How to prevent resistance to crop protection products

How to prevent resistance to crop protection productsDiseases, bacteria and weeds can become insensitive to crop protection products. When this happens, they can neutralise the effect of certain products and thus these products have no (or less) effect. In that case, we speak of resistance. The number of resistance to plant protection products has increased considerably in recent years, which is a problem for the control of diseases and pests.

How does resistance develop?

A population of attackers (diseases, pests or weeds) never consists of organisms that are the same from a genetic point of view. As a result, one organism is more resistant to a crop protection product than another. The organisms in a population that can withstand a crop protection product (resistant) multiply, resulting in an increasing proportion of the population in the long term. As a result, a crop protection product has less and less effect on an ever-increasing part of the population and thus creates resistance. In other words, there has always been resistance within a population, but it spreads when the resistant organisms multiply and form a large part of the population. 



Speed of developing a resistance

The speed at which a population develops resistance to a plant protection product depends on three factors:
  • The reproductive capacity of the attacker (the speed of reproduction).
  • The number of resistant individuals present in the crop from the very first moment (the starting situation).
  • The selection pressure (the ratio of sensitive to insensitive organisms). 

Increased likelihood of resistance

A number of conditions increase the risk of resistance to a certain drug:
  • A relatively high number of resistant individuals in the population. 
  • A monogenic resistance (= where the resistance of a variety or cultivar to a disease is based on one gene). 
  • There is cross-resistance to the group of plant protection products in which the product used falls.
  • A high reproductive capacity which isolates the population. 
  • High viability of the resistant organisms. 
  • A continuous operation of the crop protection product that prevents the attackers from escaping. 
  • Application of the product over a large surface area, preventing immigration and thus isolating the insensitive organisms. 
  • One-sided use of a plant protection product (virtually no alternation with products from other resistance groups).
  • Favourable conditions that enable the population to develop rapidly. 

Resistance management – combatting resistance

A grower has various possibilities to limit the chance of resistance and can also take measures if resistance does occur. This is jointly referred to as resistance management. This therefore consists of preventive and reactive measures.

Preventive measures

  • Ensure the best possible company hygiene to prevent contamination. 
  • Use biological crop protection as much as possible. 
  • Reduce the number of treatments with a chemical crop protection product to the minimum and apply them in the smallest possible area. 
  • Alternate between products with different resistance mechanisms. 
  • Make sure not all sensitive organisms die so that they can continue to reproduce and make sure that insensitive organisms can't take over the population. 
  • Minimise the mixing of insecticides and acaricides, as this can facilitate the development of resistance to more than one product. 
  • Mix a specific active fungicide with an anti-specific agent (e.g. dithiocarbamates, captan, sulphur) to prevent the development of resistance. 

Reactive measures

When a resistance has been established within a crop, a grower can take a number of steps to limit the damage to the crop as much as possible:
Immediately stop using the crop protection product that causes the problem. 
Contact your crop protection specialist for further advice on the use of another plant protection product. 


Questions on resistance to plant protection products
Do you have questions about resistance to crop protection products, or would you like to get advice? Then contact crop protection specialist Jan Krouwer, or ask your question using the form below. We'll respond within 24 hours on working days.

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