A healthy farm ecosystem consists of many different types of lifeforms. Many insects, fungi and bacteria are called “beneficial organisms” because they help crops by pollinating plants, providing nutrients or attacking harmful insects. Plants that compete with crops are considered weeds. Some insects and diseases are considered pests because can harm crops. The key to managing pests and weeds on organic farms is to reduce their impact.
So what do organic farmers use instead of the agricultural herbicides, fertilizers and insecticides commonly used? The answer is complicated. Organic farmers don’t simply rely on organic alternatives to these chemicals –they work with nature to provide nutrients and control pests. When choosing planting dates, seeding rates and crop varieties, organic farmers consider what will work best to avoid pest and weed problems.
Common practices on organic farms to prevent and control pests, weeds and disease:
- Rotating crops disrupts the life cycles of pests. Pests and weeds thrive when the same crop is planted year after year. Crop rotation changes that. For example, potato beetles suffer when they emerge from winter hibernation and find themselves in a wheat field.
- Maintaining high levels of biodiversity creates habitat for birds and invertebrates that attack pests.[1],[2] Biodiversity (variety of lifeforms) can be enhanced by (i) growing many types of crops on a farm or even within a field, (ii) leaving wild hedgerows or meadows on the farm, and (iii) not spraying pesticides.
- Intercropping, the planting of two or more crops together, makes it difficult for harmful insects to find plants. For example, alternating rows of onions and carrots reduces damage by carrot rust flies, which find carrots by their smell.[3]
- Strategic planting considers pest life cycles when deciding when to plant and harvest.[4] Often organic farmers plant late to avoid the first flush of weeds and first generation of pests. They use high seeding rates because dense plantings leave less room for weeds to grow.
- Planting cover crops, unharvested crops grown solely for their benefit to the farm. They compete with weeds and provide habitat for beneficial organisms that attack pests.
- Choosing varieties bred or proven to perform well under organic conditions; these may be more resistant to pests and better able to compete with weeds.
- Tilling to uproots weeds; organic farmers use tillage when necessary but focus on preventing weed problems.
- Flame weeding uses a flame from a propane torch (tractor-mounted or backpack) to kill small weeds.[5]
- Handweeding and hoeing are used on many market gardens.
- Mulching covers bare soil (e.g., with straw or a cover crop).
- Natural allies. Plants, insects and other organisms help organic farmers control pests. For example, a cover crop of ryegrass can smother weeds and tachinid flies can parasitize cabbageworms. Beneficial organisms are creatures that perform a beneficial role in pollinating plants or attacking harmful insects. To recruit the support of beneficial organisms, farmers can provide suitable habitat by sowing plants preferred by beneficial organisms, welcoming wildflowers, or increasing biodiversity in general.
When manual control and prevention isn’t enough:
Farmers consult the lists of substances permitted by the Canadian Organic Standards. To assess which substances are allowed, rigorous reviews are conducted that evaluate consequences as far-reaching as the environmental impact of a substance’s manufacture and disposal.[6]
Organic farmers must develop a plan to prevent pests. This may include crop rotation, cover cropping or companion planting. If a pest problem arises despite preventative measures, farmers can use substances that have passed stringent reviews of the “social and ecological impact of the production and application of the substance.”[7]
Examples of allowable products:
- Bacillus thuringiensis (BT): soil bacteria that kills certain soft-bodied pests.
- Bentonite, kaolin: clay applied to leaves to discourage insect pests.
- Diatomaceous earth (DE): fossilized diatoms (hard-shelled algae), which scrape the bodies of certain insects causing dehydration.
- Dormant oils: work by covering up the breathing tubes or damaging cell walls of certain insects.
- Floating row covers (lightweight fabric): inhibit pests from landing on plants.
- Pheromone traps: Attract and trap pests or prevent mating by using pheromones (chemicals released by insects).
- Pyrethrum: botanical pesticide derived from chrysanthemums.
- Soap: damages cell walls or suffocates certain pests.
- Spinosad: an extract from soil bacteria that kills certain pests.
Footnotes:
[1] Marshall, Edward & K Brown, V & Boatman, Nigel & J W Lutman, P & R Squire, G & K Ward, L. 2003. The role of weeds in supporting biological diversity within crop fields. Weed Research. 43. 77 – 89.
[2] Reddy P.P. 2017. Weed Manipulation. In: Agro-ecological Approaches to Pest Management for Sustainable Agriculture. Springer, Singapore
[3] Uvah, I. I. I. and TH Coaker. 1984. Effect of mixed cropping on some insect pests of carrots and onions. Entomologia Experimentalis et Applicata. Vol 36. Issue 2. pp 159- 167
[4] link.springer.com/article/10.1007%2Fs13593-011-0009-1
[5] www.dal.ca/faculty/agriculture/oacc/en-home/resources/pest-management/weed-management/flame-and-steam-weeding.html
[6] Organic production systems — General principles and management standards. CAN/CGSB-32.310-2015. 10.3: Table 8 — Substance review criteria for permitted substances in crop production
[7]Organic production systems — General principles and management standards. CAN/CGSB-32.310-2015. 10.2.2 Substance reviews