March/April – 2008
Authors: Marilyn Steiner & Stephen Goodwin
In the third in a series of articles on pesticide use in an IPM environment, the authors give an update on pesticides for use with natural enemies, and highlight a strategy that will give growers the best return.
In a previous issue (Issue 97, November/December 2007) we discussed the need for a ‘Made in Australia’ minor use initiative. We also need to expand the range of pesticides available to Australian growers for use in IPM programs. In the article mentioned, we took issue with the broad definition of the term ‘reduced-risk’ pesticides as used in the USA and Canada, which embraces products with less risk to people than traditional existing products, but which nevertheless can be highly detrimental to natural enemies.
Does it really matter if the pesticides are doing a good job, you ask? Well, yes. These new generation materials may be just as prone to developing resistance problems in their target pests as the old ones, plus they are far too expensive to develop, manufacture and buy to have gathering dust on the shelf after a short effective life. How soon we forget that the reason for investing all that effort in finding a better predator or parasite wasn’t just because we were all eco-freaks, but because we had worked existing pesticides to death and they were no longer effective.
Degrees of safety: reduced-risk, biorational, or biopesticide?
The term ‘reduced-risk’ is falling out of favour these days. Now the in-phrase is ‘biorational’. This too is a term that is lacking a rigorous definition. Try this one: the US Environmental Protection Agency (EPA) identifies biorational pesticides as ‘inherently different from conventional pesticides, having fundamentally different modes of action and consequently, lower risks of adverse effects from their use’. Or this one: ‘pest control products that are relatively non-toxic to people with few environmental side-effects’. Biorational pesticides have been equated with ‘least toxic pesticides’ and ‘biopesticides’.
Minimum risk pesticides are different again. Biopesticides, on the other hand, are actually specifically regulated in the USA and thus the EPA has formed a committee to determine what makes the list.
Officially, biopesticides are subdivided into microbials such as Bacillus thuringiensis, plant-pesticides such as Bt cotton, and biochemical pesticides such as pheromones and IGRs, at least, some of them. Registration is generally faster than for more conventional pesticides, though safety is not compromised.
For the purpose of this article, let’s settle on ‘biorational’, and assume no or only minor effects on natural enemies goes along with safety to fish, fowl and Homo sapiens.
An update on pesticides for use with natural enemies
For our own list, we have selected a range of biorational materials that have (so far) a good track record of safety to a range of natural enemies used in greenhouses (see Table 1 and Table 2). We have endeavoured to cover insecticides and miticides, but not fungicides, most of which are safe. On a scale of 1 (no toxicity) to 4 (very toxic), we disqualified any active ingredient that scored 3 or 4 in two or more key natural enemy categories. These are predatory mites (e.g. Phytoseiulus persimilis, Neoseiulus cucumeris, Stratiolaelaps [Hypoaspis] scimitus), predatory beetles (e.g. Cryptolaemus montrouzieri), predatory bugs (e.g. Orius, Macrolophus), lacewings (e.g. Mallada, Chrysoperla) and parasitoids (e.g. Encarsia formosa, Aphidius colemani).
This list is compiled to narrow the field for you when searching for additional information. It should not be considered gospel, because many factors impinge on whether a product can be used with minimum impact or not. Even water can be harmful if you apply it at high pressure or often enough. Note that only active ingredients in italics have one or more registrations within Australia. It is not okay to use an unregistered product or one that is registered but not on your crop; however, it is legitimate to canvass for new products and uses and support their registration. Interested in other products in the list? Contact your Department of Agriculture or Primary Industry for information on how and where to get some action.
Multiple choice in sites of activity
At one time we were restricted to inorganic, organophosphate, organochlorine and carbamate insecticides. Nowadays pesticides are classified into nearly 30 main groups depending on their mode of action. CropLife Australia provides a listing for Australian registered products.
The lethal mechanism is still unknown for some actives, for example flonicamid (Aria®), Group 9, a broad-spectrum pesticide not yet available in Australia, but with a good safety profile for natural enemies. The new miticide acequinocyl (Kanemite®) is listed as in Group 20; it acts on mitichondrial electron transfer. Another new miticide, spiridiclofen (Envidor®), is in Group 23, an inhibitor of lipid synthesis, with a slightly better safety profile than its close relative spiromesifen (not listed in Tables). The ability to rotate between pesticides with different modes of action, while preserving natural enemies, is the key to long-term resistance management. Our current choices in a greenhouse environment are very limited and likely to remain so unless we lobby hard for change.
Green is not black and white
You should note that there are sometimes major differences in response to pesticides between insects and mites in the same general category. For example, the whitefly parasitoid Encarsia formosa is generally more sensitive than the aphid parasitoid Aphidius colemani, but there may also be regional differences in natural enemy response due to strain differences or acquired resistance. A pesticide may act quite differently on different life stages of the natural enemy. It’s a safe bet that death within the egg or pupal stage will probably not be noticed. Effects can be immediate, with twitching and toes upturned, or chronic, with apparent survival but reduction in feeding rate, egg laying, survival time, motility, mating urge, etc.
Most of us don’t hang in for the long haul. It shouldn’t be too much of a surprise that knocking off most of the pests can also lead to starvation and a sudden drop in the population that may be mistaken for pesticide toxicity. For more detailed information on effects of pesticides (including fungicides) on a wide range of natural enemies, check the websites of Koppert (http://www.koppert.nl), recently revamped and much easier to use; Biobest (http://www.biobest.be), usually good but not working well on Vista at time of writing, and the local Australasian Biological Control (http://www.goodbugs.org.au).
Developing a strategy that will give you the best return
The general characteristics of most biorational pesticides are that they have short residual activity with low persistence, and are more targeted products with a narrow spectrum of activity against pests. Another common characteristic is that most are far too expensive to waste! Therefore think prevention rather than cure, a back-up for natural enemies rather than a replacement for them. You might also consider your strategy for their use in the context of present and past global warfare. Conventional warfare is about area-wide bombardment. However, we have all seen how well-targeted guerrilla tactics, using minimal resources, can achieve the same end with far less collateral damage. Some do’s for a successful outcome:
• Do tailor each specific treatment to the most susceptible pest stage and monitoring to get the timing right.
• Do assess which natural enemies are critical to management of the pests you have, and check the right products are on hand to have least effect.
• Do target pesticide usage efficiently, using good spray technique.
• Do monitor before and after each application to assess effectiveness against the pest, any effect on key natural enemies, and the need for follow-up treatment.
• Do use spot treatments rather than area coverage so as to leave refuges for natural enemies.
• Do deploy the troops before the pests get out of hand.
The range of pesticides now available and their relative safety to both people and the environment is far better than it used to be. The focus is on environmentally friendly products, with fast-track incentives to keep them coming. Let’s all keep the pesticide companies on track by using their products in a well-informed manner and by preserving their useful life as long as possible, in a truly integrated approach. Finally, let’s continue to lobby the APVMA to introduce a special registration classification for biorational pesticides that are truly environmentally friendly.
About the authors
Since their retirement from NSW DPI, Marilyn Steiner and Stephen Goodwin have established a new business, Biocontrol Solutions, located on Mangrove Mountain on the NSW Central Coast. Biocontrol Solutions is a consulting company in the area of IPM in protected crops, particularly in the development and use of biocontrol agents. Marilyn and Stephen between them have in excess of 50 years experience. Email: email@example.com Ω
PH&G March/April 2008 / Issue 99