Home » Uncategorized (Page 2)

Category Archives: Uncategorized

Wheat Disease Update – May 31, 2018

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

 

Wednesday through Friday (May 23-25) of last week, I was in western Oklahoma (Clinton area) and at field days in the panhandle at Goodwell and Hooker (Texas County), Keyes (Cimarron County) and Balko (Beaver County). The only disease observed of significance was indicated by white heads in fields. Often this was the result of Fusarium (dryland) root rot as reported in the last update (May 17, 2018). In fields showing this root rot, the white heads and white tillers were scattered across the field with an incidence ranging from low to moderate (Figure 1). Other fields in the panhandle exhibited large areas of not just white heads and tillers, but also white secondary tillers that had not headed. In these fields, some root rot was found, but Dr. David Marburger (OSU Small Grains Extension Specialist) and I believe that many of the white tillers/secondary tillers were the result of drought, freeze, or a combination of both. Often such tillers showed clean lower stems with no indication of root rot. We believe these secondary tillers were completely white without heading because they were sloughed off as a result of the stress from drought, freeze, or a combination of both. We suspect that more of these whiteheads will show in the coming week in northwestern OK and the panhandle, but the wheat crop is quickly turning and the whiteheads may not be as evident.

 

This likely is the last update I will be sending out this season as harvest in the southern half of Oklahoma has started with the crop quickly maturing in the northern half.

 

Figure 1.  White heads of wheat due to root rot. Typically the white heads are scattered in a field and can range from a low to high incidence. Notice in the middle photo just a few tillers of an individual plant are affected. [Credit for middle photo to Brad Babek, County Educator, Washita County]

fig1a.5.31    fig3a5.17fig3b5.17

2018 Oklahoma Wheat Harvest Begins in South and Central Oklahoma over the Memorial Day Weekend

Report by the Oklahoma Wheat Commission

 

Harvest for the 2018 season has begun in Oklahoma with combines rolling in the southwestern part of the state over the Memorial Day weekend. While much of the crop has been abandoned due to severe drought conditions in western regions of the state, some elevator locations in the south-central corridor have been reporting decent yields and favorable qualities on the wheat that is being harvested (the south-central corridor received rains in early spring that were timely). We have also had reports of wheat harvest beginning in central regions of the state around the Okarche, Kingfisher, Loyal, and Omega areas. While early reports are showing favorable proteins and test weights on the wheat being harvested, many elevator locations in the western part of the state predict this will be one of the fastest wheat harvests they have ever seen. This is based on all the acres abandoned due to the severe drought conditions that have plagued this part of the state since October. It is important to note we have also seen a decline in wheat acres due to increased cotton, sesame, and soybean plantings (one elevator location mentioned they hope to take in 10% of what they would in a normal year due to the drought and increased plantings of other crops). Producers are also hopeful the predicted storms tonight and Wednesday will pass thru without causing any damage.

 

Grandfield- Wheat harvest has just started in this region with most of the custom cutters now in town. On the wheat that was harvested over the weekend, test weights were running at 62 to 63 lbs./bu. Early protein reports were showing ranges from 11.5 to 12%. Yields from some of the producers have been reported better than expected with some reports of 40 to 50 bushel averages.

 

Frederick- Early reports from this region before the weekend had reports of one load of wheat coming in at 12.7% moisture, 62 lbs./bu., and protein at 12%. No yields from the weekend have been reported, although it is predicted that harvest will move rather quickly with little wheat harvested based on abandonment in the western half.

 

Snyder- This region took in over 85,000 bushels of grain over the weekend, and harvest is just starting to move at full speed. Reports so far on test weights have been exceptional with most of the wheat weighing 60 lbs./bu. or better. There have been a couple loads where weights were running 58 lbs./bu. The quality of the wheat has not had much dockage. Yields in this area have been reported all over the board ranging from the low 20’s to mid 40’s. No proteins have been reported.

 

Altus/Lone Wolf- Test weights on the wheat in this region have been averaging 60 to 62 lbs./bu. Proteins on the wheat to this point have been ranging from 10.5 to 12.5%, with more of the wheat coming in at that 11.5 to 12% protein range. No yields have been reported, although it is predicted that harvest will move extremely fast due to decline in planted acres of wheat and abandonment from the drought.

