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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 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).
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- Unpublished research provided by Dr.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.
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
By Tom Royer, Extension Entomologist
Heath Sanders could not have made a more prophetic statement for this Extension Entomologist than when he said: “we learn something new about canola every year”. I have learned something new every year that I have been working with canola, and this year is starting to confirm his “prophesy” once again.
This has been a banner year for fall armyworms. They built up populations early, and migrated into Oklahoma earlier than “normal”, attacking sorghum and pasture grasses. Now, they are ready to attack wheat (once it emerges) and possibly, are marching in to graze on newly emerged canola. Dr. Angela Post, OSU Extension Weeds specialist reported that there were caterpillars that appeared to be either beet armyworm or fall armyworms attacking canola. We are getting confirmation on their identity, but regardless, producers need to be vigilant and protect their fields.
I have already discussed their management in wheat http://entoplp.okstate.edu/pddl/pddl/2015/PA14-41.pdf, but now need to alert canola producers about them attacking seedling canola and eliminating stand.
Look for “window pane” damage in young canola plants and/or cut plants. At this time, with canola so small, armyworm and cutworm caterpillars cannot be allowed the chance to reduce stand. The suggested treatment threshold is 1 or more armyworms per row-foot.
Consult CR-7194 Management of Insect and Mite Pests of Small Grains and CR-7667 Management of Insect and Mite Pests in Canola for specific insecticides that are registered for control. Keep in mind that beet and fall armyworms can sometimes be difficult to control, so vigilance is needed by follow-up scouting following an application to make sure control is achieved.
By Tom Royer, OSU Extension Entomologist
Our Plant Disease and Insect Diagnostic lab received samples of wheat that were damaged by brown wheat mites. Producers need to remain alert so that they don’t mistake damaged wheat from brown wheat mite for drought or virus disease.
Brown wheat mite is small (about the size of this period.) with a metallic brown to black body and 4 pair of yellowish legs. The forelegs are distinctly longer that the other three pair. Brown wheat mites can complete a cycle in as little as 10-14 days. Brown wheat mite causes problems in wheat that is stressed from lack of moisture. They feed by piercing plant cells in the leaf, which results in “stippling”. As injury continues the plants become yellow, then dry out and die. They are very susceptible to hard, driving rains which many areas have now experienced, but until then they can cause yield loss when present in large numbers.
We typically experience 3 generations per year. However, in this sample, the mites had already caused considerable damage and had laid significant numbers of diapausing white eggs that tell us they have completed their last generation of the growing season and these eggs will oversummer.
Research suggests that a treatment threshold of 25-50 brown wheat mites per leaf in wheat that is 6-9 inches tall is economically warranted. An alternative estimation is “several hundred” per foot of row. If you find active brown wheat mites in your field, 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 www.wheat.okstate.edu
Dr. Hunger traveled southwest Oklahoma this week, so I made a trip out Hwy. 60 yesterday to evaluate freeze injury and assess the overall condition of the wheat crop in northwestern and north central Oklahoma. Last week’s warm temperatures and wind have taken their toll on wheat in Kay, Grant, and eastern Garfield Counties. It is not too late for rain to save a partial wheat crop in these areas, but the “full yield potential” ship sailed long ago. Wheat sown behind summer crops is the hardest hit, and wheat in these fields could best be described as yellow and thin. If the weather turned and we received rain in the next week, I would predict that yield potential in these fields would still only be around the 15 bushel mark. Without rain, subtract around 15 bushels. Wheat planted behind summer fallow has held on a little longer, but is clearly showing the signs of extreme drought stress. If we receive rain in the next week (and continue to see rain) these fields could still make 20 – 30 bushels per acre. In the absence of rain in the near future, they will be 10 bushels per acre or less.
In addition to drought stress, we found freeze injury and greenbugs at Lamont. I was a little surprised to find freeze injury and even more surprised to find the greatest injury in the later-maturing varieties. We split several stems of early varieties such as Ruby Lee and Gallagher and did not find any injury. These varieties would have likely been at approximately GS 7 – 8 when the freeze occurred. We found significant injury in later-maturing varieties such as Endurance, but these varieties were likely only GS 6 – 7 when the freeze occurred. Conventional wisdom regarding freeze injury is that the more advanced the variety, the greater the likelihood of freeze injury. After seeing the same phenomenon last year (i.e. the greatest injury in later maturing varieties) I am changing my thinking on freeze injury and now say that all bets are off when it comes to freeze injury in drought stressed wheat.
