As winter draws to a close and spring draws near, wheat fields are starting to green up. In some situations, wheat plants exhibit a discoloration and lead us to ask what’s going on? There could be several reasons.
Fluctuating temperatures can exacerbate various disease symptomatology in a wheat crop. Two viral diseases that lead to discoloration are spindle streak mosaic virus and soil-borne mosaic virus. The wild swings in temperatures can also lead to a less concerning, but visually noticeable, leaf burning and/or purpling of the leaf tissue. Let’s explore them.
Spindle Streak Mosaic Virus (SSMV) and Soil-borne mosaic virus (SBMV)
Some viral diseases that can affect wheat are spindle streak mosaic virus and soil-borne mosaic virus. Infection for these viruses can occur from fall through spring, with symptoms showing up during green-up. Fall infection on earlier planted fields tend to display the greatest foliar symptoms. Additionally, these viruses tend to favor wetter soils.
SSMV: Symptoms appear as random, yellow to light green dashes running parallel with leaf veins. Early spring, dashes may have a nondescript appearance. With age, some dashes are pointed at one or both ends.
SBMV: Leaves of infected plants exhibit a mild green to prominent yellow mosaic. Small green islands and short streaks may be evident on an otherwise yellowed leaf.
Warm temperatures are the cure for these viruses, we can’t fix it ourselves. Symptoms typically fade as weather warms, but yield losses can occur under heavy infections and prolonged cool springs.
Leaf Purpling and Leaf Burn
It is not uncommon for cold winters to burn back some leaf tissue. Typically, leaf burn occurs on bigger plants with more foliage and varieties that are a little more sensitive to cold weather. As long as the tiller holds its green color and the crown is not damaged, the plants will be ok.
Additionally, in some environments the leaf tissue can turn purple as well. Cold, wet conditions can cause a phosphorus deficiency in wheat. This can happen late in the fall or early in the spring when soils are cool and wet. Some fields appear to have a golden or bright tan appearance when viewed from the road. Sometimes it can look like the plants are dying, but many times the leaves have started to purple along with leaf burn caused by high winds. What you should know: As the soil drains and warms up, sugar transport will resume as normal and the purple color will disappear. However, if you suspect soil test levels are low for phosphorus, you can pull soil samples to determine if you need to add phosphorus fertilizer.*
*Dennis Pennington, Michigan State University Extension
You can read more at the following links:
Soilborne Wheat Mosaic Virus from AgriLIFE Extension, Texas A&M System
Soilborne Wheat Mosaic and Spindle Streak Mosaic Virus by Christina Cowger and Randy Weisz
Wheat Spindle Streak Mosaic from University of Kentucky, College of Agriculture
Purple leaves on wheat explained from Michigan State University Extension