Are Pesticides Compatible With Biocontrol?

Ideally, a biocontrol program will proceed exactly according to plan, with excellent control of all pests on a long-term basis. Seldom, if ever, does this actually happen. Pest/natural enemy populations get out of balance for a variety of reasons, new pests or secondary pests become established, and judicious use of pesticides may be needed. When talking about the implementation of biocontrol in greenhouses, the issue of compatible pesticides is always a major part of the discussion. We talk about side effects lists that give us some indication of the acute toxicity of pesticides against various natural enemies. Usually on a scale of 1-4, these lists rate the mortality of a pesticide against a specific natural enemy (1 = 0-25%; 4 = 75-100%), and the length of time in days or weeks that residues will continue to persist and be active.

This is obviously very useful information and growers need to have an understanding of the impact of various pesticides, should they need them, on their biocontrol programs. However, there is more to pesticide effects than whether or not it kills; it is not always so black and white. There can be many different types of what are called 'sub-lethal effects'; those that don't cause death, but may reduce the effectiveness of the BCA. For example, there may be reductions in such things as: searching ability of the predator or parasite in finding prey, general movement, egg-laying (number of eggs, egg survival and hatch), lifespan of the adult, fitness of the males and/or females in mating. The list is long and it is expensive to carry out all the trials to produce this type of information. So for the most part, we get by on the bare minimum (how many adults/larvae are killed and for how long), but it is important to keep this in mind as we think about their 'compatibility'.

When think about the pesticides that can be used to support a biocontrol program, they can be broadly classified into a number of different groups based on how they should or shouldn't be used:

• Those that should never be used. These are often highly toxic to natural enemies with a persistence of 2-3 months, e.g. pyrethroids such as permethrin (Pounce), deltamethrin (Decis), and many organophosphates such as malathion.
  
• Those that are toxic to a broad spectrum of BCAs, but have a short residual period. These can be used to clean up a greenhouse (especially while effects of more persistent products that have been applied still exist) or in spot sprays. Examples of such products include abamectin (Avid) which has a residual of 2-3 weeks (probably less in warmer weather).
  
• Those that are toxic, but have virtually no residual effect. BCAs can be reintroduced almost immediately, e.g. soap, DDVP, nicotine
  
• Those that are somewhat compatible with varying levels of impact against BCAs and generally short persistence, e.g. many of the insect growth regulators such as cyromazine (Citation), diflubenzuron (Dimilin), kinoprene (Enstar II). Note: there are still some beneficials that are significantly affected by some of these products.
  
• Those that are completely compatible with all BCAs??? Are there any?

When you are using biocontrol, it is important to understand the role that pesticides have to play in supporting the program. Equally important is to know their limitations, and to appreciate that our knowledge base is far from complete.