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Bird cherry oat aphids in wheat: showing up in large numbers

By Tom Royer, OSU Extension Entomologist

I have received several reports of (and photos, Figure 1) of bird cherry oat aphid (BCOA) numbers in winter wheat that will require treatment with an insecticide

Bird cherry oat aphid

Bird cherry oat aphid

 

Severe bird cherry oat aphid infestation

Severe bird cherry oat aphid infestation

Bird cherry oat aphids are small (2mm) olive-green aphids with a red-orange patch surrounding the base of each cornicle (Figure 1). Old, wingless, overwintering adult aphids are darker, almost black.  At this time, you may also find winged aphids that have moved in to the field (Figure 2).

Winged bird cherry oat aphid

Winged bird cherry oat aphid

What are my suggestions regarding control of bird cherry oat aphid in winter wheat?

  • Unpublished research provided by Dr. Kris Giles (OSU) and Dr. Norm Elliott (USDA-ARS) along with studies conducted in South Dakota, Minnesota, and North Dakota on spring wheat indicated that BCOA causes yield loss before wheat reaches the boot stage. Approximately 5-9% yield loss occurs when there are 20-40 BCOA per tiller (average 7%).
  • Visible damage from bird cherry-oat aphid is not very noticeable so infestations may go unnoticed. It is very important to check fields for infestations and make treatment decisions only after a field has been checked.

My suggestion for making a treatment decision is as follows:

If greenbugs and bird cherry oat aphids are both present, use Glance n’ Go to scout, which can be accessed at http://entoplp.okstate.edu/gbweb/index3.htm.  Published research from Giles and Elliott showed that Glance n’ Go sampling will work with both aphids if they are both present.

If bird cherry-oat aphid is present alone, count the number of aphids present on each of 25 randomly-selected tillers across a zigzag transect of the field. The reason that you can’t use Glance n’ Go is that the most available research suggests that the threshold is too high to effectively use Glance n’ Go.

Look for evidence of parasite activity in the form of mummies (Figure 3).  A rule of thumb is that if 5-10% of the aphids are mummies, more than 90% are already parasitized.  If mummies are not present, use the guidelines below to make a treatment decision.

Parasitized bird cherry oat aphid

Parasitized bird cherry oat aphid

If, after thoroughly scouting your field, you can identify that infestations are spotty, consider spot spraying with a ground rig.

Use the YIELD LOSS TABLE to determine a potential YIELD LOSS from the aphids.  Then estimate your CROP VALUE and calculate your CONTROL COSTS.  Use those numbers to estimate PREVENTABLE LOSS.    If estimated PREVENTABLE LOSS is greater than CONTROL COSTS, Treat; otherwise, Don’t Treat.

 

Here is an Example:

 

Step 1:  Estimate YIELD LOSS:

 

  • Total # aphids_______525___________/25 tillers = average # aphids/tiller_____21_____

 

Step 2:  Estimate CROP VALUE:  (Crop Value = Yield potential X Price per bushel)

  • Yield potential__40____ bushels/acre X price per bushel $____4.50____ per bushel

 

CROP VALUE = $___180____

 

Step 3:  Estimate CONTROL COSTS: (Control Cost = Insecticide Cost + Application Cost)

 

  • Insecticide cost $___6_____ /acre  +  Application Cost       $ ____3_____/acre

 

CONTROL COSTS $_____9_____/acre

 

Step 4:  Estimate PREVENTABLE LOSS (Crop Value X Yield Loss from Aphid)

 

  • Crop value/acre $___180_____  x Yield Loss from aphid ___0.07_____

 

PREVENTABLE LOSS $____12.60______/acre

 

IF PREVENTABLE LOSS $___12.60_____ is greater than CONTROL COSTS $___9.00_____ TREAT

 

IF PREVENTABLE LOSS $________ is less than CONTROL COSTS $__________                                   DON’T TREAT

 

Check CR-7194, “Management of Insect and Mite Pests in Small Grains” for registered insecticides, application rates, and grazing/harvest waiting periods.

It can be obtained from any County Extension Office, or found at the OSU Extra Website at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2601/CR-7194web2008.pdf

Wheat disease update – 19 March 2016

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist

Oklahoma:  This past week I looked at wheat around Stillwater as well as in central OK (Blaine County NW of Oklahoma City; Kingfisher just NW of OKC; Apache in Caddo County SW of OKC), and in SW OK around Altus.  I saw wheat as far along as approaching flag leaf emergence to at growth stage 6-7.  The more advanced wheat typically was planted relatively early and not grazed.  Everywhere I was had sufficient moisture, although areas in southwestern and western OK were getting to a point where some rain definitely would be beneficial.  In addition to my observations, I’ve received numerous reports that I’ll summarize here.

