Pershang Hosseini - Department of Agronomy and Plant Breeding, Bu-Ali Sina University, Hamedan, Iran
Goudarz Ahmadvand - Department of Agronomy and Plant Breeding, Bu-Ali Sina University, Hamedan, Iran
Mostafa Oveisi - Department of Agronomy and Plant Breeding, University of Tehran, Karaj, Iran

Phelipanche aegyptiaca is one of the most important parasitic weeds in some crops including potato. There is a delay between host planting and appearance of broomrape species called lag phase. Time of this period is vary with different hosts, broomrape species and planting date. Lag phase is an important period for the precise herbicide usage timing and it’s predictable by thermal time models like Weibull equation. Predictive models can be useful to choose the best management options and times and, thereby, improve weed control. 2 years experiments with 6 planting dates used for estimating lag phase of P. aegyptiaca and potato. Every week, potato plants were carefully hand harvested from 50 cm-long rows in four random samples in each experiment, roots were washed and P.aegyptiaca infestation was measured by counting the smallest visible attachments. The lag phase estimated with fitting Weibull model to cumulative attachments of P.aegyptiaca data and thermal time (soil temperature). The result showed that, late planting decreased lag phase. 30 days difference in planting date shortened lag phase from 390.46 to 311.59 GDD and thereby, time for using herbicides and finally reducing herbicides usage.

Thermal time model, Soil temperature, Weibull model, potato