Soybean Diseases in Arkansas
Asian Soybean Rust - Questions and Answers
County Agents
The following questions were submitted by County Extension
Agents attending:
Arkansas Soybean Rust Workshop
Delta District Conference, Brinkley Convention Center , Brinkley , AR
November 30, 2004
(Questions collected by Cliff Coker; SBR = Asian Soybean Rust)
1. When should we start scouting for SBR?
As soon as soybeans are in the late vegetative stages (V6+) but
just before blooming (R1 R2)
Table 2.1. Description of Vegetative Stages
V-E Emergence Cotyledons above the soil surface
V-C Cotyledon Unifoliate leaves unrolled sufficiently so the
leaf edges are not touching
V-1 First-node Fully developed leaves at unifoliate nodes
V-2 Second-node Fully developed trifoliate leaf at node above
the unifoliate nodes
V-3 Third-node Three nodes on the main stem with fully developed
leaves beginning with the unifoliate nodes
Vn nth-node n number of nodes on the main stem with fully
developed leaves beginning with the unifoliate nodes
Vegetative Stages
Plant to V-E; Average number of days 10; Range in number of days
5-15
V-E to V-C; Average number of days 5; Range in number of days 3-10
V-C to V1; Average number of days 5; Range in number of days 3-10
V1 to V2; Average number of days 5; Range in number of days 3-10
V2 to V3; Average number of days 5; Range in number of days 3-8
V3 to V4; Average number of days 5; Range in number of days 3-8
V4 to V5; Average number of days 5; Range in number of days 3-8
V5 to V6; Average number of days 3; Range in number of days 2-5
V6 and later; Average number of days 3; Range in number of days 2-5
Table 2.2. Description of
Reproductive Stages
Stage No.- R-1; Abbreviated Stage Title - Beginning Bloom;
Description - One open flower at any node on the main stem
Stage No.- R-2; Abbreviated Stage Title - Full Bloom;
Description - Open flower at one of the two uppermost nodes on the main stem
with a fully developed leaf
Stage No.- R-3; Abbreviated Stage Title - Beginning Pod;
Description - Pod 3/16 inch long at one of the four uppermost nodes on the main
stem with a fully developed leaf
Stage No.- R-4; Abbreviated Stage Title - Full Pod; Description
- Pod 3/4 inch long at one of the four uppermost nodes on the main stem with a
fully developed leaf
Stage No.- R-5; Abbreviated Stage Title - Beginning Seed;
Description - Seed 1/8 inch long in a pod at one of the four uppermost nodes in
the main stem with a fully developed leaf
Stage No.- R-6; Abbreviated Stage Title - Full Seed; Description
- Pod containing a green seed that fills the pod cavity at one of the four
uppermost nodes on the main stem with a fully developed leaf
Stage No.- R-7; Abbreviated Stage Title - Beginning Maturity;
Description - One normal pod on the main stem that has reached its mature pod
color
Stage No.- R-8; Abbreviated Stage Title - Full Maturity;
Description - 95 percent of the pods have reached their mature pod color; 5-10
days of drying weather are required after R8 before the soybeans have less than
15 percent moisture
Reproductive Stages
R1 to R2; Average number of days 0*, 3; Range
in number of days 0-7
R2 to R3; Average number of days 10; Range in number of days
5-15
R3 to R4; Average number of days 9; Range in number of days
5-15
R4 to R5; Average number of days 9; Range in number of days
4-26
R5 to R6; Average number of days 15; Range in number of days
11-20
R6 to R7; Average number of days 18; Range in number of days
9-30
R7 to R8; Average number of days 9; Range in number of days
7-18
*Stages R1 to R2 generally occur simultaneously in determinate
varieties. The time interval between R1 and R2 in indeterminate varieties is
about 3 days.
The above growth stage information was reproduced from
Ashlock et al, Arkansas Soybean Production Handbook at the following website
address:
http://www.uaex.edu/Other_Areas/
publications/HTML/MP-197.asp
2. What is the temperature range at which SBR can
survive?
