Spring temperatures, pollination- a refresher – Facts for Fancy Fruit

Spring temperatures, pollination- a refresher

Spring temperatures

It seems like spring is progressing slowly, and in some respects it is. At this time of the year, the rate of plant development depends largely on temperature. The warmer it is, the faster plants develop. Early in the season we hope for cool weather to slow down bud development. This is so buds don’t develop too much early in the season and become vulnerable to frost damage. This year is highlighted with the thick black line on the graph. As you’ll see, we’re about average for the last few years. Most of the recent upswing in the accumulated GDD is due to a few warm days last weekend.

Lafayette temperatures

Lafayette temperatures

Pollination – a refresher

Then a little later in the spring, we’re hoping for warmer weather for good pollen tube growth.
As we all know, apples require cross pollination, so for example Golden Delicious pollen will not fertilize Golden Delicious flowers. We rely on bees and other insects to transfer pollen from one apple variety to another. Most apples will successfully pollinate most other varieties, with the exception of triploid varieties such as Jonagold and Winesap. Once the pollen is transferred to the stigmatic surface of a flower, it has to be recognized and then grow down the style to fertilize the ovule resulting in a seed and fruit set. Generally, without seeds, apple fruits will not develop adequately. The problem here is that the ovule is only receptive for a few days so rapid pollen tube growth down the style is necessary. And this all depends on the temperature. When it’s 50-60 F, pollen tube growth is slow, and don’t grow much at all when it’s cooler than 50F. Above 60 F and pollen tube growth is much quicker and fruit set is much more likely. So now that we have open flowers in many parts of the state, we’re hoping for days above 60, and preferably in the 70s. In many parts of the state temperatures over the next week are forecast to be in the 60-70 range so hopefully we’ll have good pollination weather and have good fruit set.

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