Farmers and technicians like to use biorationals because they have a very positive residue profile: the active ingredients do not create a residue as they are naturally occurring substances (e.g. maltodextrin in Eradicoat); or they can be degraded quickly and easily (e.g. natural pyrethrins in Breaker); or the active is not actually applied to the produce (e.g. pheromones for mating disruption in Cidetrak).
Another important reason for the use of biorationals is that, generally speaking, they are compatible with the use of beneficial arthropods as a complementary tool to manage pests (e.g. Bacillus thuringiensis used for Turex targets only lepidopteran pests and has no impact on pollinators, predators and parasitoids of the most important pests). In addition biorationals pose a lower risk to workers applying the products, bystanders and consumers of the produce. In fact they have a significantly better environmental profile overall.
But, something that is not always taken into consideration is the contribution of biorationals to resistance management.
Due to the stringency of the registration process, there are today fewer and fewer available active substances and modes of action for insecticides, acaricides, nematicides, fungicides and bactericides. Most new active substances that are developed act on a single point of a metabolic process: they tend to be very selective and in many cases unique to the pest to be controlled. This is good as they are quite specific (and therefore avoid collateral damage to other species) but it also means that the pests can easily develop resistance to the active. The reduction of available products and the potential for the development of resistance to new actives represents another serious challenge to growers.
Managing resistance is one of the most important contributions biorational products can make. In many cases they have a different mode of action from the conventional products. They act in multiple sites which makes it more difficult for the pest to develop resistance: for example Cu2+ (from copper compounds as Kocide) blocks multiple enzymes of fungi and bacteria that lead to a disorder of many metabolic processes in the interior of the cell. In some cases their mode of action is physical, as with maltodextrin (Eradicoat) that covers the spiracles the insects use to breathe; or Bacillus amyloliquefaciens (Amylo-X) or Thrichoderma sp. (Tusal) that cover the surface of the vegetable preventing attack of disease pathogens. They can be natural pathogens of the pests, as in the case of Beauveria bassiana (Botanigard), a natural fungus that causes a disease in many insects and mites; or Bacillus thuringiensis (Turex) that colonizes the intestine of lepidopteran species. No recorded instances of resistance have been found to these pathogens.
Nor is it possible for resistance to develop to pheromones. The pheromone used for mating disruption is a chemical synthetized substance identical to the substance that females of the insect release to attract males for mating and reproduction. By creating an atmosphere saturated with this substance, males cannot detect where the females are. If the population were to create a mechanism of resistance that mechanism would effectively reduce the mating process and the population would not survive: no reproduction = no survival.
In these programmes the use of Certis’ Biorationals is critical to grow produce in many cases without detectable residues or with less than three active substances detected, but always under 30% of the EU-Maximum Residue Limit, as is demanded by the European Food Retailers. During the discussions about the production protocol to be used in the crop, one of the crucial factors is also how to avoid resistance to the essential active substances used and this is where the Certis contribution is so important. For example:
- It is a common practice to use fungicides by drip irrigation in greenhouses for vegetables, especially for the control of powdery mildew. The risk of promoting resistance is very high due to the long period of time with sub-lethal dose in the plant. In this regard Certis promotes products like Armicarb (Potassium H carbonate).
- The use of Botanigard (Beauveria bassiana) disrupting the cycle of pests such as white flies, aphids and thrips minimizes the risk of resistance to conventional products.
- The use of Eradicoat (Maltodextrin) to control resistant rust mite and white flies in vegetables thanks to its physical mode of action.