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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  • Unpublished research provided by Dr.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

Brown wheat mite showing up in winter wheat

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.

A closeup of a brown wheat mite. Photo courtesy Franklin Peairs, CSU.

A closeup of a brown wheat mite. Photo courtesy Franklin Peairs, CSU.

Brown what mite can severely damage wheat that is already stressed due to drought or other adverse environmental conditions.

Brown what mite can severely damage wheat that is already stressed due to drought or other adverse environmental conditions.

Brown wheat mites are about the size of a period at the end of a sentence and can be difficult to see with the naked eye.

Brown wheat mites are about the size of a period at the end of a sentence and can be difficult to see with the naked eye.

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.

Brown wheat mite eggs in soil.

Brown wheat mite eggs in soil.

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

Northwestern / north central Oklahoma wheat update – drought, greenbugs, and freeze

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.

Wheat in the Lamont test plot was approximately GS 7 - 8. Flag leaves were rolled and plants were starting to abort tillers.

Wheat in the Lamont test plot was approximately GS 7 – 8. Flag leaves were rolled and plants were starting to abort tillers.

 

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.

Freeze injury was greatest in late-maturing varieties at Lamont.

Freeze injury was greatest in late-maturing varieties at Lamont.

 

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.

 

Greenbugs were alive and well at Lamont

Greenbugs were alive and well at Lamont

Parasitic wasps were keeping greenbug populations under control in this field

Parasitic wasps were keeping greenbug populations under control in this field

Active and parasitized greenbugs on the same plant

Active and parasitized greenbugs on the same plant

 

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.

 

Plants that look healthy on the exterior could contain damaged wheat heads

Plants that look healthy on the exterior could contain damaged wheat heads

A closeup of the damaged wheat head from the picture above

A closeup of the damaged wheat head from the picture above

Although freeze injury to plant tissue in this field was severe, the wheat heads were mostly left unscathed

Although freeze injury to plant tissue in this field was severe, the wheat heads were mostly left unscathed

A closeup of a head from the freeze-injured wheat shown above. Although tissue damage is severe, the growing point and wheat head are still viable

A closeup of a head from the freeze-injured wheat shown above. Although tissue damage is severe, the growing point and wheat head are still viable

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.

Army cutworms reported in some Oklahoma wheat fields

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. Photo courtesy Sug Farrington, Cimarron County Extension Educator.

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!

Army cutworm injury in wheat. Photo courtesy Sug Farrington, Cimarron County Extension Educator.

Army cutworm injury in wheat. Photo courtesy Sug Farrington, Cimarron County Extension Educator.

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.

Winter grain mites in northcentral OK

Jeff Bedwell forwarded reports of winter grain mites in Major and Alfalfa counties over the past week. This does not appear to be a widespread problem, but growers should check wheat fields to see if winter grain mites are present. We had a lot of issues with winter grain mites and brown wheat mites in Oklahoma last year. Unfortunately, many of these fields were not diagnosed until the damage was severe and visible from a distance. In this case, a rescue treatment was still effective at controlling the pest, but some yield loss had already occurred thus reducing the return on pesticide investment.

Winter grain mites are small (about 1 mm long) with black bodies and orange-red legs. Winter grain mites complete two generations per year and the adults can live for up to 40 days. The generation we are dealing with now resulted from oversummering eggs laid last spring. The second generation peaks in March/April and results from eggs laid in January/February.

Image

Winter grain mites on wheat near Blair, Oklahoma.

 

Scouting
Winter grain mites are not a problem you will notice in a timely fashion while standing up. You will need to get close to the soil surface and move residue to find these pests. Winter grain mites are light sensitive and prefer calm air to windy conditions; therefore, scouting early in the morning, late in the evening, or on cloudy days generally works best. Be sure to look under residue in no-till fields and under clumps of soil in conventional-till fields.

Scouting for winter grain mites requires getting close to the soil surface and moving residue to disturb mites.

Scouting for winter grain mites requires getting close to the soil surface and moving residue to disturb mites.

Injury

Winter grain mites feed by piercing plant cells in the leaf, which results in “stippling”.  As injury continues, the leaves take on a characteristic grayish or silverish cast.  Winter grain mites are more likely to cause injury in wheat if it is already stressed due to lack of moisture or nutrients. Also be advised that freeze injury can easily be confused for winter grain mite injury.

Wheat damaged by winter grain mite often has a silver or grayish appearance from a distance

Wheat damaged by winter grain mite often has a silver or bronzed appearance from a distance

When to spray
There are no established thresholds for winter grain mite. Healthy, well-fertilized wheat plants can generally outgrow injury, so it takes large numbers to justify control. If there is injury present AND large numbers of mites (~10 per plant) present in grain only wheat this time of year, you might consider control. If the wheat is to be grazed, I would simply monitor the situation in most cases and only spray if injury became severe.

