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Biopesticides for Organic Agriculture

Over the past several years, the number of organically acceptable biopesticides registered in Canada has increased. While organic producers should not rely on biopesticides as their primary means of pest control, these products may be a useful tool in those situations where cultural and mechanical pest management practices have consistently failed to keep pests below acceptable levels. However, the effective use of these products depends on the user having a good understanding of what they are and how they work, as their modes of action differ considerably from that of conventional products such as copper or sulphur.

What are biopesticides?

Biopesticides may be loosely defined as pest control products which are derived from natural materials such as animals, plants, bacteria and minerals. Biopesticides may be microbial, with a beneficial microorganism as the active ingredient; or biochemical, where the active ingredient is based on a naturally-occurring substance which typically controls pests in a different (generally less toxic) manner than a conventional pesticide. The most familiar biopesticides are those products based on the bacteria Bacillus thuringiensis (Bt), a commonly used insecticide in organic agriculture, however many other active ingredients are available.

Acceptability for Organic

It is important for organic growers to be aware that some biopesticides are not acceptable for use in organic agriculture. For example, BotaniGard is a bioinsecticide based on an insect-killing fungus that is registered for use on some greenhouse crops but the currently registered formulations are not allowed for use in organic production. Organically acceptable products based on this fungus do exist, but they are not currently registered in Canada. Even where a biopesticide is generally organically acceptable (e.g. is listed by the Organic Materials Review Institute), it may not be acceptable to all certifying bodies in Canada. Additionally, many biopesticides that are widely used by organic producers in other countries are not registered in Canada and cannot legally be used here. One example are products based on neem oil - although used extensively in the U.S., these products are not registered in Canada. The moral of the story is to always check that a biopesticide can legally be used on your crop and that it is acceptable to your certification body, before using it for the first time.

Effective use of Biopesticides

Although many biopesticides are formulated, packaged and applied in a very similar fashion to conventional pest control products, the active ingredients on which they are based are quite different. These products, many of which are based on living organisms, are much more susceptible to slight changes in conditions which would have little to no impact on the performance of conventional products. Handling, storage and expectations around efficacy therefore need to be adjusted accordingly. Considerations include:

• Biopesticides are not normally intended to be "silver bullets", and should always be used in conjunction with other pest control tactics. Many of these products are labelled for suppression rather than control, meaning that a smaller portion of the pest population is controlled.
  
  
• One of the most important factors influencing efficacy of biopesticides is correct timing of applications. Many of these products are designed to be preventative and won't work once pests are present in large numbers. This is particularly true for many biofungicides, which are based on beneficial microbes that colonize the surfaces of plant roots and act as a barrier to invading plant pathogens. If the pathogen has already invaded the roots prior to application, the biopesticide will not have any impact on it. Timing can also be influenced by the life stage or activity of the pest. Many bioinsecticides (e.g. the Bt products) work best against younger insects and control is greatly reduced when applied against older stages.
  
  
• Thorough coverage of plant surfaces is also critical to the efficacy of most biopesticides. Because most of these products require direct contact with the pest to be effective, all affected plant parts must be thoroughly covered. This can be a challenge when targeting pests such as aphids or leafrollers, which are typically found in protected locations under or within the leaf.
  Biopesticides can be extremely sensitive to environmental conditions such as sunlight, rain, humidity or temperature. The active ingredient in Bt products is sensitive to ultraviolet radiation, and its efficacy may be reduced after prolonged exposure to sunlight. There are several products which are intended for suppression of various plant pathogens in soil. These contain live spores of beneficial microbes which suspend activity at lower soil temperatures and their efficacy will be greatly reduced if they are applied to cool soils.
  
  
• Because of their environmental sensitivity, many biopesticides have limited residual activity. Biopesticides which work by forming barriers on exposed plant surfaces (e.g. Surround WP - registered for suppression of insect pests on some crops) are often dislodged by wind or rain. Others are quickly degraded and don't provided long term control. For these products, repeat applications may be necessary.
  
  
• Biopesticides can also be impacted by conditions in the spray tank. Factors to consider include temperature, pH and other compounds in the spray water, compatibility with other products and life of the spray mix. For example some biofungicides which contain beneficial fungi should not be tank mixed with fungicides. Other products break down or otherwise change when left in spray tanks for extended periods, so pay careful attention if product labels specify that the product should be sprayed within a certain period of mixing with water.
  
  
• Because biopesticides often contain live organisms, they may have specialized storage instructions. It is not uncommon for labels to specify that a product can be stored for a several months if refrigerated but only a few weeks if stored at room temperature. This is in contrast to many conventional products, which can often be stored for much longer periods.

In conclusion, biopesticides can be a useful tool for harder-to-control pests in organic production systems. However it is important to ensure the products are registered in Canada and acceptable to your certifying body. Furthermore, attention to specific application and storage instructions on product labels is particularly important to ensure optimum efficacy of biopesticides. Failure to closely follow instructions related to timing and environmental conditions can result in disappointing results with these products. At the same time, it is important to balance the level of pest suppression with any costs associated with applying the product. To do this, it can be helpful to leave untreated portions of the field as a check when trying biopesticides.