Posts Tagged: onion
Visitation by honeybees is the single most important factor for onion seed set in commercial fields, said Rachael Long, UC ANR Cooperative Extension farm advisor in Yolo County.
“The more honeybees that visited the onion flowers, the higher the seed yield,” Long said.
If insecticides are applied repeatedly prior to onion bloom, honeybees were less likely to visit once the flowers opened up.
“If you spray three times in the spring before onion bloom, there was less honeybee activity during early bloom,” Long said. “We weren't sure why. We didn't see any dead bees. Honeybees might be repelled by the insecticide because, if a spray took place close to bloom, their visitation was significantly reduced, but increased later during bloom, as if the insecticide affects wore off.”
Yolo and Colusa county farmers play an important role in worldwide onion seed production. Many different varieties of onions are grown in the region to produce seed ideal for use on onion farms from Siberia to the equator and every latitude in between.
“Growing high quality onions in different areas around the world requires varieties specially adapted to a wide range of conditions, such as day length,” Long said. “In our region, you'll see a tremendous diversity of onions being grown for seed – some short, some tall, some bloom early, others later. There's also all the red, yellow and white bulb variations.”
George Weiss had been farming in Yolo County for more than 50 years when he noticed a mysterious decline in onion seed production in 2009. He paid a visit to the local UC ANR Cooperative Extension office.
“We grow onions for seed, and we weren't getting the seed yields we thought we should have,” said Weiss, 80.
He spoke with Long, who immediately began collecting information on insecticide use on the Weiss and neighboring farms.
Onion seed companies and officials at the California Garlic and Onion Research Advisory Board also observed lower yields.
“We all noticed a decline in seed production over the years, but we couldn't put a finger on what was happening,” said Bob Ehn, CEO of the California Garlic and Onion Research Advisory Board.
Long, Ehn and UC Davis entomology professor Neal Williams worked together to secure a $250,000 grant from the California Department of Food and Agriculture Specialty Crops Block Grant program to solve the onion seed mystery. Ehn's board also provided funding for research.
The sharp decline in onion seed yields began when growers were dealing with a new disease, iris yellow spot virus. The virus is spread by tiny insects called onion thrips, so growers began applying insecticides in early spring to keep the pests from moving the damaging disease around the field.
Over three years, scientists collected extensive data on insecticide use, honeybee activity, soil moisture, pollen germination, and nectar production on 29 onion seed farms of 25 acres of more. They learned that three applications of insecticide in the spring resulted in less honey bee visitation, which can reduce yield given the importance of honeybees in crop pollination.
The data analysis also concluded that:
- If farmers sprayed insecticides too close to bloom, there was less pollen germination. Typically, when a bee transfers pollen from the male to female flower, the pollen germinates right away and begins to grow, but less so after insecticide use. “There might be some chemical interaction that prevents pollen from germinating. It's not a huge effect, but there's an impact,” Long said.
- If the soil was too dry or too wet, nectar production in the onion flowers dropped way off, reducing honeybee activity and seed yields. “Honeybees need rewards,” Long said. “Their visitation to flowers is based on the ability to collect nectar. If there is little to no nectar, they will just bypass the flowers and find another source of nectar.”
- Fungicide use in onion fields did not impact honeybee activity.
- Pronounced effects of insecticides on pollinator behavior and seed set are more likely at rates of three sprays per year or more, however, even at reduced insecticide use, the researchers still saw the potential for subtle effects on both the pattern of honeybee visitation over time and the pollen-stigma interactions.
Ehn said the research furnished valuable information for California onion seed growers.
“We now know we have to be very careful about insecticide management prior to bloom time,” Ehn said. “We have to be more strategic about insecticide planning and avoid it as much as possible.”
Ehn said field research by Long, Williams and other UC ANR Cooperative Extension advisors and specialists is of critical importance to the California Garlic and Onion Research and Advisory Board.
“We are totally dependent on Cooperative Extension,” Ehn said. “Our research with Cooperative Extension stretches from Imperial County up to Tule Lake (on the Oregon border). They are our strength and anchor to get research work done that we set as a priority.”
Weiss said he highly values the research assistance from UC ANR Cooperative Extension.
“I can't pin it down in dollars and cents, but it all goes together with experience,” Weiss said.
An initiative to enhance competitive and sustainable food systems is part of UC Agriculture and Natural Resources Strategic Vision 2025.
The average American eats 21 pounds of onions per year. Indeed, our appetite for the fresh green as well as yellow, red, and white bulb onions is increasing in the United States, up 70 percent from several decades ago. A valued crop generating $1.2 billion a year, the onion currently ranks No. 2 in the vegetable industry, right behind the potato. Yellow onions account for nearly 90 percent of all onion consumption, followed by red and white varieties.
Onions, cultivated for more than 5,000 years, are one of the most versatile vegetables. They are found in every ethnic cuisine from breakfast to lunch to dinner and are rich in vitamin C and fiber. As Julia Child noted, “It's hard to imagine civilization without onions.”
With a thriving onion industry comes a “crying” need for onion seed planting stock; onions have to flower and set seed. California is a major worldwide supplier of onion seed, with growers producing about 3,000 acres of hybrid onion seed worth about $12 million, and generating an additional $40 million annually in subsequent retail sales. The major growing areas in our state are the Imperial Valley and Colusa County.
Seed companies from around the world contract with growers here in California to produce hybrid onion seed. The many different varieties include red, yellow and white bulbs, including types that are adapted to different day lengths from our northern to southern hemispheres. Growers plant onion bulbs or seedling transplants in late summer with distinct male (male fertile) and female (male sterile) onion lines in the same field. Generally, the field ratio is one row of males for every three female rows and they're tough to tell apart from a distance, but males produce pollen.
Thankfully, there are few pests of onion seed, although the recent introduction of the iris yellow spot virus vectored by the onion thrips has resulted in increased insecticide use to control this potentially devastating pest and disease. Recent research by UC Cooperative Extension specialists in Yolo County and UC Davis, however, documented that more than three insecticide sprays applied pre-bloom per year can reduce honey bee visitation to flowers. Insecticides may also interfere with the ability of female flowers to receive pollen; that is, sprays applied near to bloom time can lead to overall lower pollen germination. As a result, growers are now careful to minimize insecticide use in onion seed production fields to ensure good pollination and yields.
After cross-pollination occurs and seeds are set, growers knock down the male rows to remove them to facilitate harvesting of female lines and ensure purity of the seed. Once the female umbels dry down, they are harvested primarily by hand, placed on tarps to fully dry, and then the tiny black seeds from the florets are mechanically threshed with a combine, and cleaned and packaged for retail sales.
Although a small acreage crop in California, onion seed is an important specialty crop that significantly boosts our agricultural economy, as well as providing needed seed for farmers throughout the world.
But, before you can slice them, chop them or dice them, you have to grow them and our California growers do it best.
Additional information on onion seed production can be found at:
Onion umbel with seeds