Tuesday, March 9, 2010

Cucumbers and Pollinators: (Some) Questions Answered

When I first started my job in WNC in 2008, I was so excited to see that vegetable producers were growing cucumbers. Cucumber was the crop I worked with in my graduate work, so it was the only crop I felt mildly comfortable talking about (though it was still awkward at first).

To my surprise, in many of these production fields, I never saw a beehive. The areas that I had experience with in eastern NC, brought in at least one strong hive per acre of production. To learn more about bees, read Beekeeping and Cucumber Pollination.

How were these folks getting cucumbers? A cucumber flower must be visited multiple times by a pollinator to optimize fruit set. The answer was wild populations on pollinators and the nice sunny, warm weather that promotes activity and foraging of pollinators.

But, in 2009, growers noticed that yields were reduced and that fruit formation was off. The same varieties were grown and there was not downy mildew or other diseases in their early season crops. So what was different?

We were cool, cloudy and wet. How could you forget? The fact is, bees don't aggressively begin to forage until temperatures reach 70 F and they prefer dry conditions.

Could this lack of fruit also be due to a reduced population of wild pollinators? At this point we don't know, but it was obvious that the growers needed to do something. That something was to bring in some honey bee hives.

Here are some pictures of a female cucumber (top) and male cucumber flower (bottom), courtesy of Pollinator.com.

Below is an improperly pollinated fruit.

To see more pictures, visit pollinator.com's Cucumber Pollination: Visual Aids.

But, the growers were concerned. Bringing bees into their production was new and they had many questions - especially in regards to applying pesticides.

Here are a few of the questions that I received. Most answers are from NCSU Beekeeping Note 2.12.

  • Where can I find honey bee hives to rent?
The NCDA&CS Apiary Services and NCSU Apiculture Program have developed Bee Linked, an online market for beekeepers and growers. www.ncagr.com/beelinked
You can also find local beekeepers through the North Carolina Beekeepers Association Website. www.ncbeekeepers.org.

  • When should I apply pesticides to protect the bee hives?
Pesticides that are considered toxic to bees should be applied in the late afternoon (after 3:00 pm) or in the evening. Most honey bees have stopped foraging and have returned to the hive by 3:00 pm. This precaution will allow maximum time for the pesticide to break down before the bees come into contact the next day.
  • What other considerations are important when applying pesticides?
Do your best to minimize drift. Drifting of the pesticide from the target pest and/or crop to areas frequented by bees should be minimized and pesticide formulation is the key to this problem. "Dusts" are prone to drift and are generally more dangerous to bees that sprays or granular applications. For more specifics, read Beekeeping Note 2.12.

Aerial applications are generally more dangerous than ground equipment. This is directly related to drift. Air-blast sprayers are more dangerous that pressurized pump sprayers. Never apply pesticides when wind velocities exceed 8 miles per hour.

Never apply any pesticide directly over a beehive.

Notify beekeepers who have beehives near an area to be treated, so that they may attempt to protect their bees from inadvertent exposure.
  • Are there pesticides that are less toxic to honey bees?
Most pesticides are at least somewhat toxic to honey bees; however, the degree of toxicity varies considerably from product to product. Insecticides are generally the most likely to cause a bee kill. Below are some common pesticide active ingredients listed based on their toxicity to honey bees for a more complete list, see Beekeeping Note 2.12.

  1. Highly Toxic: Severe bee losses may be expected if these products are used when bees are present. Abamectin, aldicarb, avermectin, azinphos-methyl, carbaryl, carbofuran, chlorpyrifos, dimethoate, imidacloprid, malathion, methomyl, pemethrin, spinosad...
  2. Moderately Toxic: These pesticides can be used in the vicinity of bees IF dosage, timing, and method of application are correct. Bifenazate, disulfoton, endosulfan, fluvalinate, oxamyl, propamocarb, pyrethrum, tartar emetic, temephos, terbufos, thidicarb, zephyr...
  3. Relatively Non-Toxic: These pesticides cam be used around bees with a minimum injury IF dosage, timing and method of application are correct. Bacillus thuringiensis, chlordimeform, cryolite, cymiazole, dicofol, dinobuton, esfenvalerate, methoxychlor, myriproxyfen, nicotine, Nosema locustae, pyrethrum, rotenone, tebufenozide, trichlorfon.
Visit the NCSU Apiculture Website for more details on honey bees.

To learn about cucumber production in NC: Fresh Market Production Cucumbers and Commercial Production of Pickling & Slicing Cucumbers in North Carolina.

To learn more about Bee Colony Collapse Disorder, read a scholarly article about the problem in Colony Collapse Disorder: A Descriptive Study.


Sue Colucci said...

From a grower email this morning: *Honey*bees pollinate only down to 70F and in sunny weather, but many of our wild native pollinators (esp. orchard mason bees, on of our most energetic pollinators) work down to 50F and in cloudy or even mild rain conditions.

Thanks for the comment and for sharing the knowledge!

Sue Colucci said...

From another email this morning:
"Same thing for pumpkins and squashes. We have yield losses every year because folks here don’t hire bees.
Good article."

Thanks for the comment and to highlight the importance of honey bees especially in cucurbit production.

Amanda Stone said...

Great article Sue! I just came across another good article from Oregon, but an excellent explanation from one commercial/pollinating beekeepers view of the big, unsustainable
situation we're all in. Go to the following website: