Sustainable Forages as an Alternative to Supplemental Feeding
The second season of this two-year project was focused on determining the value of having supplemental forage available to managed colonies. Most notably, the project evaluated the impact of over-wintered rapeseed on spring build-up as it relates to colonies’ nutritional needs. This was tracked in terms of production colonies in the same apiary over the course of two seasons, where season one involved supplemental feed in the form of sucrose and pollen substitutes and season two involved access to rapeseed. Given that production colonies over-winter differently from year-to-year, therefore introducing a variable into the experiment, we also incorporated standardized nucleus colonies into the study. Here, we made up (50) 3-frame nucs and placed 25 at the rapeseed planting and 25 at an apiary 4 miles away. This allowed us to evaluate the impact of having rapeseed available to one set of colonies as opposed to an identical set (same size and genetics) on non-supplemental forage a short distance away. Further, we tracked these two different groups through summer honey production and corresponding harvest data was collected to determine whether there was a measurable difference to the build-up of nucs on rapeseed as it relates to honey production. Finally, we experimented with the post-flowering mowing of the rapeseed plot and followed it with buckwheat in an effort to determine whether offering forage during the late season dearth held any advantages in relation to offering supplemental feed in the form of sucrose and pollen substitutes.
The attraction of planting rapeseed in our area for the purposes of building colonies is that it fills the nutritional gap between early season forage (i.e.. red maple, river birch, henbit, etc.) and the primary nectar flow (i.e.. blackberries, holly, tulip poplar). This “gap” is dependent upon the accumulation of growing degree days which ultimately determines when various nectar sources flower (as opposed to the lunar calendar). Rapeseed, as a nectar/pollen source, is most beneficial in our area when the accumulation of growing degree days is even-paced or “average.” 2014 was not necessarily average. January was decidedly below average with single-digit lows during the first, third, and fourth week of the month. February was average, followed by a cool March (3-4 degrees below normal) that resulted in a slow accumulation of growing degree days. Rapeseed in our area typically flowers in late March, bridging the significant red maple flow of February-early March with the primary flow of mid-to-late April. However, given the slow spring (and possibly the relatively severe die-back caused by the Polar Vortex event in January), the rapeseed did not begin flowering until the second week of April. Meanwhile, April, in terms of weather, was average, and May was 3-4 degrees above normal with below normal precipitation. Consequently, the primary nectar flow arrived on time, just a week after the rapeseed plot began blooming. Further, the hot, dry weather of the later half of May cut short the rapeseed plot’s bloom period by over a week. Therefore, the value of having rapeseed available to over-wintered colonies was mitigated in 2014 by the accumulation of growing degree days as it related to significant nectar sources in our area.
As a way to eliminate the variable of over-wintered production colony strength from year-to-year and to reduce the possibility of genetic variation from colony-to-colony in accessing the value of rapeseed forage, a side experiment was conducted involving nucleus colonies (nucs). In the first week of April, (50) three frame nucs were made and newly mated queens introduced. Half of these colonies were placed at the rapeseed plot and half four miles away on available forage. These two groups (same size and related queens) were evaluated weekly in terms of build-up throughout the spring. Build-up was quantified both in terms of frames of brood and frames of drawn comb (nucs were started on foundation). In both cases, there was not a significant difference between the colonies stocked at the rapeseed plot and those that were stocked on available forage. As stated above, the explanation for this would be assumed to be related to the way in which the season progressed in terms of growing degree days which “closed the gap” between the availability of rapeseed forage and the availabiity of native forage.
Following spring build-up, all colonies were relocated to summer production yards. Since summer honey production is the practical manifestation of spring build-up and, consequently, available nutrition, this experiment should be indicative of the effect of rapeseed on a colony’s pre-production growth. Accordingly, colonies that were stocked at the rapeseed plot in Spring went on to surprisingly produce 9% less honey during the summer flow than those stocked on native forage. Reasons for this may be related to stocking rates, since the rapeseed plot was also stocked with 40 production colonies in addition to the 25 nucs, and/or maybe this is further evidence of the “closing of the gap” phemomenom referenced above. In any case, the evidence suggests that the nucs raised with access to 6 acres of rapeseed showed no advantage over nucs raised on native forage.
Impacts and Contributions/Outcomes
Rapeseed can be difficult to get rid of if it goes to seed. With this in mind, the plot was mowed proactively after the field was about 90% post-bloom. Also factoring into this decision was the reality that there was abundant forage available for pollinators at that point in the season, rendering the last of the rapeseed forage insignificant. After mowing, we used a broadcast spreader to sow 250 pounds of common buckwheat (a mix of Mancan and Manor). We then drug the planting with a drag mat to increase seed-to-soil contact. We chose buckwheat because it geminates quickly and has broad leaves that quickly “smother” and out-compete weeds. Further, it flowers quickly–6 weeks from seed–and re-seeds readily, so multiple stands are possible in a single season.
At the time of planting, the decision to not spray a burn-down herbicide on the rapeseed residue was made partly due to input concerns and partly due to an interest in seeing what would happen. As it turned out, the mowed rapeseed was rejuvenated (see figure) to the extent that it out-competed the seeded buckwheat. However, as the heat of summer waxed, the rapeseed, being a cool season crop, began to wane in relation to more adaptable “weeds” (see figure). Finally, as powdery mildew became a factor in the rapeseed, the weed pressure overtook the planting, some of which was beneficial to the bees (see figure, taking notice of butterfly weed).
At $65/acre planting cost, buckwheat brought very little in the way of a return on our investment, although it should be noted that incorporating a burn-down herbicide at planting would have led to a different conclusion. Moreover, the time of year (June) that necessitated it’s planting was problematic given the labor constraints at that time of the season with harvesting, processing, and moving colonies to summer yards.
- Rapeseed post-mowing showing significant weed pressure
- Rapeseed post-mowing showing regrowth
- Rapeseed post-mowing showing weed competition
1558A Gardner Hall Addition, North Carolina State University, Dept. of Entomology, Campus Box 7613
Raleigh, NC 2769-7613
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Lenoir, NC 28645
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