Yellow wheat caused by low temperatures
Photo by Brian Waldschmidt, Harper County Extension agentYellowing wheat from cold weather injury in Harper County, early February 2012. Many fields of wheat around Kansas have begun to take on a yellowish cast over the past couple weeks. There are several factors that can cause yellowing at this time of year:
- Cold temperature leaf injury
- Nitrogen deficiency
- Poor root development
- Leaf burn from liquid fertilizer application
- Atrazine carryover
- Leaf rust or tan spot
Determining the cause of the yellowing can be important. Some causes require a solution, such as applying more nitrogen; some causes are temporary and do not require any corrective actions; and some causes are beyond the control of producers.
To determine the cause of the yellowing, check the following:
* What parts of the plant are affected? Is the yellowing on older lower leaves only, newer leaves only, on the tips, or on the entire plants? If the yellowing is on lower leaves, that indicates nitrogen deficiency. If it is only on newer leaves or leaf tips, that could indicate cold temperature leaf burn or barley yellow dwarf. If entire plants are yellowing, that might indicate atrazine carryover, liquid fertilizer burn, or drowning.
* What have the temperature and growing conditions been over the past 30 days? If there has been a sudden drop in temperatures while leaves were green, you might suspect cold injury or leaf tip burn.
* Are fields unusually wet or dry? If soils are excessively wet, roots can drown and nutrient uptake can be greatly reduced, resulting in yellowing of lower leaves first, then entire plants. If soils are very dry, root growth will often be stunted and plants will gradually become chlorotic, then turn bluish or brown.
* What is the pattern in the fields? If the yellowing is in streaks in the field, that implies a fertilizer application problem, or possibly atrazine carryover. If it is mostly on terrace tops, that might indicate a weather-related problem that would affect exposed plants first. If it is occurring in primarily in low areas, that might indicate freeze injury where cold air settled or drowning. If the yellowing is uniform throughout the field, any of the factors above could be the cause.
* Are other wheat fields in the general region of yours also yellow, or just a few scattered fields? If fields in the entire region are yellowing, that would imply a weather-related problem. If it is specific to just one or two fields, that implies a management-related or field-specific soil problem.