We have found varying reports and very limited scientific
information on this. Given that the soybean rust pathogen is an obligate
parasite and has no overwintering spore stage, we believe that it will not
survive where its preferred hosts cannot survive. In the U.S. , this means areas
that do not freeze for extended periods in the winter, such as along the Gulf
Coast typically in Southern Florida and Southern Texas . So the temperature
range would be 32 F and above although the information we have found suggests
optimum temperatures for rust development tend to be in the range of 65 80 F.
3. What is the geographic range of SBR? (How far will SBR
spread?)
In the world, the soybean rust pathogen ( Phakopsora
pachyrhizi ) is now known to be present in all major soybean producing
countries of the world, the most recent introduction being the continental
U.S.A. See the following figure.
*Image reproduced from Monte Miles PowerPoint Presentation 2004,
modified by Rick Cartwright 12/04. Base map courtesy of Mapquest.com .
4. What is the threshold level for SBR?
Generally, there is no widely accepted fungicide decision
threshold level for soybean rust. The disease is capable of increasing very
rapidly under the right conditions and moving long distances in a short time.
Rust diseases can be underestimated because a field may look fine to the eye,
yet actually have a high level of recent infection. Then, in a few days when
rust pustules develop, the grower will be very surprised by the "apparent" speed
of the disease. We will likely recommend the first fungicide treatment (the most
critical according to experts in other countries) based on growth stage of
soybeans in the field if soybean rust has been detected nearby. In other words,
we will not wait until soybean rust can be detected in every field on a farm
before we recommend spraying. The proper growth stage in other countries with
environmental conditions similar to ours in late spring early summer would be
R2-R3 (see stages listed above in Question 1). Given the fungicides we will work
with, this would also mean a second application would be recommended about 14-21
days after the first to provide satisfactory control of the disease under a
favorable environment. The need for the second application may be dependent on a
number of factors in the South including whether hot, dry weather sets in
which would likely minimize the disease. The need for a second application could
be monitored by careful scouting starting about 10 days after the first
application and it would be a good idea to collect leaves from the treated
field, place them in a plastic bag containing a moistened (all free water
squeezed out) paper towel, seal with some air so the bag is partially inflated;
then observe for rust pustule development on the bottom of the leaves over the
next 1-3 days (a bioassay). The bioassay would supplement field observations and
provide some idea of when the fungicides from the first application were
starting to lose activity.
5. When should the first fungicide application go out for
SBR control in a field that has SBR present?
See Question 4. The first
application is absolutely critical according to experts in other countries. It
provides the bulk of control for the potential epidemic and should be made about
growth stage R2-R3. This application timing also corresponds to the best overall
control of other soybean diseases in the South using fungicides, including
frogeye leaf spot and aerial blight. We are not currently anticipating
applications prior to R1 (first flower), even though rust symptoms may be
encounterd during the vegetative stages. Apparently, the disease really takes
off when the plants enter the early reproductive stages so it makes economic
sense to delay the first fungicide application until then, if at all possible.
This has been the case in South America from what we can gather. Nevertheless,
if we encountered a runaway early epidemic on small soybeans then we would
likely make the field judgment to spray but we believe this will not be a
routine situation.
6. How do I identify SBR? How do I determine the disease
is SBR?
This is a rather inconspicous rust disease, similar to other
bean rusts. First of all, check the bottom leaves of plants first then work your
way up the plants. Scout randomly as windborne diseases can land wherever. Look
at the underside of leaves with a 14-30X hand lens with good light. Heavily
infected leaves will obviously look "rusted" on the underside but early infected
leaves are hard to distinguish. Pustules may be tan to reddish brown with a
little yellowing around them (chlorosis) and range from 0.5 2 mm in size. They
will be restricted by the small leaf veins. They should be raised a little, like
a little mountain and if fully developed will have a pore (opening) in the top
but this is difficult to see. Under the right conditions, spores may have oozed
out of the pustule and these may appear as clear or off-white, tiny clusters
made up of shiny (sometimes) little grains of sand. Placing leaves in a plastic
bag with a moistened paper towel overnight can help distinguish rust as the
pustules will swell and exude lots of spores if they are at the right stage of
development.
