Thermal Time Model for Egyptian Broomrape (Phelipanche aegyptiaca) Parasitism Dynamics in Carrot (Daucus carota L.): Field Validation

Abstract

Carrot, a highly profitable crop in Israel, is severely damaged by <i>Phelipanche aegyptiaca</i> parasitism. Herbicides can effectively control the parasite and prevent damage, but for optimal results, knowledge about the soil-subsurface phenological stage of the parasite is essential. Parasitism dynamics models have been successfully developed for the parasites <i>P. aegyptiaca, Orobanche cumana</i>, and <i>Orobanche minor</i> in the summer crops, tomato, sunflower, and red clover, respectively. However, these models, which are based on a linear relationship between thermal time and the parasitism dynamics, may not necessarily be directly applicable to the <i>P. aegyptiaca</i>-carrot system. The objective of the current study was to develop a thermal time model to predict the effect of <i>P. aegyptiaca</i> parasitism dynamics on carrot growth. For development and validation of the models, data was collected from a temperature-controlled growth experiment and from 13 plots naturally infested with <i>P. aegyptiaca</i> in commercial carrot fields. Our results revealed that <i>P. aegyptiaca</i> development is related to soil temperature. Moreover, unlike <i>P. aegyptiaca</i> parasitism in sunflower and tomato, which could be predicted both a linear model, <i>P. aegyptiaca</i> parasitism dynamics on carrot roots required a nonlinear model, due to the wider range of growth temperatures of both the carrot and the parasite. Hence, two different nonlinear models were developed for optimizing the prediction of <i>P. aegyptiaca</i> parasitism dynamics. Both models, a beta function model and combined model composed of a beta function and a sigmoid curve, were able to predict first <i>P. aegyptiaca</i> attachment. However, overall <i>P. aegyptiaca</i> dynamics was described more accurately by the combined model (RMSE = 14.58 and 10.79, respectively). The results of this study will complement previous studies on <i>P. aegyptiaca</i> management by herbicides to facilitate optimal carrot growth and handling in fields infested with <i>P. aegyptiaca</i>.