Synopsis: First king bloom on Empire, one of our earliest blooming varieties at the Hudson Valley Research Laboratory orchards (mid-Hudson Valley), occurred April 29th. From April 29th – May 5th, the mean daily temperature was 52.8F, ranging from 48.3F to 57.3F. Over the past 6-days cloudy and wet weather prevailed with cool or mild temperatures.
Environmental conditions have been generally poor for pollinator flight activity hampered by cloud cover and rain through early to mid stages of bloom. Aside from wind driven pollen distribution in apple where pollinator trees are upwind, its is likely orchards experienced a pollination deficit last week.
For apple, pollination must occur within 2 to 4 days after the flowers open for fruit to set. As these cool temperatures reduced pollinator flight, decreased pollination of the king blossoms are likely. Maintaining and conserving pollinators during upcoming pest management applications should be taken into account using tools with low impact to pollinators during pollination.
We are presently at or near full bloom in most apple varieties. Temperatures on May 7th & 9th (Monday and Wednesday) are forecast to be in the low 70’s with partly cloudy skies. These two days will be critical for fungicide applications. It will also be important for pollinations as temperatures creep into the low 70’s.
Improving pollination has been shown to increase production owing to larger and better-shaped fruit and/or a greater number of fruit per tree. Research is presently underway to use electrostatic sprayers to apply pollen during bloom. Results have shown increased apple fruit set between 56 and 75 percent higher compared to natural pollination in Washington State trials.
Orchard Pollination: Pollinizers, Pollinators and Weather
Excerpts taken from Penn State’s Dr Robert Crassweller
Cold periods during flowering can reduce pollination and subsequent fruit set. Pollen may fail to germinate when temperatures are below 41°F, and pollen tube growth is extremely slow below 51°F. Therefore, in some situations, temperatures could be warm enough for bees to fly (65°F for the honey bee, 5 to 10 degrees cooler for bumble bees and solitary bees), but if the weather turns cold, the pollen tubes may not grow fast enough before the embryo sac deteriorates.
Effective Pollination Period (EPP)
The effective pollination period (EPP) is the difference between the period of time for pollen tube growth and that of ovule longevity. The longer the effective pollination period, the greater the likelihood of adequate fertilization and seed development. Pollination must occur within 2 to 4 days after the flowers open; otherwise, the embryo sac will degenerate before fertilization can occur. Studies have shown that this period can vary depending on cultivar. The growth of the pollen tube and eventual fertilization of the embryo is largely dependent on temperature and its relationship to the effective pollination period.
The EPP was introduced in the mid-1960s as a way of establishing the time frame between when a flower is pollinated and when the embryo becomes unreceptive. After pollination it takes a certain time for the pollen tube to reach the embryo sac. Once a flower opens, the embryo has only a limited time when it is receptive. If the pollen tube does not reach the embryo before it degenerates, then the flower will not set. The length of the EPP will vary by flower position within the cluster and by certain cultural practices. In general, the EPP can be as short as 3 days and as long as 12 days; Delicious has one of the shortest EPPs. Williams and Wilson developed a temperature response index to allow the estimation of the time required for a pollen tube to grow to the embryo (see below). The index is based on the daily mean temperature over a period of days. When the index reaches or exceeds 100 percent, the pollen tube should have reached the embryo and fertilized the egg. As an example, suppose the average mean temperature over the past five days had been 50, 54, 50, 52, and 59 degrees. Pollen tube growth would be expected to be 14 + 20 + 14 + 17 +50 = 115 percent, meaning pollen tube growth would have taken slightly less than 5 days.