The ‘delicate dance’ of pollen collection

In Tasman Kiwifruit orchards, an intricate process takes place each year to guarantee effective pollination and abundant fruit yield.

Central to this delicate dance is the careful collection, processing, and application of male pollen—a critical component in supplementing natural kiwifruit pollination.

Steve Spark from Pollen Plus South Island Ltd says: “We have been collecting and milling pollen in the Tasman districts for 18 years.  It’s a process that was developed back in the 80s but is still very effective today.”

Steve explains that there are various reasons for harvesting and applying kiwifruit pollen.

“When it’s raining bees won’t fly, which can disrupt pollination, particularly if the rain continues for several days. Some orchards may also not have enough male vines evenly distributed across the block for effective pollination, or the existing males might not synchronise satisfactorily (open at the same time as the female flowers).

“Hayward requires 40 bee visits for successful pollination, and during wet springs, this sometimes may not happen. As a result, growers need a reliable alternative to guarantee pollination.”

Collecting male pollen begins with harvesting male kiwifruit flowers before they fully open. The timing is critical to preserve the pollen within the anthers—the part of the flower that contains the pollen and its viability. These freshly harvested flowers are swiftly transported to a specialised facility known as a pollen mill.

“Pollen Plus South Island employ a team of 100 to pick the unopened male flowers over  last three weeks in November, then delivered regularly throughout the day to the mill,” Steve says.

At the pollen mill, flowers undergo precise techniques to extract and prepare the pollen.

“We use rotating drums called tumblers to separate the anthers from the flower. The anthers then go into ovens to dry the pollen overnight before it is finally processed and packaged and sealed into 250-gram jars,” explains Steve.

After processing, pollen can be stored for up to eight years in a freezer, providing growers with an insurance policy for future rain events that might affect pollination.

The next step is applying the pollen onto the female plants, which growers do using various methods. Dry application is the most common whereby pollen is dispersed by modified leaf blowers or similar. This blows the pollen onto the female flowers and bees can also transfer pollen onto other flowers as they visit them.

Wet application is the other common method which involves using a boom sprayer to apply pollen in solution to the flowers. Pollen is mixed in deionised water and spray aid and then sprayed directly onto the opened flowers. This system can use more pollen but does allow pollination to occur during rain when the bees are not flying. The wet pollen application method is good insurance when the weather conditions are not conducive to good bee pollination, providing a safeguard against poor pollination rates.

“Applying supplementary pollination helps growers maximise the chances of improving fruit set and fruit size which is often associated with improved dry matter (taste), and increased yields of higher-quality fruit,” Steve adds.

Biosecurity measures restrict pollen movement from the North Island to the South Island due to PSA (Pseudomonas syringae pv. actinidiae) disease, but there are no restrictions on moving pollen from the PSA-free South Island to the North.

“We first supply pollen to local kiwifruit growers without access to a pollen mill, and any surplus can then be offered to North Island growers who don’t want pollen from orchards affected by PSA. Many growers handle their own flower harvesting, and we process their flowers and return pollen to them to ensure they have a reliable supply for future seasons,” Steve explains.

The ability to harvest and store male pollen for extended periods has significantly reduced pollination risks for growers, and it has also led to trials with other fruits crops such as apples and more recently cherries to ensure consistent pollination.

“Apples didn’t perform as well since apple flowers produce less pollen than kiwifruit. Currently, there’s some research in cherry pollen, so we’ll have to wait and see,” Steve concludes.