Fluctuating temperatures affect crop growth
By Randy Buhler
Colorado State Extension Logan County Agent, Agronomy
Plant development has been skewed by an abnormal progression of temperatures this spring. The roller coaster-like fluctuation in higher highs and lower lows as compared to what we think of as "normal" can cause plant development to be reduced and delayed. These plant-development problems apply to our crops, weeds, landscape trees and shrubs, and even lawns and pastures. Changes in plant development progression in turn will affect insects, diseases, and management activities. Crop scouting takes on a greater role in deciding when to do what than does the calendar.
Plant physiology has threshold temperatures. Each species has a preferred temperature to start growth and activity as well as an upper threshold temperature beyond which plants are too stressed to perform growth and development. At either the lower or upper threshold temperatures, the plants shift into a survival mode to protect themselves from injury or death. Seed companies are looking at genetic engineering and other plant breeding techniques in an effort to widen these threshold temperatures for our major crop plants.
Roller coaster temperatures can result in increased soil insect damage, higher incidence of soilborne seedling diseases, greater stress on early plant growth, longer infection time for leaf and stem diseases, delayed forage harvest, and an increased susceptibility to heat stress when temperatures finally do moderate. Delayed forage harvest is undesirable because it carries through the entire season and reduces total yield. Increased time of exposure to insect and disease pests can cause economic damage when you ordinarily would not experience an economic loss.
Temperatures have been on a roller coaster. Soil temperatures are recorded by the automated weather stations maintained by the Northern Colorado Water Conservancy District (www.ncwcd.org). There are stations at Wiggins, Ft. Morgan, Brush, Sterling, Crook, and Ovid that serve the irrigated area along the South Platte River in northeastern Colorado. Another source is the CoAgMet (http://ccc.atmos.colostate.edu/~coagmet/index.php) stations scattered across the farming areas of Colorado.
The lower threshold temperature for some winter annual weeds is 40 degrees Fahrenheit. For alfalfa and winter wheat the lower temperature is 45 degrees. For corn, it is 50. For sorghum and summer annual weeds, the lower threshold is 55 to 60. For dry beans and proso millet, 60 degrees.
Paying attention to soil temperatures can take some anxiety out of the decision of when to start planting. A week or 10 days of temperatures at or above the threshold should occur before you assume the soil can maintain an ideal temperature for crop emergence and growth. This years record proves even that waiting period can be perilous on occasion.