Watermelon pollination

Beekeepers in the Pacific Northwest are not blessed with the high honey yields of beekeepers in other regions of the country. They are more reliant on renting their bees to pollinate crops and fortunately the agriculture of the PNW has a variety and abundance of commercially grown crops that require or benefit from honeybee pollination. In our work as the PNW Tech Team, Ellen and I are fortunate to work with our beekeepers and sample their colonies while pollinating many different crops in the region. This is the first installment of a series of ‘Crop Pollination Profiles’ where I’ll outline the basics of cultivating each crop and the role the bees play.

Watermelons are widely grown near Hermiston in Eastern Oregon

Watermelons are widely grown near Hermiston in Eastern Oregon

Colonies pollinating watermelons near Hermiston, OR

Colonies pollinating watermelons near Hermiston, OR

Young watermelon plant growing through plastic mulch

Young watermelon plant growing through plastic mulch

Watermelon (Citrullus lanatus) is a vine-like annual in the Cucurbit family with cucumbers, squash, gourds and other melons. It favors an abundance of sunshine, warm nights and loose, well-drained soil.

Melons require a good deal of water and grow well in sandy/loamy soils with the aid of irrigation. Watermelons are commercially cultivated in raised soil rows with individual plants being spaced 2-3 feet apart with 5-8 feet between rows. Typically black plastic mulch with drip irrigation underneath is used to facilitate ideal growth conditions. The plastic sheeting provides several benefits including, increasing soil temperature, moisture retention, and weed control.

Watermelon rows alternating with rows of wheat for windbreak

Watermelon rows alternating with rows of wheat for windbreak

Often a cereal crop (e.g. wheat) is inter-sown between melon rows to provide windbreak and protect young plants.

Female flower with visible ovary

Female flower with visible ovary

Watermelon plants are self-fertile and bear separate male and female flowers on the same plant. Flowers are approximately 1-inch in diameter and range from pale to bright yellow.

Forager on male flower

Forager on male flower

The pollination window is drawn out over a few months with plants producing a new flush of blooms after picking mature fruits. Hired colonies are required for longer than most crops with colonies being placed in fields from late May until early September. Pollination rental rates are in the range of $60-$70/colony. While the overall bloom of a field is drawn out, individual female flowers are only receptive to pollination for a single day. Flowers open early in the morning and close by the afternoon with peak pollination occurring in mid-morning.

Proper pollination is essential to achieve well sized symmetrical fruits. Colonies are stocked at 1.5-2 colonies/acre depending on grower preference. Bees can forage pollen and nectar from watermelon but the flowers aren’t particular attractive if alternative forage exists nearby. Watermelon pollen is bright yellow and the photo below shows the lack of alternative forage available to bees in this field.

Pollen trapped from colonies in watermelon fields showing low diversity of forage available

Pollen trapped from colonies in watermelon fields showing low diversity of forage available

Due to the relatively low flower density, limited amount of pollen and nectar available, and extended duration of pollination bees may require supplemental feeding while in watermelons to remain in robust health.

Written By: Dan Wyns

Dan Wyns has written 17 post in this blog.

I was introduced to honey bees over a decade ago while in New Zealand on a working holiday and have been consumed with caring for and learning about them ever since. Prior to joining BIP I was a commercial beekeeper in New Zealand and western Canada where I was fortunate to gain a diversity of beekeeping experience across a variety of climates and agricultural landscapes. I joined BIP in 2014 as a member of the PNW tech transfer team and spent 3 years working with beekeepers across OR, WA and ID. The addition of a Tech Transfer position in Michigan has allowed me to carry on working with bees and beekeepers while relocating to my home state.  I was born in Grand Rapids, raised in Grand Haven, and studied in Ann Arbor so the opportunity to serve the beekeeping community here is especially satisfying. My family roots run deep in Michigan horticulture and I look forward to continuing that tradition by working to promote colony health and support local agriculture.

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