Wheat

Early Season Wheat Diseases and Fungicides

By: Dr. Pierce Paul, OSU Extension

The wheat crop in Ohio is now between early boot (Feekes 10, in the south) and approaching Feekes 8 (flag leaf emergence) in northern counties. Cooler-than-usual conditions over the last few weeks have slowed the crop down considerably, but as temperatures increase, the crop will advance through several growth stages over a relatively short period. Cool conditions have also kept foliar diseases in check, but Septoria, and to a lesser extent, powdery mildew are still showing up in some fields. Septoria tritici leaf spot is favored by cool, wet conditions similar to those experienced over the last several weeks. It usually shows up first on the lower leaves as yellowish flecks that later develop into irregularly-shaped, brownish-gray lesions, with easily-seen dark-brown to black spots (called pycnidia) in the center. Cool temperatures and high relative humidity are also required for the development of powdery mildew. Typical symptoms of powdery mildew are whitish fungal growth (pustules) on the surface of leaves and stems. If the variety is susceptible and conditions continue to be favorable, a fungicide application may be warranted to prevent both diseases from reaching the flag leaf before grain-fill.

Septoria tritici leaf spot on wheat – note the black dots (pycnidia) inside the lesion.

Most of the fungicides commonly used on wheat are rated as very good or excellent against Septoria and good or very good against powdery mildew. See the attached chart for fungicide options and efficacy. Remember,

Powdery mildew on wheat leaf – as the name suggests, note the powdery, white pustules.

always read and follow the labels when making an application. For both diseases, a single application between Feekes 8 and Feekes 10 would be sufficient to protect the flag leaf and minimize yield loss. However, applications made at these early growth stages will not provide adequate control of late-season diseases like head scab and Stagonospora glume blotch. So, you should scout fields before making your fungicide application decisions. If powder mildew and Septoria levels are low as the crop approaches heading (Feekes 10.5), you may be better off waiting to treat fields at anthesis (Feekes), as this will help to suppress head scab, which is still the most damaging and important disease of wheat in Ohio, while at the same time provide very good control of Septoria, powdery mildew, and late-season diseases such as Stagonospora and rust.

 

 

Wheat Growth Stages

OK, Mother Nature is not cooperating which means we can’t talk about corn and bean planting so let’s talk about the crop we do have growing – Wheat

Source: K-State University

Knowing what growth stage your wheat crop is at is essential for nitrogen, herbicide and possibly fungicide applications.  Most of the wheat I have seen in the county so far is between Feekes 5 and Feekes 6.

Feekes 5 is the time to be making your last nitrogen applications and applying herbicides as needed for weed control.  However at Feekes 6 you should cutoff for nitrogen applications to avoid leaf injury.  Additionally some growth regulator herbicides, like 2, 4-D and dicamba should not be applied.

Wheat Between Feekes 8 and 10 and Disease Concerns

Source: Dr. Pierce Paul, OSU

 

Now is the time to take a closer look at your Wheat field … In between rain showers!

 

Wheat is now between Feekes 8 (flag leaf emergence) and Feekes 10 (boot) across the state. Feekes 8 marks the beginning of the period during which we recommend that you begin scouting fields to determine which disease is present and at what level. Septoria tritici leaf spot is usually one of the first to show up, and it has already been reported in some fields. So far, it is restricted to the lower leaves and severity is low in most of the affected fields. This disease is favored by cool (50-68F), rainy conditions, and although it usually develops early in the season, it really does not cause yield loss unless it reaches and damages the flag leaf before grain fill is complete.

Like many other foliar diseases, Septoria reduces grain fill and the size of the grain. It usually does not affect the number of spikelets per spike, an important yield component that is defined very early in the development of the plant. A fungicide application at this time will control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, protect the flag leaf, and minimize grain yield loss. If the weather conditions continue to be rainy and favorable for foliar disease develop, spores will continue to be produced or blown in from other areas, and new infections will occur, particularly if the variety is susceptible.

