About Me

Amanda De Oliveira Silva

Amanda De Oliveira Silva

I have served as an Assistant Professor and Small Grains Extension Specialist at Oklahoma State University since August 2019. I believe that close interaction with producers is vital to understand their production strategies and to establish realistic research goals. My program focuses on developing science-based information to improve the agronomic and economic viability of small grains production in Oklahoma and in the Southern Great Plains.

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Assessing potential freeze damage on wheat

Amanda de Oliveira Silva, Small Grains Extension Specialist

Temperatures dropped below freezing in the past hours in northwestern Oklahoma and Panhandle (Figures 1 and 2), and freezing temperatures are expected across most of the state tomorrow morning (April 21) (Figure 3). There is a potential for freeze injury to Oklahoma wheat. The extent of that will depend on several factors, including the growth stage of the plants, how low the temperature will get, and how long it stays at those cold temperatures.

Figure 1. Minimum air temperature (in Fahrenheit) over the past 24 hours at each Mesonet station. Figure courtesy Oklahoma Mesonet.
Figure 2. Number of hours spent at or below freezing (32°F) over the past 48 hours at Mesonet station. Figure courtesy Oklahoma Mesonet.
Figure 3. Freezing temperatures are predicted for most of Oklahoma on Wednesday morning, April 21, 2021. Figure courtesy Oklahoma Mesonet, Weather Forecast Office.

What are the temperatures that can damage the wheat plants?

This will depend on the growth stage of the plants. Anecdotal evidence suggests varietal differences in resistance to spring freeze injury, but this is likely due to differences in plant growth stages when the freeze event occurred. Earlier maturing varieties are more likely to be injured from these recent freeze events than later maturing varieties because they are likely more advanced. The susceptibility of wheat plants to freeze injury steadily increases as we progress through the spring from jointing to heading and flowering. Figure 4 below is a general guide to the minimum temperature threshold and its impact on yield. Keep in mind these temperature thresholds are not exact but provide a decent rule of thumb. Temperatures closer to the soil surface might be higher than those reported by weather stations one meter above the soil surface, especially if moisture is present. It is difficult to have exact numbers because each freeze event is unique. While a field at the jointing stage could spend two hours at 24 F, it is possible that the same amount of injury could occur at a 28 F temperature that was sustained for a more extended period.

Figure 4. Temperatures that can cause injury to winter wheat at different growth stages. Source: Kansas State University publication C646: Spring Freeze Injury to Kansas Wheat.

How long should I wait to assess the injury?

Another important thing to keep in mind is that we need to be patient before assessing freeze injury. The extent of a significant freeze event may not be apparent 1 or 2 days after. If warm temperatures return quickly, you should wait about 5-7 days before determining the injury. Suppose temperatures remain cool after the freeze event. In that case, it may take 10-14 days before the extent of the injury can be fully assessed.

What are some freeze injury symptoms to look for?

A typical freeze injury symptom is leaf tips turning yellow and necrotic (Figure 5). This is very often just cosmetic and will not hurt yield in the end. More severe damage can result in the entire leaf turning yellow to white, and the plants become flaccid (Figure 6). You may even notice a “silage” smell after several days.

Figure 5. Leaf tips which have turned necrotic due to freezing temperatures. Photo taken in March 2017 courtesy of Josh Bushong, OSU Northwest Area Extension Agronomist.
Figure 6. More severe freeze damage causing the leaves to turn yellow-white with plants losing their overall turgidity. Source: Kansas State University publication C646: Spring Freeze Injury to Kansas Wheat.

The most important plant part to check is the developing head (i.e., growing point)

This will be important for areas of the state with fields with plants at flag leaf emergence stage. Sometimes we can see what look like healthy plants overall, but the developing head has been damaged or killed. To get a look at the developing head, you can slice the stem open lengthways. A healthy growing point will have a crisp, whitish-green appearance and be turgid (Figure 7). Often, you can lightly flick the head, and if it bounces back and does not break, it is still healthy. If it is mushy, limp, and breaks or parts of it break off when you lightly flick it, it has been compromised. It may also have a brown color (Figure 8, right). Another indication that the growing point has been compromised is that the next emerging leaf is necrotic, and the lower stems are discolored, with lesions and enlarged nodes.

Figure 7. Close up of a healthy wheat head (growing point) above the second node with whitish-green color and turgid.
Figure 8. Plants that appear healthy could have damaged heads. The photo on the left shows a healthy head, and the photo on the right shows a freeze-damaged head.

Freezing at the boot stage may cause the head to be trapped by the sheaths of the flag leaf resulting in issues with head emergence (Figure 9). The whitish tips of the awns indicate that it was exposed to freezing temperatures and that the flower parts could have been compromised. Freeze during the flowering stage may result in flower sterility via the death of the anthers (male organ) and consequently poor kernel set and grain yield losses (Figure 10).

Also, the percent of damaged heads may not translate into percent yield loss. For example, there is still an opportunity for wheat to produce additional tillers and/or retain secondary tillers at the jointing stage. Whether or not these tillers can compensate for larger tillers that were lost due to freeze will depend on the subsequent weather. If conditions are favorable, there is a chance for late-emerging tillers to have a shot at producing grain. If the wheat is more advanced (which is the case for most Oklahoma wheat), it will be more challenging to make this type of recovery.

Figure 9. Freeze at the boot stage may cause the head to be trapped in the boot and not being able to emerge properly.
Figure 10. Freeze during the flowering stage may result in sterility via death of the anthers (male organ) and consequently poor kernel set and grain yield losses.

A few points to consider:

Every freeze event is unique and freeze injury needs to be checked on a field by field basis – 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.

The amount of injury observed will depend on – the growth stage of the plants, how low the temperature got, and how long it stayed at those cold temperatures. Other factors such as elevation, residue cover, and moisture can influence the observed temperature within the canopy as well. Because of the number of influential factors, it is important to check each field. It is possible to have variability in injury symptoms among fields and even within fields.

It will take a few days to see how bad things are – Symptoms may start to appear mid-next week and will likely be identifiable by the end of the following 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.

Additional Resources

Contact your local Extension office.

C646: Spring Freeze Injury to Kansas Wheat.

Aphids: Bird Cherry-Oat Aphids and an Invasion by the “English” (Grain Aphid that is) and Armyworms: Decisions……

This article was written by Dr. Tom A. Royer, Extension Entomologist

The good news is that Oklahoma has a healthy, good-looking wheat crop. Now, it must be protected from any swarming hordes of insect pests that want to eat it!  Dr. Kris Giles has been surveying wheat fields in SW and Central Oklahoma. I have been collecting data from our wheat plots in Chickasha, Stillwater, and Lahoma. Dr. Giles found increasing bird cherry oat aphid (BCOA) numbers, and its main natural enemy (Lysiphlebus testaceipes) may have been set back by the record cold temperatures that we experienced in February. I have seen mixed populations of English grain aphids and bird cherry oat aphis in our wheat plots.

Sometimes, aphid infestations are overlooked. Bird cherry-oat aphid infestations do not produce visible damage until they become very numerous and English grain aphids often bury themselves in between the seeds where they blend in. So check your field for bird cherry oat aphid, English grain aphids. 
Bird cherry oat aphids are olive green to dark green with two rusty patches that surround their “tailpipes” (cornicles).  They feed on plant juices with their piercing sucking mouthparts. They can reproduce rapidly, so fields should be scouted to make a determination as to the need to control them.                                                                                   

Lady beetles and most importantly, the Lysiphlebus wasp that parasitizes them, often control bird cherry oat aphids.  Parasitized aphids swell up and form “mummies” that can easily be seen (below).  If an aphid infestation has 10-15% mummies, the rest are probably also parasitized.     

BCOA and aphid mummy

English grain aphid is larger than either greenbug or bird cherry oat aphid (0.125 inches), green with long black cornicles and legs that have alternate bands of green and black. Their appearance is sometimes characterized as “spidery”. Suggested thresholds are 5 per stem at flag leaf, and 10 per stem at head emergence through milk stage.

English Grain Aphids in a wheat head

My suggestion is to scout the field beforehand to determine if there are GROWING numbers of bird cherry oat aphids that could be or are of concern.  Count bird cherry oat aphids on each of 25 randomly selected tillers across a zigzag transect of the field and note mummy activity. If 10 to 20% of bird-cherry oat aphids are mummies, and there are numerous lady beetle larvae in the wheat, consider control.  If wheat heads have emerged, look for English grain aphids imbedded in the head.

Unpublished research provided by Dr. Kris Giles (OSU) and Dr. Norm Elliott (USDA-ARS) combined with studies on spring wheat from the Dakotas and Minnesota indicate that 20-40 BCOA per tiller causes 5-9% yield loss before wheat reaches the boot stage.  My suggestions: if BCOA numbers average 10-20 per tiller, figure on a 5% loss, if 20-40 per tiller, figure a 7% loss, and if BCOA aphids are more than 40 per tiller, figure a 9% loss.

Estimate APHIDS PER TILLER_______ /tiller =       Total # aphids ______/25 tillers

Estimate CROP VALUE $_______/acre =                 Expected yield ______bushels/acre X $ _____/bushel

Calculate CONTROL COSTS $______/acre =           Insecticide $______/acre + Application $____/Acre 

PREVENTABLE LOSS $_____/acre = Crop value $________ X______loss from aphids/tiller .   

If PREVENTABLE LOSS IS GREATER THAN CONTROL COSTS                             TREAT

IF PREVENTABLE LOSS IS LESS THAN CONTROL COSTS                                      DON’T TREAT

Here is a Table of Preventable Loss estimates for bird cherry-oat aphids for expected yields of 30 to 50 bushels per acre, expected wheat prices of $3.00, $3.50, and $4.00 per bushel, and bird cherry-oat aphid numbers of 10-20, 20 to 40, and over 40 per tiller.

This cool, rainy spring weather, while providing excellent growing conditions for wheat, is also foodstuff for “producing” armyworms. Armyworm infestations typically occur in late April through the first two weeks of May. They feed on leaves and awns, (below left) and occasionally clip the head from developing plants. The head clipping (below right) I have noticed over the years is mostly restricted to secondary tillers with very small, green heads that contribute very little to yield.

Since armyworm infestations tend to occur more frequently around waterways, areas of lush growth, or areas with lodged plants, check them first to determine the size of the infestation. Early signs of an infestation include chewed leaves with ragged margins.  You may find “frass” i.e. the excrement from armyworm caterpillars, around the base of wheat stems and clipped heads.  Also, look for evidence of armyworms parasitized by the wasp Glyptapanteles militaris. This parasitoid attacks armyworms as well as several other caterpillars. When the larva emerges, it produces a cottony cocoon (below right) about the size of a Q-tip. Scout for armyworms at five or more locations looking for “curled up worms” (below left)

Armyworm caterpillars tend to feed at night, so another good strategy is to bring a flashlight, shine it on the emerged wheat heads after dusk and count armyworms that are feeding on the heads and plant stems. 

The suggested treatment threshold for armyworms is 4-5 caterpillars per linear foot of row (bottom left). Generally, no control is needed if wheat is past the soft dough stage unless there is visible head clipping, and caterpillars are present and feeding.

If a producer is considering a fungicide application, this might be an opportune time to evaluate your field for bird cherry oat aphid, English grain aphid and/or armyworms. If NEEDED, combine an insecticide with a needed fungicide application to control multiple pests.  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 Oklahoma 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 – 14 April 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

      Last week (08-April) in southwestern OK, Gary Strickland (Jackson County Extn Educator) reported seeing only very little stripe rust, but that tan spot was still present in the lower canopy.  Southwestern OK has been hot and dry, so conditions in that part of Oklahoma have not been at all favorable for foliar disease development.  Also last week, Bryan Vincent (Crop Consultant; north-central OK) reported seeing mostly tan spot and powdery mildew across northern OK, with little to no rust, but some barley yellow dwarf starting to appear as well as aphids.  Greg Highfill (Woods County Extn Educator) also reported heavy tan spot in a no-till, wheat- after-wheat field.

