Preharvest intervals indicate the amount of time that must elapse between the herbicide application and crop harvest. Failure to observe the preharvest interval may result in herbicide residue levels in the harvested portion of the crop in excess of established limits. Also, livestock grazing or foraging treated soybean is not allowed on the labels of many postemergence soybean herbicides. Table 1 contains information regarding preharvest intervals and grazing restrictions for a number of postemergence soybean herbicides.
Table 18 from the OSU Weed Control Guide shows the PHI and feeding restrictions for postemergence soybean herbicide applications.
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. Today I will focus on the heading stages Feekes 10.2 through Feekes 10.5 .
FEEKES 10.1-10.5 – HEADING
Figure 1. Wheat flag leaf, ligule, awns and head at Feekes 10.5.
Heading marks the emergence of the wheat head from the leaf sheath of the flag leaf, and is subdivided into stages based on how much of the head has emerged.
Stage 10.5 is shown in Figure 1.
- 10.1 Awns visible, head beginning to emerge through slit of flag leaf sheath.
- 10.2 Heading one-quarter complete.
- 10.3 Heading one-half complete.
- 10.4 Heading three-quarters complete.
- 10.5 Heading complete.
If you need a reminder on how to determine the different heading growth stages, watch this video.
Scout for insects, weeds, and diseases. A fungicide application may be considered to protect heads from scab.
Check fungicide label for pre harvest interval restrictions and proper growth stage for application.
Click here to go to an earlier post containing the 2023 Wheat Fungicide Ratings.
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.
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.
Mother nature is finally cooperating, allowing us to get some corn and beans in the ground. Later this summer it will be time for postemergence herbicide applications. The table below from the “2022 Weed Control Guide” lists important information on rainfast intervals, spray additives and crop size for soybean postemergence applications.Click on the table to print a camera ready copy
Mother nature is finally cooperating, allowing us to get some corn and beans in the ground. Later this summer it will be time for postemergence herbicide applications. The table below from the “2022 Weed Control Guide” lists important information on rainfast intervals, spray additives and crop size for corn postemergence applications.
Click on each page to print a camera ready copy
by: Erdal Ozkan, OSU
Whenever I give a presentation about the need to calibrate a sprayer and how to do it, there is always someone asking me this same question: “I have a rate controller in the cab that regulates the flow rate of the sprayer regardless of the changes in sprayer ground speed. I just enter the gallons per acre application rate, and the controller does the rest, just like a cruise control in a car. So, should I still calibrate the sprayer? The answer is, Yes, a calibration should be done. Although the rate controllers do an excellent job with regulating the flow rate of nozzles to keep the application rate constant regardless of the changes in travel speed, a manual calibration at least once a year is needed for two reasons: 1) to ensure the rate controller is functioning properly, 2) the rate controller is not forced to operate outside the pressure operating range for the nozzles on the sprayer boom. Let me elaborate on both points I made and share with you the reasons why a manual calibration of a sprayer is a good idea. Continue reading
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.
by: Dr Mark Loux, OSU
There is a lot of speculation about herbicide shortages for the 2022 growing season, and some products are apparently getting more expensive and/or scarce now. This will affect herbicide buying and weed management decisions for the 2022 season. The two main active ingredients that we’re hearing about right now are glyphosate (Roundup, others) and glufosinate (Liberty, others), for which prices have increased substantially. There will likely be limited supplies of other pesticide active ingredients as well, but in the short term, a shortage of these two active ingredients poses some major challenges for corn and soybean production. The purpose of this article is to discuss ways to minimize the impact of herbicide shortages, primarily glyphosate, on corn and soybean production. As you search for alternatives to these two herbicides and others, the weed control guides and technical guides produced by University Extension and industry are an important tool for planning weed management programs and herbicide purchases.
Some guiding principles based on our experience that may help with decisions, especially where glyphosate will not be in all applications:
- Spring tillage is an option to replace herbicide burndown. Can cause long-term compaction problems if tilled when too wet. Waiting until weeds are large makes tillage less effective. Weeds that survive tillage will be difficult to control with POST herbicides. In other words, till when soil conditions are fit and before weeds are huge.
- Where it’s only possible to use glyphosate once, it may be needed most in the burndown. Saflufenacil can be added for enhanced control of rye and ryegrass, and marestail. ACCase herbicides (e.g. clethodim, quizalifop) can then be used for POST grass control in soybeans. Glufosinate, Enlist Duo, or XtendiMax/Engenia can be used for many broadleaf weeds, especially the glyphosate-resistant ones. Where residual herbicides are omitted, or do not provide enough control, we would expect POST treatments to struggle more in the absence of glyphosate with weeds such as lambsquarters. So use residuals. Glyphosate is still more than just a grass herbicide.