Soybean Update
John M. Woodruff
UGA – Crop & Soil Science
August 2007
Acreage: Georgia farmers will plant 220 thousand acres of soybeans this year says a
USDA/NASS report released 6/29. We think the actual acreage is much higher. Many of
you have indicated that 2007 soybean plantings are 2 to 4 times that of 2006. In southern
counties, there was active soybean planting until mid-July. Don’t be surprised if the
actual 2007 Georgia soybean acreage is 300,000 acres or slightly higher when final
reports are in.
We are getting many calls regarding soybean problems or concerns. Here are
some encountered:
Poor Root Nodulation/Nitrogen fixation: Soybeans in some fields have few or no root
nodules at R1-R2 growth stage. It usually takes 30-40 days for root nodules to form but
plants should be well nodulated by R1 growth stage. Problem fields have not been
planted to soybeans before or for many years. The problem could be related to failure to
supply inoculant or failure to use viable inoculant. Inoculant viability can sometimes be
destroyed during storage by heat, or by premixing with seed fungicide and molybdenum.
Should growers apply sidedress N to such fields? In fields with very poor growth or
stands or with weeds, probably not, but in clean fields with good stands, there could be 810 bu/A yield response to applying 45-50 lbs N/A.
Lesser Corn Stalk Borer: Heaven forbid! 2007 is turning out to be a really bad year for
lesser corn stalk borer infestation across south GA. This insect thrives under hot, dry
conditions which has been the case in many areas.
Lesser Corn Stalk Borer outright kills small soybean seedlings, and can severely
injure larger plants causing them to lodge and slowly die. The Lorsban 15G treatment has
provided fair but not consistent good control of the lesser. We are not encouraging further
treatment in older soybeans this late in the season. The insect may not be a problem next
year, but growers should be especially watchful for lesser corn stalk borer injury anytime
there are hot, dry conditions at and after planting time.
Manganese Deficiency: Soybean manganese deficiency has been fairly common on
Atlantic Flatwoods soils this year. The problem is usually associated with high soil pH
and wet soils in the Atlantic Flatwoods area. Foliar treatments with about ½ lb MN/A
from manganese sulfate have generally been effective. Since Mn does not translocate
from old to young soybean leaves, there has been, in some cases, need to make two foliar
sprays. Any foliar Mn spray should be made prior to R1 first bloom. Georgia research,
from the 1970s, shows that there is no yield response to late-season Mn.
Dimilin/Boron Sprays: Many of you say that growers are applying Dimilin/boron
sprays to soybeans. This is great. Properly applied, this treatment should give season-long
control of velvetbean caterpillar and, usually, 1-3 bushel/A yield increase. We see one
frequent problem. Many growers are making this treatment too early. It should be made
at R3 growth stage-the time when the first pods start to elongate. This is usually about 2
½ to 3 weeks after the first blooms appear on the soybean plants. Making the treatment
too early will result in upper canopy leaves unprotected from late season infestations of
velvetbean caterpillar.
Bloom Abortion: Some growers are reporting extensive abortion of soybean flowers
and are concerned about the impact this will have on soybean yield. Abortion of soybean
flowers certainly doesn’t look good but usually has no impact on soybean yield-at least
for fields producing up to 60 bu/A. Why soybeans abort blooms is not clear, but it seems
that , as long as leaves are developing, few pods are set on determinate varieties.
Apparently, developing leaves have first priority for photosynthate. If it’s any comfort, I
have never failed to see a soybean crop develop to normal yield because of aborted
flowers. There are two axiliary flower stalk buds at the base of each primary flower stalk
on the soybean plant. These will develop if the soybean aborts flowers from the primary
stalk.
MARK YOUR CALENDARS
INFORM YOUR FARMERS,
AND PLAN TO ATTEND.
