By Dan Wiersma and Ev Thomas
Did you know alfalfa has a codependency issue?
Alfalfa forage crops depend on seed production. Growing alfalfa seed depends on bees for pollination. Bees depend on the pollen and nectar resources of alfalfa flowers for reproduction and survival. Thus, alfalfa and bees are codependent.
When thinking about alfalfa, most forage producers think only about the ability to grow high tons of alfalfa forage for feeding livestock. But there is another fascinating side to the alfalfa industry — seed production. Most alfalfa seed production occurs in the western U.S. states such as California, Idaho, Nevada, Oregon and Washington. This climate often allows for low disease incidence, along with ideal seed drying and harvesting conditions. Nearly 80 million pounds of alfalfa seed is produced annually in the U.S.
Lower plant populations
Alfalfa seed growers plant in a variety of soil types including low desert areas. Ideally, alfalfa seed fields are planted in 30-inch rows and at very low seeding rates. A low plant density results in more extensive flower development, better pollination, and higher seed yield. Most seed production fields are irrigated. Vigorous flowering is encouraged by turning off the water for a short period to stress the crop.
Two key challenges to growing an alfalfa seed crop are weed and insect control. Weeds are a challenge throughout the process from early establishment through harvest, final cleaning and conditioning. Some weed species are extremely difficult to separate from alfalfa seed after harvesting, so prevention is the best practice.
Insect pests can affect the yield and quality of alfalfa seed crops and require careful monitoring during the seed production season. An especially damaging insect pest is the Lygus bug because it feeds on buds, flowers and seed pods of alfalfa. Complicating chemical insect management is the fact that you have beneficial bees in the same field as your insect pests. Growers need to spray fields at night when the bees are not active to avoid killing these essential pollinators.
Bees pollinate alfalfa
Alfalfa flowers must be tripped and cross-pollinated to produce seed. This involves the use of bees to acquire and move pollen among plants in a field. Alfalfa’s unique flower type with a forceful tripping mechanism makes honeybees reluctant to pollinate the crop. As a result, leafcutter bees are the primary species for alfalfa seed production these days.
Introduced to the U.S. in the late 1930s, leafcutter bees increase seed yield dramatically compared to pollination with honeybees. While great pollinators for alfalfa, the leafcutter bee is solitary and only lives a few weeks during the summer.
Leafcutter bees build small nests from leaf material and then gather nectar and pollen as a food source for future offspring. When complete, the female leafcutter bee lays her eggs in the nest and then dies without ever seeing her offspring. The eggs overwinter as large larvae in these leaf-lined cocoons, emerging the next spring to repeat the cycle again.
Pollination of an entire field of alfalfa may require 40,000 to 60,000 leafcutter bees per acre. Culturing bees requires a high level of expertise and experience. Bee emergence from a cocoon is encouraged with temperature manipulation and synchronized with the beginning of alfalfa flower emergence. Growers often invest $500 or more per acre to purchase leafcutter bees for pollinating their seed crop.
Zones protect germplasm
Recently, the alfalfa seed industry introduced varieties with genetically enhanced traits to the market. This created a new challenge in protecting the purity of conventional seed varieties. Some growers prefer seed without the presence of genetic traits (also known as adventitious presence non-detect or AP non-detect) for use in organic forage production or in regions where alfalfa hay is sold into sensitive overseas markets.
The National Alfalfa and Forage Alliance (NAFA) helped develop the concept of grower opportunity zones (GOZ) in key seed-producing states as a strategy for coexistence of genetically enhanced alfalfa seed and conventional varieties. These zones are isolated areas or counties where greater than 80 percent of growers choose to produce either genetically enhanced alfalfa seed or grow conventional alfalfa varieties.
Next time you walk your alfalfa field, remember the incredible effort of the leafcutter bees who labored to help bring seed to your farm. Like alfalfa plants and bees, a strong partnership exists among alfalfa seed producers, seed companies and forage growers.
Genetically enhanced alfalfa varieties bring opportunities for improved weed control and forage quality to alfalfa growers. At the same time, new technologies raise the need for good stewardship, since many forage growers require conventional varieties without the presence of genetically enhanced genes. Working together, we will grow an even better alfalfa industry.
Wiersma is the alfalfa business manager with DuPont Pioneer. Thomas is retired from the William H. Miner Agricultural Research Institute and president of Oak Point Agronomics Ltd.
Used by permission from the April 2016 issue of Hoard's Dairyman.
Copyright 2016 by W.D. Hoard & Sons Company, Fort Atkinson, Wisconsin.
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