 

Sentinel- As of Tuesday morning, one sample was tested, but the moisture was too high.  Producers are hopeful they will be able to start harvest within the next day or two in this region.

 

Clinton- As of Tuesday morning, no wheat had been taken in this region. 

 

Hinton-  As of Tuesday morning, no wheat had been taken in this region.

 

Union City- One sample was taken at 14% moisture as of Tuesday morning, so producers are  hopeful that within in the next day harvest will get rolling in this region.

 

Banner- As of Tuesday morning, no wheat had been taken in this region.

 

Okarche- Wheat harvest has begun in this region on Memorial Day, with a few loads received. Test weights on the earlier harvested wheat was lower with ranges from the mid 50’s to 58 lbs./bu. Protein averages on earlier reports are coming in much better than the past couple years with ranges of 12 to 14% being reported. No yields were reported at this time.

 

Kingfisher- Harvest began over the weekend in this region with test weights averaging anywhere from 60 to 62lbs./bu. Proteins have been reported from as low as 10.9% to as high as 14%. Most of the proteins are coming in at 11.5% or higher on this earlier harvested wheat. Some yields have been reported to be making in the mid 40’s on what has been received so far. Keep in mind, much of the wheat has been abandoned west of the Kingfisher trade territory due to the persistent drought conditions that have existed since October.

 

Omega- Harvest has begun in this region on some of the earlier planted and heavily grazed wheat. Yields on the earlier wheat were reported to be making in the low 20’s.  Test weights were being reported at 56 to 58 lbs./bu.  Protein on one load of wheat was reported at 17.4%, and that variety was Doublestop CL+.  Producers are hopeful they will get into wheat that have better test weights and yields in this area towards the end of the week.

Wheat Disease Update – May 17, 2018

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

Although not as obvious as in previous weeks, powdery mildew is still hanging on in Oklahoma, and has even moved up onto the heads in some fields. One such field is my foliar fungicide trial here at Stillwater. Examining this trial yesterday revealed many of the lower heads were lightly to moderately infected with powdery mildew (Figure 1). This is one of the few times I have seen powdery mildew move onto wheat heads in Oklahoma. It is important to note that these infected heads are the ones produced on the lower tillers beneath the main, taller tillers. I did not find any powdery mildew on any of the higher heads. This appears to me to be a light to moderate infection severity, but I have not had a lot of experience with powdery mildew on wheat heads, so this is just my estimation. Exactly how much of an impact this powdery mildew will have on yield and test weight may be hard to determine because the level of powdery mildew on these heads seemed to be fairly constant across all treatments.

 

Figure 1.  Powdery mildew on wheat heads in a foliar fungicide trial near Stillwater, OK. Note lower heads in background also show powdery mildew, but there was no powdery mildew on higher heads.

fig1a5.17  fig1b5.17

 

Yesterday, I also observed leaf rust on scattered leaves in the foliar fungicide trial at Stillwater (mostly in the not-sprayed control plots). Typically this was just a couple pustules scattered on a leaf, but there were a few leaves as shown in Figure 2. If you enlarge Figure 2, you can see what looks like the remnant of stripe rust stripes with a few telia (small black dots) associated with the stripes. There also appears to be a pustule or two of powdery mildew. As indicated, leaves infected to this level were not common, but this does indicate that leaf rust is starting to appear and may increase a bit over the next 7-10 days. However, this is a late infection as this trial is at late milk to early soft dough. Hence, the leaf rust will have only a minimal impact on yield even if it does increase significantly.

 

Figure 2.  Leaf rust on a flag leaf at Stillwater, OK on May 16, 2018. Note that some inactive stripe rust also is visible in the center of the leaf (you will have to enlarge the photo to see this) but it appears to be “shutting down” as indicated by the small, black telia. A lesion or two of powdery mildew also is present.

fig25.17

 

Finally, Brad Babek (County Educator, Washita County in southwestern Oklahoma) reported increasing areas of white heads in wheat fields (Figure 3). In cases where I have observed such heads this year, it has been due to dryland (Fusarium) root rot. Typically the roots will be rotted and often the lowest part of the stem is discolored (dark) and often there is a pinkish-purple color associated with the lower tiller and roots. Splitting such a tiller often reveals a stem filled with white or pinkish-white fungal growth (Figure 3).