There will be a Crops Field Day at the Southeast Georgia Research and Education
Center, August 29, 9:30AM-3:30PM. The field day will feature crop varieties, culture
and tillage systems, and pest management strategies for improving crop yields and
profits. For more information, contact Will Duffie, 706/554-2119, or wduffie@uga.edu
Harmony GT XP for Escaped Pigweed Control in Soybeans
UGA – Crop & Soil Science
Eric Prostko
Over the last few days, I have received several inquiries about the use of
Harmony GT XP 75DF (thifensulfuron) for the control of large, escaped pigweeds in
soybeans. After checking around with a few folks, most people would agree that this
herbicide is very active on pigweeds. According to the label, Harmony GT XP will
control pigweeds that are 8" tall. Other reports suggest that it will control a 12" tall
pigweed. The use rate of Harmony GT XP in soybeans is 1/12 oz/A (0.004 lb ai/A) and
costs approximately $1.17/A. Harmony GT XP can be applied anytime after the first
trifoliate leaf has expanded but not later than 60 days before harvest. Keep in mind that
this herbicide is an ALS-inhibitor. Consequently, Harmony GT XP will NOT control
ALS-resistant pigweeds. Growers who use Harmony GT XP on their soybeans should
also expect some crop injury. It has been described to me as a bad case of Classic injury
(terminal chlorosis, squatty upper internodes, blackened veins on undersides of leaves).
When using Harmony GT XP in soybeans, include a NIS (0.25% v/v) or COC (1% v/v).
Harmony GT XP can also be tank-mixed with glyphosate. Do not use Harmony Extra on
soybeans. Harmony Extra is a combination of Harmony (thifensulfuron) + Express
(tribenuron) and would cause severe crop injury.
Phillip Roberts
UGA – Entomology Dept.
Dimilin Application Timing: Historical data indicate that the probability for treating
foliage feeding caterpillars in soybeans is high in the Coastal Plain of Georgia. For this
reason, growers commonly apply a preventive application of Dimilin when managing
foliage feeding pests. Foliage feeding caterpillars commonly observed in soybeans
include the green cloverworm, velvetbean caterpillar, and soybean looper. Dimilin is an
insect growth regulator with long residual that typically provides control of green
cloverworm and velvetbean caterpillar for the remainder of the season when applications
are properly timed. Dimilin will not control soybean looper so fields will still need to be
scouted for loopers and pod feeding insect pests such as stink bugs, corn earworm, and
fall armyworm.
The optimal time to apply Dimilin is from full bloom to early pod-fill (R2-R3 Stages).
All soybean leaves should be developed when Dimilin is applied. If treatment is made
too early there will be untreated/unprotected leaves in the upper canopy. Dimilin is
commonly applied in a tank-mix with Boron for yield enhancement.
Old Lesser Cornstalk Borer Damage: Lesser cornstalk borers infested seedling
soybeans to varying degrees during the past two months. Some stand loss occurred and
Lorsban treatments (either preventive or reactive after emergence) were made in some
areas. Some plants which appear normal at this time did sustain some feeding damage on
the main stem by lesser cornstalk borers. Recently we observed plants snapping or
breaking at or just below the soil surface when shaking plants over a drop cloth to
dislodge insects. Examination of the main stems of “snapped” plants appeared to have
old lesser damage.
Disease Management Update for Soybeans
UGA – Plant Pathology
Bob Kemerait
As of Thursday, 2 August 2007, Asian soybean rust is not known to be present in
Georgia on soybeans, kudzu, or any other host. The nearest confirmed soybean rust is
located in research plots in Quincy (Gadsden County), Florida and in sentinel plots in
Baldwin County, Alabama. Conditions have been favorable over the past few weeks
(periodic rain showers) for rust to spread into the state. We continue to scout for rust
across Georgia carefully and have not yet found it.
A current weather system moving into Georgia from the Gulf of Mexico threatens
to bring rain and conditions that will further favor the development and spread of rust.
Downy mildew of soybean is being found in some parts of the state at this time,
especially in eastern Georgia. Downy mildew is easily identified as yellow spots on
leaves with a characteristic tuft of fungal growth on the underside of each spot. One may
need to look carefully to see the fungal growth, which is typically a grey color. The
University of Georgia typically does not recommend spraying fungicides for control of
downy mildew because a) the disease is not believed to cause significant yield losses, and
b) our fungicides for control of soybean diseases less effective against that type of
fungus. (Note: Strobilurin fungicides should have a bit of activity against downy
mildew. Triazole fungicides and chlorothalonil will not have activity.)
