Predicting timing of downy brome (Bromus tectorum) seed production using growing degree days

Abstract

Downy brome in dryland winter wheat presents a major constraint to the adoption of reduced tillage cropping systems in the Pacific Northwest of the United States. Effective suppression of downy brome during fallow periods depletes seed in the soil and reduces infestations in subsequent winter wheat crops. Delayed tillage operations or delayed herbicide applications in the spring increase the risk for production of viable downy brome seed during fallow periods. In a series of studies, downy brome panicles were sequentially sampled at Pendleton, OR, and Pullman, WA, in 1996 and 1997, and at nine locations around the winter wheat growing region of the western United States in 1999 and 2001. Cumulative growing degree days (GDD) were calculated using local, daily maximum, and minimum air temperature data. A simple GDD model based on the formula GDD = (daily maximum temperature [C] + daily minimum temperature [C])/2, with a base temperature of 0 C and a starting point of January 1, was used to calculate cumulative GDD values for panicle sampling dates. Number of seed germinating per collected panicle was recorded in greenhouse germination tests. Estimations of degree days required for production of viable downy brome seed were made using nonlinear regression of germination on GDD. The GDD value at which viable seed can be found on plants (i.e., when seed germination > 0) was of interest. Estimates of the GDD values at which viable seed could be found in the three studies ranged from 582 GDD at Bozeman, MT, to 1,287 GDD at Stillwater, OK, with a group of GDD values for Pendleton and Pullman around 1,000. Variation in seed-set GDD among locations may be attributed to differing climatic conditions that control vernalization at the various locations or to differences in vernalization requirements among downy brome biotypes (or both).

Accounting for Fitness: Combining Survival and Selection when Assessing Wildlife-Habitat Relationships

“…We calculated several climate variables used for survival models. Growing degree days (GDD) were estimated as the number of degrees above 5º C for each mean daily temperature (Ball et al, 2004), summed over the growing season (beginning 1 March and ending with the tracking date of that year). We also developed a dryness index, which was the GDD for that year divided by the cumulative spring precipitation since the 1 March beginning of the growing season.…”

Comparative plant responses of Puccinellia distans and Puccinellia nuttalliana to sodic versus normal soil types

“…GDD were calculated using a standard GDD model for C 3 grasses (Ball et al, 2004;Klepper et al, 1988)…”

Initial growth and development of southern sandbur based on thermal units

“…In the literature, Bt values = 0 o C are usually considered for weeds and crops in temperate climate, such as barley (Hordeum vulgare) and wheat (Triticum aestivum) (Cao & Moss, 1989;Kirkby, 1995;Shirtliffe et al, 2000;Ball et al, 2004), while for sunflower (Helianthus annuus), Granier & Tardieu (1998) (Kish & Ogle, 1980;Medeiros et al,. 2000), for corn crops (Gadioli et al, 2000), and for forage Panicum virgatum (Sanderson & Wolf, 1995 The ability to predict phenological stages, such as flowering and development and dispersal of weed seeds, may aid the development of management practices (Ghersa & Holt, 1995).…”