 

Figure 3.  Whiteheads on wheat tillers in Washita County (western Oklahoma). Photo and report credit to Brad Babek, County Educator, Washita County.

fig3a5.17fig3b5.17

Wheat Disease Update – May 5, 2018

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

This past week I was at field days in southwestern Oklahoma (Apache and Altus), and northeastern Oklahoma (Afton). I did not see a single leaf or stripe rust pustule at any location. Wheat in southwestern OK ranged from at flowering to kernel formation, and typically was short (less than knee high). There were a few exceptions to this, namely a couple fields near Apache that had been planted on summer fallow ground. Wheat in these two fields looked good with some powdery mildew on the low to mid-canopy. There also was evidence of root rot (white heads) that was caused by Fusarium (Figure 1). This root rot was at a low incidence. By contrast, wheat in northeastern OK was at flowering and typically was over knee-high, thick, and with high yield potential. On many varieties, powdery mildew was heavy in the low and mid-canopy, and in a few instances also was present on the flag leaf (Figure 2). Besides powdery mildew, Septoria leaf blotch was heavy throughout the lower leaves of most varieties. In northeastern OK it appears that if a fungicide is going to be sprayed, that needs to be applied as soon as possible.

 

Based on my observations this past week and the recent report from Dr. Clark Neeley (see below), it appears that rust pressure is low across Texas and Oklahoma. Based on Dr. Neeley’s report, it appears that leaf rust has started to appear, but is still somewhat limited. Hence, although there still is time for the rusts (especially leaf rust) to impact Oklahoma, it does not appear there will be an early season (during heading) high rust pressure as in most years. I still would be watchful and if you have a variety known to be susceptible to leaf rust with good yield potential (>about 30 bu/acre) I recommend considering a fungicide application. Be sure however, that your wheat has not matured past the allowed time (as indicated on the label) for the fungicide you apply. Additional information related to foliar fungicides can be found on the fungicide label and in OSU Current Reports 7668, Foliar Fungicides and Wheat Production in Oklahoma, which is available at:

http://wheat.okstate.edu/wheat-management/diseasesinsects/CR-7668web2018.pdf.

 

Reports from other states:

Texas – 4-30-2018; Dr. Clark Neeley; Small Grains/Oilseed Extn Specialist; Texas A&M AgriLife Extension.  “I was attending field days across Central Texas last week and saw mostly leaf rust as I travelled around. Pressure was strong at Thrall, McGregor and Temple, TX, but wheat is pretty far along in all three locations. Mostly in the milk and soft dough stage. I was in a variety trial and producer’s field in Abbott, TX just north of Waco and leaf rust was nearly undetectable despite the field only receiving a Tilt fungicide application at topdress. Stripe rust was still active on ‘Patton’ border there, but teliospores were appearing and thus was shutting down. Did not find any stripe rust in any of the trial entries. I found no or negligible amounts of stripe rust on trial entries at all locations except McGregor. I did find low levels of stripe rust there on flag leaves of HRWW varieties ‘TAM 304’ and ‘WB 4303’ and SRWW variety ‘USG 3120’. Will be at field days later this week and the following week in the Rolling Plains and Northeast Texas and will try to post updates then for those regions.”

 

Figure 1.  Fusarium (dryland) root rot observed on a wheat tiller from a variety demo near Altus, OK. Note the reddish-purple color near the tiller base with fuzzy reddish-purple fungal growth also present inside the split stem (bottom photo).

fig1a5.5fig1b5.5fig1c5.5

 

Figure 2.  Powdery mildew on the flag leaf of a wheat plant in the variety trial near Afton, OK.

fig25.5

Join us May 11th for the 2018 Lahoma Wheat Field Day!

2018 Lahoma program

Wheat Disease Update – April 26, 2018

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

 

