2024 seems like a year of citricola scale. This season, pest control advisors have reported significant numbers of citricola scale in the San Joaquin Valley. Citricola scale, a soft bodied scale insect is sap sucking pest of citrus that thrives in cooler temperatures. This pest is not a problem every year, but may quitely build up population and explode when weather conditions are favorable. It cause damage by sucking sap leading to twig death and reduce yield. Citricola produces honeydew, thereby making leaves and fruit covered with black sooty mold. Damage thresholds are low for, 1 adult scale/twig or 0.5 1st instar/leaf. It can be best managed by understanding how and when to apply treatments. A field day will teach PCAs how to recognize various life stages, differenciate between live and dead scales, and discussion of best management options available.  

When: Tuesday September 24, 2024, 9:00-11 am

Where: Lindcove Research and Extension Center; 22963 Carson Ave., Exeter, CA 93221

Register for the event using this link

 Instructor: Dr. Sandipa Gautam

 Course Objective: To teach PCAs how to recognize the various life stages of citricola scale and the natural enemies that attack them. Identify between a dead and a live scale and field demonstration of pesticide efficacy. Citricola scale management strategies will be discussed.  

 9-9:30 a.m. Registration: Lindcove REC

9:30-11 a.m.

A. Powerpoint presentation by Sandipa Gautam on the biology of citricola life cycle, identification, and its natural enemies. Efficacy of foliar and soil applications for citricola scale control will also be discussed.

B. Identification citricola scale and differentiation between live and dead scale

C. Field demonstration of citricola scale infestation, sampling methods, and effects of insecticide treatments to control scale.

Continuing Education 2.0 other units pending approval.

In 2024, there has been an increasing report of significant numbers of citricola scale in the San Joaquin Valley. Damage thresholds are low for citricola scale, 1 adult scale/twig or 0.5 1st instar/leaf.  Because this pest produces a large number of eggs (1000/female), populations can build up quickly under right weather conditions. Cooler and wetter weather conditions in April/May meant higher egg hatch and nymph survival increasing the infestation in 2024 season.

•Citricola scale trial, 2013;  Citricola scale trial 2014 •Citricola scale trial, 2015; Citricola scale trial, 2016 •Citricola scale trial, 2017; Citricola scale trial 2018 •Citricola scale trial, 2019 ; Citricola scale trial 2023

Based on the CIMIS weather station data, we have enough degree days for the second generation of California red scale. Crawlers have started emerging.

Degree days as of June 27, 2024

BMPs for CRS Management

• Monitor for CRS
• Pheromone cards for monitoring males, weekly or per flight.
• Leaf/twig sampling – sample the edge, interior or top of the tree. Determine if the scale is alive or dead by rubbing your thumb.
• Management choices for CRS – Mating disruption (CheckMate CRS), Biological control Aphytis melinus release; insecticides (Check UCIPM guidelines)  
• Spray applications are most effective when populations consist of immatures and are synchronized. Spray as crawlers of the first or second generation are emerging. Expect first generation crawlers beginning this week in Kern, Tulare counties and in 1-2 weeks depending on location of your orchard.  
• Plan for a thorough coverage (750-1000), drive <1.5 mph, except for Movento – apply at 250 GPA.

Based on traps placed at LREC citrus blocks, California red scale season began with Biofix on March 10. Pest Control Advisors in Kern, Tulare, and Fresno County reported that they have seen activity, but the numbers have been low. If you haven't caught fliers on the traps yet, you are likely to catch some this week.

Figure. CRS male. Note the CRS has feathery antennae and a brown band through the waist.

What is CRS Biofix?

CRS Biofix is the start of California red scale activity for this season. As weather warms up and heat units are accumulated above the lower developmental threshold of this insects, overwintering females start producing crawlers which develop. Males' complete development and fly to find third instar females to mate. Mated females then produce crawlers which is the First Generation of Crawlers, observed 550-degree days after the biofix.

 What do males on the trap cards mean for management?

Pest control advisors have long used pheromone cards to monitor males and degree days to predict successive life event (crawler emergence) for timely management of CRS. Trap numbers may be different depending on the management choice.

Figure. 2. Pheromone card. To estimate number of males/trap, count the insects inside square boxes and multiply by 5. 

 IGRs and mating disruption – few male scales on the card as these options affect males more than it does females. You may have lower males on card but have high CRS populations.

• • Aphytis and Movento – Aphytis targets third instar females, thus affecting females more than it does to males. Also, Movento controls CRS on twigs but not on wood. If Aphytis or Movento or both are used, you may see higher males. If Movento was used, check the inner canopy branches, top of the tree for CRS patches.

Citrus entomology group will monitor degree days for four counties and update it biweekly on ucanr website  https://lrec.ucanr.edu/Citrus_IPM/Degree_Days/

Stay tuned for updates.