Abstract:Crop cycles in spring canola (Brassica napus L.) and carinata (Brassica carinata A. Braun) are controlled by temperature and photoperiod. In the central region of South America, which accounts for 90% of South American rapeseed crop production, farmers seek to sow as early as possible to maximize yield even though early sowing dates expose crops to a higher probability of frost occurrence that had not been quantified before. Our objective was to model phenology for one spring cultivar of canola (?Rivette?) and one of carinata (?Avanza 641?) and assess the probability of frost occurrence during flowering and grain filling in the central region of South America. For the estimation of frost risk, we modeled phenology resulting from 15 April to 15 August sowing dates at 12 locations (from 31.16˚ to 34.20˚ S latitude). We assumed that the critical period spans from 100 to 500 growing degree days (GDD) after flowering. Under early sowing dates, carinata tends to have a longer cycle (200 GDD more than canola) although both crops had a similar cycle lengthunder a late sowing date. Predicted and observed flowering dates showed an average difference of 1.6 and 0.95 d for canola and carinata, respectively. Carinata has a lower probability of suffering frost events, and early sowing dates result in a greater exposure to frost damage. The results of this work will enable farmers and stakeholders to know the potential frost risk when defining a sowing date for canola and carinata. © 2022 The Authors. Agronomy Journal © 2022 American Society of Agronomy.