- Author: Sandipa Gautam
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. CRS female (overturned) showing crawlers. Crawlers move around looking for feeding spot, settle and spend life on the same spot.
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.
- Author: Sandipa Gautam
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!
- Author: Sandipa Gautam
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!
- Author: Sandipa Gautam
Monitoring California red scale populations by using pheromone traps and degree days
California red scale is an armored scale that attacks all citrus varieties. It attacks all aerial parts of the tree including leaves, fruits, twigs, and branches by sucking on plant tissue with its long filamentous stylet. Heavy infestations cause leaf yellowing and drop, dieback of twigs, and occasional death of the infested tree. Heavily infested fruits with patches of California red scale may be downgraded in the packinghouse. Growers use monitoring methods, i.e., pheromone trapping, examining fruit, and bin counts (at harvest) for making treatment decisions.
In the San Joaquin Valley, many citrus growers rely on the use of pheromone traps to monitor male-scale flights. Following the biofix (first male flight) degree day units (DD) are used to predict when the next crawler emergence or next-generation flights is occurring. Degree days are heat units accumulated above the lower developmental threshold of an insect and have been long used to monitor the seasonal activity of California red scale populations. Knowing when the most vulnerable life stage of the insect is present helps growers make timed insecticide applications.
Citrus IPM research group led by Dr. Sandipa Gautam at Lindcove Research and Extension Center updates degree day accumulation in the San Joaquin Valley counties. Information for different counties can be found here.
Pheromone traps are used to monitor either weekly changes in male flights or to track densities during flights, especially the fourth flight.
The squares represent 20% of the card – you count what is inside the squares on both sides and multiply by 5 to estimate the total number.
How to use pheromone traps for weekly monitoring male flights?
- Monitor 5 to 6 orchards that have a known population of California red scales every week,so thatyou can determine when flights are occurring and time sprays.
- Change the sticky cards weekly and the pheromone lure caps monthly through October.
- Use two to four pheromone traps per10-acre block;add two traps for each additional10 acres.
How to use trap card information to make management decisions?
- Hang pheromone traps with a fresh lure in early March to detect the biofix (first male flight). Historically, biofix for Kern County occurs around the 1st of March, and biofix for Tulare, Fresno, and Madera Counties occurs around March 15.
- Use the biofix and degree-days to predict when crawler emergence or next flight is occurring. Degree days are accumulated heat units over the lower developmental threshold of California red scale.
- Crawler emergence for first-generation will occur 550 degrees days after biofix.
- Subsequent flights will occur at intervals of 1,100-degree days after the biofix of the first male flight (1,100 DD for 2nd flight; 2,200 DD for 3rd flight; 3,300 DD for 4th flight and 4,400 DD for 5th flight). Subsequent crawler emergence for the 1st, 2nd, and 3rd generation occurs at 550 DD, 1650 DD, and 2750 DD after the biofix.
- Check the Lindcove Research and Extension Center Website for updated information on accumulated degree day
How to use pheromone traps to determine areas of heavy infestation?
- Use 2 to 4 pheromone traps per10-acre block;add 2 traps for each additional10 acres.
- Time placement of traps at the beginning of the biofix for the flight and remove them at the end of each flight and count scales and record the numbers.
In the past, when an average of more than 1,000 scales are trapped during the 4th flight and fruit is infested with scale at harvest, a pesticide application is planned for the next season. However, this threshold of 1,000 scales per flight developed in the 1980s is no longer a stand-alone tool for determining when treatments are necessary. It is critical to use other tactics, such as fruit and twig examination.
Note that pheromone cards are not reliable predictors of scale populations on their own. In all orchards in all growing regions,whether Aphytis wasps are released or not, conduct visual inspections of citrus fruit once a month during August, September, and October to confirm that fruit is free of scale.
Situation 1: Scale densities on traps may be high, but the fruit is free of scale:
- When Movento or Admire (and generics) are used because they remove scale from leaves and fruit but not the wood of the tree.
- Aphytis prefer to attack virgin female scales and the males may escape parasitization, resulting in a high number of male scales on traps.
Situation 2: Very few male scales on traps, but the scale is found on fruit
- When insect growth regulators (buprofezin and pyriproxyfen) are used, the frequently molting male scales are more affected than female scales.
- When mating disruption is used, males cannot find the trap cards so their densities on traps can be very low. A threshold of 50 scales per flight is helpful in determining if mating disruption is effective.
Consult UCIPM guidelines for management options.
- Author: Sandipa Gautam
Citrus thrips field day at LREC
On April 22, Lindcove Research Center hosted the first field event of year 2022! A field day was dedicated to discussing information on citrus thrips biology, differentiating citrus thrips from flower thrips, citrus thrips damage, and management options available. Rain forecast limited the activity to indoors. The event was kicked by Dr. Sandipa Gautam talking about citrus thrips biology, monitoring, and management options.
Key discussion questions were on the gallon per acre usage for thrips spray application. Marco Rilandi asked about the precedence of gpa used on research trials and the efficacy of day or night applications. Discussions revealed that most PCAs under optimal conditions would choose to recommend ~200 gpa for thrips spray. Other questions discussed were citrus thrips management in organic orchards. For hands-on activity, participants observed citrus thrips and flower thrips under microscopes and observed scarring damage on fruit.
For information on monitoring and management, please visit these resources. Citrus thrips talk
UCIPM guidelines for citrus thrips management.
Participants of the Citrus thrips Field DayInsert Image
Dr. Gautam lecturing on citrus thrips
Can you tell citrus thrips from flower thrips?