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Organic Agriculture Centre of Canada

Organic farms provide habitat for many beneficial organisms, including pollinators and insects that prey upon or parasitize pests. In this article, we focus on creating insectaries – strips of plants that support beneficial insects. The subject is currently being studied by Organic Science Cluster researchers.

You can leave weeds or strips of insectary plants along the edges of the fields. The smaller the field, the more effective this is. In some cases, the perimeter may include trees and bushes. You can also have strips of insectary plants throughout a field. Beneficials can travel along these ‘habitat highways’ and disperse into the fields. Larger and more connected strips provide more benefits than small isolated patches.

Living mulches can be insectary plants. To reduce competition, overseed the living mulch seed after the crop is established. Also, crops can be used. For example, unharvested mustard greens, broccoli side shoots and fava beans flower late into the fall and provide food for pollinators, parasitoids and hoverflies.

Consider the following when selecting insectary weeds, flowers or cover crops.

• Does the plant provide habitat for beneficials? The plants should provide shelter and/or food (e.g., pollen, nectar, prey).
• Does the plant attract pests? Insectary plants can harbour pests as well as beneficials. For example, carrot rust fly damage is worse when Queen Anne’s lace surrounds fields.
• Is the plant invasive? Be careful not to create future weed problems.
• Does the plant fit in your crop rotation? Do not exacerbate pest problems by planting related crops, such as oilseed radish and cabbage, two years in a row. Buckwheat and phacelia, however, are excellend insectary plants which are unrelated to other crops.
• Does the plant offer more than one benefit? Aim for plants that help you in many ways. Tall strips, for example, can provide sheltered or shaded microclimates for crops. Cut flowers can be sold at farmers’ markets. Buckwheat supports many pollinators and beneficials. In particular, it is a great host for hoverflies (which pollinate crops and control pests). Buckwheat can also break up compacted soil, control weeds and make phosphorus more accessible to other crops.
• Does it fit into your management? Look at the time and money needed to establish and maintain the crop. Weeds are free but need to be controlled. When comparing seed costs, consider the seeding rate. Many small-seeded crops (e.g., white clover) have very expensive seed but low seeding rates. Consequently, the cost per square metre may be similar to that of cheaper seed with a high seeding rate.
• Can you grow a mix of plants? A combination of plants often supports more beneficials, and plants that bloom in succession can provide nectar and pollen for a long period of time.

To prevent insectary plants from going to seed or to stimulation migration of predators, you can mow the insectary plants. For example, flowering dandelions provide an essential early source of pollen and nectar when not many other plants are in bloom. Once they are mowed, the beneficials will move into surrounding crops. Sickle-bar mowers are gentler on the beneficials than flail and rotary mowers.

By planting, mowing and tilling different strips at different times, you can maintain several life stages of the plants at one time. This allows you to have flowering plants throughout the season without ever letting them go to seed.

Avoid overfertilizing the insectary. High levels of nitrogen will lead to more vegetative growth and delay flowering, the most valuable stage. Also, if your insectary plant or blend contains legumes, a low level of nitrogen in the soil will stimulate nitrogen fixation. 

Creating insectaries on your farm can be as simple as not mowing the field edges. Or, you can develop a complex system of living mulches and flowering crops planted and mowed in succession. The challenge is to reap the greatest benefits of the insectary plants without incurring significant costs (i.e., competition with crops, increase in pests).

Insectary plants

• Legumes (e.g., alfalfa, vetch, fava beans, clover)
• Brassicas (e.g., mustard, radish, alyssum)
• Umbellifers (e.g., Queen Anne’s lace, parsley, wild parsnip, cilantro, dill)
• Aster family (e.g., yarrow, tansy, sunflower, goldenrod, echinacea, coreopsis, cosmos)
• Buckwheat
• Phacelia

This article was written by Janet Wallace on behalf of the OACC with funding provided by Canada’s Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).  The Organic Science Cluster is a collaborative effort led jointly by the OACC, the and industry partners. For more information: oacc@dal.ca or 902-893-7256.

Posted April 2012