7. What is the economic impact of SBR?
Soybean rust is capable of defoliating soybean plants prior to
seed development. The earlier and heavier the disease, the greater the resulting
yield loss because the leaves drop off earlier too. Entire fields have been
defoliated in other countries when fungicides have not been used for control.
Yield losses in these cases have been measured or estimated to be as much as
80%. We do not know how favorable our environment will be for soybean rust but
in other countries with similar environments, losses have been reported from as
low as 10% up to 50% - so this first year or two we will have to assume the
potential for heavy yield losses under the right conditions and act accordingly.
On the other hand, properly timed fungicide applications can reduce the loss
potential to a very low level so we can control the disease.
8. Is SBR treatable with current fungicides?
Yes, however our currently labeled fungicides are not the most
effective choice. Therefore, we asked for and have received approval to use
certain triazole fungicides in addition to the strobilurin and chlorothalonil
fungicides already registered. The most effective treatments in other countries
have consisted of either mixtures of strobilurins and triazoles or rotation of
the two chemistries in sequential applications. And we will be able to do that
in 2005 as well. Another reason we asked for additional fungicides is the supply
situation. There are so many acres of soybeans in the U.S. , that there was not
an adequate amount of any one fungicide to cope with this potential problem.
Therefore, we asked for additional materials to increase our supply options in
dealing with this potential threat.
Currently, Quadris (stobilurin) and Heandline (strobilurin
just registered on December 1, 2004 ) have full labels for soybeans. Bravo, Echo
and other chlorothalonil fungicides are also registered as is Topsin and TM85
(thiophanate-methyl). It is our understanding that Quadris and Headline are
pretty effective in preventing infection by the soybean rust pathogen but are
not as good if the disease is already established. Bravo, Echo and other
chlorothalonil fungicides are also considered preventative but apparently are
not used as widely because they do not have systemic properties and thus are not
as effective on soybean rust, especially when plants are actively growing. It is
our understanding that Topsin and TM85 (thiophanate methyl) are not effective
against soybean rust although they are effective against frogeye leaf spot.
As far as Section 18 Approved Fungicides for Arkansas , we now
have Tilt, Propimax and Bumper (propiconazole products) available, along with
Folicur (tebuconazole) and Laredo EC and EW (myclobutanil). These are all
triazole fungicides, locally systemic and capable of not only preventing
infection by the soybean rust pathogen but also capable of killing and
suppressing the pathogen after infection to some degree. Certain sources refer
to this as "curative", a term we consider misleading because these fungicides
will not fully cure the infection, but they do a much better job of controlling
an established rust disease if it has not progressed very far compared to the
strobilurin or chlorothalonil protectants.
We have also requested the premixed products Statego
(trifloxystobin + propiconazole; stobilurin + triazole) and Quilt (azoxystobin +
propiconazole; Quadris + Tilt; strobilurin + triazole) for Section 18 use in
Arkansas during 2005 on soybeans but these are still pending approval.
In fungicide trials in other countries, Quadris and Headline
either tank-mixed with one of the aforementioned triazoles or in rotation with
them, have proven effective in controlling soybean rust using two properly timed
(R2-R3 then R4 R5) applications. The premixes Stratego and Quilt have also
been effective when applied twice.
9. What is the treatment level for SBR?
See the answer to Question 4.
Basically, until we have more experience under our conditions, we will likely
recommend the first fungicide treatment based on growth stage (R2-R3) if soybean
rust is found in the immediate area and a second (14-21 days later) if
conditions favor rust development.
10. Will SBR overwinter in our environment?
Not in Arkansas . It may be able to survive further south near
the coast, most likely in Florida or Texas (if found there eventually) but it is
possible that it could survive wherever a host survives further south.