      More recently, although still scattered and light, both leaf and stripe rust (more so stripe) appears to be increasing across Oklahoma.  Lanie Hale (Manager, Wheeler Brothers) sent out the following report.  “Yesterday, Will Bedwell and I scouted 22 wheat fields in southern Major, northeastern Dewey, and northwestern Blaine Counties.  The wheat variety was unknown to us in most of the fields.  In seven of the fields, we found leaf and/or stripe rust in isolated areas, certainly not widespread across the fields.  We found powdery mildew in a few fields, but only where the canopy was heavy and dense.  Septoria and/or Tan Spot was noted on lower leaves in most fields.  Many of the fields had infestations of Bird Cherry Oat Aphids ranging from light to moderately heavy.  We saw several Lady Beetles and larvae in fields; I only saw one mummified aphid indicating not many parasitic wasps are present.  One of the fields had been sprayed over the weekend.  The flag leaf is emerging in most fields we scouted.  We did not scout any field with 100% emerged flag leaves.”

      Yesterday around Stillwater, I saw wheat that ranged from flag leaves emerging to wheat headed, although by far and away most of the wheat was at the boot/pre-boot stage (GS 9 or so).  By far, the most prevalent disease I observed was powdery mildew (Figure 1).  Stripe rust also was present, but at a low incidence.  I also noted quite a few spots or patches of barley yellow dwarf in various trials, but in contrast to other reports, I saw very few aphids.

      Given these reports and observations, it is advisable for producers to start watching their fields closely and prepare for applying a fungicide, especially if growing a variety susceptible to either rust and/or the other foliar diseases.  For more information on fungicides and their use, see OSU CR-7668, which can be found at:  https://extension.okstate.edu/fact-sheets/foliar-fungicides-and-wheat-production-in-oklahoma-march-2016.html.

Figure 1. Wheat leaves observed near Stillwater, OK on 4-13-2021 with powdery mildew and stripe rust (top photo) and with stripe rust (bottom photo).

Perhaps the most striking observation is that wheat streak mosaic (Figure 2) is starting to be reported across both Oklahoma and Texas as a couple of samples have tested positive for Wheat streak mosaic virus in the last week.  For more information on this and other mite-transmitted viruses, please see OSU EPP 7328 that can be accessed at:  https://extension.okstate.edu/fact-sheets/wheat-streak-mosaic-high-plains-disease-and-triticum-mosaic-three-virus-diseases-of-wheat-in-oklahoma.html

Figure 2. Wheat streak mosaic virus has been observed in northwestern Oklahoma and western Texas.

Wheat Disease Update – 30 March 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

Reports of foliar diseases, especially stripe and leaf rust, are starting to increase in southern Texas and around Stillwater. First, here is an update sent out on 24-March by Dr. Amir Ibrahim (Regents Professor & Small Grains Breeder/Geneticist; Texas A&M AgriLife Research). Dr. Ibrahim is finding both stripe rust and leaf rust increasing across southern Texas.

“I visited our small grains trials at McGregor (18 miles southwest of Waco, TX) on March 18, 2021.  Stripe rust (caused by Pstriiformis Westend. f. sp. tritici Eriks.) continues to be active (Figure 1; photo on the left).  Leaf rust (caused by Puccinia triticina Erikss.) is beginning to move to the middle canopy (Figure 1 – photo on the right).”

Figure 1. Stripe and leaf rust observed by Dr. Amir Ibrahim in southern Texas in mid-March.

