Building a Resilient Insecticide Spray Program

By Lukasz Stelinski

For many Florida citrus growers, pest management has become closely tied to Asian citrus psyllid control. That is understandable. The psyllid vectors the bacterium associated with citrus greening, and long-term disease pressure has pushed many operations toward frequent insecticide use. But frequent spraying comes at a cost. The more often the same chemistry is used, the faster resistance can develop, especially if rotation is not practiced. At the same time, repeated sprays can erode the natural enemy community that helps suppress psyllids and other pests. The result can be a program that becomes more expensive, less effective and harder to sustain over time.

A more resilient spray program starts with a change in mindset. The goal is not simply to spray often or to kill as many psyllids as possible with every application. The goal is to suppress pest populations while preserving the usefulness of available chemistries and maintaining as much biological control as possible. In practice, this means thinking carefully about timing, spectrum, rotation and whether a spray is needed at all.

That last point deserves more attention than it has traditionally received. One of the most important lessons from recent work is that calendar-based spraying is not always the best use of insecticides. In groves with high HLB incidence, it may be possible to reduce the number of sprays substantially by treating only when psyllid populations exceed an action threshold. This matters because every unnecessary spray adds cost, increases selection for resistance and can disrupt beneficial predators and parasitoids.

ROTATE TO AVOID RESISTANCE

The first principle of a resilient program is simple: Resistance is built by repetition. Psyllid populations in Florida and elsewhere have shown substantial reductions in susceptibility to several important insecticides. That means no chemistry should be treated as if it will remain effective forever. A program that returns repeatedly to the same mode of action, especially in consecutive generations, creates selection pressure that drives resistance. Rotation is therefore the foundation of long-term program durability.

PROTECT BENEFICIALS

The second principle is just as important: Not all sprays have the same biological cost. Intensive spray programs can reduce important natural enemy groups such as spiders, parasitoids, lady beetles and lacewings. When those predators are reduced, biological control of psyllid immatures also declines. This can be especially important during flushing periods, when psyllid populations have the greatest opportunity to increase.

THINK THRESHOLDS

The third principle is that fewer sprays can sometimes work as well as more sprays, provided that they are better timed. Recent work comparing threshold-based and calendar-based psyllid management showed that spray frequency could be reduced from eight applications per year to as few as three to four in some cases, with little difference in psyllid numbers and with lower management costs. Economic thresholds in the range of 0.5 to 1.0 adult psyllid per tap sample appeared especially promising. Every spray that can be avoided without sacrificing control helps preserve the efficacy of the tools that remain.

This does not mean that spraying should stop. It means that sprays should be made with greater purpose. In a threshold-based program, psyllid populations are monitored routinely, and insecticides are applied only when populations reach a level likely to justify treatment. This reduces unnecessary applications and lowers the total seasonal selection pressure imposed on the psyllid population. It also creates more room for beneficial insects to contribute to suppression. A resilient program should therefore combine two ideas that fit naturally together: threshold-triggered decisions and disciplined rotation of modes of action. Monitoring tells you when to spray. Rotation tells you what not to spray repeatedly.

For growers, this means separating the season into practical treatment windows rather than treating every spray choice as an isolated decision. If a threshold is exceeded, choose an effective material from one mode of action group. If the next threshold-triggered spray is needed later, rotate to a different mode of action. Do not come back with the same group simply because it worked last time.

SELECT THE RIGHT SPECTRUM

Broad-spectrum products still have a place, but they should be used strategically. They tend to fit best in periods when their biological cost is lower, such as dormant-season or near-dormant applications aimed at reducing overwintering psyllid populations. In contrast, during major flush periods when beneficials are active and psyllid reproduction is concentrated on new growth, selective products are often the better fit. This is where insecticide spectrum becomes an important management tool.

Selective products may not always produce the same immediate visual knockdown as broad-spectrum materials, but they often fit better into a season-long integrated program because they preserve more of the biological control already present in the grove. That matters because psyllid management is not only about the direct toxic effect of the spray. It is also about whether the grove retains enough predator activity to help suppress later population buildup.

PUTTING IT INTO PRACTICE

In practical terms, a resilient mature-tree program might look something like Figure 1. Consider one or two dormant-season sprays against psyllids when reproduction is lowest. Thereafter, continue with regular psyllid monitoring using tap sampling. When populations remain below threshold, do not spray. If a threshold is exceeded, apply one insecticide that is appropriate for that time of year and pest situation. At the next threshold-triggered event, rotate to a different mode of action. During periods when preservation of beneficials is especially important, such as summer, lean toward more selective materials.

MONITORING MATTERS

Monitoring is central to making this type of program work. Psyllid management is most efficient when it is tied to flush and actual pest density. Adults may be present at low levels for long periods, but that does not always justify intervention. New flush is where eggs are laid and nymphs develop, and it is also where biological control can have a major impact.

There is also an economic reason for monitoring. Every avoided spray saves money immediately in product, labor, fuel and equipment use. It may also save money later by slowing resistance development and preserving beneficials that reduce the need for additional sprays. If a grove supports spiders, lacewings, lady beetles and parasitoids, those organisms are already contributing pest suppression. Every unnecessary broad-spectrum spray risks reducing that free service.

SUMMING IT UP

In the end, building a resilient insecticide spray program is about discipline. Monitor first. Spray when thresholds justify it. Rotate modes of action intentionally. Match insecticide spectrum to the job. Use broad-spectrum products where they fit the best, not where they fit the easiest. Protect selective tools by not overusing them. Preserve beneficials whenever possible.

This approach will not eliminate psyllids or HLB pressure, but it can help maintain the effectiveness of existing chemistries longer, lower avoidable costs, reduce unnecessary disruption of beneficial arthropods and build a program that performs better over the long run.

Lukasz Stelinski is a professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.