primrose. These data show that both weed species are highly sensitive to 2,4
-D and Clarity, regardless if they are mixed with glyphosate or Gramoxone.

Agraonomoy Notes PJ


The addition of Valor was less effective on both species. Regardless of
planning a few weeks ahead will dramatically improve early-season we
tra dollars per acre.

It must be noted that cotton planting should be delayed for approximate
cation, and 21 days for Clarity. The planting restriction for Valor is 14
herbicide rate and tillage type.

Table 1. Control of wild radish and cutleaf evening primros
with hburndown applications".

Herbicide Wild Radish Cutleaf evening
% control at 4
Roundup Wmax 22 oz 80 60

2,4-D 16 oz + 97 97
Roundup Wmax 22oz
Clarity 8 oz + 94 94
Roundup Wmax 22oz

Clarity 8 oz + 96 83
Gramoxone Max 32 oz

Valor 2 oz + 76 70
Gramoxone Max 32 oz

Taken from: Culpepper, S., D. S. Carlson, and A. York. Journal of Cotton SI
b Weeks after treatment.

Dr. Jason Ferrell
Extension Weed Specialist

which herbicide is used,
ed control for only a few ex-

ly 30 days after 2,4-D appli-
to 30 days, depending on


science 9:223-228 (2005)

Agronomuy Notes P

Roundup Originat Max replaced 6y

Roundup PowerMax

Effective for the 2008 season, Roundup Original Max has been discontinued. It is being replaced
by Roundup PowerMax. PowerMax is a 5.5 lb gallon and is very similar to Original Max, but
contains a different surfactant combination. It is my understanding that PowerMax is less likely to
foam in the tank and will provide more consistent performance relative to Original Max. The
price of PowerMax will be competitive with other standards in the market.

Dr. Jason Ferrell, Extension Weed Specialist
jfcrrcll@uf l.cdu

7opdressing WIeat witH Nitrogen

Wheat should be topdressed with nitrogen (N) in late January or early February. This will help spur
tillering and vegetative growth. A total of 90-120 lbs/A of total N is usually adequate for top
yields. Include about 15 lbs sulfur/A with the N to prevent sulfur deficiencies. Weed control meas-
ures should be done when weeds are small and some materials can be mixed with liquid N to save a
trip and application costs. It will be very important to scout for disease and insects and control
measures may be profitable with wheat prices at an all time high. Most fungicide applications
should go out from the flag leaf to early head emergence stage.

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

I Wfeat Peant Population and BTiering

- m.

bS~Kk' t

Wheat can be planted at about 100 Ibs of seed/A for
high yields but will vary with seed size. Best yields are
obtained when about 18-24 seed per foot of row is
planted. If wheat is planted in 7.5 inch rows that means
that there are about 35-45 plants per square foot that
\\ill emerge and that each of these plants will have 2-3
tillers to make top yields. In some cases there are many
less plants, and 5 tillers per plant are needed for best
yields if nitrogen is applied early and other nutrients are
not limiting.

Higher plant populations from high seeding rates cost
more and do not make higher yields. Lodging and dis-
ease problems can also be more serious with high plant

Wheat plant with 2 ntller on Januay 17. Dr. David Wright, Extension Agronomist
lPhoto: David Wright North Florida REC, Quincy
wright@ufl.edu IAgronomy

Notes PA