Chapter 25

Pesticides for Grapevines

Managing Pesticide Resistance

Resistance is a genetically-based characteristic that allows an organism—insects, for instance—to survive exposure to a pesticide dose that would normally have killed it. Resistance genes occur naturally in individual pests because of genetic mutation and inheritance. They spread throughout pest populations due to a process of selection brought about by repeated pesticide use. Resistant populations develop because the resistant individuals survive and subsequently reproduce, and the trait for resistance is “selected” in the next generation, while the susceptible individuals are eliminated by the pesticide treatment. If the treatment continues, the percentage of selected survivors will increase and the susceptibility of the population will decline to a point that the pesticide no longer provides an acceptable level of control.

Guidelines in Managing Pesticide Resistance

The success of any pest management program depends of the correct application of pesticides when needed. Careful use makes pesticides more effective and reduces the likelihood of pesticide resistance, pest resurgence, secondary outbreaks, crop injury, and hazards to humans and the environment.

Adopt an Integrated Pest Management Plan

The decision to use an insecticide, or take some other action, against an insect infestation requires an understanding of the level of damage or insect infestation the vineyard can tolerate without an unacceptable economic loss.

Consider Alternative (non-chemical) Pest Management Measures

In keeping with IPM principles and strategies, a resistance management plan should comprise as many alternative, non-chemical pest control tools and methods as possible, as long as they contribute effectively to managing the pest.

Avoid Persistent Chemicals

Pests with resistant genes will be selected over susceptible ones whenever pesticide concentrations kill only the susceptible pests.

Apply Only Recommended Pesticide Application Rates

The correct application rate should always be used. Reducing pesticide application rates to reduce costs may appear to provide the pest control desired, but this is only temporary.

Optimal Spray Coverage

Using lower pesticide rates other than recommended by the manufacture increases the risk of pests surviving the initial contact, thereby increasing the potential for resistance.

Optimal Spray Coverage

Another means of retarding pesticide resistance is to increase the effectiveness of pesticide application. This involves maintaining and calibrating equipment and following recommendations for water volumes, spray pressures, and temperatures, thereby providing more uniform coverage.

Pesticide Mixtures

Pre-formulated mixture products and some tank mixes have proven to be relatively successful in controlling insect pests and in delaying resistance development.

Use Different Modes of Action

When resistance to a pesticide arises, not only does this resistance render the selecting compound ineffective, but it also confers cross-resistance to other chemically related compounds. This is because compounds within a specific chemical group usually share a common mode of action (MoA).

Use Long-Term Rotations

Resistance management strategies for insects, weeds, and fungal pathogens all include rotating classes of pesticides (e.g., pesticides with the same mode of action such as pyrethroids, organophosphates, carbamates, etc.). For example, with fungicides, it is suggested that classes be rotated every application.

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