Figure 1. Volunteer wheat growth after harvest.
With winter wheat planting season fast approaching, producers may be facing some difficult planting decisions. The current drought monitor indicates that roughly 30% of the state is experiencing abnormally dry conditions. This is a real concern for producers who remember the autumn of 2012 when large fields of winter wheat did not germinate due to extremely dry conditions. In other areas where crops were lost this summer due to hail, producers may be anxious to get something else growing to replace the first crop and provide cover to the soil.
Factors affecting the success of winter wheat can be impacted by grower’s decisions. In South Dakota, the recommended planting time for winter wheat is September 10-October 10. Areas further north may want to consider planting earlier than areas further south. Winter wheat will survive the winter better if it is planted in time to develop 2-3 leaves and at least one tiller in the fall.
Many of the seasoned winter wheat producers, plant at 1.1-1.2 million PLS (pure live seeds) per acre. Planting into abnormally dry soil may necessitate a higher planting rate to account for poor germination. In areas where grasshopper populations are at or above thresholds around the fields, increased planting populations can also reduce the impact of grasshopper feeding.
The goal with winter wheat is to produce one main head with one to two tillers. A good plant stand can decrease the tendency of winter wheat to produce late tillers, which contribute to uneven maturity in thecrop and can use precious soil moisture.
Choosing the right winter wheat variety for your area is a very important step for many producers. Varieties will vary in maturity, winter hardiness, disease resistance and grain quality. SDSU performs winter wheat variety trials at 15 locations across South Dakota each year. Results can be found on the Winter Wheat Variety Trial Results page. Consider as much performance information as possible when selecting a variety, and give more weight to information from trials close to home, as some varieties may be better suited to certain geographic areas. Also pay close attention to relative performance over many locations. This type of performance is an indication of “yield stability”. Good yield stability refers to the ability of a variety exhibit high yield potential at many locations over years. For example, a variety that ranks in the upper 40% at all locations exhibits better yield stability than a variety that is number one for yield at one location but ranks in the lower 40% at some other locations. Performance over multiple years is also very important. Growing conditions in a single season may favor certain varieties, providing a poor representation of yield potential over time. For example, growing conditions in 2018 tended to favor later-maturing varieties and the absence of stripe rust allowed susceptible varieties to perform better than average. A good rule of thumb is to plant 65%-75% of your acres to varieties with a proven track record (i.e. a good multi-year average) and plant the remaining 25%-35% to a promising new variety.
Good Quality Seed
Using certified seed is a good option for producers. However, if producers choose to use their own wheat as seed, it is recommended that they get a germination test and seed count done. For more information, contact the SDSU seed testing lab. Using good quality, healthy, clean seed is very important.
Prior to planting, insecticide seed treatments may be applied to the seed. There is evidence that the addition of the insecticide seed treatment can reduce aphid populations in the field and also reduce the incidence of Barley yellow dwarf virus, which is vectored by the aphids. However, these treatments are generally not effective against grasshopper populations, which may require a foliar border treatment immediately after emergence.
Fungicide seed treatments provide protection from soil-borne pathogens that may interfere with seed germination or plant establishment. These pathogens may cause damping off of young seedlings or may cause root rots leading to reduced plant vigor. Seed-borne pathogens such as loose smut pathogen can lead to systemic infection that result in smutted wheat heads. The greatest value of a seed applied fungicide is to prevent catastrophic loss to seed-borne pathogens. However, not every field benefits from fungicide seed treatments. A fungicide seed treatment may be beneficial in fields with a history of poor plant stand establishment, poor drainage, non-rotated, and where non-certified seed is being used. For information on fungicide seed treatment products, see the 2018 South Dakota Pest Management Guide - Wheat (under seed treatments).
No-tilling winter wheat into stubble is a recommended crop management practice in central and western South Dakota. Snow trapped by the stubble adds moisture and insulates wheat seedlings against cold temperatures, thereby reducing risk of winterkill. Seeding winter wheat into broadleaf crop residue can help reduce insect, weed and disease issues. However, seeding into wheat residue is still common because of the increased winter hardiness associated with this practice.
Breaking the Green Bridge
Winter wheat planting is also a time when management decisions for certain diseases and insect pests need to be made. An example of such a disease is Wheat streak mosaic virus (WSMV). This virus is transmitted by the wheat curl mite (microscopic mites that are blown by wind) and can be devastating in winter wheat. However, this virus can also effectively be managed through elimination of what is called “the green bridge”. The green bridge refers to volunteer wheat and grassy weeds within a field. These can host insect vectors and other pathogens until winter wheat emerges. To reduce the chance of WSMV and other pathogens and pests surviving on the green bridge, the volunteer wheat and grassy weeds within the field should be destroyed at least two weeks before winter wheat planting. A burn down herbicide application is the best way to destroy the green bridge.
Other pests that may take advantage of the green bridge include Hessian flies as well as common aphid pests of wheat. In South Dakota, Hessian fly reports have been steadily increasing. Part of this trend may be the drought conditions that were experienced in 2017 that resulted in many previous wheat fields being planted back to wheat. Another factor that can impact Hessian fly populations is planting date. Earlier planted wheat is at a risk for Hessian fly infestations.
Check Herbicide Labels
Producers should check labels of herbicides used this past year in areas intended for winter wheat this fall to insure that there are no plant-back restrictions on wheat for those areas.
Winter wheat insurance is available to producers in all counties in South Dakota. The final planting date is 15 October.