Overall wheat condition started to improve around Nash and Jet, I would say that much of the wheat in this area is CURRENTLY in fair to good condition. I emphasize the currently in the previous sentence, as the only difference between wheat in the Cherokee area and wheat to the east was about one week’s worth of moisture. Some terrace ridges had already started turning blue and moisture was starting to run out. Without rain wheat in this area will rapidly deteriorate from good to poor. One consistent theme throughout the day was greenbugs. Many sites had evidence of parasitic wasp activity (i.e. aphid mummies), but the presence or absence of parasitic wasp activity varied field by field. Dr. Royer has indicated that greenbugs still need to be controlled in drought stressed wheat. If parasitic wasps are active, the best decision is to let them do the aphid killing for you. If no mummies are present, then insecticide control could be justified. The only sure way to make this determination is to use the glance-n-go sampling system.
Similar to Lamont, we found freeze injury in the Cherokee and Helena areas. Many of the worst looking fields (extensive leaf burn) had only superficial injury and should recover if moisture allows. Conversely, some plants that showed no outward signs of freeze injury had injured heads within. Most fields I surveyed had less than 10% injury, but one field was a complete loss. On the surface the 10% injury field and 100% loss field looked the same, so I cannot over stress the importance of splitting stems. I have received a few additional reports of freeze injury from Kay County this morning, so it is important for producers throughout northern Oklahoma to evaluate their wheat on a field by field basis.
A final note on freeze injury. Freeze injury appeared to be worst in no-till fields and in areas where residue was heaviest. Based on my observations, this was not due to winterkill or poor seed to soil contact. My best explanation is that the lack of soil cover in conventional till fields allowed stored heat to radiate from the soil surface and slightly warm the crop canopy. The insulating effect of residue in no-till fields did not allow radiant heating to occur. Given the pattern of freeze injury in fields with varying degrees of residue across the field, I feel pretty confident in this analysis of what occurred.
Please use the comment section to share pictures or descriptions of wheat in your area.
This article is provided by Dr. Tom A. Royer, OSU Extension Entomologist
Sug Farrington, Extension Educator in Cimarron County received a sample of “worms” that were collected by a producer in his wheat field. They turned out to be army cutworms.
Unlike the fall armyworm, this caterpillar overwinters in Oklahoma, tolerates cold and feeds throughout the winter months. Adult army cutworm moths migrate to Oklahoma each fall from their summer residence in the Rocky Mountains. They seek bare or sparsely vegetated fields (like a newly prepared field ready for wheat planting, or a field that was “dusted in” and had not yet emerged) and lay eggs from August through October. The eggs hatch soon after being deposited, which explains why a producer might see different sizes of larvae in a field. Army cutworms feed throughout the winter and molt seven times before they turn into pupae in the soil. Most larvae will be gone by late March and adult moths begin emerging in April and fly back to the Rocky Mountains to spend the summer.
Army cutworms can cause severe stand loss of wheat if not controlled. Cutworm damage often goes unnoticed through the winter because the caterpillars grow slowly and don’t get big enough to cause noticeable damage until temperatures warm in the spring. Unfortunately, that is also an indication of poor growing conditions due to drought (which cutworms also like), so it becomes important to check the fields for cutworms. If you notice a field at this time of year with a numbers of starlings or black birds feeding in a concentrated area of your wheat field, they are likely feasting on army cutworms!
Sample a field by stirring or digging the soil to a depth of two inches at 5 or more locations. Also, turn over those dried up cow patties, as they are a favorite hiding place for army cutworms. The cutworms will be “greenish grey”, and will probably curl up into a tight “C” when disturbed. A suggested treatment threshold is 2-3 caterpillars per foot of row when conditions are dry (like we are experiencing this winter) or 4-5 caterpillars per row-foot in fields with adequate moisture. Control suggestions are listed in Current Report-7194 Management of Insect and Mite Pests in Small Grains.
Army cutworms are also a potential pest of canola. Scout fields just as you would in wheat. The suggested treatment threshold for cutworms in canola is 1-2 per row-foot. Current recommendations for control of army cutworms in canola are listed in CR-7667, Management of Insect and Mite Pests in Canola.
by: Tom Royer, OSU Extension Entomologist
Fall armyworms are active this fall. I checked a field of wheat this past weekend with significant damage from fall armyworms that averaged 6-7 fall armyworms per square foot. Scout for fall armyworms by examining plants in several (5 or more) locations in the field. Fall armyworms are most active in the morning or late afternoon. Look for “window paned” leaves and count all sizes of larvae.
Examine plants along the field margin as well as in the interior, because they sometimes move in from road ditches and weedy areas. The caterpillars were widely distributed in the field that I checked, suggesting that they were the result of a large egg lay from a recent adult moth flight. The suggested treatment threshold is 2-3 larvae per linear foot of row in wheat with active feeding. We won’t get relief from fall armyworms until we get a killing frost, since they do not overwinter in Oklahoma.