Many growers are asking our county agents for advice for timing fungicide
applications for the control of Asian soybean rust. When I am asked for spray guidance, I
offer the following suggestions.
Scenario 1. Asian soybean rust is not known to be active in your region.
A. Growers may choose to apply a fungicide to their soybean crop before the
diseases threatens their fields. Reasons for making such a decision are to 1)
insure protection of the crop from rust, 2) provide protection from other diseases
of soybean, e.g. frogeye leaf spot, and 3) time a fungicide application at a time
when the grower is already “making a trip across the field”, for example when an
insecticide is being applied.
Potential risk of such an application: Soybean rust may not ever occur in the
field during the current season or may arrive so late as to be of little consequence.
Fungicide options for scenario 1: Growers can choose to use any of the
fungicides labeled for control of soybean rust at this time. Growers should
consider the cost of each fungicide. Growers may choose to use a fungicide that
is proven effective not only against rust, but other diseases as well. It is believed,
but not always easy to document, that strobilurin fungicides, such as Quadris,
Quilt, and Headline, will have a longer protective window (approximately 3
weeks) than common triazole fungicides (approximately 2 weeks) such as Folicur
and other tebuconazole products, Laredo, and TOPGUARD.
B. Growers may follow scouting reports and monitoring of sentinel plots for the first
reports of rust detection in Georgia or in counties in neighboring states. Once rust
is detected in a grower’s region, and the commercial soybean crop has reached
reproductive growth, then the grower should initiate a fungicide program. The
advantages to waiting until rust is in a grower’s region before initiating a
fungicide program include a) fungicides are applied for maximum effectiveness at
a critical time and b) fungicides are not applied if not needed, saving grower time,
labor, and money. NOTE: Once rust is detected in a region, growers should be
prepared to make a fungicide application; however there is no need to PANIC!
Rust is a very aggressive disease once it builds in a field; however it takes time to
reach a point where it is overwhelming. Once rust is detected in sentinel plots,
growers should have enough time to start their fungicide program.
Potential risk for such an application: There is the remote possibility that
soybean rust could affect a commercial field before it is detected in sentinel plots.
Management of rust is best achieved by applying fungicides before rust is
established in a field. Once rust is detected in a field, it becomes more difficult,
or even impossible to control if infection is severe enough.
Fungicide options for Scenario 2: Assuming rust has not reached a grower’s
fields, he can use any of the fungicides labeled for control of rust, noting that use
of chlorothalonil for management of rust has been less successful than other
products. If there is the potential that rust has infected a commercial field, the
grower should use a triazole fungicide or a triazole/strobilurin mix to insure
curative and protective activity.
Scenario 2. Asian soybean rust is active in your region.
If Asian soybean rust is active in a grower’s region, the grower should apply a
fungicide to protect his crop once the crop enters reproductive growth. If it is
possible that rust has already infected a commercial field, the grower should use
either a triazole fungicide or a triazole/strobilurin mix to insure curative activity
for control of the disease. Domark, TOPGUARD, and Folicur (and likely other
tebuconazole products) seem to offer the best levels of curative activity.
Fungicides currently labeled for control of Asian soybean rust in Georgia:
Quadris (azoxystrobin)
Headline (pyraclostrobin)
Alto (cyproconazole)
Punch (flusilazole)
TOPGUARD (flutriafol)
Caramba (metconazole)
Laredo (myclobutanil)
Tilt/Bumper/PropiMax (propiconazole)
Folicur/Orius/Uppercut (tebuconazole)
Domark (tetraconazole)
Quadris Xtra (azoxystrobin + cyproconazole)
Quilt (azoxystrobin + propiconazole)
Stratego (trifloxystrobin + propiconazole)
Headline SBR (pyraclostrobin + tebuconazole)
Bravo/Echo/Equus (chlorothalonil)