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Warm Temperatures Prompt Early Wakeup in Winter Wheat
Record-high temperatures in winter wheat country the week of February 14 have spurred the winter wheat crop into breaking dormancy and beginning the spring push to harvest.
Normally, that's a sign that spring has sprung. This year, however, fields are greening up several weeks earlier than normal, prompting wheat growers to apply topdress nitrogen and herbicide.
"The wheat has really taken off," says Jared Jones, field marketer at Mid-Kansas Co-op in McPherson, Kansas. "We are already spraying, and we typically never do that in February."
Unfortunately, early green-up could also set the stage for a spring freeze to wreak havoc on the crop, says Romulo Lollato, wheat and forage specialist at Kansas State University. Lots of spring growth followed by a freeze could cause severe damage to the 2016 winter wheat crop.
Lollato says winter wheat varieties with short vernalization periods may be released from winter dormancy and possibly have been growing for a few days during this unseasonably warm period. Winter wheat loses some of its winter hardiness each time it breaks dormancy due to warm temperatures, although some of the winter hardiness can be regained if temperatures gradually get colder again.
"Nighttime temperatures are at or below freezing, which helps keep things in check," Jones says. "Colder temps at night help slow things down a bit."
What Can Happen With a Freeze
Much of winter wheat country is still in the tillering stage. The growing point is near the soil surface at this time and is protected against injury. Most freeze damage at this stage occurs to leaves. The leaves can become twisted and light green to yellow in color, and are burned at the tip within one or two days after freezing.
In the first hollow stem, or jointing stage, the developing wheat head has started to move up the stem. Wheat at this stage can usually tolerate temperatures in the mid to upper 20s with no significant injury. If temperatures get into the low-20s or lower for several hours, there can be some injury to the lower stems, the leaves, or the developing head. If it is windy during the nighttime hours when temperatures reach their lows, this increases the chance of injury. In Texas and Oklahoma, wheat is reaching the jointing stage and would be more vulnerable to freezing temperatures. From Kansas north, it hasn't and as such, remains safe for now.
However, continued warm temperatures will prompt quick spring growth. That means the crop is using stored moisture earlier than normal. "Water use increases linearly with the increase in biomass from jointing until heading," Lollato says. "The larger the wheat’s biomass or leaf area, the more water the crop will require to maintain its canopy structure. Greater water use during the winter months will reduce the amount of profile soil moisture for the spring, which might not be a problem in years with sufficient spring precipitation. However, excessive use of the current available water can play against wheat yields if the spring turns out dry."
The specialist adds that mild temperatures could favor the formation of stripe rust or other wheat leaf diseases. Texas and Oklahoma released a few reports of active stripe and leaf rust infections in the past couple weeks. These require both cool temperatures and dampness, the latter of which is in short supply in many areas of winter wheat country.
Still, producers will want to keep a close eye on conditions in the south to stay abreast of northward moving wheat diseases, and begin to scout fields for disease infestations.