“We visited the naturally inoculated Rust Evaluation Nursery at Castroville, TX today. The nursery is about 196 miles from Texas A&M University’s main campus in College Station, where we are based.  We also visited our trials at Uvalde, TX today. Stripe rust is not very active at both Castroville and Uvalde. Leaf rust is now picking up, especially at the Rust Evaluation Nursery at Castroville. Stripe rust is very actively spreading at the Agronomy Farm near our main campus in College Station as of our last visit on March 23, 2021. Stripe rust is also active in our trials in Greenville (50 miles northeast of Dallas). No reports yet of leaf or stripe rusts in the Texas High Plains. Leaf rust is also developing in our trials at Wharton (60 miles southwest of Houston).”

      In Oklahoma, both stripe and leaf rust (Figure 2) have been observed in trials around Stillwater and near Perkins (about 15 miles south of Stillwater).  Also recall in my update of 15-March, I indicated seeing powdery mildew, Septoria/Stagonospora (Figure 3) on lower leaves in many trials. These diseases also are present, and with the relatively cool and windy weather in the forecast, I expect the incidence and severity of all these diseases to increase.

Figure 2. Wheat showing pustules of the fungi that cause stripe rust (top two photos) and leaf rust (bottom photo). [Observation & photo credit for middle and bottom photos; George Wallace, Oklahoma State University]
Figure 3. Powdery mildew (upper photo), Septoria/Stagonospora (middle photo), and tan spot (bottom photo credit; Gary Strickland, Jackson County Educator, observed in mid-March).

First Hollow Stem Update – 3/17/2021

Amanda de Oliveira Silva, Small Grains Extension Specialist

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8”, or the diameter of a dime) of stem below the developing grain head (see full explanation). The latest FHS results from OSU forage trials in Chickasha (Table 1) and Stillwater (Table 2) are listed below. For an additional resource, see the Mesonet First Hollow Stem Advisor.

We use an accelerated growth system to report the earliest onset of FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.

Table 1. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/29/20 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.

Table 2. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/21/20 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.

  • Additional resources available:

Wheat Disease Update – 15 March 2021

This article was written by Dr. Bob Hunger, Extension Wheat Pathologist

Although relatively quiet, some wheat diseases have started to appear across Oklahoma over the last week.  For example, around Stillwater I am starting to observe patches of wheat showing symptoms of the wheat soil-borne mosaic (SB)/wheat spindle streak mosaic (SS) complex.  So far, I have observed these symptoms only in susceptible varieties in Dr. de Silva’s variety demo and in my SB-SS nursery.  These virus diseases are not a problem in Oklahoma or the central plains due to effective and durable genetic resistance in nearly all wheat varieties planted in Oklahoma for the last four decades.  However, planting a variety susceptible to either or both of these virus diseases could be an invitation to having an occurrence of these diseases.  It seems as though only far northwest Oklahoma and the panhandle have environments that limit the occurrence of these two virus diseases.

      In trials around Stillwater towards the end of last week, I found sparse powdery mildew and fairly abundant Septoria/Stagonospora leaf spot on leaves of ‘Ruby Lee’ (Figure 2).  This was in Dr. Brett Carver’s dual purpose observation nursery, which is an early planted nursery.  In no trials did I find either leaf or stripe rust, although Dr. Amanda de Oliveira Silva had found both leaf rust and powdery mildew in her demonstration trial in later January before the hard freeze and snow occurred in early to mid-February.

Figure 1.  Wheat showing reaction to the wheat soil-borne mosaic (WSBM)/wheat spindle streak mosaic (WSSM) complex. Left photo:  Wheat breeder line susceptible (left) and resistant (right) to WSBM. Center photo: Symptoms typical of WSBM.  Right photo:  Symptoms typical of WSSM.

Figure 2. Upper photo are symptoms on a wheat leaf indicative of Septoria or Stagonospora leaf blotch found near Stillwater on 13-Mar-2021.  The lower photo is of a wheat leaf with symptoms indicative of tan spot observed in southwest Oklahoma by Gary Strickland, (County Educator; Jackson County), 3-11-2021.

