How have recent cold temperatures impacted your wheat crop? Are you concerned that the fluctuating winter temperatures, continued cold, winter with little snow cover, and questionable fall establishment due to late planting, could impact cold tolerance of late-planted wheat? As spring arrives, dead patches of wheat could have resulted from any number of individual stress factors or a combination of several factors such as excessive or low moisture, wind desiccation, heaving, temperature extremes, or disease.
A couple of viral diseases of wheat are favored by cold weather. Wheat soilborne mosaic virus and wheat spindle streak mosaic, both survive in the soil in association with a root-infecting fungal organism. The fungal organism produces swimming spores that can enter the roots of a wheat plant in autumn during cool and wet periods and carry the virus along with it. If the fungus and virus enter the wheat plant during cool, fall weather, it has a greater potential to damage the wheat plant than if it infected the plant during the spring.
This spring, if wheat plants are infected with wheat soilborne mosaic virus, the new, unfolding leaves will have a mottled appearance with parallel yellow and green dashes and streaks. Disease development slows down as spring temperatures warm up, so symptoms are often confined to the lower leaves. Plants infected with wheat spindle streak mosaic virus will have long, yellow, spindle-shaped streaks (elongated spots wider in the middle than at the ends). These two viral pathogens often infect the wheat plant at the same time. Management for these pathogens includes using resistant wheat varieties and avoiding continuous wheat cultivation.
Now is a good time to scout your fields and assess the quality of your wheat stand. Check for new green growth and dig green and brown plants to look at their root systems. Cut stems to find the growing point and check its health. Count wheat plants over a 20-foot span in five areas of your field for a period of several weeks (including nice sunny weeks) and until the crop grows 8 to 10 inches tall to judge whether any damage may have occurred and to determine whether plants will outgrow injury. Plant health can also be determined now by digging plants, placing them in a warm spot, and watching for new, white root regrowth from the crown.
As a general guideline, an adequate stand is estimated by the number of tillers or heads per square foot. Sixty to seventy tillers often define an adequate stand; however, productive tillers may be hard to estimate at this time. Instead, another general rule is 20 live plants per square foot should be adequate for high yield, and 15 live plants per square foot would be worth keeping if they are healthy, have good leaf growth, and appear to have potential for tillers to form. If plants are not healthy UW Extension’s critical threshold is 12 to 15 live plants for turning over a field. The decision to replant should be automatic if you scout and find less than 12 live plants per square foot.
This scouting method should help provide information for making decisions about planting another crop or fertilizing your existing wheat crop. Dr. Shawn Conley, UW Extension Specialist, also has a useful blog with tips for assessing wheat and nitrogen application online at The Soy Report: Factors to Consider While Assessing Your 2017 Winter Wheat Crop Stand and Spring Nitrogen Timing.
Dr. Loretta Ortiz-Ribbing is the UW-Extension Crops & Soils area agent for Fond du Lac and Dodge counties and may be reached at 920-929-3171 or Loretta.OrtizRibbing@ces.uwex.edu.