Volunteers in the orchard and how to look after themWeather & Environment
This article was written by Dr Katja Hogendoorn, Dr Scott Groom, and Professor Andy Lowe from The University of Adelaide for the spring Australian Fruitgrower magazine.
In every orchard, thousands of volunteers are contributing to productivity on a daily basis. These volunteers include predatory insects and mites, insect eating birds, bats and parasitic wasps. In this article, we focus on one group of volunteers in particular: the pollinators. We will explain why it is important to look after them and what can be done to enhance their populations.
Pollinators contribute a dollar value of $632 million per year to apple and pear production in Australia. Good pollination is crucial to achieve the symmetrical, class 1 fruit that makes the industry profitable. Most growers lease hives for pollination, but in orchards throughout the country, there is a suite of insects providing free pollination services. These volunteer pollinators include feral honey bees, many species of flies and wasps, and at least 17 species of native bees.
The services provided by volunteer pollinators should not be ignored or taken for granted. Without them, the enterprise of growing fruit becomes vulnerable to disturbance. To explain this, let’s take a look at the potential consequence of relying on a single species: the honey bee.
Imagine the Varroa mite, which causes viral epidemics among honey bees, entering Australia. Feral honey bees and their free pollination services would collapse. Increased demand and higher maintenance costs would drive up the lease price for hives, and hence lead to higher production costs and lower profits. This is not just a thought experiment: the mite is present nearly every country in the world. In New Zealand hive lease went up by 300 per cent in response to the incursion, despite the relatively low reliance on feral honey bees, and the presence of bumblebees. In Australia, the price hike might be even higher.
Looking after bees
The question then becomes, how can we mitigate such events? The answer to this question should not surprise anyone who is acquainted with risk management: we reduce risk by diversifying. The presence of a diversity of volunteer pollinators, which are not impacted by the epidemic, reduces the reliance on honey bees alone and therefore helps to secure pollination now and in the future.
So what can be done support these valuable volunteers in the orchard? Over the last three years, Agrifutures Australia through the Rural R&D for Profit program has overseen a national project to improve support for crop pollinators in agricultural landscapes. The More productive agriculture: guidelines for effective pollinator management and stakeholder adoption project includes a research team from the University of Adelaide, which has investigated how orchardists can provide for native bees. And here is their advice:
Give them food!
Native vegetation in close proximity to the orchard increases the presence of bees, and the seed number in apples. But flowers on the orchard floor are also really important, especially when the crop is not in flower. Flowers provide bees with pollen and nectar.
Pollen supplies the protein they need to reproduce. Nectar provides the carbs, which allow bees to fly. But pollen and nectar are also important resources for the other orchard volunteers. For example, larvae of lady birds, lacewings and hoverflies help to control aphids in the orchard. The adults need to feed on pollen to produce the eggs. And because flying is high octane business, nectar is important for all flying insects, including the parasitic wasps that help to control caterpillars. Below, we will point out some useful plants and planting strategies.
Give them shelter!
Most bee species in the orchard are solitary and make nests in the soil. Soil nesting bees often use slightly moist, little trafficked patches of open soil, for example in the headland or in herbicided spots at the end of a row. Reed bees dig their nests in twigs with pithy centres. They can benefit from bundles of dead blackberry stems (20 cm long, ~1–2 cm wide) attached to the trellis
Don’t create a toxic environment!
To enhance the services of all volunteers, use integrated pest management (IPM). Opt for early biological control in combination with softer insecticides. When bees are active on the crop, spray at night if possible. Avoid tank mixing of insecticides and fungicides, as this can make a really harmful cocktail. And think deeply before you use systemic insecticides, such as neonicotinoids. They remain present in the trees and soil for a long time and can run off into neighbouring vegetation. Spider mites have developed resistance to many insecticides and miticides. That means that using these can lead to uncontrollable outbreaks, as their predators (mites and a range of insects) are not resistant.
Over the years, the team from The University of Adelaide has investigated which species of flowers are visited by the native bees that pollinate apples. It turns out that the bees visiting apples are generalists that benefit from a large range of flowers. Many of these species have more than one generation, so they also need food when the apples are not flowering.
Food plants include flowering weeds such as dandelions and capeweed. Alternate mowing between rows to allow flowering of these volunteer weeds is an easy and cheap strategy to provide food.
A better option is to plant some really useful species of local native plants in or around the orchard. The local native species differ between locations, rainfall and soil type. Therefore, advice given here is of a general nature. More specific advice about local species can be obtained from local native nurseries and land care groups, from Greening Australia and the state’s sustainable agricultural officers, and, in South Australia, from Trees for Life.
For ground cover, plants can include for example, self-seeding understorey plants such as Wahlenbergia, Brachycome, Chrysocephalum and Dianella, combined with more permanent long- flowering plants such as Goodenia, Hibbertia and Scaevola and a range of native peas, for example Pultenaea, Eutaxia and Lotus (all pictured, in order, below left).
For a hedgerow, one could think of combinations that include shrubs such as Bursaria, Callistemon, Melaleuca Leptospermum Banksia Grevillea, Hakea and Acacia (pictured, in order, below right).
The above plants can be planted using tube-stock from local native nurseries. It may be possible to arrange financial support and community involvement through local land care groups, in particular if a number of orchardists collaborate to get this under way at a larger scale.
A useful alternative for larger areas of plantings is direct seeding. This is quick and cost effective and can be done with minimal labour and site preparation, but diversity can be lower as it relies on the availability of large amounts of seeds. The application typically includes Acacia, Eucalyptus, Melaleuca, Bursaria, Callistemon and Casuarina. Direct seeding is done by a service provider, for example, Trees for Life, in SA, Greening Australia or Direct Seed (Victoria). The method has had good success in southern Australia (e.g. 4500 ha of restoration has been achieved in SA by our industry partner Trees for Life).
It is useful to remove weeds prior to planting, and the perimeter should be fenced to protect the young plants from feeding by kangaroos and rabbits. In the first few years, occasional weeding is needed, and in dry summers, a drink of water will help the young plants to survive.
More information about plantings will soon be available through the AgriFutures Securing Pollination website.
Acknowledgement: This project is supported by funding from the Australian Government Department of Agriculture, Water and the Environment as part of its Rural R&D for Profit program.