Did you know rind scarring damage caused by the same pest could look different in mandarins and sweet oranges?

A NEW extension article "UCANR publication 8708", brings you a pictorial guide to help differentiate between the damages caused by the same pest on mandarin species and sweet oranges.

Early-season insect pests, such as katydids, earwigs, and citrus thrips feeding on newly developing fruit can cause rind scarring damage. Resulting scar damages can lead to the downgrading of fruit in packinghouses causing huge economic losses for growers. Highly valued for the fresh citrus fruit (unblemished), managing these surface-feeding pests and minimizing their damage is vital to California citrus growers. Several resources, such as “Photographic Guide to Citrus Fruit Scarring” UCANR publication 8090, published in 2003 exist to help identify various types of damages. But previous work was mainly based on work with sweet oranges.

With the increasing acreage of mandarins in California, the need for identifying early season rind scarring damage caused by several pests was recognized. Dr. Bodil Cass led a group of researchers from UC Davis in evaluating grower data and conducting experiments at the Lindcove Research and Extension Center. The results of this research are now published as a photographic guide that provides information on how three early-season pests cause damage to mandarin species compared to sweet orange.

What are the main findings?

• Damages caused by early-season pests are different in tango mandarin and clementine mandarin.
• Katydids do not cause feeding damage on tango or Afourer mandarins.
• Katydid damage on clementine looks like worm damage on sweet orange. It can cause maturing fruit to split and then drop.
  
  Figure. 1. Pictorial summary showing the different types of damages caused by katydid feeding on young and mature fruit. 

Low average daily temperatures in 2023 is delaying California red scale season.

Sandipa Gautam

UCCE IPM Advisor

California red scale is a common pest of California citrus attacking leaves, twigs, fruit by sucking plant sap. If the scale numbers are high serious damage can occur to the trees and highly infested fruit may be downgraded in the packinghouse.

Biology and seasonal phenology of California red scale

California red scale has an interesting life cycle. CRS start out as mobile crawlers from overwintering females from a previous season (Figure 1), which only remain mobile until they find a suitable location to begin feeding. Once they start feeding, they do not move and go through development being attached to the feeding spot. Males are the only other moving stage (Figure 2). They go through active feeding stage (instars) and a dormant period (molting). Females molt twice and males molt four times and emerge as fliers. Males then find and mate with third instar female. Afterwards, gravid female starts producing crawlers, hence completing the life cycle. In the San Joaquin Valley, there are four complete generations of CRS. In years with warm winters/hot summers, fifth generation crawlers/immatures have been found.

Figure 1

Figure 1. CRS female (overturned) showing crawlers. Crawlers move around looking for feeding spot, settle and spend life on the same spot.

Figure 2

Figure 2-2

Figure 2. CRS male adult (top) and CRS males on trap card (bottom)

Monitoring male flights using Pheromone trap cards (Figure 2) and using degree days to predict the next life event - crawlers, male flight is a most used method for monitoring CRS seasonal activity in the San Joaquin valley. After every 550-degree day unit accumulation above the lower developmental threshold of CRS, 53°F, something important happens. My team at Lindcove Research and Extension Center has been monitoring degree days in Kern, Tulare, Fresno, and Madera counties. However, we have not had a biofix (first male flight) this year. Please visit https://lrec.ucanr.edu/Citrus_IPM/Degree_Days/ for degree day updates.

The average mean temperature in 2023 has been lower, what does this mean for CRS season?

Temperature data from CIMIS Station, Kern Co., shows that the cumulative heat units above the CRS lower developmental threshold trails lower than earlier years in 2023. To date, no male fliers have been caught in Kern Co. which is usually a week or more ahead of Fresno, Tulare, or Madera Counties. This indicates that CRS is developing, but at a slower rate than it had been in earlier years (Figure 3). Expect CRS male flights, crawler emergence to be 2-3 weeks late than normal years, at least for the first generation. If the summer temperature pattern stays similar to earlier years, we will have a delay in second and third generation too!

The effect of low temperature delaying the development, thereby affecting emergence and flights, will likely affect spray timing for CRS control in 2023 season.

Figure. 3. Cumulative degree days above the lower developmental threshold, 53°F, for CRS. Note, 2023 (green line) trails below other years.

California red scale trial- 2022

During 2022, our group studied the impact of multiple insecticide treatments on California red scale. The trials took place at the Lindcove Research and Extension Center. The trials were conducted as single tree applications and replicated 10 times. One application was made on July 28, following the crawler emergence. We rated the twigs on 23 September and twigs and fruit on 12 October for the presence of live California red scale. We also rated fruit for infestation by CRS, 0=no red scale, 1=1-10 scale, 2= >10 scales/fruit. The insecticides applied were Movento 10 fl. oz, Sivanto 14 oz, Centaur 46 oz, Senstar  20 oz, and Esteem 16 oz. All insecticides were applied with 1% Omni 6E 415 oil. Foliar applications of insecticides were made using a 100-gal high-pressure D30 diaphragm pump sprayer with mechanical agitation with a hand wand sprayer containing D6-nozzle at 250 psi. Treatments were applied in 750 gallons of water, except for Movento which was applied in 250 GPA, and Centaur which was applied at 1,000 GPA.   

