Honey bee hives moved in to pollinate a carrot seed crop. Lindsay Bourke
AUSVEG represents the biosecurity interests of vegetable and potato producers and the industry.
In 2017–18, vegetable and potato production was valued at $2.3 billion (LVP). Major crops include potatoes, carrots and lettuce. Potato production alone was valued at $558 million (LVP). Exports of vegetables, including potatoes, were valued at $255 million.
Australia’s diverse climate and soils accommodate vegetable cultivation in all states and territories, ensuring a constant supply of fresh vegetables. Australian vegetable growers provide the majority of fresh vegetables consumed in Australia and an increasing amount of fresh vegetables consumed overseas.
A wide variety of vegetable crops require insect pollination. Some of these crops require insect pollination to produce a crop, such as pumpkin, squash, zucchini, cucumber and swedes. Other vegetable crops which require insect pollination are ‘seed-only’ crops. The pollination requirements for vegetable species grown for seed vary widely and depend on whether a plant is self-pollinating or requires cross-pollination to facilitate seed set. Some of the major seed vegetable crops grown in Australia include carrots, cauliflower, cabbage, broccoli and beetroot.
Honey bee pollinating cucumber. Kathy Keatley Garvey, UC Davis Department of Agriculture
Pumpkin, squash, zucchini and other cucurbits
Pumpkin, squash and zucchini (Cucurbita sp.) have male and female flowers. The male flowers have five anthers and are usually more numerous than female flowers. The male flowers have anthers fused into a central column. The female flowers are easily recognised by the large circular ovary at the base of the flower. Inside the female flower is a three-lobed stigma. The female flowers produce more nectar than male flowers; however, nectar from male flowers has higher sugar content. The proportion of male and female flowers is affected by temperature, day length, the proportion of fruit already set and the season. Flowers of both sexes are typically open for only a single day, after which male and insufficiently pollinated female flowers will drop.
Insects are required to move large quantities of pollen for fertilisation of the numerous ovules within the female flowers. The most successful pollinators are active in the morning, when pollen is released. The flowers of most varieties open in the morning and close again in or by the early afternoon. The timing of opening and closing can, however, be affected by weather conditions.
The pollen grains are large and sticky and are transferred by insects rather than wind. Honey bees visit pumpkin and squash to collect both pollen and nectar. As the nectaries surround the base of the flower, bees have to climb completely to the base of the flowers, and past the stigma or anthers to collect nectar. Large quantities of pollen must be delivered to a female flower if it is to set a marketable fruit. Cross-pollination also delivers larger individual fruits.
The flowers are visited by both honey bees along with a variety of other insects. Pollination is usually the result of a number of bee visits with the seed number of fruit also increasing with increasing numbers of bee visits. Some varieties will cross pollinate each other and should be kept separate if the seeds are to be harvested. Recommendations for honey bee stocking rates vary between one and eight hives per hectare. It is probably worth keeping records of the percentage of female flowers that set fruit in different parts of a field, so it can be determined if enough beehives are being used.
Honey bee on squash blossom. Kathy Keatley Garvey, UC Davis Department of Agriculture
Carrots for seed
Pollination of carrots (Daucus carota) is important for commercial seed production. Carrot flowers are in the form of an umbel. There is usually a primary umbel, which is produced first, and then a series of increasingly smaller lower order umbels. The primary umbel is the most important for seed production. The plants will flower for between 4 and 6 weeks. The umbel is made up of groups of individual florets. The florets are presented in a number of discrete groups of flowers. The flowers around the outside of the group open first and those in the centre last. It takes about 7 days for all the florets on an umbel to open. The anthers dehisce during the first and second day after the flowers open. The stigma remains viable for about a week.
Although carrot flowers have both male and female parts, much seed production has shifted to hybrid seed production. To achieve this, lines that are male sterile or male fertile are produced. A male-sterile line produces the seed and has non-functional male parts. The pollen must be moved from a male-fertile line to a male-sterile line, producing hybrid seed. As only the male-fertile lines produce pollen, pollen-foraging insects will not normally visit both male-fertile and male-sterile lines except by accident. Usually only nectar foragers visit both lines and pollinate the crop. Hybrid carrot crops are usually planted with five or six male-sterile lines interspersed with three male-fertile lines.
Some lines appear to be very attractive to insects. The difference in attractiveness was probably due to the amount of nectar being produced.
Although a number of insects visit carrot flowers and pollinate them, some species of flies may be better pollinators than honey bees. Honey bees tend to stand high enough so their bodies do not have good stigma contact, which reduces their effectiveness. They may, however, transfer some pollen with their feet. However, managed honey bees are currently the only insects available in sufficient numbers to provide the necessary pollination services. For this reason, large numbers of honey bees need to be introduced to pollinate carrots. They need to be prepared so they have a high demand for nectar because bees are mostly visiting carrot flowers for a nectar reward. Colonies should therefore have large numbers of bees. Sugar syrup should not be fed and pollen traps should not be used, as both of these measures increase the number of pollen foragers.
As the crop flowers for 6 weeks, it is worthwhile considering introducing further hives as flowering progresses to replace any foragers that have deserted the crop. Because some hybrids appear to be not particularly attractive to bees, it is important that there are sufficient bees visiting the crop. To determine if bees are deserting the crop over the flowering period, you should count the bees in an area over a 1–2 minute period at the start of flowering, and see if it decreases over the flowering period. If this happens, more colonies should be introduced gradually throughout the flowering period.
There is not a lot of information about recommended hive stocking rates for carrot seed production, however, 10 hives per ha are commonly used in Tasmania, which is a major carrot seed production area.
Additional fact sheets and web links about the pollination of vegetables are listed below. Please be aware that some of the information was developed overseas, and environmental and seasonal variations may occur.
The Pollination Program (Agrifutures Australia and Hort Innovation)
Vegetables for seed pollination fact sheet
Capsicum pollination fact sheet
Cucurbits pollination fact sheet
Crop pollination requirements (including cantaloupe, cucumber, squash and other vegetable crops), the University of Georgia
Carrot seed profile, Tasmania Department of Primary Industries, Parks, Water and Environment
Bee pollination of cucurbit crops, University of Nebraska
Honey bee pollination of cantaloupe, cucumber and watermelon, University of California
Pumpkin and squash production, Ontario Ministry of Agriculture, Food and Rural Affairs
| Annual value of vegetable production (excluding potatoes) 2007–18
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| Distribution of vegetable production (excluding potatoes) by state and territory 2017–18 (based on LVP)
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The pollination text is an excerpt from Mark Goodwin (2012) Pollination of Crops in Australia and New Zealand. Agrifutures Australia Publication No. 12/059
The industry overview and graphs on the value of production and crop distribution are from the National Plant Biosecurity Status Report, Plant Health Australia, Canberra
