Great Bend Tribune
Published May 17, 2020
The Drought Monitor report continues to indicate intensification in extreme Southwest Kansas with much of western Kansas in now considered abnormally dry or in moderate drought. Remember this is as of last Tuesday so recent rains may not factor in. Abnormally fry conditions were indicated for mush of North Central Kansas. The eastern third of Barton County is listed as abnormally dry and the western two-thirds as in moderate drought. The six to ten day outlook (May 19 to 23) indicates temperatures above normal, and normal precipitation for the state. Looking out eight to fourteen days (May 21 to 27) indicates slightly above normal precipitation and temperatures. Good news temperature-wise for summer row crops. From May through July, predictions are for equal chances of above or below normal temperatures and slightly above normal precipitation.
There are reports of stripe rust on wheat in Barton County. With the weather conditions of the last week, it’s hardly surprising. Producers will need to aggressively scout for this and other leaf diseases with much of the wheat heading out now. They will have to weigh the potential yield, the disease resistance of their varieties, the value of the crop, weather, and the cost of treatment when deciding whether or not to spray. And decisions for most need to be made soon. For some, the decisions is likely pretty easy after evaluating obvious freeze damage. For others, the damage may be there, just not readily apparent yet. This leads to today’s discussion, the weather rollercoaster producers are on and planting their summer row crops.
While not overly common, it isn’t unusual to have a frost or freezing temperatures in late April or early May. The severity was unusual. Two things matter here, soil temperature and air temperature when discussing planting and early crop growth. Another consideration is where these plants originally came from; corn from Mesoamerica, soybeans from Southeast Asia, and grain sorghum for sub-Saharan Africa. Finally, sorghum and corn are grasses so the seed remains in the ground and the seed leaf protected by the coleoptile emerges from the soil. The growing point remains in the ground an extended period of time before emerging above the soil. For dicots like soybeans, the whole seed emerges from the soil and the cotyledons, the seed leaves, serve as a food and photosynthesis source as true leaves are established. Here at emergence, the growing point is above the soil. So briefly how does weather, especially temperature, matter?
- There are recommended minimum two inch deep soil temperatures for planting. At temperatures above the minimum germination proceeds more rapidly, below that more slowly and there is an increased there for insect and disease damage. However, except under extreme moisture conditions, an insecticidal/fungicidal seed treatment can handle things. Air temperature before emergence isn’t a factor here.
- After emergence, air and soil temperature both matter. Cool soil temperatures slow root development, nutrient uptake, and nutrient movement. Air temperature affects the growth rate of the above ground structures. Now go back to our severe freezes recently. If the seedling had emerged under these conditions, it would in all likelihood, killed the cotyledons and any other aboveground plant structures. This would have killed the growing point and the plant is dead. For corn, the growing point remains protected in the soil until the plant is approximately twelve inches tall. So if any corn was up, it may have damaged leaves or even killed all the above ground plant structure but unless the cold penetrated to the growing point, the plant will recover. Can successive cold over several nights at this stage do in plants, it can but isn’t likely. As the plant grows ad approaches twelve inches, it is more likely for more permanent damage to occur.
- Finally, it doesn’t take freezing temperatures to hurt a plant, especially those from warmer areas such as soybeans, cotton, and even some sorghums, but especially cotton. Essentially the cold can shock the system and severely interfere with grow for the life of the plant, especially something like cotton. This is why we look to recommended air and soil temperatures and not just for that day or week but to insure temperatures low enough to shock the plant aren’t in the forecast.