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.
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
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
This weekend is the annual Citrus Fruit Display and Fruit Tasting Event at Lindcove REC!!
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 10, Friday, we 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. High school FFA citrus judging team will participate on judging damages from 3:30 PM to 5:30 PM.
December 11, Saturday, we 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 for $5! Several varieties, Cara Cara, Navels, Mandarins, lemons will be available.
As of July 2021, I joined the UC Agriculture and Natural Resources as a Cooperative Extension Area Citrus IPM Advisor at Lindcove Research and Extension Center. I am very excited in my new role and for the opportunity to serve San Joaquin Valley that grows ≥ 75% California citrus. My role in this position is to develop research and extension program for citrus pests focused on issues that are important to growers in the San Joaquin Valley.
A good pest management program evolves to respond to factors that influence pest pressure. Change in weather conditions over the last decade, pesticide resistance in citrus thrips and California red scale, potential expansion of Asian citrus psyllid into the San Joaquin Valley and increasing reports of mealybug infestation demand targeted research to solve these issues and an effective extension program to inform stakeholders. With years of experience working with citrus pests and passion to serve the community, I feel prepared for my role as an IPM advisor.
My current research projects focus on citrus thrips resistance monitoring and resistance management, evaluating hydrogel baiting systems for ants, and postharvest system's effect on export concern pests (bean thrips, mites, California red scale and Fuller rose beetle). Extension activities include development and delivery of educational programs on citrus pests. Future research projects will be designed to address SJV grower's pest management needs.
I can be reached at 559-592-2408 (ext. 1156) and firstname.lastname@example.org. Follow me on twitter @Sandipa_gautam (UCANR Citrus IPM) for news on Citrus IPM events. I look forward to interacting with you!