What to spray
Malathion is the only product labeled for wheat in Oklahoma that has winter grain mite on the label. There are many additional products, such as some of the pyrethroids and chlorpyrifos, that are effective at controlling winter grain mite, but they don’t have a specific label for them. These products can be applied under 2ee regulations; however since this pest is not specifically labeled, the user assumes all responsibility for the application of the product.  It is also important to read and follow label directions regarding grazing restrictions for these and all pesticides.  Consult OSU Current Report 7194 Management of insect and mite pests in small grains for a more complete listing of available pesticides.

Fall armyworm on the march!

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.

Fall armyworm damage is characterized by window panning on wheat leaves. Injury can sometimes be greater in field margins as armyworms sometimes move in from adjacent road ditches or weedy areas.

Fall armyworm damage is characterized by window panning on wheat leaves. Injury can sometimes be greater in field margins as armyworms sometimes move in from adjacent road ditches or weedy areas.

Fall armyworms are generally most active early in the morning or late in the evening. Spray when 2-3 armyworms per linear foot of row are present.

Fall armyworms are generally most active early in the morning or late in the evening. Spray when 2-3 armyworms per linear foot of row are present.

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.

Wheat streak mosaic virus showing up

Add wheat streak mosaic virus to the list of possible causes of yellowing wheat in Oklahoma. Wheat streak mosaic virus is transmitted by the wheat curl mite, which oversummers on grasses such as volunteer wheat and corn. The wheat curl mite cannot survive more than two weeks without a green host, hence the recommendation to make sure that all grass plants are dead two weeks prior to planting. You can find more information on the wheat curl mite and wheat streak mosaic in OSU Fact Sheet EPP-7328 – Three virus disease of wheat in Oklahoma

The photo below is from our wheat variety trial at Kildare. As you can see there is significant yellowing in some of the plots. Our first thoughts were that either wheat soilborne mosaic virus and/or wheat spindle streak mosaic virus were causing the symptoms; however, the yellowing was present in many varieties that are resistant to both these diseases. The Disease Doctor, Bob Hunger, collected samples for analysis in the OSU Plant Diagnostic Lab. Tests showed that wheat streak mosaic was the culprit.

Wheat streak mosaic virus is responsible for yellowing at our Kildare variety trial. All varieties are affected by the disease, but as shown in this picture the severity of the reaction differs somewhat by variety.

Wheat streak mosaic virus is responsible for yellowing at our Kildare variety trial. All varieties are affected by the disease, but as shown in this picture the severity of the reaction differs somewhat by variety.

We are facing this problem because I did not follow my own recommendations. While the plot area was mostly clean at the time of planting, there was some volunteer wheat present. We planted anyway and sprayed glyphosate right after planting. In the past wheat streak mosaic virus was primarily a northwestern Oklahoma issue and we could get by with late burndown on wheat ground in central Oklahoma. Our Kildare plots are a prime example that this is no longer the case. We have to control volunteer grasses (wheat, corn, grain sorghum, etc.) in a manner that will break the green bridge for at least two weeks prior to planting.

So, what is next for our plots at Kildare? There are some variety differences in reaction to the wheat streak mosaic virus. We will rate plots and include this information in our wheat variety comparison chart. I anticipate the plots will continue to go downhill and it is yet to be determined whether or not we will be able to harvest useable data from the location. We will certainly try again next year and apply our turndown earlier.

 

Oklahoma wheat update 03/28/2014

On Friday, March 28th I made a tour through northwestern Oklahoma to diagnose a few problem fields and get a better feel for the wheat crop condition. I have provided a brief description of what I saw below. I did not make it to southwestern Oklahoma this trip, but by all accounts the wheat is dry, brown, and barely hanging on. A best case scenario in areas southwest of Apache this year is a poor wheat crop. It will have to rain a lot between now and harvest for this to happen.

Reports from Apache eastward are somewhat better. The wheat crop in this area still has potential, but the potential is declining. A farmer from the Hinton area called yesterday and indicated that moisture could still be found about 1 inch below the soil surface, but the top is still very dry. We need a soaking rain to move nitrogen into the rooting zone and to perk the crop up post dormancy.

My first stop this morning was at Lamont. Wheat in this area is smaller than normal and is at approximately Feekes GS5. There were several yellow areas in fields and uneven wheat. Much of this yellowing appeared to be nitrogen deficiency, but not all of it was due to insufficient top dress nitrogen. We simply have not had enough moisture to get good movement of top dress N into the rooting profile and for the wheat crop to take up applied N. Some of the yellowing was also due to drought stress. Some of the yellowing could have been due to brown wheat mite and/or winter grain mite activity (described more below).

