emergence prediction of flixweed (descurania sophia) and common lambs quartes (chenopodium album) using thermal model

prediction of seasonal weed seedling emergence patterns is useful in weed management programs. this study was carried out in research fields of islamic azad university – karaj branch in 2009-2010. five crop fields were chosen including: barley, sugar beet and three wheat fields and in each fields between 3 to 5 sites selected randomly. three quadrates were fixed in each sites for studying weeds emergence. weeds emergence was weekly measured during growth season. three models including logistic, gompertz, and weibull, were used to describe weed seedling emergence against thermal time. gompertz model showed the best fit to data. flix weed emergence in barely field started after receiving 5 gdd and reached maximum emergence after 190 gdd. also in wheat fields with similar canopy, weed seedling emergence started in the same time. although weed seedling emergence in these fields was started in 60 gdd and reached maximum emergence after 260 gdd, however weed seedling emergence of common lambs quartes in wheat fields didn’t show similar patterns. in conclusion, growth rate of common lambs quartes increased to the maximum rate with receiving less gdd in compare to flixweed. this phenomenon may be related to their different phonological characteristics of two weeds.