First Hollow Stem Update – 3/12/2021

Amanda de Oliveira Silva, Small Grains Extension Specialist

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8”, or the diameter of a dime) of stem below the developing grain head (see full explanation). The latest FHS results from OSU forage trials in Chickasha (Table 1) and Stillwater (Table 2) are listed below. For an additional resource, see the Mesonet First Hollow Stem Advisor.

We use an accelerated growth system to report the earliest onset of FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.

Table 1. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/29/20 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.

Table 2. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/21/20 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.

Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.

  • Additional resources available:

First hollow stem update – 3/9/2021

Amanda de Oliveira Silva, Small Grains Extension Specialist

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8” or the diameter of dime) of stem below the developing grain head (full explanation). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

The latest FHS results from our forage trials in Chickasha (Table 1) and Stillwater (Table 2) are listed below. Several wheat varieties in Stillwater and a few in Chickasha have reached or passed the 1.5 cm threshold.

The Mesonet First Hollow Stem Advisor and the updates we provide give an indication of the FHS stem conditions in a particular area. However, because of the number of factors that can influence when FHS occurs, it is extremely important to check for FHS on a field-by-field basis

Table 1. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/29/2020. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements from non-grazed plots. Varieties that have reached FHS are highlighted in red.

Table 2. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/21/2020. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements from non-grazed plots. Varieties that have reached FHS are highlighted in red.

Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.

  • Additional resources available:

Potential risk of leaf injury from topdressing N this week (too hot and windy!)

Amanda de Oliveira Silva, Small Grains Extension Specialist and Brian Arnall, Precision Nutrient Management Specialist

The forecast indicates hot (~75 F) and windy (~20-30 mph) conditions this week in Oklahoma (Mesonet). If you plan to topdress N to wheat, be aware that there is a high risk of causing leaf burn due to the predicted weather.

When comparing application methods, a stream bar is better than a flat fan for topdressing N in general. A flat fan would burn and even kill the wheat if used this week. However, using a stream bar under 20-30 mph wind is also problematic, as the wind will spread out the stream over the wheat, making it splash over larger areas result in more foliar burn.

Streamer nozzles provide uniform application of UAN in a wide variety of environmental conditions.

What rate can I apply without causing leaf burn from N this week?

There is a high risk of causing leaf burn by applying any rate (20 to 200lbs/ac) of N in the next 2-3 days (March 8-11, 2021). If using streamer nozzles the total amount of leaf damage could be small resulting in no yield loss. In this case, applying N this week may result in streaked fields later, but the wheat should grow out of it if conditions are appropriate. However, as you start to increase coverage (i.e. the amount of leaf burn) there is a threshold at which yield is lost. In cases with flat fan the high N rate will potentially kill the majority above ground biomass and negatively impact yield.

Other options to reduce the potential risk of injury. Wait to topdress N when the weather cools down (if you believe you will be able to get into the field before jointing) or split the N rate between now and sometime before jointing. If you want to apply and are very worried about tissue damage, one option is to dilute the UAN with water. Usually a 50/50 (UAN/H2O) ratio does a good job of reduction impact of the salt in UAN. 

If you have questions, please feel free to reach out to us!

Brain Arnall at b.arnall@okstate.edu

Amanda de Oliveira Silva at silvaa@okstate.edu

First Hollow Stem Update – 3/5/2021

Amanda de Oliveira Silva, Small Grains Extension Specialist

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8” or the diameter of dime) of stem below the developing grain head (full explanation). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

The latest FHS results from our forage trials in Chickasha (Table 1) and Stillwater (Table 2) are listed below. A few more wheat varieties in Stillwater have reached or passed the 1.5 cm threshold.

The Mesonet First Hollow Stem Advisor and the updates we provide give an indication of the FHS stem conditions in a particular area. However, because of the number of factors that can influence when FHS occurs, it is extremely important to check for FHS on a field-by-field basis

Table 1. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/29/2020. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements from non-grazed plots. Varieties that have reached FHS are highlighted in red.

Table 2. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/21/2020. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements from non-grazed plots. Varieties that have reached FHS are highlighted in red.

Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.

  • Additional resources available: