Cropping options to follow an early terminated wheat crop could be similar to those for full-season crops. At this point in the season, viable crop options are still corn, soybeans, and sorghum.
Regardless of which crop you choose to plant, weed control will likely be needed. Despite insufficient precipitation to produce a crop, many fields will still have emerged weeds and all fields will have a weed seed bank likely to emerge and compete with the summer crop. In addition, any remaining wheat will need to be terminated. Burndown of summer annual weeds present at planting is essential for successful double-cropping. Glyphosate will be effective for terminating wheat, but if glyphosate-resistant kochia and/or pigweeds are present, alternative treatments such as paraquat may be required.
General agronomic considerations, herbicide carryover, and weed management will be addressed for each crop in the following sections.
In some regions, planting corn later can move critical corn growth stages around pollination to later in the growing season, after the most intense heat. This strategy has been adopted by some growers in areas that often encounter heat and moisture stress during the growing season, even though crop insurance cutoff dates for planting corn may be too early for this practice. However, in many dryland conditions, planting date is not a very good predictor of corn yield in fields with lower yield potential (<200 bu/a).
Hybrid relative maturity and target seeding rate can be like earlier planting dates until the month of June. Fertilization focusing on nitrogen (and other nutrients as needed based on soil testing) is still a critical practice to increase the likelihood of high attainable yields. If planting is delayed, longer maturity hybrids will be a good option to produce biomass for silage and grain, if they can reach maturity before a hard freeze.
Depending on application date, herbicide rate, and soil and environmental conditions, carryover of Group 2 herbicides such as chlorsulfuron (Glean, others), metsulfuron (Ally), sulfosulfuron (Outrider, others), triasulfuron (Amber, others) will be a concern. If Beyond was used in Clearfield wheat, Clearfield corn hybrids will allow replanting at any time, otherwise, the rotation interval is 8.5 months. If Aggressor was used in CoAxium wheat, the interval is 120 days.
If grassy weeds such as downy brome have become established in wheat, control prior to planting will be very important. However, they will likely be controlled by glyphosate or atrazine used to terminate wheat. Using a Group 1 herbicide such as clethodim (Select, others) or quizalofop (Assure, others) to terminate wheat will prevent corn planting, as these products have rotation restrictions, as mentioned for Aggressor. In addition to atrazine, residual herbicides such as mesotrione (Callisto, others) and Group 15 products (S-metolachlor, Dual; acetochlor, Harness; dimethenamid-P, Outlook; or pyroxasulfone, Zidua) should be used and can be included in the burndown application.
Soybean is a very good alternative crop. A dense soybean canopy may reduce herbicide costs compared to leaving the field fallow. Still, a residual herbicide should be applied at or before, or at planting time.
From a variety selection, planting a variety with the same or perhaps even slightly later maturity rating (compared to a typical planting date) will allow the crop to develop a larger canopy before flowering. Planting a variety that is too much later in maturity, however, increases the risk that the seeds may not mature before frost, especially if long periods of drought slow growth. The goal is to maximize the length of the crop’s growing season. The earlier you can plant, the higher the yield potential of the crop if moisture is not a limiting factor. From a fertilization standpoint, a soil test before wheat termination is recommended. Seeding rate can be similar to that for early planting dates, and row spacing could be narrower (15-inch or less), if this is an option with the available planting equipment. Narrow rows also offer the benefits of increasing early-season light capture, suppressing weeds, and reducing erosion.
If Group 2 herbicides are in the sulfonyl urea family and have the potential to remain in the soil after harvest. If an herbicide such as chlorsulfuron (Glean, Finesse, others) or metsulfuron (Ally) has been used, the most tolerant double crop will be sulfonylurea-resistant varieties of soybean (STS, SR, Bolt)
Chemical control of pigweeds at or before plating is especially important for soybeans. Dicamba (XtendiMax, Engenia, or Tavium) or 2,4-D (Enlist) can be used to control emerged pigweeds if soybean varieties with corresponding herbicide resistance traits are planted. Dicamba may also provide a bit of residual activity for pigweeds and kochia. However, a residual herbicide program that includes multiple effective active ingredients is important. Herbicides to consider include metribuzin, Group 14 herbicides (flumioxazin, Valor; sulfentrazone), and Group 15 herbicides listed previously.
Sorghum is another crop option with optimal planting time usually around late May and early June for late-maturing hybrids. Seeding rate and row spacing are similar to those recommended in normal planting dates (see recent Sorghum management eUpdate article). For N fertilization, a key component for the estimation of N application rates is the yield potential. It is also important to consider potential residual N from the wheat crop, mainly under the current conditions of very low production for wheat.
Sorghum will also have rotation restrictions to Group 2 herbicides. Igrowth hybrids are tolerant of imazamox (Beyond); however, current herbicide labels do not address rotation restrictions for these hybrids. Similarly, the Aggressor herbicide label does not address rotation restrictions for Double Team hybrids, which are tolerant of quizalofop.
Weed control before planting is critical for successful grain sorghum production. Both a thorough burndown program and an effective residual herbicide program is needed for both grasses and pigweeds to preserve double-crop sorghum yields. Using atrazine and a Group 15 herbicide product at planting is highly recommended for successful double crop sorghum production. One important difference from other crops discussed is that pyroxaulfone (Zidua, others) is not labeled for use in grain sorghum. Herbicide-tolerant grain or forage sorghum hybrids will allow the use of additional herbicides (imazamox, Imiflex; quizalofop, First Act; nicosulfuron, Zest) that are effective on summer annual grasses, but have little to no activity on pigweeds.
Less information is available regarding the herbicide carryover potential of wheat herbicides to cover crops. There is little or no mention of rotational restrictions for specific cover crops on the labels of most herbicides. However, this does not mean there are no restrictions. Generally, there will be a statement indicating “no other crops” should be planted for a specified amount of time, or that a bioassay must be conducted before planting the crop.
For more detailed information about herbicides, see the “2023 Chemical Weed Control for Field Crops, Pastures, and Noncropland” guide available online at https://www.bookstore.ksre.ksu.edu/pubs/CHEMWEEDGUIDE.pdf or check with your local K-State Research and Extension office for a paper copy.
The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.
Ignacio Ciampitti, Farming Systems
Sarah Lancaster, Weed Management Specialist
Adrian Correndo, Postdoctoral Fellow