Even when using the most effective products available for psyllid control, insect population reductions can be short lived (one to two weeks). This is of special concern because psyllids may be carrying the citrus greening pathogen into a grove not yet infected with the disease. Due to the constant movement of psyllids between groves, cooperation among growers is needed for effective control. Working together to develop a plan for coordinated grove sprays will help to more effectively reduce psyllid populations.
When planning a coordinated spray involving a number of groves in close proximity, completing the application as quickly as possible is important to minimize psyllid re-colonization from untreated to recently treated areas. Use of aerial applications is the most realistic manner for achieving this goal. Aerial applications can be made using either fixed-wing aircraft or helicopter. In some situations, aerial applications cannot be used due to flight path obstructions or proximity to restricted areas such as bodies of water. In these cases, ground sprays could be used, concurrent with the aerial applications, to treat localized targets.
Picking A Product
Immature psyllid stages are difficult to control due to their inaccessibility, immobility, and the rapid growth of new flush. Thus, broad-spectrum insecticides used for targeting adult psyllids are the products of choice, particularly with aerial applications. Aerial applications are less likely than ground sprays to penetrate deep into the canopy where some psyllids may be located. However, adult psyllids are mobile insects that will likely contact the insecticide residues, thus providing control of those adults not contacted directly by the spray application.
Grove operations may also dictate what products can be applied at certain times due to restricted entry intervals and preharvest intervals (PHIs). In the case of fresh fruit destined for overseas markets, maximum residue levels will also influence product choice.
Timing Is Everything
Aerial applications tend not to penetrate deep into unexpanded leaf flush where psyllid eggs and young nymphs may be present. Thus, coordinated grove spray programs will likely have the most benefit in overall psyllid population reduction when the majority of the treated groves have very low levels of new flush present (or between major periods of new flush growth). The winter dormant months are an ideal time for such sprays. However, careful coordination is important during this time due to harvesting activities. Therefore, materials with short PHIs such as pyrethroids are the best choice during this period. Using pyrethroids during the dormant period takes advantage of their long residual while minimizing their negative impacts on beneficial insects and mites.
Another opportune time for a large-scale coordinated effort would be the period just prior to the summer flush that usually occurs following the onset of summer rains in late May. At this time, the bloom period will have ended, the spring flush has hardened off, and there will be a low level of new flush present. An application at this time of the year will reduce the population of psyllids that reproduced on the spring flush, and flush associated with bloom, so that lower numbers of psyllids will be present when the protracted summer flush period begins. It is best to do this as late as possible before the summer flush to avoid conflicts with harvest activities and spare beneficial populations, which are most active in the spring. Use of pyrethroid insecticides should be considered with caution at this time due to their long-lasting effects on natural enemies.
A third window of opportunity for a coordinated grove spray is the period of August through early September, when adult psyllids can be targeted just prior to the fall flush. While the hot summer temperatures typically result in overall lower numbers of psyllids during this time, continuous sporadic flushes will result in sustained presence of psyllids in the grove. Controlling the psyllid population at this time will help to prevent rapid buildup of psyllid populations on the fall flush when the cooler conditions are more favorable for rapid psyllid development. Organophosphate insecticides that typically have long PHIs may be appropriate to use at this time.
The use of coordinated aerial grove sprays is not the sole answer to managing psyllid populations, but could serve as a foundation on which growers can build their individual grove programs. While each situation will be different, the benefits of a team approach in terms of psyllid control and reduced need for repeated insecticide applications may be well worth it in the long run.