Results from previous studies have shown that the greatest benefits from foliar fungicide applications were seen when applications were made to a susceptible variety between Feekes 8 and 10. This is largely because most of our major foliar diseases usually develop and reach the flag leaf after Feekes 8-9. However, the residual effects of a Feekes 8-9 fungicide application will not adequately protect the head from late season diseases such as head scab and Stagonospora glume blotch or the flag leaf from rust and Stagonospora leaf blotch. In addition, some of the fungicide that effectively control foliar diseases are ineffective again, or are not recommended for control of, head scab.

There are several very effective fungicides available for use on wheat see the post above or  (see resource chart). Carefully read labels before making an application.

Yes, Another Article About Freeze Symptoms in Winter Wheat

Source: Dr. Laura Lindsey, OSU

After a (short) second round of winter last week, there has been some concern regarding winter wheat. As a reminder, the magnitude of freeze damage depends on: 1) temperature, 2) duration of temperature, and 3) wheat growth stage. During the cold snap last week, the majority of winter wheat in Ohio was at the Feekes 6 to 8 growth stage. In northern Ohio, temperatures were in the low 30s to upper 20s. In Southern Ohio, temperatures were mostly above 30°F with a dip to 26°F on April 23, recorded by the CFAES weather system in Pike County. Underneath the snow, temperatures were warmer (Figure 1 records the temperature under the snow on April 21).

A few years ago, we conducted a freeze chamber experiment to examine the effect of low temperature on winter wheat at several growth stages (Table 1). Keep in mind, actual yield reductions in the field can be quite variable depending on the weather for the remainder of the growing season. At Feekes 6 growth stage, temperatures >20°F caused no damage. However, by Feekes 8 growth stage, temperatures of 25°F to 28°F caused a 10 to 25% reduction in wheat yield. These temperatures were from the crown of the wheat plant, not air temperature.

What to look for: After a freeze event, wait one to two weeks after active growing conditions resume to check for visual signs of freeze injury. Make sure to examine several areas of the field as landscape features influence the micro-climates within fields. Small differences in temperatures can cause large differences in damage and grain yield.

At Feekes 6 growth stage, damage from freezing will cause discoloration of the leaf tissue, with leaf tips or edges exhibiting symptoms first (Figure 2). However, discoloration does not necessarily indicate a reduction in grain yield. At Feekes 6 growth stage, damage can also be assessed by carefully cutting the wheat stem lengthwise to expose the developing spike at the first node. Damaged spikes will appear discolored and shriveled. A healthy, developing spike should be rigid and whitish-green (Figure 3).

Figure 2. At Feekes 6 growth stage, freeze damage causes yellowing of browning (necrosis) of the leaf and stem tissue. Wheat plants pictured (left to right) were exposed to temperatures of 3, 14, 21, 28, and 39°F corresponding to death of 100%, 80%, 50%, 25%, and 0% death of the plant tissue.

Figure 2. At Feekes 6 growth stage, freeze damage causes yellowing of browning (necrosis) of the leaf and stem tissue. Wheat plants pictured (left to right) were exposed to temperatures of 3, 14, 21, 28, and 39°F corresponding to death of 100%, 80%, 50%, 25%, and 0% death of the plant tissue.

Figure 3. At Feekes 6 growth stage, freeze injury causes damage to forming wheat spike within the stem. Wheat spikes pictured (left to right) were exposed to 39, 28, 21, 14, and 3°F temperature treatments. At 3°F, the wheat spike appears discolored and deformed.

Figure 3. At Feekes 6 growth stage, freeze injury causes damage to forming wheat spike within the stem. Wheat spikes pictured (left to right) were exposed to 39, 28, 21, 14, and 3°F temperature treatments. At 3°F, the wheat spike appears discolored and deformed.

At Feekes 8 growth stage, damage from freeze may include yellowing or browning of the flag leaf. The flag leaf may appear twisted or in a spiral (Figure 4). As the plant continues to grow, the wheat spike may get stuck in the leaf sheath, causing a crooked appearance at heading (Figure 5). (Although, this phenology can also be associated with spikes that emerge quickly due to warm temperatures.)

