|The effects flowering date has on pollination
Studies in New Zealand have shown cherimoya trees generally have a flowering period of two months, usually somewhere between December and February, with about 80% opening during the middle four weeks. There can be daily variations in flower numbers ranging from 0 to 100 per tree, with a total of approximately 1,000 flowers over the entire two months.
Pollen viability appears high, except at the start and end of flowering when lower viability can result in poor fruit set and retention. Fruit set in the middle period is generally high and a large percentage of flowers pollinated (5090%) should produce fruit that will stay until harvest. Flowers should be pollinated regularly throughout the flowering peak to maximise crops of exportable fruit, with early and late opening flowers best avoided.
Flowers opening on cool nights (below 12ºC) and in low humidity can result in poor pollination and tend to produce few fruit.
The studies also showed pollination date has a big effect on the number and average weight of seeds in fruit. The average seed weight of 0.7g at the start of flowering can decrease to less than 0.2g at the end, which causes a drop in the average fruit weight as hormones released from seeds are essential for fruit growth. The later in the season flowers were pollinated, the more seeds the fruit contained. Fruit from flowers pollinated at the peak of flowering were found to have a desirable level of 11 seeds per 100g of flesh, compared with an unacceptably seedy 59 seeds in fruit from flowers pollinated at the end of flowering.
Cropping potential appears to be greatest in the third and fourth week during the flowering peak when flower numbers, fruit set and average fruit weight are highest. At the start of flowering, flower numbers and fruit set can be low, while at the end of flowering the average fruit weight, fruit set and a high seed content result in fruit of an undesirable quality caused by the decreasing average seed weight.
Though the flowers pollinated earliest give the earliest fruit, its usually less effective in terms of percentage of fruit set and size. However, the earliest fruit is most desirable because anticipation is greatest and prices are highest.
Potential cropping of cherimoya for each pollination day, from a study done in New Zealand on the White variety
In this study January 13 had the best overall results