11. How did SBR get here?
There have been many rumors and crazy talk about this. However,
if you go to
http://www.nhc.noaa.gov/archive/2004/IVAN_graphics.shtml
and watch the
little graphic movie of hurricane IVAN in September, you will recognize how the
fungus got here. A key element in the hurricane movement from South America to
the southern U.S. was the fact that soybean rust was discovered in Columbia
(north of the equator) earlier in 2004. This allowed spore production in an area
that a Carribean hurricane could then collect from the South American continent
and move northward. If you look at where the disease has been found in the U.S.
to date, the discoveries match IVAN's path. It is likely that the disease could
have been found in an even wider area but it was so late in the year that hosts
were disappearing rapidly when the first observation was made in Louisiana .
States where soybean rust has been confirmed since November 10,
2004.
Graphic prepared by Rick Cartwright, 12/1/2004 PPT presentation.
12. Variety sensitivities, are any varieties resistant to
SBR?
Strong resistance is not available in U.S. soybean varieties
although some resistant varieties are under early development by various
breeding programs. Slow-rusting and tolerant varieties may exist but we are not
yet aware of which ones they might be in U.S. germplasm. Slow-rusting varieties
would basically make the disease easier to control with fungicides so they could
be valuable if we can figure out which ones they are. For the time being,
management will be based on fungicides, probably two applications.
13. What happens if I don't treat?
If conditions favor rust development, you will lose a lot of
yield potential much more than the cost of two fungicide applications as
much as 30 bu/A yield loss or more on high yielding soybeans and you will supply
spores to all of your other fields, former friends and neighbors in the
surrounding area.
14. When should we expect to see SBR on the plant?
Based on South America , soybean rust may first be visible on
the lower leaves of plants in the late vegetative to early reproductive stages
(R1-R2).
15. What conditions favor the spread of SBR and at what
rate or how quickly will SBR spread?
According to reports elsewhere, favorable conditions for the
soybean rust pathogen would be 65-80 F (mild to warm temperatures) with long dew
periods (12 hours) or intermittent periods of cloudy, rainy weather. Spores may
be able to be transported many miles in a short time, however, the number of
spores moving and the number of susceptible host plants where they are landing
also affect spread as will the environmental conditions where they land.
16. What other plants will SBR attack/effect? Legumes
like alfalfa?
The following information was gleaned from various sources by
R.D. Cartwright
Host Plants for: Phakopsora
pachyrhizi (Asian Soybean Rust)
17. Is SBR spread by rains/weather?
Yes. See Question 11 answer.
Clearly, windborne spores of the disease can be moved great distances in a short
time by weather phenomena (hurricanes, fronts, etc) but this is true of many
plant pathogens.
18. Can SBR be spread by men or equipment from field to
field?
Although this is theroretically possible, by the time you see
rust pustules in a field, the pathogen has passed your area and has infected
fields some distance away in the direction of the prevailing winds. So physical
movement by walking fields and scouting is of minor concern. Rust diseases do
not really need any help, but are clearly able to move long distances by natural
means.
19. How long can the spores stay alive?
There are various reports. The longest period of survival that
we could find in the literature was around 50 days under ideal conditions but
this seems rather extraordinary for the type of spore the soybean rust pathogen
employs. More likely is a matter of days or a couple of weeks as is commonly
reported for rusts. Samples collected in Arkansas during November 2004, then
held for 2-3 weeks in the refrigerator, saw a rapid decline in germination of
spores from the leaves. Also, ultraviolet light will kill exposed spores outside
in a matter of days. In summary, urediniospores are rather short-lived and
cannot survive harsh conditions (UV, hot and dry, freezing temps, etc) so rust
pathogens overcome this with sheer reproduction (rapid cycling, thousands of
spores produced over a short time).
20. What control measures are available?
Highly resistant varieties are not available. Ther is a lot of
research activity by Midwestern Soybean Breeding Programs and private seed
companies to identify both partially resistant (slow-rusting) and highly
resistant varieties and germplasm. So far, we have not found any practical
information on partially resistant varieties to recommend in 2005 and highly
resistant varieties are several years away. Hopefully, we can evaluate varieties
in 2005 and 2006 for partial resistance to soybean rust in the South, assuming
the disease overwinters and becomes an established problem.
Cultural practices may help but remain unproven under our
conditions. For example, in countries currently battling soybean rust, growers
have apparently started to shift more to wider rows in order to slow the rust
epidemics a little, gain a little extra time to react with fungicides, and
improve coverage of the fungicides with ground applications. Wider rows has
apparently not resulted in a reduced number of fungicide applications, however,
which currently average two per season in parts of Brazil where soybean rust is
a routine problem.
Planting early has been suggested as a way to avoid rust in
Arkansas , or "outrun" the worst of the epidemics. This is a complicated subject
and there are pros and cons to this approach. In general, earlier planting has
not solved the rust problem in other countries but some experts indicate that,
depending on weather patterns and the presence of spores, it may help a little.
Again, it has not eliminated the need for 2 or more fungicide applications in
countries where it has been tried and can provide an earlier window for rust to
get starter and thus, a wider window for rust development in a given region.
Thus, earlier planting can provide the rust pathogen a building bridge to later
planted fields.
Planting earlier maturing varieties has also been suggested as a
way to minimize the risk of soybean rust. If yield potential is the same, then
earlier maturing varieties may have a shorter window of risk to soybean rust
because the days that these varieties spend in reproductive growth stages (most
susceptible time for rust) are fewer. However, this may depend on planting date,
since early planting of early maturing varieties actually may extend the
reproductive period. So optimum planting date remains an important consideration
for high yield potential in soybean in Arkansas .
This information at the following
link was written by Chris Tingle in
response to these questions about early planting, early maturing soybean
cultivars, wider rows and soybean rust.
21. Will seed treatment help control SBR?
No. Soybean rust is not seedborne.
22. When, what
rates, and what materials are to be used to control SBR?
In preparation for the arrival of soybean rust in the United
States , a national Section 18 emergency exemption request was prepared by South
Dakota and Minnesota in early 2004 and most soybean states, including Arkansas ,
prepared "tag-a-long" requests during the spring of 2004. EPA continues to
review this request and some additions but has approved certain materials
already for 2005. The nature of the request meant that once soybean rust was
confirmed in the continental U.S. , then the states would have the right to
proclaim an emergency condition for use of the approved fungicides.
The following table lists the current status of fungicides that
are labeled in Arkansas for 2005 as well as some that are pending. The State
Plant Board is planning to declare the emergency in early January, 2005 so that
the fungicide distribution and application systems will have adequate time to
move the specific fungicides into our region. Although cutting it close, this
should give the supply/application system a couple of months to prepare, which
should be adequate. Products approved on the Section 18 Exemption can be used
until 2007.
Fungicides Approved as of 12/6/04 for control of soybean rust in Arkansas during
2005 (PDF)
2005 Recommendations will emphasize either tank-mixing or
rotation of different chemistries (e.g. stobilurin + triazole or one following
the other) to minimize development of fungicide resistant populations of the
soybean rust pathogen.
Under favorable conditions, two applications will usually be
needed with the first typically made about R2 R3 and the second 14 21 days
later during R4 R5. Applications will likely not be needed from R6 and later
(too late) and applications before R1 will probably not be of benefit either.
Close scouting will be the key to success in management of soybean rust with
fungicides. The first application will be the most critical for successful
management, depending on the environment and resulting disease intensity.
Application volume will be 5-10 gallons per acre by air and
10-20 gallons per acre by ground. Some products will recommend a surfactant to
improve canopy coverage so the label should be read and followed closely.
Topsin, TM85 and possibly other thiophanate-methyl fungicides
are approved for use on soybeans in the U.S. but this chemistry does not have
good activity on soybean rust. Thiophanate-methyl is effective on frogeye leaf
spot of soybean.
