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Title: Hydrothermal emergence model for ripgut brome (Bromus diandrus)

item GARCIA, ADDY - Universitat De Lleida
item TORRA, JOSE - Universitat De Lleida
item RECASAENS, JORDI - Universitat De Lleida
item Forcella, Frank
item ROYO-ESNAL, ARTIZ - Universitat De Lleida

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2012
Publication Date: 1/1/2013
Citation: Garcia, A.L., Torra, J., Recasaens, J., Forcella, F., Royo-Esnal, A. 2013. Hydrothermal emergence model for ripgut brome (Bromus diandrus). Weed Science. 61:146-153.

Interpretive Summary: Ripgut brome (aka great brome) is a weedy grass of Mediterranean-type climatic regions, such as Spain and California. Although it can be an appreciable problem for livestock grazing in rangelands and arable fields after crops have been harvested, it also is a serious competitor with actively growing crops like winter barley and wheat. By knowing when ripgut brome seedlings emerge in autumn relative to when winter cereals are planted, farmers can time the preparation of seedbeds and sowing of their crops to minimize populations of ripgut brome. To do so, however, requires knowledge of environmental factors that govern seedling emergence of this weed. Emergence of seedlings was monitored in several fields in different years in northeastern and southern Spain. Additionally, soil temperature and soil moisture were simulated in each of these fields for the corresponding years. These two variables were combined into an index referred to as hydrothermal time (HTT) for the top two inches (5 cm) of soil. HTT is nearly identical to growing degree days, except that it includes soil moisture as well as soil temperature. Using data from select fields in northeastern Spain, a mathematical model was created to simulate emergence of ripgut brome seedlings. We examined the accuracy of the model by comparing predictions to observations in other fields in northeastern Spain as well as data from entirely independent field and populations in southern Spain. The model simulations compared highly favourably with observations for all sites, which means that this new model likely can be used at any location (including California) where ripgut brome causes problems. Researchers, farm advisors, and the agrichemical industry will benefit from using this model by assisting farmers in making wise decisions regarding seedbed preparation and planting dates wherever high ripgut brome populations exist. These decisions will enable farmers to minimize the densities of this important weed in their winter cereal fields prior to deciding if additional mechanical or chemical control tactics are necessary.

Technical Abstract: A model that describes the emergence of ripgut brome (Bromus diandrus) was developed using a two-season data set from a no-tilled field in northeastern Spain. The relationship between cumulative emergence and hydrothermal time (HTT) was described by a sigmoid growth function (Chapman equation). HTT was calculated with a set of water potentials and temperatures, iteratively used, to determine the base water potential and base temperature. Emergence of ripgut brome was well described with the Chapman function. The newly developed function was validated with four sets of data: two of them belonging to a third season in the same field and the other two coming from independent data from southern Spain. The model also described the emergence successfully in different field management and tillage systems. This model may be useful for predicting ripgut brome emergence in winter cereal fields of semiarid Mediterranean regions.