Comparison of Morphological Development Indexes for Switchgrass and Bermudagrass

In 1994, the Crop Science Society of America (CSSA) appointed an ad hoc committee to study various developmental indexes for crops. As part of this committee's activity, our objective was to compare three developmental indexes for use with switchgrass (Panicum virgatum L.) and two indexes for use with bermudagrass [Cynodon dactylon (L.) Pers]. Two cultivars of switchgrass (Alamo and Cave-in-Rock at Stephenville, TX, and Kanlow and Cave-in-Rock at Ames, IA) were scored once or twice weekly during primary growth according to the Nebraska index, the Texas Agricultural Experiment Station (TAES) index, and the BBCH (European) uniform decimal code. Two hybrids of bermudagrass (Midland and Tifton-44 at Fayetteville, AR, and Coastal and Tifton-44 at Stephenville) were scored once or twice weekly during a spring and summer growth cycle according to the BBCH system and an index developed for bermudagrass (West index). The main difference among scales was that the Nebraska and TAES scales were developed for perennial grasses, whereas the BBCH index is a generic scale with some stage descriptors not applicable to perennial grasses. The indexes share several common stage descriptors, but with different decimal codes. For bermudagrass, the main limitation with the BBCH system was that it applied to grass crops having a well-defined main stem and sideshoots (tillers) and a relatively uniform maturation of the shoots. The BBCH Principal Growth Stages 2 and 3 were difficult to reconcile with the West system, which does not define tillering, whereas subsequent principal stages are reconcilable with minor modifications. We conclude that the BBCH index would require substantial modification to adapt the system for perennial forage grasses.