Almonds are susceptible to frost once they begin to flower. As a flower progresses through bloom (i.e. dormant > pink bud > full bloom > petal fall > small fruit), it becomes more susceptible to cold temperatures. Frost killed flowers/small fruits are easy to identify as the color of the tissue changes. Flowers affected by bloom often have wilted petals or blackened pistils. At petal fall and later, the damage often appears as brown or black tissue within the ovary. This can be identified by cutting the flower/nutlet in half.
The photo provides a comparison of flowers affected by frost and a healthy flower. Note the darkened, off-color tissue of the three flowers on the right. All of these have been killed by the frost.
Flower sensitivity to cold damage has been studies. Additional information on this can be found here.
John E. Lasgoity
March 5, 2023How can one tell if the flower has not been pollinated?
How important is the timing on a bloom spray? I’m well past the height of boom and haven’t been able to apply the spray.
Davidd
April 29, 2023John,
It is very hard to know if a flower is pollinated. The stamens can be viewed to see if the pollen has been removed. This is often a sign that the flower has been pollinated. Sometimes the pistil will appear slightly gray, but still alive (not brown).
RE: spray timing: It depends on your varieties. Butte is very susceptible to brown rot, and a bloom spray in wet conditions is critical. For Nonpareil, the petal fall timing is one of the most important timings. Missing this will increase the risk of a variety of diseases, including anthracnose or jacket rot.
If the timing has been missed by a few days, disease occurrence will be minimal. If it has been several weeks with several rain events, the inoculum will build, and losses will increase. I know this is not really an answer, but there are many variables that affect the need and importance of timing.
David