The insecticide that provided the best control in terms of reducing the percentage of fruit infested with >10 scales was Movento (Figure 4). Treatments, namely, Centaur, Senstar, Sivanto, and Movento significantly reduced the total CRS/fruit compared to control. In September, treatments did not significantly reduce CRS/twig compared to the control. In October, Centaur, Sivanto, and Movento, significantly reduced the mean number of mean live CRS on twigs (Figure 5). Treatments should be applied to provide thorough coverage according to the size of the trees, except for Movento which is recommended at 250 GPA at See the UCIPM guidelines for California red scale for more application details.  

Figure 4. Mean live CRS per fruit on October 12 counts following insecticide treatment. All treatments were applied with 1% oil.

Figure 5. Mean live CRS/twig before and after treatments. Treatments were applied on July 28. Pretreatment count was done on July 25, and post-treatments counts were done on September 23, and October 12, respectively.  

This weekend Lindcove hosts the annual citrus fruit display.

Event: Oranges, mandarins, lemons, limes, grapefruit, pomelos, and citrons and many other citrus varieties – 180 citrus varieties will be on display

Place: Lindcove REC, 22963 Carson Avenue

Time: 9:00 AM to 12:00 PM.

December 9, Friday, LREC fruit display and tasting is open for the citrus industry from 9:00 AM to noon. Taste fruit at your leisure and discuss low seeded varieties and new varieties with Tracy Kahan and Mikel Roose and pest and disease management issues and horticultural issues with various UC researchers. Following the UC safety guidelines, fruit display tables will be setup outdoors in an open space.

Dr. Gautam is organizing a display of citrus disorders for FFA students from 2:00 PM to 5:00 PM. 

December 10, Saturday, LREC open from 9 AM to noon for the public to taste 180 varieties of citrus. Master Gardeners will be assisting and providing answers to backyard horticultural questions. Take a bag home of freshly picked varities for $10! Several varieties, Cara Cara, Navels, Mandarins, lemons will be available.

Hope to see you!

California red scale is a key pest of citrus in California. Its life cycle starts as crawlers produced by overwintering females from the past season. Crawlers move and find a suitable place to start feeding. Once they have settled they do not move. Traditionally growers have managed scale populations using insecticides. Insecticide applications give the best results when the population is at the most susceptible stage and is uniform.

California red scale: crawlers emerging from female (left), fruit infested with CRS (right)

Pheromone trap cards (catch males) and degree days accumulation (predict the next life event - crawlers, male flight) is the most used method for monitoring red scale population activity in the San Joaquin valley. For the last several month's Entomology research team at Lindcove Research and Extension Center has been monitoring degree days in Kern, Tulare, Fresno,  and Madera counties. The latest update as of July 07, 2022, shows that degree day accumulation in all these counties has exceeded 1650, degree days, a threshold for the second-generation crawler emergence. Pheromone traps are used to monitor male flight activity. Following the biofix (first male flight), degree days are used to predict when the crawler emergence or next-generation flight takes place.  This helps growers make timely spray applications to target the most susceptible life stage. Please visit Degree Days for county-wise information. Degree days are taken from CIMIS weather stations in different counties.

When to spray insecticides?

• First and second generations have a more synchronized population. The current population in the SJV is the second generation.
• Crawlers and first instars are the most susceptible stage (thin wax layer).

Degree days as of July 07, 2022: Degree days are heat units accumulated above the developmental threshold, 53°F, for California red scale.

Kern County: 1939 DD. Second-generation crawlers started emerging at 1650 DD. Make spray application without delay! Crawlers and white caps (first instar) are the most insecticide-susceptible life stage.

Tulare County: 1695 DD. Second-generation crawlers are out. Plan to make an application in the coming week. Crawlers and white caps are the most insecticide-susceptible life stage.

Fresno County: 1764 DD. Second-generation crawlers are out. Plan insecticide application without delay. Crawlers and white caps are the most insecticide-susceptible life stage.

Madera County: 1715 DD. Second-generation crawlers are out this week. Plan insecticide applications. Crawlers and white caps (first instar) are the most insecticide susceptible life stage.

What to apply?

UCIPM guidelines have a list of recommended products to use for managing California red scale populations. UCIPM guidelines have been recently updated to include updated information. Please check it out!

The goal is to maintain CRS at a level that does not result in more than 5% fruit infested at harvest (>10 scales). Pheromone cards may not be a good indicator of field population based on your pest management choices.

• Aphytis release blocks – pheromone cards overestimate scale numbers, as Aphytis attacks third instar females.
• Insect growth regulator/mating disruption – pheromone cards underestimate scale numbers as these treatments affect males more than they affect females. For determining if mating disruption is effective – use a threshold of 50 scales per flight.
• Movento/Admire – not a reliable predictor, especially if you have a history of scale infestation as these products do not kill scale on wood or scale.

Drop a comment below about your experience with CRS management in 2022!