Although reports of powdery mildew continue to come in from around the state, perhaps the more important news is that other foliar diseases have started to become active. On April 24, Septoria tritici blotch (Figure 1) was prevalent on lower leaves throughout the variety trial near Walters, OK. Walters is located in southwestern Oklahoma about 20 miles south of Lawton and 10 miles north of the Texas border. Although interesting, Septoria tritici blotch is not the disease of concern as in this trial there also was active leaf rust on lower leaves (Figure 2) and stripe rust on the leaves just below the flag leaf. Dr. Brett Carver (OSU Professor/Wheat Breeder) and Branden Watson (OSU PaSS Graduate Student) also reported active stripe rust at various levels in trials located near Chickasha, OK in central Oklahoma (Figure 3). The photo from Dr. Carver (the right photo in Figure 3) shows much more severe stripe rust than was seen near Walters. These observations indicate that both stripe and leaf rust are increasing through southern and central Oklahoma. This activity will increase through the coming weeks as the forecast indicates continued moisture (rains and dew) coupled with moderate temperature. Wheat in southern Oklahoma was approaching or was actively flowering, so the option of using a fungicide to protect yield potential either is at hand or may be too late. Typically foliar fungicides should be applied for wheat rust control between flag leaf emergence and complete head emergence (Feekes’ growth stages 8 to 10.5). Some fungicides (e.g., Aproach, Headline, Nexicor, Priaxor, and Twinline) are so labeled. However, some fungicides (Tilt, Quilt Xcel, and Trivapro) are labeled for a later application (Feekes 10.5.4, which is the end of flowering with the kernel watery ripe). Many others no longer have a growth stage deadline, but rather are limited by a pre-harvest restriction. That is, there must be a certain number of days that elapse between application and harvest. For some fungicides (Caramba, Folicur, Proline 480, and Prosaro) this is 30 days. For Absolute Maxx, it is 35 days, and for Aproach Prima, it is 45 days. For some fungicides it is a combination of growth stage and days between application and harvest. For specific information, please consult the label for the fungicide. Most fungicides labeled for wheat rust control must be applied by the start of flowering (Feekes’ growth stage 10.5). The only fungicides I know of that have a label allowing for a later application are Tilt, Quilt Xcel, and Trivapro, which can be applied up to Feekes’ 10.5.4 (end of flowering with the kernel watery ripe). In addition to these application deadlines, there often are required pre-harvest intervals so you must allow for a specific number of days to elapse between application of the fungicide and harvest.  For specific information, please consult the label for the fungicide. Additional information related to foliar fungicides also can be found in OSU Current Reports 7668, Foliar Fungicides and Wheat Production in Oklahoma, which is available at: http://wheat.okstate.edu/wheat-management/diseasesinsects/CR-7668web2018.pdf.

 

Figure 1.  Septoria leaf blotch on lower wheat leaf in the variety trial near Walters, OK.

4.26fig1

 

Figure 2.  Leaf rust on lower wheat leaves near Walters, OK on April 24, 2018.

4.26fig2

 

Figure 3.  Stripe rust on a wheat leaf (not a flag leaf) near Chickasha, OK on April 24, 2018 (top photo credit to Mr. Branden Watson; bottom photo credit to Dr. Brett Carver).

4.26fig3a4.26fig3b

Wheat Disease Update – April 13, 2018

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

Powdery mildew (Figure 1) continued to be the primary wheat foliar disease this past week in Oklahoma. Around Stillwater, I have seen powdery mildew on the lower and mid-leaves with severities reaching 90% on the lower leaves. A preponderance of powdery mildew also was indicated by the scouting reports sent in from counties across the central tier of Oklahoma to Zack Meyer (Extension Educator; Kingfisher County) where mildew was reported in Washita and Kingfisher Counties at a light (<25%) severity on lower and mid-leaves. Across the northern tier of counties in Oklahoma, powdery mildew was reported to Josh Bushong (Area Extension Agronomy Specialist; northwest district) from Noble and Garfield Counties at light and heavy (>25%) severities on the lower and mid-leaves. Wheat in central Oklahoma was reported at growth stages 8-9 (flag leaf emerging to flag leaf fully emerged). In northern Oklahoma, wheat was extremely variable with growth stages from 2-8 (tillering to flag leaf emerging) being reported. Again, I want to thank all the educators that participated in this pilot program for reporting powdery mildew, leaf rust and stripe rust, and I would encourage more participation to facilitate the warning of these three foliar diseases of wheat.

