by Bill and Mary Weaver
Researchers at the Southwest Michigan Research and Extension Center completed interesting pollinator research recently. “We wanted to see,” explained Dr. Zsofia Szendrei, MSU Entomology Department, “if strips of flowers incorporated into cucumber fields would provide a better pollinated cucumber crop.
“We looked for flowers for these strips that would be blooming before and during cucumber flowering, to habituate bees to come to the cucumber field; that would not require special management; and that would also not become a weed problem or a source of other pests.”
The cucumbers were on black plastic with drip irrigation. Taking a cue from the winter rye windbreaks sometimes incorporated into intensive vegetable production in southwestern Michigan, researchers simply removed strips of black plastic intended for cucumbers to make room for planting multiple strips of the three chosen flowers: Yellow mustard (Brassica hirta), buckwheat (Fagopyrum esculentum), and sweet alyssum (Lobularia maritima). Flower strips were seeded either by hand or with small, single-row hand planters.
“We looked for flowers known to be good forage crops for bees, that provided both nectar and pollen from early in the season and continuing beyond cucumber pollination,” explained Szendrei. “The flower strips were 20 meters long and one row wide, embedded in a sea of cucumbers. We expected to see that bees from nearby areas are attracted to the flowers, and that bees would move out of the flower strips into the cucumber field. Our goal was to compare the number of honeybees and wild bees of various types on the cucumber flowers and in the flower strips.
The results of the study, however, had not fulfilled the researchers’ expectations. “The bees came to the flowers, but they tended to stay in the flowering strips, particularly in the buckwheat and yellow mustard, (which are known to produce copious amounts of nectar that is very attractive to bees), instead of moving out into the cucumbers.
The end result, though, was not a crop of small, misshapen cucumbers. Wild, ground-nesting squash bees pollinated the cukes—most likely. Squash bees, which only produce one generation a year, specifically collect pollen from cucurbits to feed their young and to provision them for the winter in their 4-to 5-celled underground nests as prepupae.
Squash bees (Peponapis pruinosa) are found wherever cucurbits occur, from northern Mexico throughout most of Continental U.S. In Ohio, most squash bees emerge from the ground as adults in early July, about the time summer squash, cucumbers, and morning glory — another possible pollen source for them — are flowering. They feed for a while and then begin building and provisioning their underground nests about the time pumpkins begin flowering.
Based on this research, Szendrei made a number of recommendations at the December 2015 Great Lakes Expo in Grand Rapids. “First, learn to distinguish between squash bees and other bees.
“Second,” she continued, “it might not be the best scenario to put non-crop flowers right in your vegetable fields. Field margins or hedgerows could be better and more permanent places where bees can nest and find food.”
“Third, consider what you might do to increase the numbers of squash bees and other wild pollinators near your cucurbit fields long-term,” if you regularly grow cucurbits (squash, pumpkins, or gourds), or also cucumbers or melons, which are a different plant family but have similar flowers and heavy, sticky pollen.
Since squash bees and many other solitary bees, including bumblebees [which are very efficient pollinators of pumpkins] make their nests in the ground, manage your hedgerows and the margins between fields where there is undisturbed soil from year to year. These areas provide secure nesting sites at the depth at which these bees make their nests so they won’t be disturbed from one year to the next.
Also, managing perennial wildflowers in those areas can provide pollen and nectar through the season for wild bees. You could also plant some flowers specifically for the bees. But to make a difference five years down the road, you should plant at least 100 square feet (a 10X10 plot) of them, so they can reseed and gradually expand their area.
Next, advises Szendrei, look at your farm on Google Earth. “How diverse is the landscape around your farm? How much natural, wild area is there nearby where flowering plants can grow and bees can nest? This will give you an idea of how much work you need to do yourself. You’re not particularly looking for wooded areas. They’re not especially helpful. Areas like meadows and hedgerows are more likely to be chosen as nesting sites and to harbor bee-friendly wildflowers.”
In making your field plans for next year, try to plant next year’s cucumber and cucurbit plants fairly close to this year’s vine crops. Squash bees tend not to travel far. Also, you’ll be conserving next year’s squash bees if you use no-till or conservation-till on last year’s cucurbit field. Squash bees often nest right in the soil under the plants they were pollinating. Tilling next spring can tear up the nests containing the overwintering prepupae or metaphorphosing almost-adults.
Also, try to avoid, when sensibly possible, using neonicinitoid insecticides on crops near your vine crop fields, and do all spraying after 5 to 6 PM. Many sprays can be toxic when the bees take a direct hit, but will be much less toxic or not toxic at all after the chemical has dried the next morning when the bees start foraging again.
Don’t leave puddles containing insecticide remnants when you clean out your sprayer.
Even if you begin managing your hedgerows and grassy areas for the benefit of your wild bees, don’t presume that their populations will build quickly. Four to five years is a reasonable amount of time to wait before you expect to see enough development of recently established hedgerows to expect a significant increase in wild bee numbers.
Finally, be cautious about relying on wild bees too heavily for your cucurbit pollination. A study published by the National Academy of Sciences, after the above presentation was given, sounded the warning that in many agricultural regions across the country, between 2008 and 2013, wild bee populations had declined by 20-some percent. Serious mismatches are occurring between the declining numbers of wild bees and the rising need for pollination of crops.
You can’t go wrong, however, by providing the best habitat for wild bees possible on your own farm. Part of the decline of wild bee numbers can be attributed to the current upsurge in acreage planted in “wall to wall” corn and soybeans, which takes away both wildflowers and potential nesting sites for wild bees. This study showing declining wild bee populations was co-authored by Rufus Isaacs of Michigan State University.
Floral strips in cucumber fields
by Bill and Mary Weaver