Several people have asked about planting soybeans in rows and
spraying fungicides with a 3-nozzle directed spray assembly over each row
(banded/directed coverage) using a ground rig. This seems like a good idea and
we would recommend contacting Dr. Dennis Gardisser at
dgardisser@uaex.edu for information on this and other application
questions. Methods that maximize coverage will be the most successful with a
disease of this type.
23. Several growers in Crittenden Co. have asked where it
was found, and if it was on them would they be informed?
The first sample was collected near I-55 north of West Memphis
and Marion on "straggler" green plants visible from the road. We do not know who
farmed this field and in our surveys, we simply stopped along major highways
when we saw a few green plants. While we know the geographic coordinates of the
sample sites, we do not know whose fields they come from for the most part.
Since the disease was introduced by Hurricane Ivan and since it cannot
overwinter in Arkansas , there is no point in trying to determine whose fields
it was collected from. Since the Crittenden County discovery, it has been found
in most counties along the eastern edge of Arkansas anyway. It appears that
disease development on all plants collected from all sites and in all states was
similar, again supporting a widespread introduction by Hurricane Ivan at a
particular point in time (over a few days at most). What we will have to worry
about is will it overwinter along the Gulf Coast and, if so, when will it move
back into Arkansas next spring or summer. We will be monitoring for the disease
starting in April 2005 and certainly WILL report when and where it is found then
so that growers can get prepared as it moves northward.
24. If areas are going to be sprayed, will it be
mandatory in that given area? If not will multiple sprays be necessary?
At this time, there are no plans to either make fungicide
treatment mandatory nor offer an incentive (cost share) to spray affected
fields. It will be the grower's choice as far as is planned right now.
If conditions are favorable for soybean rust and it is detected
in a field prior to R3, then two fungicide sprays will likely be needed and
recommended. If it moves in late, like R5, then only one spray may be needed. Or
if an early spray is made at R1 R3 and then the weather turns hot and dry for
a long period, only one spray might be needed.
In general, though, two fungicide applications are the rule in
countries where conditions favor rust development and resistant varieties are
not available.
25. Is there a possibility for SBR to over-winter inside
the grain bins on seed?
No. Urediniospores of the soybean rust pathogen are not very
tough and they will die in a few weeks at most. The soybean rust pathogen is an
obligate parasite and can only survive long-term inside the leaves of its living
host. If the host tissue dies, the rust pathogen dies.
26. Samples are bound to be collected never used- will
research cause SBR to hit sooner?
All researchers that now have samples collected in the U.S. will
control the samples closely and plans are to destroy them before the growing
season in the South. If soybean rust does survive along the Gulf Coast and move
northward in 2005, and becomes established throughout the soybean production
regions of the U.S. , then field research can begin. Until it is routinely
established on its own, researchers will not re-introduce it. As a matter of
fact, the leaf and plant samples we collected in Arkansas and maintained in
plastic bags in the refrigerator no longer have germinable rust spores. The
fungus died a couple of weeks after being stored. Also, it is not legal to
transport soybean rust samples across state lines even now so researchers have
been warned to maintain close control over any samples. The research community
will rely on natural infection during 2005, if it occurs, and be very
conservative about this pathogen for the first few years.
27. Will SBR overwinter in fields flooded for duck season
if the field never completely freezes during the winter in the deepest part of
the field?
No.
28. How much does Syngenta stock currently cost?
Apparently, it has been rising since last December and the
soybean rust news has not changed it too much. As of December 12, Syngenta stock
was trading at $20.70 per share best we could tell.
http://www.syngenta.com/en/investor/stockchart.aspx?stock=NYSE
29. Should growers continue to
plant the same amount of soybean acres?
Unless they have a more profitable alternative. While the
potential expense of additional fungicide applications is serious, high yielding
soybeans should still be profitable, especially if prices rise during 2005 when
and if soybean rust is first found in the southern U.S. Other countries continue
to expand soybean production, even in areas where rust control requires two
fungicide applications. In these areas, soybean yields and quality are the
highest ever. On the other hand, dryland and other low yield potential soybean
acreage may better be diverted to other crops like grain sorghum. Irrigated
acreage can be diverted to rice, corn or cotton depending on the farm but
soybean will still be a valuable commodity in the South.
