Wheat

Field Observations Thru May 5

Throughout the growing season I will post information on different pests or issues I am seeing in our fields in Knox County.  This week, not much happening in our fields due to the cold, wet weather. Below are a some to observations to keep an eye on.

Alfalfa Weevil

 Even with the chilly weather we have experienced the last 2 weeks,  we have accumulated enough growing degree days for alfalfa weevils to be active. These cold temperatures may have slowed feeding but the temperatures haven’t been cold enough to kill the weevil larvae.  We are concerned that as soon as it warms they will speed up their feeding again with a vengeance.  Scout your fields now, not when excessive feeding grabs your attention.  Keep in mind that at a certain point, early harvest is preferable to treatment.

Click here for Alfalfa Weevil Scouting Guide

Here is a video about scouting weevils in alfalfa:  https://forages.osu.edu/video

Alfalfa Weevil Update  – C.O.R.N. Newsletter

Wheat 

Even with chilly temps wheat is growing at a good pace.  Most of our week is passing through Feekes 7 and is in (or soon will be ) in Feekes 8.  As our wheat approaches Feekes 9 it is time to scout your fields and evaluate your stand/yield potential and determine if fungicide applications are warranted.  2023 Wheat Fungicide Ratings can be found in this post from earlier this week.

Wheat Growth and Development – Feekes 7

Today managing your wheat crop requires knowledge of the different growth stages of the plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Each week throughout the rest of the growing season I will discuss the various wheat growth stages I am seeing in our wheat fields and management issues at each stage.  This week I will focus on Feekes 7.  While growth stage does vary throughout the County, most of our field are at or beyond Feekes 7 growth stage.

Feekes 7 – Second node of stem 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 the 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 distinctly different (darker) shade of green than the rest of the stem.  The next-to-last leaf is just visible.

Note: 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, then your wheat is still at Feekes Growth Stage 6. Wheat will still respond to N applied at Feekes 7.0 if weather prevented an earlier application; however, mechanical damage may occur from applicator equipment. Demand for water and nutrients increases. Temperatures lower than 24 degrees Fahrenheit can damage the developing head.

If you need a reminder on how to determine if wheat is at Feekes GS 7, watch this video.

Management

Plant growth regulators may be applied at this growth stage. Scout for insects, weeds, and diseases.

Weed Response to Postemergence Herbicides in Small Grains

When determining your herbicide program for spring applications, the stage of the wheat crop should be considered.  The majority of wheat herbicides labeled for application at certain wheat growth stages have very short windows in which they can be applied.  The popular broadleaf weed herbicides 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restriction are outlined in a in a post last week (Herbicide Applications on Winter Wheat).

Another consideration you should take into account when planning a spring herbicide application is the plant back (or recrop) restrictions to double crop soybeans.  Many of the herbicides listed in Table 19,  have soybean plant back restrictions greater than the typical three month time period between spring applications and double crop soybean planting.  The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double crop soybeans after wheat.

Herbicide Applications on Winter Wheat

When determining your herbicide program for spring applications, the stage of the wheat crop should be considered.  The majority of wheat herbicides are labeled for application at certain wheat growth stages and some commonly used herbicides have very short windows in which they can be applied.  The popular broadleaf weed herbicides 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restriction are outlined in Figure 1.

Wheat Growth and Development – Feekes 6

Today managing your wheat crop requires knowledge of the different growth stages of the plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Each week throughout the rest of the growing season I will discuss the various wheat growth stages I am seeing in our wheat fields and management issues at each stage.  This week I will focus on Feekes 6.  The recent warm weather has stimulated wheat growth.  While growth stage does vary throughout the County, some of our field are at (or soon will be) Feekes 6 growth stage.

Feekes 6 – First node of stem visible (jointing)
The first node of the stem becomes visible as a result of internode elongation. Nodes are stacked and move up as the internodes elongate much like a telescope. Sensitivity to low temperatures increases as the developing head is pushed up by the expanding stem. Crop water demand increases to about 0.25 inch per day. Approximately 25 percent of the total dry matter is accumulated by this stage.

Management.

Consider a first fungicide application under significant disease pressure. Do not apply dicamba or 2,4-D after wheat reaches jointing and avoid equipment with wide tires.

If you need a reminder on how to assess if wheat is at Feekes GS 6, see this video: https://www.youtube.com/watch?v=D_f3VrqzV5c.

 

Wheat Growth and Development – Feekes 5

Today managing your wheat crop requires knowledge of the different growth stages of the plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Each week throughout the rest of the growing season I will discuss the various wheat growth stages I am seeing in our wheat fields and management issues at each stage.  This week I will focus on Feekes 5.  Most of our wheat has progressed to the Feekes 5 growth stage.

