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!

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?

1. 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.
2. Change the sticky cards weekly and the pheromone lure caps monthly through October.
3. 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?

1. 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 1^st of March, and biofix for Tulare, Fresno, and Madera Counties occurs around March 15.
2. 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.
3. Crawler emergence for first-generation will occur 550 degrees days after biofix.
4. 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 5^th flight). Subsequent crawler emergence for the 1^st, 2^nd, and 3^rd generation occurs at 550 DD, 1650 DD, and 2750 DD after the biofix.
5. 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?

1. Use 2 to 4 pheromone traps per10-acre block;add 2 traps for each additional10 acres.
2. 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.

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? 

Citrus mealybug has been increasing issue in the San Joaquin Valley in last 3 years. It has been reported from Kern, Fresno, Tulare, and Madera counties in the past years. It is a hemipteran pest that feeds on plant sap, reducing tree vigor and affects yield. Mealybug excrete honeydew which gets on leaf and fruit surfaces where sooty mold grows.

Mealybugs are soft, oval flat, distinctly segmented insects covered with white mealy wax, giving it a dusted in flour appearance. Females lay eggs in egg sacs loosely held by white cottony flint. Crawlers when hatched are yellowish in color but soon develop waxy covering once they start feeding. Adult females are 3-5 mm long, wingless, with pinkinsh body covered in white mealy wax. Males are winged and take a longer time to develop then females. 

Although seasonal phenology of citrus mealybug in the San Joaquin Valley is not well understood, we found actively producing live female populations (with some egg hatch) in first week January. This means that it is just not cold enough for these insects to trigger their overwintering habits. Mealybugs are know to have multiple overlapping generations per year. Females cannot fly and are dispersed either by crawling between trees, assisted transport by ants, birds, wind, machinery or labor.

With the weather warming up, this is a great time to start checking your orchards, especially if you had mealybug infestation last year. Sampling studies that we initiated this week (February 9, first sampling date) already showed crawler activity.

Where to look for crawlers and first instars?

When eggs first hatch, the crawlers are yellowish in color and found around areas where egg sac is. They soon start feeding and develop a dusty white mealy wax covering. Crawlers usually disperse to neighboring leaves and start feeding and are commonly found along the midrib. 

• If you still have fruit on the tree, check the fruit. Mealybug likes clusters, check for any signs of mealybug infestation. Eggs can be present on navel end or the areas where fruit is touching, or where the fruit is joined to the twig.
• On leaves with signs of sooty mold - usually found in inside canopy of the tree.
• Between twigs inside canopy of the tree