At nearly all the places I stopped, I observed varying levels of stripe rust, leaf rust, aphids, and powdery mildew, with powdery mildew being by far the least prevalent.  Stripe rust typically was scattered across fields, but there were some significant hot spots.  In some fields (for example the variety trial at Kingfisher) I saw no stripe rust.  Greg Highfill (Extn Educator, Woods County) and Darrell McBee (Extn Educator, Harper County) sent me the photo below showing stripe rust they found this past week.  They indicated the stripe rust was scattered and not common, but this does mean that spores are present in the field and will increase with favorable (cool and wet) weather.  They also indicated finding a little powdery mildew.  I also heard reports of severe stripe rust in susceptible varieties such as Pete, Garrison, and Everest.

 

Stripe rust in northwestern Oklahoma - Photo courtesy Greg Highfill and Darrell McBee

Stripe rust in northwestern Oklahoma – Photo courtesy Greg Highfill and Darrell McBee

More severe hot spots of stripe rust were reported by David Nowlin (Extn Educator; Caddo County), who sent the following photo of stripe rust on ‘Pete’, which is highly susceptible to stripe rust.

Stripe rust in Pete in Caddo County - photo courtesy David Nowlin

Stripe rust in Pete in Caddo County – photo courtesy David Nowlin

 

Similar reports regarding stripe rust were made by Dr. Brett Carver.  He also has reported seeing considerable chlorosis (yellowing) often with the lack of sporulation.  I saw the same type of yellowing with no sporulation at Kingfisher yesterday (see photo below).  I’m not sure of the cause of this yellowing, but I don’t believe it to be from rust or other foliar diseases because it is widespread in its distribution on lower leaves.  Perhaps it is the result of the environment.

Yellowing in wheat at Kingfisher

Yellowing in wheat at Kingfisher

In no-till fields near Altus and Apache I saw striking tan spot on lower leaves along with numerous pseudothecia of the tan spot fungus on the wheat residue in the field.  Near Altus, this was combined with stripe rust presence such as described above.  In such a case, applying a fungicide early to catch both of these diseases should be considered, especially if the field at this point has a good yield potential.  For more information to help make this decision, see OSU CR 7668 available at www.wheat.okstate.edu

tan spot

tan spot

 

Reports/excerpts of reports from other states:  

Texas : I’ve only received two reports from Texas this past week.  One is from a former student that now lives in the Weatherford, TX area.  He indicates that stripe rust is in the area.  The other report is from David Nowlin (Extn Educator, Caddo County), who indicates a colleague of his located near Denton, TX sent him the following report on 15-March.

“We’re getting hammered with strip and leaf rust as well as powdery mildew on our varieties down here in Denton, TX. We’re just a little further ahead of you. Wheat is not as far along as we normally see.

Kansas:  Dr. Erick DeWolf; Extn Plant Pathologist; Kansas State University; Manhattan, KS; Mar 19, 2016: “The wheat crop is growing rapidly throughout Kansas. The crop in the more advanced fields are approaching jointing in the northwest and are about a week away from flag leaf emergence in the south central and southeast portions of the state.  The crop is generally considered to be about 3 weeks ahead of schedule with respect to normal growth and development. There are multiple reports of leaf rust and stripe rust in Texas, Oklahoma, and other surrounding states.

The Crops Extension team has been busy scouting for disease in recent weeks. We are finding active leaf rust and stripe rust in the state. Leaf rust was reported in west central and northwest, Kansas with most activity in counties bordering Colorado. Low levels of leaf rust were also observed in research plots in Riley County, which is located in northeast Kansas. The winter has been very mild in Kansas and it is very likely that the leaf rust has overwintered in the state. Stripe rust was reported in multiple counties this past week. Stripe rust is generally at very low levels with most activity reported in the southeast portion of the state.  Tan spot and powdery mildew have also been reported in some areas of the state.”

 

 

Freeze injury update 21 March 2016

Temperatures over the weekend were cold enough to cause injury to the Oklahoma wheat crop. As shown in the figure below from the Oklahoma Mesonet many areas of Oklahoma spent several hours below 28F. While temperatures in the wheat canopy might have remained slightly higher than reported air temperatures, they were still probably low enough to result in significant injury to wheat.

 

Hours spent below 28F March 18 - 20

Hours spent below 28F March 18 – 20

 

A few points I would encourage everyone to consider:

Every freeze event is unique – the temperatures and time durations we use regarding freeze injury are rules of thumb and are not exact. I have seen instances where conventional wisdom would indicate complete crop loss and we skate through with minimal damage.
It will take a few days to see how bad things are – Symptoms may start to appear later this week and will likely be clearly identifiable by the end of this week. Healthy wheat heads will remain turgid with a green color. Damaged wheat heads will be bleached, yellow, or brown and will easily break when pushed against. I anticipate that we will not have any partial “blanking” of wheat heads and that most wheat heads will either be okay or a complete loss. This post from last year has some pictures showing tell tale signs of freeze injury. The linked post also serves as a reminder that while freeze is the concern of the day, the potential worsening of drought conditions in NW Oklahoma has the potential to do far more damage.

