Thursday, July 11, 2013

Rainy Days Pollination Blues!

 Guest post by David L. Green, retired commercial bee keeper, former editor of small newspaper, teacher. You can visit his website and his blog

Partially pollinated cucumbers. © Dave Green, 2013

With seven inches of rain in five days, bees had very little time to work. They delivered enough pollen grains so that the cucumbers did not abort, but not enough to flesh them out.

The one at left is a total lack of fertilization of the seeds at one end - that meant that the flesh did not grow, and the cuke had a "tail." Three more are slightly better. The one at the bottom has few of the incipient seeds fertilized in the middle, giving a waist to the cuke. These poorly pollinated cukes grow slowly and quickly get tough, sometimes bitter, as well.

If bee populations are normal, this problem should straighten out when the weather is more suited to bee flight. If you get very many like this in good pollination weather, you have a shortage of bees, and may need to work on increasing bee populations or hand pollinate.

My garden is pollinated by a mix of bees, with the bulk of the workload carried by bumblebees and honey bees, but we also have green sweat bees, squash bees, digger (Anthophora) bees, tiny Ceratina bees, and leaf cutter bees doing some of that work.

To make a perfect cucumber, you need to get almost all of the incipient seeds fertilized. That requires two grains of pollen - one for the embryo and one for the seed coat, so each perfectly pollinated cuke represents several hundred grains of pollen delivered to the flower.

A lot of folks think that, if they see a bee in a flower, that pollination is accomplished. But it's not an on/off switch. It's a progressive thing. It takes many bee visits to deliver all the pollen needed for multi-seeded fruits.

Every year, more and more gardeners report the symptoms of lack of pollination in their gardens. The problem seems to be accelerating.

It represents one of our most urgent environmental problems - pollinator decline. Our bees are disappearing. Some of that is due to habitat loss; some due to monoculture and its feast or famine pattern of intense bloom, followed by barrenness; some is from new diseases and parasites; but the worst and most difficult problem to solve is the loss caused by pesticides.

When cotton blooms, bees focus on those nectar-rich blossoms, and drop by the millions when the cotton is sprayed. In July clover is in full bloom in the orchard floor, and more millions of bees die when the fruit is sprayed. Community mosquito sprays are supposed to be applied when bees are not working, but this time limit is very poorly observed, and many more bees are dropped from applications done when they are out. And many gardeners plaster Sevin dust all over their gardens without thought of the bees.

All four of these cases I mentioned are illegal applications, because the label directions forbid them, but label enforcement is rare and usually amounts to a slap on the wrist, if anything.

So, if we do not begin to protect our pollinators - we lose much of the vitamin C (fruits) in our diet. Food costs will rise; only the rich will be able to afford many of the most nutrient-rich foods we have. We are left with grains that do not need bees - but remember that "man shall not live by bread alone."

© Dave Green, 2013
Retired pollination contractor


  1. Mr. Green, I enjoyed your article and I thank Dr. Moisset for posting it. I recently focused on pesticides in my blog "Pollinator Gardens", and in particular the neonicotinoid pesticides and their threat to a number of species. I'm glad to see that you agree that "the worst and most difficult problem to solve is the loss caused by pesticides".

    Dr. Moisset rebuked me for not mentioning all the other problems bees face in my blog; you did mention some of them. Kudos. But you (correctly, to my mind) fingered pesticides as the worst problem.

    I've spoken in public on this until I was blue in the face, and attended many other talks by eminent scientists on this topic. Many of them carefully lay out all the different factors that could be involved. No headlines, no public response. In fact, I've heard representatives of Syngenta and Monsanto and Bayer use this quite cleverly: when they speak about the challenges facing bees, they focus exclusively on diseases or mites, diverting attention away from their chemicals.

    Those of us who speak out on these issues to the public have to learn to be effective public communicators. That means giving a clear message, as you did. Recently I appeared on television with beekeeper Dave Schuit who had brought almost all his hives safely through the Canadian winter, only to lose 70% of them in a day at corn planting time. When the TV interviewer asked Dave what was the cause, he said "neonicotinoids on the corn seeds". The camera then turned to me and the question was repeated. I mentioned that bees had multiple challenges, but that the biggest one was neonics. This was perhaps not good scientific form (I didn't hedge and haw about maybe this and maybe that), but Dave had just lost his livelihood and I felt the most likely culprit needed to fingered and named.

    Thanks for speaking out on this topic.
    Clement Kent

  2. "To make a perfect cucumber, you need to get almost all of the incipient seeds fertilized. That requires two grains of pollen - one for the embryo and one for the seed coat" isn't quite right. Each pollen grain has two nuclei: one fertilizes the egg to produce the embryo and the other fertilizes two polar nuclei in the ovule to produce the triploid endosperm that "feeds" the growing embryo. So, in theory, only one pollen grain is needed to make one seed. But I've heard that the ratio is more like 100 pollen grains per seed, due to pollen loss on the stigma and pollen competition within the style.

    1. Thanks for your comment. It makes sense.