Vigilance required to prevent insecticide resistance in horticultural crops

Resistance management of crop production products is a factor of modern horticulture which requires ongoing attention and commitment to best use guidelines. The overuse or misuse of a chemical control option on an insect, pathogen or weed can lead to those target populations becoming resistant to that chemical.

There are many factors that can lead to an insecticide, fungicide or herbicide not controlling the desired target, such as the spray equipment not being calibrated correctly, weather conditions such as wind or rain impacting the product coverage, or the product being past its expiry date. These factors can be corrected easily by the spray applicator reviewing and adjusting their spray programme where needed. However, if the target resistance to the product is causing a lack of control, a much more in-depth control strategy is required.

The Insecticide Resistance Action Committee (IRAC) defines insecticide resistance as: ‘a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species’.

Resistance of pests, i.e. disease, insect or weed, to a pesticide, fungicide or herbicide develops when genetic variability in a small number of individuals within a population allows those individual to survive when control methods are applied.

Over time, if continued exposure to the same chemicals occurs, then the whole population becomes resistant. At this point further control with the resistant product is no longer possible. In many cases the resistance to one chemical will impact the effectiveness of different chemical actives that belong to the same chemical group.

Insecticides are grouped by their mode of action, i.e. how they control an insect, to help users make informed decisions on insecticide use.

Some of the main insecticide groups used in vegetables include:

• Group 1 (carbamates and organophosphates) includes products such as Methafos 600, Pyrinex and Diazinon. These are broad spectrum insecticides with strict guidelines on their use in crops.
• Group 3 (pyrethroids and pyrethrins) contains products such as Karate Zeon, Talstar and Mavrik Aqua Flo. These are generally knockdown, broad-spectrum insecticides with a range of target insects.
• Group 4 (neonicotinoids) contains products such as Actara, Solvigo and Confidor. This group often offers a systemic control option for pests and is commonly used in seed coatings.
• Group 28 (diamides) products tend to be more targeted to specific pest species, such as caterpillar pests and some piercing or sucking insects.

Rotating between different insecticide groups, following resistance management guidelines following label directions can all help reduce resistance in a given pest population. For further information on resistance management check the Insecticide Resistance Action Committee (FRAC) website www.frac.info.

While we should always be aware of possible resistance developing in an insect population, this is not always the cause of an insecticide failing to control an insect pest. Before considering resistance, we need to check the right product was used at the right time, with the correct coverage, targeting the correct life stage of the pest.

For more information on product selection and best use guidelines for pest and disease management, please contact your local Fruitfed Supplies Technical Horticulture Representative.