Dr. Tony Windham (twindham@uaex.edu)
and Dr. Chris Tingle (ctingle@uaex.edu)
have been working on different economic scenarios and this information will be
available soon.
30. If a grower decides to reduce his soybean acreage,
what should he plant on that acreage?
See answers to question 29.
31. Is SBR in our area right now?
Soybean rust was found on "straggler" green soybean plants in
the following Arkansas counties between November 18 and November 30, 2004 .
After November 30, frost pretty much eliminated these plants and the rust
disease on them. Clay, Greene , Mississippi , Poinsett, Crittenden, Lee, Desha,
Lincoln and Chicot. It was likely also on these plants in Cross, St. Francis,
Phillips , Arkansas , Jefferson, Drew and Ashley counties but not observed
before the frost. It was not found west of Crowley 's ridge in northeast and
east central Arkansas . Again, this area corresponds exactly to the path of
Hurricane Ivan in September as it moved northwards just east of Arkansas . Frost
will push the disease further south all winter and we will have to wait and see
if it survives on a living host along the Gulf Coast .
32. How are farmers going to manage SBR/ what can farmers
do to help prevent the disease?
See Previous Question Answers on Management Options.
33. Will SBR wipe out my crop?
Under the right conditions, soybean rust has caused up to 80%
yield losses. Heavy damage to yield is associated with early entry of soybean
rust into a field (R1-R3); conditions very favorable for rust development
(70s-low 80s with 12 hour leaf wetness per 24 hour period) etc.; and NO
fungicide treatment at the correct timings. The following image from Embrapa in
Brazil illustrates the destructive power of the disease under ideal conditions.
34. Will SBR overwinter in northern Arkansas ?
NO
35. How many fungicide applications and at what cost will
be needed to control SBR? Is it worth it?
Under favorable conditions we are guessing that it will require
TWO applications, one during the flowering to early pod set stages (R1 R3) and
a second 14 -21 days later during R4 R5. Costs will vary but a working average
will be between $30 - $36 per acre for the materials approved so far and this
includes application costs. It is possible that some combinations of materials
and application could reach $45 per acre but this will be on the high side.
Figuring $36 per acre and $6 soybeans, you will need to protect at least 6 bu
per acre to break even. Since the disease has been shown to cause yield
reductions of 20 40 bu per acre under severe conditions on 60 bu yield
potential fields in other countries, fungicide applications would definitely be
worth it under these circumstances. Nevertheless, this is a significantly higher
input than we have been used to in soybean so low yield potential and dryland
beans will likely not be profitable if two applications have to be used and
soybean prices stay low.
36. Do growers need to plant certain maturity group
varieties at different times of the year?
Please see the answers to
Question 20.
37. If we take samples and store them in refrigerators
etc., can we harbor the spores or will they die soon?
Ours died in about two weeks, which seems consistent with the
literature.
38. If we spray early(before) SBR detection, will it do
any good?
Assuming soybean rust is in the area and detection is imminent,
then spraying preventatively during the R1 R3 growth stages would be wise. On
the other hand, spraying before R1 in other countries has been shown to be a
waste of money and not result in any better control than spraying at R1 R3.
The best idea is to monitor closely and pay attention to our network next year
so that you will have time to react if we start to detect the disease.
39. What are the best fungicides to use?
See answers to Question 22.
A mixture of a strobilurin (Quadris or Headline) plus a triazole (Tilt,
Propimax, Banner, Folicur) or sequential applications of each chemistry will be
considered the best approach at managing the disease. Two applications of Quilt
or Stratego (premixed strobilurin + triazole fungicides) should also be
effective if approved for use in time.
40. How late is too late to spray?
Based on other countries, R6 (full pod) is too late. Prior to
that stage, we would still recommend at least one treatment if rust were
developing.
41. How do you scout for SBR?
Random is the best idea, especially in the spring when weather
patterns favor widespread infection. Within a field, areas that favor long dew
periods such as tree lines or low spots should be checked. Prior to detection in
a given area, it is probably a good idea to cover lots of territory each day
rather than focus on a field or group of fields within a spot. For example,
consultants may consider scouting a couple of fields on each of their farms each
day then switch to different fields the next day, rather than scout a farm or
group of fields each week. In other words, try to scout across all the
geographic areas each day so that you don't get a rude surprise the next week.
42. What is my potential loss from and how much will
yields be reduced by SBR?
See answers to Question 33.
43. How do you control SBR?
See answers to Question 20.
44. Is it better to plant an early maturing variety or
is it better to plant early (in general) regardless of maturity?
See answers to Question 20.
45. Will SBR overwinter on host plants like vetch, etc at
extremely cold temperatures?
No. According to the literature, cold temperatures eliminate the
pathogen in a given area and it must then survive in frost free areas further
south.
46. Do I need to stock up on fungicides , NOW?
Fungicide companies have assured us that supplies will be
adequate in the U.S. for 2005, should we have to spray for soybean rust. These
companies have had several years to prepare and they have the shortage problems
in South America to learn from a few years ago so they should be ready. These
companies are actively discouraging the hoarding of fungicide stocks by growers
or dealers or regions, which seems wise since we do not know which areas will
need it the most although we can assume the southern states will need fungicides
first. We would recommend you calculate the needs for your farm and contact your
dealer about normal booking programs and purchase accordingly.
47. At what point in the life of the soybean plant does
SBR effect the plants?
The pathogen can infect the plants at most stages but damage
seems confined to the reproductive stages, from flowering onwards.
48. What is the life cycle of SBR?
This rust pathogen only uses urediniospores in its disease
cycle, as far as we can tell from the literature. Thus it survives on a living
host, infects leaves, produces pustules in 6-12 days under favorable conditions,
produces urediniospores which spread by wind to other leaves and hosts and the
cycle continues until unfavorable weather (or winter) stops it.
http://www.cai.iastate.edu/SoybeanRust/Lifecycle.swf
has a brief animated life cycle developed by Iowa State University
scientists.
49. Will SBR ruin the U.S. soybean industry?
Who knows? Ironically, it seems to have improved production in
South America where growers now take better care of their soybeans and fungicide
applications have resulted in higher yields and better quality than before
soybean rust arrived. And researchers will find resistant varieties in a
reasonable time, which will make this just a routine problem like we face in
other crops each year. Our guess would be that the U.S. soybean industry will
adjust, we will control this problem and the industry will remain active or even
improve.
50. What stage of growth are soybeans safe from infection
by SBR?
Infection may occur at most any stage but after R6 infection
should not have an economic impact on that field, however spore production could
impact younger fields nearby or in the direction of prevailing winds.
51. What temperatures (low and high) will kill SBR
spores?
We have not been able to find the exact temperatures that are
lethal to the spores, however, we know that freezing (32 F) will kill the fungus
and that spores will die in the refrigerator (35 40 F) in 2-3 weeks. And we
also know that the disease does not do well in very hot temperatures (> 88 F)
according to reports from other countries. This does not mean the fungus will
die if exposed to 90 + degrees but that it will not function well.
52. Will SBR be a problem during 2005, and into the
future?
We do not know for sure but the probability is that it will
survive along the Gulf Coast and then move northward becoming a problem at least
in the Mid South for 2005 and possibly the entire soybean area of the U.S. in
the future. Even if we do not see it in early 2005, farmers have so much
anticipation for soybean rust that it will be a problem for us during the early
growing season anyway, as we monitoring, scout, sample and put out false alarms.
Regardless of its presence, we are likely to make a number of unnecessary
applications and other mistakes prior to its true arrival. Hopefully, we can
work through this period together, using good monitoring and reasoned judgment
but it will cause an increased workload for University personnel, farm supply
dealerships, applicators, growers, consultants and others.
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