A presentation at the recent Citrus Pest & Disease Prevention Committee State of the Central Valley meeting in California highlighted the importance of scouting for Asian citrus psyllids (ACP) in groves. Scouting becomes even more critical as the risk of ACP and HLB, the disease the insect transmits to trees, rises.
The presenter, University of California (UC) Riverside Extension Specialist Monique Rivera, said that citrus groves first should be evaluated where ACP is most likely to be found. Start with flush points, particularly flush points on the edge, she advised.
Rivera said UC researchers use two types of scouting for ACP: passive and active. Passive scouting uses traps — yellow sticky cards or other traps that are hung in trees. The cards need to be checked and/or replaced every two weeks to get the best catch of early finds of ACP populations.
Passive trapping has two advantages: 1) traps can be strategically placed at the edges of groves, where ACP first arrive and 2) traps are constantly in the trees.
The big disadvantage is that trained labor is needed to look at the cards to assess whether they contain ACP or other insects. Card traps have some other disadvantages. Contact with wind and dust affects whether the trap remains sticky and can capture psyllids. If a card loses its stickiness, it needs to be replaced to get an effective ACP catch. This presents the issue of false negatives: Psyllids may be in the grove but not on the traps. Traps are best for low-level infestation detections, said Rivera.
Active scouting for ACP is a matter of walking a grove and looking for visual signs of ACP. Rivera advised focusing on flush points and looking for eggs and nymphs. Adults can also congregate on flush points, but it’s not a guarantee that they will be found with this method. A 10X magnifier is needed to examine the leaves.
Another useful technique is tap sampling. “There’s kind of an art to this,” Rivera said. “I’m hoping that at some point we can make some sort of scouting video.”
To tap sample, Rivera uses a full-size mallet to beat the thicker part of the branch, holding a white clipboard underneath the bulk of the foliage. ACP then fall onto the clipboard, where the scout can evaluate the insects.