Overall, I think freeze damage should be minimal from this most recent cold snap. At Feekes 6 growth stage, wheat is still fairly tolerant of cold temperatures. In the southern portion of the state, where wheat stage was more advanced, temperatures tended to be warmer. However, the best way to assess for potential damage is to scout your field after active growing conditions resume this week. For more information, see our new ‘Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat’ FactSheet: https://ohioline.osu.edu/factsheet/anr-93

Figure 4. Twisting or spiral appearance of the flag leaf can be caused by low temperatures. Photo credit: Greg LaBarge.

Figure 4. Twisting or spiral appearance of the flag leaf can be caused by low temperatures. Photo credit: Greg LaBarge.

Figure 5. At Feekes 8 growth stage, damage may include yellowing or browning of the flag leaf. The wheat head may get stuck in the leaf sheath causing a crooked appearance at heading.

Figure 5. At Feekes 8 growth stage, damage may include yellowing or browning of the flag leaf. The wheat head may get stuck in the leaf sheath causing a crooked appearance at heading.

Should you expect any freeze damage to winter wheat? Most likely, no.

Source: Laura Lindsey, Alexander Lindsey, OSU Extension

The incoming cold temperatures are not likely to impact winter wheat. The magnitude of freeze damage depends on: 1) temperature, 2) duration of temperature, and 3) wheat growth stage.

 

Prior to the Feekes 6 growth stage, the growing point of wheat is below the soil surface, protected from freezing temperatures. Most of the wheat in Ohio is at the Feekes 4 (beginning of erect growth) or Feekes 5 (leaf sheaths strongly erect) growth stage and should be unaffected by the incoming cold temperatures, predicted to be mid- to low 20s on Wednesday and Thursday.

At Feekes 6 growth stage, our research has shown only a 5% reduction in wheat yield at a temperature of 20°F for 15-minute duration and 50% reduction in wheat yield at a temperature of 12°F for 15-minute duration. (Although, it should be noted, there is a great deal of variability in response due to environmental conditions for the remainder of the growing season. Additionally, greater soil moisture levels can help buffer against short-term temperature fluctuations.)

For more information on Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat, please see our new FactSheet: https://ohioline.osu.edu/factsheet/anr-93

Wheat Growth Stages and Associated Management- Feekes 6.0 through 9.0

Source: Laura Lindsey, Pierce Paul, Ed Lentz, OSU Extension

It is important to correctly identify winter wheat growth stages to enhance management decisions, avoiding damage to the crop and unwarranted or ineffective applications. Remember, exact growth stage cannot be determined by just looking at the height of the crop or based on calendar dates. Remember to stage several plants from several areas within your field.

Here, we will focus on staging wheat Feekes 6.0 through 9.0.

Feekes 6.0: At Feekes 6.0 growth stage, nodes are all formed, but sandwiched together so that they are not readily distinguishable. The first node is swollen and appears above the soil surface. This stage is commonly referred to as “jointing”. Above the node is the head or spike, which is being pushed upwards eventually from the boot. The spike at this stage is fully differentiated, containing future spikelets and florets.

Growers should remove and carefully examine plants for the first node. It can usually be seen and felt by removing the lower leaves and leaf sheaths from the large wheat stems. A sharp knife or razor blade is useful to split stems to determine the location of the developing head. A video showing how to identify the Feekes 6.0 growth stage can be found in the video below.

Feekes 7.0: At Feekes 7.0 growth stage, the second node becomes visible. This stage is characterized by the rapid expansion of the head and a second detectable node. Look for the presence of two nodes- one should be between 1.5 and 3 inches from the base of them stem and the other should be about 4 to 6 inches above the base of the stem. These nodes are usually seen as clearly swollen areas of a distinctively different (darker) shade of green than the rest of the stem. The upper node may be hidden by the leaf sheath; you may have to run your fingers up the stem to feel for it. If only one node is present, the wheat is still at Feekes 6.0 growth stage. Wheat will still respond to nitrogen applied at Feekes 7.0 if weather prevented an earlier application; however, mechanical damage may occur from applicator equipment. A video showing how to identify the Feekes 7.0 and 8.0 growth stages can be found here: https://www.youtube.com/watch?v=PZ7Lvsux1y8

