David Holden
It has been almost nine years since the Asian citrus psyllid (ACP) was first found in California. At that time I predicted that it’s expansion into the citrus industry in our state would not be like that as it had occurred in Florida a few years earlier. In Florida it was first found in 1998 and by 2000 was spread throughout 31 citrus producing counties of Florida (https://entnemdept.ufl.edu/creatures/citrus/acpsyllid.htm). The obvious differences throughout the two states in climate with wind (hurricanes), temperatures, and humidities would preclude it from advancing as fast in California as it did in Florida. This prediction has proven to be correct, but we did not anticipate that it would move so freely along transportation corridors as we moved fruit from one district to another for packing. In hindsight we should have predicted this possibility. Our more temperate weather in the interior San Joaquin valley has also help to reduce it’s rapid spread. A more normal winter as we experienced this past season also reduced overwintering populations considerably.
With all this being said, am I concerned about the presence and spread of this pest? I sure am! Huanglongbing (HLB) disease (the citrus killing disease associated with ACP) was first discovered in the San Gabriel valley in Los Angeles county in 2012 (https://ipm.ucanr.edu/PMG/PESTNOTES/pn74155.html). Slowly but surely it is expanding it’s territory in Los Angeles and Orange counties and we need to be vigilant to slow that expansion down as researchers look for solutions to stopping the effects of this pest and it’s associated disease.
Recently the Ventura County ACP-HLB Task Force updated many of us with the progress in the fight of these two pests. My walk away highlights from the meeting are in the following bullet points:
- Population densities were very low this past winter and early spring (from December to May).
- ACP is much harder to control in the fall than in the spring or early summer
- The lower temperatures of winter helped to kill the nymphal stage of the ACP along with hardened off winter leaves not providing a source of food for the young nymphs.
- Treatment threshold levels for ACP was established at finding 1/2 nymph per flush of citrus when inspecting for it.
- When looking for this pest, heavier populations are quite often found in the southeast sections of the orchards and it tends to be in the border regions heavier than in the interior of the orchard. Effective border treatments are key to controlling this pest.
- The use of Actara in the fall and Danitol in the winter seems to provide the best control for the adults and nymphs of this pest.
- It may take two fall treatments to knock this pest down below threshold levels.
We in the citrus industry in Ventura county have done an amazing job keeping this pest in check. Let us not give up the fight as we go through this 2017 season.
