The spray window for sclerotinia stem rot is 20-50 per cent flower and for cabbage seedpod weevil is 10-20 per cent flower. See the Canola Encyclopedia for the most detailed description of these stages, including images. (Look for Stage 6.)
To assess flowering stage, count all “flowers” — which includes open flowers, aborted flowers and developing pods — on the main stem. Plant population is not a major factor in staging, but because stands with fewer plants per square foot (say five or fewer) can have more flowers on the main stem, you could bump up the counts by a couple of flowers to estimate the flower stage for reduced plant stands.
Count main stem flowers at a few sites in the field and take an average to come up with flowering stage for the field. For example, if you check 10 random plants and three or four are at 30 per cent flower and some are at zero percent, the average is probably around 15 per cent.
At 10 per cent flower, the main stem will have around 10 open flowers. It takes two to four days to go from first flower to 10 per cent bloom.
At 20 per cent flower, the main stem will have 14 to 16 open flowers. Canola can reach 20 per cent bloom within four to five days after first flower.
At 30 per cent flower, petal drop will be happening. If those petals are infested with sclerotinia spores, infection can start within a day. This stage will be reached six to 10 days after first flower.
At 50 per cent flower, the crop is at its “most yellow.” Main stems will have 20+ flowers AND developing pods on the main stem, and side branches are starting to flower. This stage can last a week or more in crops with lower plant counts that result in higher numbers of secondary branching. If track growing degree days (GDD), it takes about 300 GDD to go from first flower to 50 per cent flower.