Organic farming and Integrated Pest Management
By Dr. Sam Jones
DPhil Chemical Ecology, MSc Entomology, BSc Hons Chemistry, BSc Hons Zoology Entomologist, Chemical Ecologist
At it’s heart, organic farming seeks to minimise the environmental impact of the food industry and protect the ecological resources that are essential for food production both now and in the future. But it comes with its own challenges, especially when insect pests affect crop yields.
Integrated Pest Management is a science-based, decision making approach that coordinates the use of a range of different strategies to optimise control of pests. Ultimately the aim is to control pests as and when needed, and not to use blanket control measures unnecessarily. For this reason, Integrated Pest Management is ideally suited to organic farming systems. Both systems share common foundations entrenched in ecology and concerns for human, environmental and economic health.
The foundation of any successful IPM program is monitoring for the presence of pests, so population control measures are undertaken only when required. Monitoring also provides feedback on the effectiveness of those control strategies. Monitoring can be achieved through visual inspections, sampling or traps. None of these methods are exclusive and they can be used together, but most commercially available options rely on traps, usually with an appropriate pheromone lure.
Many factors can potentially affect the success of a monitoring program, and I will give a brief discussion of each below:
- Pheromone Lures – A pheromone is a form of chemical communication used by many insects, often to attract mates. We replicate these chemical compounds to use in our traps, but the accuracy of replication directly affects trap success. It is therefore important that a pheromone lure uses high quality chemical components and the ratios reflect those in nature. These considerations are further complicated by the type and quality of dispenser used. The pheromone will be absorbed onto a dispenser of some kind; typically, these are rubber plugs or plastic vials. Different materials release the pheromone at different rates and poor-quality materials contain contaminants which can react with the pheromone, severely affecting performance. It is therefore paramount that a quality lure is used to achieve sensitive monitoring. It is also important to remember that no matter how effective a pheromone, catch rates will not improve if used in an inappropriate trap.
- Trap design - The type of trap to use depends upon the behaviour of the insect and the location used. Here, you should seek the advice of experts on which of the many trap designs to use. For example a delta trap with a sticky board is the most suitable option for small tortricid moths such as the Codling moth, Cydia pomonella, and the plume moth, Grapholita funebrana but a funnel trap (Unitrap) is a much better solution for the crop pests, Spodoptera frugiperda (Fall armyworm) and Spodoptera exempta (African armyworm).
- Trap Colour – Trap colour can significantly impact attraction of certain insects. Western Flower Thrips, an important pest of horticultural crops, are strongly attracted to a specific tint of blue (pantone colour 279), more than other shades of blue and other colours including yellow. Even if colour does not matter to your intended pest, it is good to choose a colour that is less attractive to beneficial insects; for example, green traps catch fewer bees than white or yellow traps.
- Trap Positioning – Positioning of traps can strongly influence performance. Monitoring of the Wood Leopard Moth, Zeuzera pyrina, requires the trap to be positioned above the tree canopy in orchards while for the Diamond Backed Moth, Plutella xylostella (a pest of Crucifers), traps should be positioned 20cm above the ground surface. The directional facing of a trap is also often important. Traps located in the South facing side of citrus trees catch more Mediterranean Fruit Flies than traps located elsewhere while traps should be positioned in the North-East quadrant of trees when monitoring for the Peach Twig Borer, Anarsia lineatella in orchards.
The decision to start your chosen pest control strategy is typically taken when an action (or economic) threshold is reached i.e. a specific number of insects caught per trap over the period of a week. The action threshold is set based on both the severity of damage caused by the insect and the relationship between insects caught and estimated population size: for example the Agricultural Development and Advisory Service (ADAS) advise inaction for weekly catches below 30 moths for the Large Fruit Tree Tortrix moth, Archips podana compared with 3 for the Codling Moth, Cydia pomonella, a far more destructive pest. The choice of which pest control strategy to use depends upon the crop and pest. Nowadays, a variety of organic friendly options exist, including physical control, natural oils and chemicals, biopesticides and biocontrol agents.
To conclude, monitoring as part of an IPM program is ideally suited to an organic farming system. The low density and high specificity of insect pheromone trapping systems used for monitoring ensure that any impact upon populations of non-target species is minimal. If used correctly these products provide reliable data upon which appropriate decisions can be made to ensure that yield losses are minimised. Not only do the traps indicate when control should be considered but they also provide direct feedback on the success of any adopted control strategy.
Pheromone trapping systems are the most appropriate management solution for these pests. The pheromone used is the sex pheromone produced by female moths to lure males and is the most potent of all the pheromones I have worked with at IPS.
Weeks after working with this pheromone I will still be surrounded by an accompanying cloud of moths on trains, in pub gardens, walking my dog etc. I made the mistake of opening a vial of the pheromone in my wife’s car during trials. Days later, my wife, who is a vet, was then shocked to find a cloud of moths suddenly appear while involved in an important surgical procedure.
A pheromone dispenser is a device that slowly releases the pheromone over a time period, usually 4 to 6 weeks, and is used to lure insects to a trap, such as a Delta trap or Funnel trap (see images). Typically, the device used for this pest is a rubber septum onto which a small amount of pheromone is absorbed. While these dispensers perform adequately, we wanted to improve upon this performance by investigating other dispenser formats.
We therefore decided to run a six-week trial to compare three different dispenser formats: the standard rubber septum, a polymeric vial and a wax formulated plug (see image below). Delta traps with sticky glue boards to catch the moths were used, with one trap per tree in a long avenue of mature Horse Chestnut Trees located near Ware in Hertfordshire.
Over the six-week trial period one dispenser format clearly outperformed the other two versions. The wax plug significantly improved attraction with much greater numbers present on sticky boards. The images below show the obvious difference in catch rates. In fact, the Delta trap with sticky board was found to be inadequate as a control solution due to how quickly the board became saturated with insects. Wing scales (tiny modified hairs that contribute to the wing colours of butterflies and moths) of thousands of these tiny moths forms a brown dust that quickly coats the glue surface reducing the tackiness and curtailing performance. With the dramatic improvement in attraction we therefore decided that the most appropriate trap to use was a funnel trap which can hold much greater numbers of moths and does not use a sticky surface. We have just completed a trap trial that ran over two seasons and we will report on these results very soon.