Feekes 8.0: At Feekes 8.0 growth stage, the flag leaf is visible, but still rolled up. This growth stage begins when the last leaf (flag leaf) begins to emerge from the whorl. This stage is particularly significant because the flag leaf makes up approximately 75% of the effective leaf area that contributes to grain fill. It is therefore important to protect and maintain the health of this leaf (free of disease and insect damage) before and during grain development. When the flag leaf emerges, three nodes are visible above the soil surface. To confirm that the leaf emerging is the flag leaf, split the leaf sheath above the highest node. If the head and no additional leaves are found inside, Feekes 8.0 is confirmed and the grower should decide whether or not to use foliar fungicides to manage early-season and overwintering fungal diseases. Nitrogen fertilizer applications at or after Feekes 8.0 growth stage may enhance grain protein levels, but are questionable with respect to added yield. Moreover, additional N may increase the severity of some foliar diseases, particularly the rusts.

Feekes 9.0: Feekes 9.0 growth stage begins when the flag leaf is fully emerged from the whorl with the ligule and collar visible. From this point on, leaves are referred to in relation to the flag leaf (e.g., the first leaf below the flag leaf is the F-1, the second leaf below is F-2, and so forth). A video showing how to identify Feekes 9.0 and 10.0 growth stages can be found here: https://www.youtube.com/watch?v=OHGhq0qSM1o&t=22s

Is It Too Early to Apply Nitrogen to Wheat?—-Yes

Source: Laura Lindsey, Ed Lentz, OSU Extension

With melted snow and warmer weather in the forecast, is it time to apply nitrogen to wheat?

The short answer. Wait until green-up to apply N to wheat.

The long answer. Wheat does not require large amounts of N until stem elongation/jointing (Feekes Growth Stage 6), which is generally the middle or the end of April depending on the location in the state and spring temperature. Ohio research has shown no yield benefit from N applications made prior to this time. Soil organic matter and/or N applied at planting generally provide sufficient N for early growth until stem elongation.

Nitrogen applied prior to rapid uptake by the plant has the potential to be lost and unavailable for the crop. Nitrogen source will also affect the potential for loss. Urea-ammonium nitrate (28%) has the greatest potential for loss, ammonium sulfate the least, and urea would be somewhere between the two other sources.

Ohio research has shown that yield losses may occur from N applied prior to green-up regardless of the N source. The level of loss depends on the year (losses are smaller if the ground is not frozen or snow/ice covered). This same research did not observe a yield increase from applications made prior to green-up compared to green-up or Feekes Growth Stage 6 applications. Keep in mind that green-up is a descriptive, relative term and not a definable growth stage. Our definition of green-up is when the new growth of spring has covered the dead tissue from winter giving the field a solid green color- thus, growing plants.

There is a legitimate concern that wet weather may prevent application of N at early stem elongation. Ohio research has shown a yield decrease may occur when N application is delayed until Feekes Growth Stage 9 (flag leaf fully emerged). Thus, a practical comprise is to topdress N at any time fields are suitable for application after initial green-up to early stem elongation. There is still a potential for loss even at green-up applications. To lessen this risk a producer may want to use a N source that has a lower potential for loss such as urea or ammonium sulfate. ESN (polymer-coated urea) is another option but it needs to be blended with urea or ammonium sulfate to ensure enough N will be available for the crop between Feekes Growth Stage 6-9. The source of N becomes less important as the application date approaches stem elongation. The percentage of urea and/or ammonium sulfate would need to be increased with ESN for application times closer to Feekes Growth Stage 6. A producer may want to consider the use of a urease inhibitor with urea if conditions are favorable for volatilization losses: warming temperatures, drying winds and no rain in the forecast for 48 hours.

A split application of N may also be used to spread the risk of N loss and to improve N efficiency; however, Ohio State University research has not shown a yield increase from this practice compared to a single application after green-up. In a split system, the first application should be applied no sooner than green-up. A small rate should be applied with the first application since little is needed by the crop at that time and the larger rate applied closer to Feekes Growth Stage 6.

In summary, a producer may get away with applying N prior to green-up on wheat. However, university data has not shown a yield advantage for these early applications, but results have shown in certain years a major N loss and yield reduction from applications prior to green-up. Why take the risk? Just wait until green-up; the wheat does not need most of the N until April and May anyway.