Feekes 5 – Leaf sheaths strongly erect. 

The beginning of the stem elongation phase.  The pseudo-stem is strongly erect and leaf sheaths are elongated. The developing head reaches the terminal spikelet stage and is pushed up into the pseudo-stem.

Terminal spikelet occurs at Feekes 5. This stage marks the completion of the spikelet initiation phase. At this stage, the number of spikelets per head has been determined.   Stress during this stage can reduce total number of kernels per head.

The first hollow stem stage occurs when there is approximately 0.6 inch of hollow stem below the developing head.  Crop water use is about 0.1 inch per day.

Management.

Ideal time for second nitrogen application if split applying in the spring.  Tillers developing after this time are not expected to contribute to yield.  If Grazing, cattle should be removed from dual-purpose wheat before first hollow stem

When and How Much Nitrogen to Apply to Wheat

Wheat has already reached green-up across the state so spring N may be applied anytime fields are fit. Keep in mind that research has shown no yield benefit to early N applications as long as the application was made by Feekes – 6 (one visible node).  If you need a reminder on how to assess if wheat is at Feekes GS 6, see this video: https://www.youtube.com/watch?v=D_f3VrqzV5c.  Nitrogen applied early has the potential to be lost since wheat will use little N until after jointing. Urea-ammonium nitrate (UAN) or 28% has the greatest potential for loss and ammonium sulfate the least. Urea will have little potential for loss as long as it does not volatize. No stabilizer will protect the nitrate component of UAN, which is roughly 25% of the total N in UAN at application time.

Ohio State University recommends the Tri-State Fertilizer Recommendation Bulletin for N rates in wheat. This system relies on yield potential. As a producer, you can increase or reduce your N rate by changing the value for yield potential. Thus, a realistic yield potential is needed to determine the optimum N rate.  To select a realistic yield potential, look at wheat yield from the past five years.  Throw out the highest and lowest wheat yield, and average the remaining three wheat yields.  This three-year average should reflect the realistic yield potential.

Table 10 in the Tri-State Fertilizer Bulletin recommends 120 lb N for yield goals of 100 bu/A, 110 for 90 bu/A crop, 90 lb for 80 bu/A crop, and  80 lb for a 70 bu/A crops. These recommendations are for total N. If you prefer to be more specific, the following equation may be used for mineral soils, which have both 1 to 5% organic matter and adequate drainage:

N Rate = (1.33 x Yield potential) – 13.

No credit is given for previous soybean or cover crops, since it is not known if that organic N source will be released soon enough for the wheat crop. The Tri-State Fertilizers Bulletin recommends that you subtract from the total (spring N) any fall applied N. I would take no more than a 20 lb/A credit even if you applied a larger amount. Whether you deduct fall N depends how much risk you are willing to take and your anticipated return of investment from additional N. Based on the equation above and deducting 20 lb from a fall application, a spring application of 100 lb N per acre would be recommended for a yield potential of 100 bu, 90 for 90 bu potential; and 70 for a 80 bu potential.  Nitrogen rate studies at the Northwest Agricultural Research Station over the past 20 years have shown the optimum rate varies depending on the year. However, averaged over years, yield data from these studies correspond well with the recommendation equation given above. These studies have also shown apart from one year, yields did not increase above a spring rate of 120 lb N per acre.

Wheat generally does not benefit from a nitrification inhibitor since temperatures are relatively cool at application time and the application is made to a growing crop, this is especially true as the crop approaches Feekes – 6. However urea may benefit from a urease inhibitor (products containing NBPT) if conditions for volatilization exist for several days after application. These conditions would include an extended dry period with warm drying temperatures (risk increases with temperatures above 70°F) and evaporating winds. Urea applications need at least a half inch rain within 48 hours to minimize volatilization losses unless temperatures remain relatively cool. The urease inhibitor will prevent volatilization for 10 to 14 days with the anticipation of a significant rainfall event during this time.

ESN or polymer coated urea will reduce the potential for N loss from leaching, denitrification, and volatilization. Since these conditions are unlikely to occur in most years, it may not be economical to use this product. Cool weather may prevent the timely release of N from ESN, so if ESN is applied, it should be mixed with urea or ammonium sulfate and be no more than 60% ESN.

A split application of N may be used to spread the risk of N loss and to improve N use 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 smaller 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 – 6.

Wheat Growth and Development – Feekes 3&4

Today managing your wheat crop requires knowledge of the different growth stages of the plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Each week throughout the rest of the growing season I will discuss the various wheat growth stages I am seeing in our wheat fields and management issues at each stage.  This week I will focus on Feekes 3 & 4.  Most of our wheat has progressed to the Feekes 4 growth stage.

Winter dormancy – Vernalization. 

Gradually lowering temperatures and shortening day length induce winter hardiness in winter wheat.  Vernalization requirements range from three to eight weeks of temperatures below 50 degrees Fahrenheit.

Management. Manage stocking density in dual-purpose wheat systems and try to maintain 60 percent canopy coverage.

Feekes 3 – Completion of tillering.

Once requirements are met, the growing point differentiates and the embryonic head reaches the double ridge stage.

 

Double ridge. The primordia, which differentiate into spikelets, become visible after vernalization requirements are met. Floret initiation starts slightly above the middle portion of the microscopic head and moves outward. The number of florets initiated determines the potential number of kernels per head.

Depending on the season and planting date, some tillering occurs in the spring. Genetic potential and environmental conditions determine the number of tillers on a plant.  Tillers with three or more leaves are nutritionally independent from the main stem.

Management. If fewer than 70 tillers per square foot are present, an early nitrogen application can increase spring tillering and help compensate for thin stands.  Avoid excess nitrogen.

Feekes 4 – Leaf sheaths lengthen (spring greenup).

Leaf sheaths begin to lengthen. The pseudo-stem, a succession of leaf sheaths wrapped around each other, starts to become erect.

Management. Ideal time to make single spring nitrogen applications based on yield goal. Begin scouting for insects and weeds.

Double-Crop Soybean Weed Management

by: Dr. Mark Loux, OSU Extension

It’s been a tough summer in parts of Ohio to do anything on a timely schedule and there are some weedy fields.  The best advice we have for big weeds in full-season soybeans is to increase rates and the complexity of POST herbicide applications, while still adhering to cutoffs for the application of certain herbicides as much as possible.  Dicamba products, XtendiMax, Engenia, and Tavium, cannot legally be applied to Xtend and XtendiFlex soybeans after June 30.  This cutoff date pertains to use in double-crop soybeans also.  If you are planning on planting Xtend or XtendiFlex soybeans in double-crop fields and using dicamba as a burndown, apply before Friday.  There isn’t a cutoff date for most other POST soybean herbicides – it’s based on either crop stage (eg R1) or days before harvest.

Double crop soybeans usually need some type of weed control program, although how weedy they get depends upon weeds surviving down in the wheat that can take off once they receive light; how much rain we get in July, which drives additional weed emergence and rate of soybean growth; and how fast the soybeans grow and develop a canopy.  Control can occur via the use of pre-plant/preemergence burndown herbicides, followed by POST as needed.  It’s also possible to accomplish this with one early POST application in Enlist soybeans, using Enlist Duo or a combination of Enlist One with glyphosate or glufosinate.  And also in LLGT27 soybeans with a combination of glyphosate and glufosinate.  Herbicides need to address marestail in many fields, which is often lurking in the wheat ready to regrow.  Marestail that are taller and get cut off by the combine will be more difficult to control than the smaller intact ones below the cutter bar.  Herbicide options vary depending upon the weeds and what type of soybeans are planted.  More effective options include:

  • Glyphosate or glufosinate + Sharpen (1 oz) + MSO – any soybean, prior to emergence
  • Glyphosate or glufosinate + 2,4-D – any soybean, at least a week before planting
  • Enlist Duo; glyphosate or glufosinate + Enlist One (Enlist soybeans) – PRE or POST, no wait to plant
  • Glyphosate + XtendiMax or Engenia (Xtend or XtendiFlex soybeans) – PRE, apply by June 30
  • Glyphosate + glufosinate – PRE in any soybean, PRE or POST in LLGT27 soybean

​​​​​​​It is possible to include residual herbicides with a PRE burndown treatment, but their value in this situation is questionable.  Residual herbicides with long recrop intervals to corn should be avoided.  POST options in double-crop include glufosinate, glyphosate, Enlist One/Duo, and conventional herbicides, depending upon the type of soybean planted.  One caution here is to avoid excessive injury to soybeans that slows growth and development since this is likely to reduce yield due to the short season.  Weed emergence is reduced and variable in July compared with May and June.  Where burndown herbicides are used, but there is still a need for POST herbicides to control a flush of late-emerging weeds, consider reduced rates.  Research we conducted back in the 1990s demonstrated that weeds up to 2 inches tall can usually be controlled with half of a typical labeled rate.  When we planted soybeans in early June, the single application of a half-rate provided adequate control, versus early May when a second application was needed.  So this should be a suitable approach for double-crop soybeans.  Just be sure to start with an effective burndown at planting, and apply when weeds are well within the 2-inch size.