% damaged heads might not = % yield loss –  It is still relatively early in the growing season and there is still opportunity for smaller (two nodes or less) wheat to produce additional tillers and/or retain secondary tillers. Whether or not these tillers are able to compensate for larger tillers that were lost due to freeze will depend on moisture and weather. IF (and that is a big if) weather conditions remain favorable, late emerging tillers in central and northern Oklahoma might still have a shot at producing grain. It will be tougher for more advanced wheat in southern Oklahoma to make this type of recovery.

 

Wheat disease update – 04 March 2016

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist

Oklahoma –  Foliar diseases are becoming active in Oklahoma.  Around Stillwater I have found both leaf and stripe rust, powdery mildew, and septoria.  Incidence/ severity of all these foliar diseases is relatively light, but I am especially watching what happens to the leaf and stripe rust.  The leaf rust pustules are small and on lower/older leaves indicating that leaf rust likely overwintered in Central OK.  The stripe rust pustules were on the upper leaves of ‘Pete’ wheat (see photo) indicating the spores causing these initial infections likely blew up from the south.  With rain and cool wet weather in the forecast, I definitely expect for there to be an increase in foliar diseases.  Around Stillwater, I also have seen quite a few aphids (mostly bird cherry-oat but also a few greenbug) and many lady beetles.  However, no symptoms yet of barley yellow dwarf.

 

Stripe rust on Pete 03/04/2016

Stripe rust on Pete 03/04/2016

Gary Strickland (SWREC Dryland Cropping Systems Spclt – Jackson Cnty) relayed to me that in SW OK he has seen leaf rust in fairly high levels on lower leaves of Endurance and other wheats, and has heard reports of stripe rust but has not seen any himself.

Yesterday I traveled to north-central OK (Alva).  On the way there and while there I visited several fields and found a few very small leaf rust pustules.  Overall the wheat from I-35 over to Alva (Hwy 11) looked good and was greening-up nicely.  Also while in Alva, numerous producers, etc. relayed reports of mostly leaf rust showing up across central OK, such as leaf rust around Geary, OK, etc.

Regarding rust incidence/severity in Texas, I talked to a wheat breeder in Texas last week and he indicated that wheat in southern Texas was showing both leaf and stripe rust but had not yet reached a severe level.  Early next week I’ll be at a meeting of wheat pathologists and should be able to find out more about diseases in Texas.

All these reports indicate the potential for significant foliar disease on the current wheat crop.  Genetic resistance in some of wheat varieties helps protect against the foliar diseases, but fungicides also provide an excellent management tool to protect not only yield, but also quality (test weight).  To help with deciding if and when to apply a fungicide, Dr. Jeff Edwards and I earlier this week updated and revised CR 7668 (Foliar Fungicides and Wheat Production in Oklahoma – March 2016).  It can be found at www.wheat.okstate.edu.  This Current Report discusses the significant aspects related to using fungicides to manage wheat foliar diseases.

One point I want to be sure to emphasize when using fungicides is the importance to not exceed the maximum amount of a fungicide applied to a crop in a single year.  Such a consideration couldespecially be an issue when more than one fungicide application is made.  In many states through the southeastern region of the U.S., two fungicide applications on wheat are more common, with the last application typically targeted toward Fusarium head blight (scab).  In Oklahoma, where scab usually is not a concern, deciding when to make a single fungicide application typically is the only consideration.  However, if you have early disease pressure from stripe rust or have early season powdery mildew, tan spot, or Septoria leaf blotch in no-till fields, more than one application may be needed to adequately manage these diseases.  In these situations, care must be taken to insure label compliance.  For example, if an early application of a generic form of tebuconazole is applied at 4 oz/ac, a subsequent application of any fungicide containing tebuconazole around heading would put you over the 4 oz limit for the crop season.  Thus, be sure to read the label to determine the maximum amount of a chemical that can be applied in a single season and the exact amount of a chemical(s) that is in a fungicide.