Figure 1.  Severe powdery mildew on lower wheat leaves.

fig1.4.13

 

There were not any reports this last week regarding foliar diseases from Texas, and there still have not been any significant reports of stripe or leaf rust across Oklahoma. There was one report of stripe rust in south central Oklahoma from Anderson Farms located near Ardmore, OK. As you can see in Figure 2, the lower leaf shows a heavy infection of active stripe rust while the top leaf shows a heavily infected leaf that has transitioned to the dormant (telial) spore stage of stripe rust. This happens as temperature rises with both day and night temperature being important. Typically day temperature needs to consistently be above about 75-80 F and night temperature about about 65 F. This transition along with very limited reports of stripe rust in Texas and Oklahoma indicate that stripe rust should not be a major factor in wheat this year in Oklahoma. Leaf rust could still develop, but inoculum will need to increase, and to date, there has not been widespread weather (cool and moist) that favors either rust.

 

Figure 2.  Active wheat stripe rust (lower leaf) and stripe rust that has transitioned to the telial (dormant) stage on wheat in south-central Oklahoma.  (Photo credit: Anderson Farms near Ardmore, OK).

fig2.4.13

 

The only other observation this week has been “spots” of barley yellow dwarf as reported last week. However, after the recent freeze events, these barley yellow dwarf “spots” are more difficult to discern because there is widespread burning of leaf tips from the freeze, which has a masking effect.

Wheat Disease Update – 6 April 2018

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

 

Powdery mildew (Figure 1) is showing up on lower leaves in fields and trials around Stillwater, and I have also had reports of powdery mildew on lower leaves from Extension Educators around the state. I also have seen ‘hot spots’ indicative of barley yellow dwarf (Figure 2) around Stillwater, but did not find any aphids associated with these spots. From Texas, Dr. Clark Neely(Small Grains and Oilseed Extension Specialist; Texas A&M AgriLife Extension) relayed to me on April 4 that, “Overall, I think we have avoided the stripe rust and what little was around is shutting down now. Leaf rust is around, but seems lighter than normal for the moment.” Across Oklahoma, wheat leaf and stripe rust still are largely absent, although a few “stripes” of stripe rust were found by Zack Meyer here at Stillwater this morning at an Extension Educators in-service training. This lack of the rusts in Oklahoma is supported by the recently implemented scouting program involving Oklahoma Extension Educators. This program asks county educators to look for and report weekly the occurrence of stripe rust, leaf rust, and/or powdery mildew they observe in commercial fields, variety trials, or variety demonstrations located in their counties. This information is reported by county educators from counties across southern Oklahoma to Heath Sanders (Area Extension Agronomy Specialist; southwest district), from counties across mid-Oklahoma to Zack Meyer (Extension Educator; Kingfisher County) and from counties across northern Oklahoma to Josh Bushong (Area Extension Agronomy Specialist; northwest district). The incidence and severity of these three wheat foliar diseases can then be more accurately summarized and disseminated to facilitate decisions related to applying a fungicide to help manage these diseases on susceptible varieties. For the week ending on April 5, observations reported from across southern and mid-Oklahoma (Jackson, Dewey, Washita, Blaine, and Kingfisher Counties) indicated no leaf or stripe rust and only one report of powdery mildew on lower and mid-leaves in Washita County. It is still a bit early for reports to come in from across northern Oklahoma. Thanks are extended to all the educators that participated in this pilot program, and I would encourage more participation to facilitate this reporting program.

 

Figure 1.  Powdery mildew observed April 5 on lower leaves of wheat in trials around Stillwater, OK.

fig0

 

Figure 2.  Likely barley yellow dwarf (BYD) “hot spot” observed on wheat in early April (top photo). As time proceeds, these hot spots will develop stronger symptoms of BYD including leaf discoloration ranging from yellowing (middle photo) to purpling in some varieties (bottom photo).

fig1

fig2

fig3

2018 OSU Wheat Field Day Schedule Announced

We have 32 different stops lined up to talk about a lot of good wheat varieties available to producers. As the weather can force us to change plans at the last minute, please contact your local county Extension office with any questions on the date, time, and location. The schedule listed below is also available on the home page of the wheat.okstate.edu website or by clicking here.

 

A special thanks goes out to the area and county Extension personnel and grower cooperators on helping get these field days scheduled!

2018 OSU wheat field days

 

Impact of recent cold temperatures on Oklahoma wheat

Temperatures on Easter into Monday (Figure 1) and last night into this morning (Figure 2) dipped low enough throughout a large portion of the state to potentially cause some level of injury to the wheat crop. There were a number of areas that spent a significant amount of time with temperatures in the mid to lower 20s over the course of these two cold snaps. Areas in the northwest and into the Panhandle even got as cold as the mid to upper teens. On top of all that, we have cold temperatures forecasted again for later this week.

