25 July 2014

Biological Warfare! Organic Management of Pests 101

This blog post was written by postgraduate student Andrew Kirk in the course, Research Methods in Ecology (Ecol608). Andrew revisits a Lincoln University research area that looks at managing insect pests in organic crops from 2007.

 
Organic visions in Tuscany, Italy courtesy of Chavelli
on Flickr creative commons





Interested in organic agriculture? You're not alone. Many of us were drawn to agriculture somewhere along the line by visions of warm summer days, rolling hills, and pesticide-free produce. However, if it were that simple, everyone would grow crops organically. No 20th Century farmer would have ever abandoned the traditional practices for the forbidden fruit of the synthetic chemical. Alas, organic agriculture is tough and it most definitely is dirty.

While the challenges faced in an organic production system are numerous, we will focus here on the strategies available for the management of arthropod pests. A tremendous resource is available on this topic in the 2007 work of Zehnder, Gurr, Kuhne, Wade, Wratten, and Wyss. That review will serve as the foundation for my discussion.

The framework outlined by these authors is based on the idea of Integrated Pest Management (IPM). As the name indicates, this type of regime incorporates preventative measures, instead of simply relying on reactive measures such as the application of agrichemicals. Most conventional agriculture systems would fit the latter description, leaning heavily on agrichemicals to solve a problem after it has taken hold. However, most farmers are intelligent, practical people. Synthetic chemicals, pesticides in our context, are often very cheap in the short-term compared to the cost of integrating Ecosystem Services into every level of production. There is no doubt, on the other hand, that pesticide residue is everywhere in our world, even on organic produce that we would like to assume to be safe. For instance, have a quick look at the toxicity report for copper sulphate, one of the most widely applied organic pesticides. With that in mind, what steps can be taken to minimise the use of chemicals on our crops?

The first phase of organic pest management includes the cultural practices that can help regulate pest populations. Most basic among these is site selection. An interesting example here is the geographic distribution of fruit production in the United States. 65 per cent of this production can be found in Western states with an arid summer climate that is inhospitable to many of the devastating insect and fungi pests of horticulture. Anecdotally, much of the fruit grown in other highlighted areas of that map is native to its respective location and has internal mechanisms for dealing with pest problems. On a more local level, many "old-timers" in an agricultural community will often gladly impart some knowledge about the best site for a particular crop.

Isolation and rotation are also of particular importance in devising a strategy for cultural management of pests. Essentially, the idea is to disrupt the spread of a particular pest by limiting the area in which it thrives. One can achieve this by planting a diverse range of crops, or rotating them, to create a wider range of environments for a pest to deal with. One can easily see how this idea conflicts with the monoculture situation found in many developed countries. On the other hand, veering away from monoculture will increase the cost of management in many instances. Proponents of an IPM system will probably counter-argue that this investment will be returned through reduced input costs and spillover benefits. So maybe we'll keep moving!

Inter-row and under-vine cover crops are often used as a
substitute for crop rotation in Viticulture, for the purpose
of attracting beneficial insects to compete with harmful
insects. Photo by Bela Hausmann on Flickr creative
commons.
Next, we turn to the ecological engineering to initiate our second phase of pest management. At the centre of this idea is the encouragement of ecosystems that allow the natural enemies and competitors of a given pest to thrive. This practice, known as conservation bio-control, is a relatively new idea in the applied ecology field. It requires one to do more than introduce a natural enemy as a bio-control agent, but to also manipulate its surroundings to create the desired result. It's sort of like being the referee of the football match and giving one side water breaks while the other team runs laps around the field. This is somewhat of an indirect approach to ecological engineering, though.

A more direct route might be found in intercropping, which works similarly to crop rotation. The core of both strategies is to make it as difficult as possible for the pest to establish a large core population. A variation on these is what is known as trap cropping. As the name indicates, this entails the luring of a pest species to a more attractive plant than the commercial crop in question. Zehnder et al. mention a classic example in New Zealand sweetcorn production, where the southern green stink bug is cleverly lured to the black mustard plant, instead.

The southern green stink bug is exhibit A of
effective trap cropping. Apparently it is
very fond of black mustard. Photo from Marcello
Consolo on creative commons via Flickr.
As alluded to before, the introduction of bio-control agents can be an important part of an organic pest management system.There are two types of bio-control releases and it is important to understand the difference. Inundation bio-control relies upon the released organisms, themselves, to alleviate the pest situation. An inoculation bio-control release takes a long view, one where the progeny of the inoculation group are expected to provide relief from the pest well into the future. Of particular note among the bio-control agent success stories is the development of Bacillus thuringensis, a fungi that is pathogenic to many arthropod species of insects. If that seems like biological warfare, it's because it is. Nevertheless, the track record of bio-control is decidedly mixed. Biological systems are complex, after all, and trying to manipulate them can be very tricky. For that reason, most researchers do not recommend bio-control agents by themselves, but rather as part of an IPM system.


Photo by jetsandzeppelins on Flickr
creative commons
Last comes the part of organic pest management that everyone likes to forget. That, of course, is the fact that some pesticides are permitted in an organic management regime. These chemicals are required to be biological or minerally-based, a definition that can seem quite arbitrary to those on the outside looking in. Rememember our old friend foe, copper sulphate! With regard to insects, though, a number of organic insecticide and pheromone products are available, but individual countries have different laws regulating their use. One interesting case is an insecticidal agent formed by the bacterium Saccharopolyspora spinosa during fermentation. This insecticide is thought to be environmentally safe in the long run, but is only permissible in the EU when obtained directly through fermentation, as opposed to a purification process. According to Zehnder et al. Discrepancy over regulation of organic insecticides represents one of the major challenges to the international trade of organic goods.
Organic reality courtesy of Antony*** on Flickr
creative commons
In truth, the organic management of pests is a challenge that deserves a review much longer than this. However, with some key concepts emphasised, you can branch out into a more detailed study of these strategies. Perhaps the most important thing to remember is that pest management starts on day one, not the day after the rains and humidity come. By understanding the life-cycle and tendencies of the pest, a grower can (try to) stay one step ahead of the pest. While that goal sounds like hard work and means less time for the enjoyment of sunny days and rolling hills, it is probably a more accurate depiction of the organic dream.


References

Zehnder, G., Gurr, G. M., K├╝hne, S., Wade, M. R., Wratten, S. D., & Wyss, E. (2007). Arthropod pest management in organic crops. Annu. Rev. Entomol., 52, 57-80.

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