South Texas – Amir Ibrahim TAMU Wheat Breeder – The wheat crop in our trials at Castroville and Uvalde, TX is at Feekes stages 5‐10, ranging from the latest winter to the earliest spring types. Growth is very lush and there is no winter kill or frost injury in either winter and spring types. Stripe rust is at 70S, in the medium to upper canopy, on our  ‘Patton’ spreader passes across the field. Stripe rust is about 60S on ‘TAM 110’. ‘Coronado’ is hammered with yellow rust at Castroville.  Stripe rust is more progressed at Uvalde. We have been getting natural and uniform stripe rust infection at Uvalde every year for the last few years. The Texas A&M AgriLife Center at Uvalde sits at the bottom of a valley with constant morning dew that favors infection. Stripe rust has also been found at low levels in the wheat breeding trials near Chillicothe in the Rolling Plains of Texas.

Texas – Dr. John Fenderson – WestBred.  “I saw rampant Stripe in Central TX on Ruby Lee.  I also saw it on sensitive lines from I-20 south anywhere it has rained.  Some spraying has occurred in the Austin area.  I also pulled wheat in the Red River corridor both sides with a lot of stripe on older leaves.  It is just waiting on the right conditions to explode.  I was all the way down in S. TX this week and I did not see stripe on the spring wheat but there was some on Winter wheat around San Angelo etc.”

First hollow stem update 03/04/2016

First hollow stem is the optimal time to remove cattle from wheat pasture (full explanation). This will be the last of the 2016 first hollow stem updates, as the vast majority of varieties are at or well past first hollow stem.

Keep in mind that the numbers reported from Stillwater are likely behind those being observed in southern Oklahoma and ahead of those observed in northern Oklahoma. The First Hollow Stem Advisor can provide an estimate of first hollow stem progress in your neck of the woods.

First hollow stem measured in wheat sown 09/15/2015 at Stillwater, OK. Varieties with ‘-‘ reached first hollow stem on a previous measurement date
Variety cm of hollow stem 03/04/16
Endurance 1.5
OK Rising
Billings
Ruby Lee
Duster
Gallagher
Iba
Bentley
Doublestop CL Plus 1.57
NF 101
WB-Cedar
WB4458
WB-Grainfield
Winterhawk
WB4515
WB4721
WB4303
SY Monument 1.5
SY Flint
SY Llano
SY Drifter
SY Wolf
SY Razor
SY Grit
Everest
1863
KanMark
Oakley CL 1.74
Larry 1.8
Zenda
Tatanka 1.81
Joe 1.1
LCS Pistol 1.68
LCS Wizard 1.43
LCS Mint 2.08
LCS Chrome 1.84
T158 1.5
Long Branch 1.73
TAM 112
TAM 204
TAM 114
AG Robust
Byrd
Brawl CL Plus 1.26
Avery 1.97
OK1059060-3 1.91
OK10126 1.41
OK11D25056 1.55
OK12621 2.18
Stardust 2.24
OK12716R/W 1.16
OK11231 1.26
OK09915C-1 1.32
OK12912C 1.17
OK12DP22002-042
OK118036R/W

First hollow stem update 02/29/2016

First hollow stem is the optimal time to remove cattle from wheat pasture (full explanation). We measure first hollow in our September-sown wheat forage plots at Stillwater each year, and normally have approximately 50% of varieties at or past first hollow stem by March 1st. I have posted first hollow stem measurements from samples taken from these plots on 02/29/16 in a table at the end of this blog. Most wheat varieties are now at or well past first hollow stem.

Keep in mind that the numbers reported from Stillwater are likely behind those being observed in southern Oklahoma and ahead of those observed in northern Oklahoma. The First Hollow Stem Advisor can provide an estimate of first hollow stem progress in your neck of the woods.

First hollow stem measured in wheat sown 09/15/2015 at Stillwater, OK. Varieties with ‘-‘ reached first hollow stem on a previous measurement date
Variety cm of hollow stem 02/29/2016
Endurance 1.0
OK Rising 1.5
Billings
Ruby Lee 2.0
Duster 2.0
Gallagher
Iba
Bentley
Doublestop CL Plus 1.4
NF 101
WB-Cedar
WB4458
WB-Grainfield
Winterhawk
WB4515
WB4721
WB4303
SY Monument 1.0
SY Flint
SY Llano
SY Drifter
SY Wolf 2.7
SY Razor
SY Grit
Everest
1863
KanMark 1.5
Oakley CL 1.3
Larry 0.9
Zenda
Tatanka 1.1
Joe 0.8
LCS Pistol 1.1
LCS Wizard 1.3
LCS Mint 1.4
LCS Chrome 1.2
T158 1.1
Long Branch 1.2
TAM 112 1.6
TAM 204 1.7
TAM 114 1.6
AG Robust
Byrd 1.7
Brawl CL Plus 1.1
Avery 1.1
OK1059060-3 1.4
OK10126 0.8
OK11D25056 1.1
OK12621 1.1
Stardust 1.0
OK12716R/W 1.1
OK11231 1.0
OK09915C-1 0.8
OK12912C 1.1
OK12DP22002-042 1.6
OK118036R/W