Harry Brook, crop specialist at the Alberta Ag-Info Centre says that the most important question to be answered this fall is, “Will my crop mature before a killing frost?”

“You can’t predict the weather,” he adds, “But you can use a variety of information sources to estimate the likelihood of getting the crop to maturity.”

Brook says to use the tools available on the Alberta Climate Information Service (ACIS) to estimate the risk and likelihood of harvesting a mature crop.

“In Central Alberta there is a 50% chance of a killing frost – where the temperature drops to -3 C in the last week of September. From that, we can estimate the number of growing degree days (GDD) until the end of September. We can expect about 350 to 400 GDD for that time during an average year. Remember, average also means there are years where the growing season does not extend to the end of September.”

Brook says that GDD is a way of calculating the heat value, from a plant’s point of view, each day.

“It is calculated adding the days’ maximum and minimum temperatures. This number is divided by 2 to get an average. Then, the base temperature is subtracted from the average. Most often 5 C is used as the base temperature, as most of our crop plants stop photosynthesis at 5 C. This system of GDD is more consistent at predicting when plant growth stages will occur.”

He says that looking at the Using Growing Degree Days to Predict Plant Stages - developed at the University of Montana and based on work by Stu Brandt from Agriculture and Agri-Food Canada (AAFC) - canola will take about 500 GDD from seed fill to swath timing.

“That would still include more warm weather once swathing stage is achieved, to get it to dry down for harvest. There are canola crops out there that will almost certainly not mature before a killing frost. Barley takes about 350 GDD to go from the soft dough to full maturity.”

He adds that another issue with this year’s crop is due to the quest to maximize yield.

“Many producers use varieties that take a longer time to mature, which work out in a hot summer. Crop yield is directly related to crop maturity. A cold or cool growing season - as we are experiencing this year - will place a lot of the crops seeded late or varieties that require more heat, at high risk of frost damage.”

“Regrowth from early hail also complicates the picture,” Brook explains. “You have a crop with mixed maturities, some starting to dry down, while plants are still flowering. If there is an approximate even split between the two crops, how can it be harvested without high losses? Even if there is only a small percentage of secondary growth, it can complicate the harvest process. Sometimes, other harvesting methods or using the crop for feed can make economic sense.”

He adds to make an informed decision. “If the crop is too immature and it is doubtful that it will mature to grain or oilseed then consider the forage option. Depending on your area and livestock demand, it can be much less of a headache than finding a home for poor quality grain or oilseeds. Leaving this decision too late will reduce its feed value and return - as a forage.”


Connect with the Alberta Ag-Info Centre:

Hours: 8 am to 5 pm (open Monday to Friday, closed statutory holidays)
Toll free: 310-FARM (3276)