Consult the newly updated OSU Fact Sheet CR-7194 Management of Insect and Mite Pests of Small Grains for control suggestions.
by: Tom Royer, OSU Extension Entomologist
Our winter wheat has taken a beating this winter, with cold weather hanging on and some areas not getting that thirst quenching precipitation to help it get a great jump start this spring. In addition, I have received scattered reports of brown wheat mites showing up and causing problems. Producers need to remain alert so that their wheat is not suffering dual problems of dry growing conditions PLUS brown wheat mite.
Brown wheat mite is small (about the size of this period.) with a metallic brown to black body and 4 pair of yellowish legs. The forelegs are distinctly longer that the other three pair. Brown wheat mites can complete a cycle in as little as 10-14 days. They will undergo up to 3 generations each year, but have probably already completed at least one or two by now. Numbers will likely decline if a hard, driving rain occurs. Spring populations begin to decline in mid-late April when females begin to lay “diapause” eggs.
Brown wheat mite causes problems in wheat that is stressed from lack of moisture. They feed by piercing plant cells in the leaf, which results in “stippling”. As injury continues the plants become yellow, then dry out and die. These mites feed during the day, and the best time to scout for them is in mid-afternoon. They do not produce webbing and will quickly drop to the soil when disturbed. They are very susceptible to hard, driving rains, but until then they can cause yield loss when present in large numbers
Research suggests that a treatment threshold of 25-50 brown wheat mites per leaf in wheat that is 6-9 inches tall is economically warranted. An alternative estimation is “several hundred” per foot of row.
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, at www.wheat.okstate.edu, or by clicking here.
By Tom Royer, OSU Extension Entomologist
I received some troubling news from the Texas Panhandle. Dr. Ed Bynum, Extension Entomologist from Amarillo, reported finding some greenbug populations that were shown to be resistant to chlorpyrifos, the active ingredient in Lorsban 4E, and other generic products (Govern 4E, Hatchet, Nufos, Vulcan, Warhawk, Whirlwind). You can read the full article by clicking on this url: http://texashighplainsinsects.net/april-12th-special-edition/ The bottom line: he tested some suspect greenbug populations using a diagnostic test that he developed for testing greenbugs in sorghum in the 1990’s, and found that they were resistant to chlorpyrifos at labeled rates.
This should not raise panic among growers in Oklahoma for two reasons. The first is that I have not heard of or received reports of any control failures for greenbugs in Oklahoma, in fact, generally greenbugs have been pretty scarce this winter.
The second reason is that it is late enough in the growing season to expect that the primary natural control of greenbugs, a tiny wasp called Lysiphlebus testaceipes (see picture to right), keeping greenbug numbers from becoming an outbreak.
The best course of action is to sample winter wheat fields with the Glance ‘n Go system.
Start by going to the Cereal Aphids Decision Support Tool on your computer http://entoplp.okstate.edu/gbweb/index3.htm and selecting the Greenbug Calculator.
By answering a few simple questions, you can determine an economic threshold for controlling greenbugs. This threshold is based on the estimated cost of treating the field and the estimated price of wheat. Once a threshold is calculated, you can print a Glance ‘n Go scouting form, take it to a field and record your sampling results. The form will help you to decide if the field needs to be treatment for greenbugs. There are several things that make Glance ‘n Go a good way to make such a decision. You only have to “Glance” at a tiller to see if it has greenbugs (no counting greenbug numbers). You can make a decision to treat “on the Go” because you stop sampling once a decision is reached (no set number of samples). Finally, you can account for the activity of the greenbug’s most important natural enemy, Lysiphlebus testaceipes.
Aphid Mummies (below)
When scouting with the Glance ‘n Go system, keep a running count of tillers that have aphid mummies and a running count of tillers that are infested with one or more greenbugs. After each set of 5 stops, the Glance ‘n Go form directs you to look at your total number of infested tillers and tillers with mummies. If there is enough parasitoid (mummy) activity, you will be directed to stop sampling and DON’T TREAT, even if you have exceeded the treatment threshold for greenbugs! Why? Because research showed that at that level of parasitism, almost all of the healthy-looking greenbugs have been “sentenced to death” and will be ghosts within 3-5 days. If they have received their “sentence” you can save the cost of an unnecessary insecticide application.
Treatment thresholds will probably fall around 2-4 greenbugs per tiller, but make sure you are using the Spring (January-May) form, not the Fall (Sept-December) form. If a field needs to be treated, check with Current Report CR-7194, “Management of Insect and Mite Pests in Small Grains”. If you treat for greenbugs and have a failure, please contact our Department and we will investigate further to determine