 

Figure 1. Minimum air temperatures (top graph) during Easter into Monday (April 1-2) and hours spent below freezing (32°F) over the past 48 hours during that same time frame (bottom graph).

April2minairtemp

April2cumulative.freeze.48hr

 

Figure 2. Minimum air temperatures (top graph) during last night into this morning (April 3-4) and hours spent below freezing (32°F) over the past 48 hours (bottom graph).

April4today.TAIR.min.grad

April4cumulative.freeze.48hr

 

Keep in mind that the temperature recorded by the nearest weather station or at your house may not quite reflect the actual temperature that the wheat canopy experienced, especially as you increase the distance from where the temperature was recorded and the field itself. Factors such as elevation and topography can influence the temperature, as well as things like large amounts of residue in a no-till situation, for example.

 

What are the temperatures that can damage the wheat plants?

This will depend on the growth stage of the plants. Anecdotal evidence suggests there are 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 the wheat plants to freeze injury does steadily increase as we progress throughout the spring from jointing to heading and flowering. Figure 3 listed below is a general guide to the minimum temperature threshold and its impact on yield. These numbers are not exact but provide a decent rule of thumb. It is difficult to have exact numbers because each freeze event is unique. While a field at the jointing growth could spend two hours at 24 F, it is possible that the same amount of injury could occur with at a 28 F temperature that was sustained for a longer period of time.

fig3

Figure 3. 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 injury?

Another important thing to keep in mind is that we need to be patient before going out an 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. If temperatures remain cool after the freeze event, it may take 10-14 days before the extent of the injury can be fully assessed. Since we still have cooler temperatures in the forecast, we will likely need to wait closer to the 10-14 days.

 

What are some freeze injury symptoms to look for?

A common freeze injury symptom is leaf tips turning yellow and necrotic (Figure 4). 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 5). You may even notice a “silage” smell after several days.

 

Figure 4. Leaf tips which have turned necrotic due to freezing temperatures. Photo taken in March 2017 courtesy of Josh Bushong, OSU northwest area Extension agronomist.

fig4

 

Figure 5. 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.

fig5

 

The most important plant part to check is the growing point. This will be important for areas of the state that have fields with plants which are at jointing or past jointing. Sometimes we can see what look like healthy plants overall, but the growing point has been damaged or killed. To get a look at the growing point, you can slice the stem open lengthways. A healthy growing point will have a crisp, whitish-green appearance and be turgid (Figure 6). 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 7). Another indication that the growing point has been compromised is the next emerging leaf is necrotic.

 

fig7

Figure 6. Close up of a healthy wheat head (growing point). Source: Brenda Kennedy and Dr. Carrie Knott, University of Kentucky

 

fig8

Figure 7. Plants that appear healthy could have damaged heads. Photo taken several years ago courtesy of Dr. Jeff Edwards.

 

fig9

Figure 8. A close up view of the damaged wheat head from Figure 7. Photo taken several years ago.

 

Also, the percent of damaged heads may not translate into percent yield loss. There is still opportunity for wheat at the jointing stage (GS 6) 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 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, it will be tougher to make this type of recovery.

 

Do drought conditions exacerbate freeze injury?

When it comes to this question, it is really a mixed bag of results. A lot of anecdotal evidence suggests drought conditions can make freeze injury worse, and that could very well be the case in some scenarios. Water in the soil is a good buffer to resist temperature swings and can prevent the soil from cooling as quickly as the air around it. Therefore, the temperature at the soil surface of a conventionally tilled field with good soil moisture may not get as cold as a similar field with dry soil conditions for example.

 

In theory, the plants themselves under drought conditions should actually be able to withstand cooler temperatures than non-stressed plants as less water content in the plant cells increases the solute concentration (i.e., it takes longer for those cells to freeze). Using the conventionally tilled field example above, we cannot automatically say that a field with dry soil conditions will have worse freeze injury than a field with adequate moisture. Also, if the weather conditions during the day(s) prior to the freeze event were warm and sunny, a significant amount of heat may still be radiated from a field with dry soil conditions and provide some buffer against freeze injury.

 

Final thoughts

Remember that each freeze event is unique. 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.