My second stop was at our Cherokee variety plots. Wheat in this area was uneven, similar to Lamont. As shown in the picture below, part of our plot area was showing significant yellowing. Initially, I thought this was due to changes in soil type/nutrient variability. Upon closer inspection, this area was infested with brown wheat mite. These symptoms have only started to show in the last week or so. Thanks to variety trial cooperator Kenneth Failes, this situation will be remedied as soon as the wind settles.

The yellow, stunted areas in our Cherokee variety trial were caused by brown wheat mite

The yellow, stunted areas in our Cherokee variety trial were caused by brown wheat mite

 

Next stop was Alva, where the trend of uneven and yellow wheat continued. As shown in the picture below, there were several fields in the area with spots of dead or nearly dead wheat. Brown wheat mites were found in most of these fields and probably weakened plants which increased the amount of winterkill. In some fields seed had been placed at the proper depth, but the seed trenches were partially filled with residue rather than soil. Residue provides less insulation than soil and likely made heavy residue areas more prone to winterkill. I also noticed in these fields that the crown of the plant had developed in residue rather than soil, which likely increased winterkill. I looked at additional no-till fields in the area with severe winter injury, but plants that were still viable. Grazed fields seemed to have greater injury than non-grazed.

Areas of winterkill in no-till wheat near Alva

Areas of winterkill in no-till wheat near Alva

 

Although seeded at the proper depth, some wheat plants in heavy residue areas had crown placement at the soil surface. This increased the severity of winterkill.

Although seeded at the proper depth, some wheat plants in heavy residue areas had crown placement at the soil surface. This increased the severity of winterkill.

I looked at a few fields south of Enid. Unlike the fields in Grant, Alfalfa, and Woods Counties, this primary issue in these fields was winter grain mite instead of brown wheat mite. The symptoms were areas of the field having a silver tint. Some areas had died or lost several tillers and these areas got bigger as the season progressed and dry conditions worsened.

Field affected by winter grain mite south of Enid. Note the silver tint of the wheat on the left side of the terrace.

Field affected by winter grain mite south of Enid. Note the silver tint of the wheat on the left side of the terrace.

 

I ended my tour at Marshall, Oklahoma where I did not find any insects, but did find some thirsty wheat. All of the insect issues I encountered today can be corrected with scouting and insecticides. Wheat winterkill was present, but rarely affected entire fields and was not that widespread. The primary concern for all of Oklahoma remains lack of moisture. There are some fields in north central and northwestern Oklahoma with good yield potential; however, the best areas are starting to turn blue due to lack of moisture. Another couple of weeks of warm temperatures and wind without rain will turn blue wheat to brown. We need moisture.

Brown wheat mite showing up in winter wheat

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 what mite can severely damage wheat that is already stressed due to drought or other adverse environmental conditions.

Brown what mite can severely damage wheat that is already stressed due to drought or other adverse environmental conditions.

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

A closeup of a brown wheat mite. Photo courtesy Franklin Peairs, CSU.

A closeup of a brown wheat mite. Photo courtesy Franklin Peairs, CSU.

Brown wheat mites are about the size of a period at the end of a sentence and can be difficult to see with the naked eye.

Brown wheat mites are about the size of a period at the end of a sentence and can be difficult to see with the naked eye.

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.

Brown wheat mite eggs in soil.

Brown wheat mite eggs in soil.

 

 

Winter grain mites in SW OK

Over the past week, I have received a few reports of winter grain mite activity in southwest Oklahoma. Winter grain mites are small (about 1 mm long) with black bodies and orange-red legs. Winter grain mites complete two generations per year and the adults can live for up to 40 days. The generation we are dealing with now resulted from oversummering eggs laid last spring. The second generation peaks in March/April and results from eggs laid in January/February.

Scouting
Winter grain mites are light sensitive and prefer calm air to windy conditions; therefore, scouting early in the morning, late in the evening, or on cloudy days generally works best. Be sure to look under residue in no-till fields and under clumps of soil in conventional-till fields.

Image

Winter grain mites on wheat near Blair, Oklahoma.

Injury
Winter grain mites feed by piercing plant cells in the leaf, which results in “stippling”.  As injury continues, the leaves take on a characteristic grayish or silverish cast.  Winter grain mites are more likely to cause injury in wheat if it is already stressed due to lack of moisture or nutrients. Also be advised that freeze injury can easily be confused for winter grain mite injury.

When to spray
There are no established thresholds for winter grain mite. Healthy, well-fertilized wheat plants can generally outgrow injury, so it takes large numbers to justify control. If there is injury present AND large numbers of mites (~10 per plant) present in grain only wheat this time of year, you might consider control. If the wheat is to be grazed, I would simply monitor the situation in most cases and only spray if injury became severe.

What to spray
There are not a lot of pesticides with winter grain mite listed on the label, and most products have grazing restrictions. Malathion and methyl parathion have been shown to provide effective control in the past. Consult OSU Current Report 7194 Management of insect and mite pests in small grains for a more complete listing of available pesticides.