Sunflower Development and Growing Degree Days (GDD) (07/21/21)
The USDA weekly crop progress report stated that by May 23, 30% of the sunflower acres were planted, and 5% of the sunflower crop was flowering as of July 18. Sunflower growth and development is related to the accumulation of heat or temperature units above a threshold or base temperature below which little growth occurs. The base temperature for sunflower is 44°F. In some crops, there is also an upper threshold temperature above which little or no growth occurs however, no upper limit has been identified for sunflower. Although temperature is the most important factor controlling the rate of plant development, other factors such as plant available water and daylight length may modify its effects. North Dakota is currently in a drought period; however, sunflower has a deep taproot allowing the crop to extract soil moisture from deep in the profile.
Accumulated growing degree-days (GDD) are used to predict plant development rate and growth stage. In sunflower, this information is used to help plan crop management decisions such as insecticide application timing or harvesting. The sunflower growth stage for a specific planting date and location can be estimated by selecting “Sunflower GDD” under the application section of the NDAWN web site. In graph 1, I used the mapping function for a May 23 planting date. Similar maps can be created for other planting dates.
Table 1 provides a short description and the approximate accumulated GDD after planting, to reach a specific growth stage. A more detailed growth stage description can be found in the extension publication “Stages of Sunflower Development”.
The flowering growth stage should be appearing soon across the state according to the growth stage calculator. Flowering is a critical stage for insect management and producers should scout sunflower fields regularly during this critical period in order to establish if economic insect thresholds are reached.
Extension Agronomist Broadleaf Crops