The cold temperatures experienced in the week of April 13-17 caused freeze injury to the 2020 wheat crop at varying degrees. The level of freeze damage depends on the region in the state, primarily because the wheat in different regions was at distinct growth stages (with varying levels of susceptibility to cold damage) and also because the different regions recorded minimum temperatures ranging from 8 to over 30 degrees F. Within a given region, factors that impacted the level of freeze damage included cropping system (which affected residue cover and sowing date), wheat variety selection, and position in the landscape.
North Central Kansas
The region encompassing Republic, Smith, Phillips, and Rooks counties showed a varying, but considerable, amount of freeze damage to the wheat crop. In general, the damage was more apparent in the western portion of this region; although some fields in Republic county also showed considerable damage. Fields that were planted at the optimum time such as those after a long fallow period were showing less leaf damage, but a large number of primary heads destroyed by the freeze. Many times, as many as 40 to 60% of the primary heads were lost. While secondary heads were mostly still alive, the crop needs moisture soon to help with recovery potential. In this region, freeze damage was accentuated by dry topsoil conditions, which currently gives the plants a desiccated appearance. For those fields that were sown late, usually after a soybean crop in this region, the combination of freeze and dry topsoil caused considerable dry back of leaves and tillers, with as many as half or two thirds of the tillers killed by the freeze event.
Central and West Central Kansas
Fields in the region between Saline and Ellis counties showed, again, varying degrees of freeze damage, with at least the same but potentially more freeze damage than in the north central region. The trends observed in the north central region were also true for this region (primary tiller loss in early sown fields, severe leaf and tiller damage to late-sown fields). However, because the wheat crop was further along in development in this region, it was at a greater risk for freeze damage. This region had slightly more soil moisture, which should help the crop compensate for the potential yield loss through secondary tillers.
South Central Kansas
As we moved from Saline County to McPherson and Reno counties, there were fewer fields showing leaf burn symptoms, so that there was essentially no sign of freeze damage in Sumner County. Evaluation of the wheat heads near Hutchinson suggested that maybe 5-10% of the primary tillers could have suffered some damage level, especially in the early-sow fields. While there is still potential that the emerging heads might be trapped in the boot, the freeze damage in this region was much less dramatic than in the central or north central regions.
The wheat crop in the northwestern portion of Kansas was also affected by the freezing temperatures. The wheat crop was not as far along in development relative to other areas of the state. With many fields either tillering or in the early jointing stages of growth at the time of the cold temperatures. This area of the state experienced the coldest temperatures (often less 15 degrees) and dry soil conditions predisposed plants to injury. Overall, the damage was less severe in the Northwestern region than in Central Kansas but some areas in Thomas, Gove and Trego Counties likely experienced significant damage. In many cases, the severely damaged fields turned yellow and eventually brown as the tissue declined and desiccated this week. The wheat in these fields will likely produce new tillers to compensate for potential yield loss, but rain is needed to help the crop recover.
Wheat variety effect on potential for freeze damage
We also saw a considerable difference among varieties in their response to the recent freeze events. It is important to note that these differences do not reflect a variety’s winterhardiness. Instead, they seem to be more related to when varieties were released from winter dormancy and started their spring growth. Varieties that began to grow early are showing more freeze damage than varieties that were released from dormancy later, regardless of sowing date. Remember that wheat’s tolerance to freezing temperatures is at its peak during the winter, and then decreases as the crop begins its spring growth – thus, the further away from the depths of the winter, the less a given variety is able to tolerate cold temperatures. In most cases, varieties that released earlier from winter dormancy (for example, WB4458, Paradise, TAM114, Zenda) were showing much more freeze damage than varieties that were released later (for example, WB Grainfied, Rock Star, LCS Chrome, Joe).
This article and information were provided by Romulo Lollato, Extension Wheat and Forages Specialist and Erick DeWolf, Extension Wheat Pathologist.
Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at firstname.lastname@example.org or call the Hays office, 785-628-9430.