|Why hand pollinate?
Before reading this section, we recommend reading about the cherimoya flower in the Description section.
The biggest problem with growing cherimoya is how few fruit will set naturally (less than 5%), with most being of poor size and shape and no good for commercial use. Natural pollination in New Zealand is mostly achieved by wind, with the standard result being small, misshapen fruit (as little pollen can reach the many pollen receiving stigmas, which then develop into fruit). Lack of pollen-transferring insects in New Zealand and the unique nature of the cherimoya further limits the chances for natural pollination.
Although a single flower will have both male and female structures, they will mature at different times. In female-stage flowers, receptivity to pollination begins just before petal separation. The flower opens in the morning with the petals separating at their tips to partially expose the glistening stigmas of the many receptive pistils. Pollinate when the petals have clearly separated. The female phase lasts all that day and the next day, and fruit set is quite high until the afternoon of the second day when the stigmas become dry.
After this time, receptivity drops rapidly, and the flower progresses into the male stage of flowering. The petals of the flower are now open wide and the anthers begin to shed their pollen. Since the receptivity of the stigmas is absent or very low at the time pollen is shed, self pollination rarely occurs, but when it does fruit are often a small irregular shape due to uneven distribution of pollen.
By naturally not synchronizing the flower to be receptive at the same time as the pollen matures, it ensures that it doesnt pollinate itself, and allows a flower only to be pollinated by another flower, which might be from the same tree (at a different development stage) or from a different tree. This improves the chance for genetic interchange, which must be an evolutionary advantage.
Hand pollination is necessary in New Zealand to set a large crop of potentially exportable fruit of good size and shape. Pollinating cherimoya is relatively fast (150250 flowers per hour) and economically viable with 6090% of pollinated flowers producing fruit. The symmetry of the fruit is directly related to pollination effectiveness.
The results of successful pollinating
Cherimoya trees in New Zealand flower for about two months (sometime between December and February, depending on the variety), with each tree producing up to 1,000 flowers, mostly on new growth. Pollinating over the entire flowering season is not recommended as the pollinating date can affect the fruit development.
Hand pollination provides many advantages to the grower, such as dictating the positioning of fruit on the tree, which makes harvesting and handling easier. Growers can also control and extend the ripening and harvest season by only pollinating every four to five days. Some studies suggest the fruits skin texture can also be influenced by the choice of pollen (male) parent. Fruit size could possibly be dictated by the amount of pollen used to set the fruit.
Next when to pollinate