Heat and drought can cause flower abortion

Hot days (28-30°C and up) and warm nights (16°C and up) from bud to mid-flowering stages can have a devastating effect on canola yield. Cool nights offer some recovery from hot days. Warm nights do not provide a recovery period, and more flowers are aborted, producing blanks along the stem. Even with a few days of heat, it can take a week for hormone balance and regular pod formation to return. Recently opened flowers with shortened stamens that don’t protrude above the petals can be a sign of heat damage. These flowers are not likely to produce pods.

Map source: Weatherfarm.com

Moisture stress during reproductive stages can cause a hormone imbalance that disrupts pod formation and seed set. In a drought, canola plants will progressively drop later flowers at the top of the main raceme and on branches, and put energy into preserving the pods it has. If moisture returns, plants can start sustaining flowers again, resulting in a stem with pods at the bottom and top but nothing in the middle. Additional symptoms of drought include leaf wilting, and flowers with smaller petals that may be off-color (pale or yellowish-orange), or flower buds that die before fully opening.