Managing citrus mealybug – does ant control help?
Sandipa Gautam, Sanjeev Dhungana, and David Haviland
UC Co-operative Extension
Starting 2019/20 season, pest control advisors started noticing citrus mealybug infestations in multiple citrus varieties that continued to increase in acreage in the San Joaquin Valley. Although present in the citrus systems, mealybugs were considered to be a minor pest and kept well under check by natural enemies until recently.
What are mealybugs?
Mealybugs are soft, oval, flat, distinctly segmented insects whose body is covered in white mealy wax. Citrus mealybug, Planococcus citri is the most common species associated with citrus. Females lay ~600 eggs in egg sacs loosely held by white cottony flint. Crawlers are yellowish, and can move or be carried by ants, birds, or the wind to start new infestations. Crawlers feed by sucking sap using straw-like stylets and soon develop a waxy covering (Fig. 1C). Like California red scale, females molt and stay as third instars until mated by a male. Males go through a pupal stage and emerge as adults with wings that fly to seek a mate.
Mealybugs prefer the inside canopy of the tree and can be found under dense leaves, between clusters of fruits, or in other cryptic places where they can be difficult to find, especially when the population is low. As the season progresses and the tree flushes, blooms, and fruit develops, mealybugs move to the parts of the tree where nutrients flow. Ongoing research on seasonal phenology suggest that there are 5-6 generations in the San Joaquin Valley. The first generation starts from overwintering adult/egg populations in late March/early April. The second-generation crawlers/nymphs move to fruit in June/July. The remaining generations each year primarily feed and multiply on the fruit.
Mealybugs produce nutrient rich honeydew that is an attractive food source for ants. Ants have been reported to defend insect colonies from predators and parasitoids. In an early infestation, ant trails can be used as an indicator to locate mealybug infestations or other sap sucking pests. Managing sugar feeding ants in citrus orchards has shown increased biocontrol of sap sucking insects. It is plausible that loss of chlorpyrifos as an ant control tool may have aggravated ants thereby aiding to increase mealybug pressure in recent years.
As mealybugs have become a reoccurring pest in citrus orchards, University of California researchers-initiated studies to work towards developing strategies to manage this pest. Research funded by Citrus Research Board and led by Gautam lab is investigating biology, field ecology, and management of mealybugs. During field visits, our observations have shown that various ant species of were present throughout the growing season attending mealybug colonies.
Does managing ant help suppress mealybug?
UC researchers have documented that managing sugar feeding ants increases biocontrol, thereby reducing the pest pressure of sap sucking insects. When ant densities are were reduced >90%, there was ~90% less mealybug on twigs and complete elimination of mealybug was reported from fruit. However, managing ants has been a challenge since the use of chlorpyrifos was banned. To address this need, UC researchers have worked to develop and test different types of hydrogel beads for delivering insecticide products to sugar-feeding species of ants.
Research led by David Haviland has focused on the experimental use of commercially-available polyacrylamide hydrogel beads for large field-scale applications. In 2023 a large-scale field trial was conducted in a 20-acre grapefruit block in Sanger, California. Two applications of hydrogel beads laced with insecticides were made on Aug 2 and August 30, 2023. Post-treatment evaluations for ant density were done on 24 trees/plot by counting the number of ants that passed through a graft union for 15 secs weekly for 4 weeks after each application. The effects of ant suppression on mealybug densities was evaluated in October 2023 by counting the number of fruits infested with mealybugs (presence/absence) on 30 fruits from the inside canopy. Insecticide treatments had variable results on ant density, with lowest ant density consistently found in plots treated with thiamethoxam. Similarly, plots treated with thiamethoxam had the lowest populations of mealybugs.
There's a lot more to this story:
https://ceventura.ucanr.edu/Com_Ag/Subtropical/?newsletteritem=100493
The past few weeks have been “fun” with pest challenges in our garden and home. In the kitchen we battled ant infestations and pantry moths. In the yard the milkweed plants have been covered with oleander aphids, the California lilac (Ceanothus) was attacked by mealybugs accompanied by ants, and paper wasps (Polistes) have been trying to build a nest on the front porch.
How to tackle each of these issues? UC IPM (University of California Integrated Pest Management) Pest Notes and Quick Tips is my go-to for all these issues.
Inside the House:
Pantry Moths
Ants
In the garden:
Milkweed and oleander aphids (Aphis nerii)
I hoped I had escaped getting the detested orange oleander aphids this year, since in recent years they usually showed up earlier in the summer, but ultimately, they appeared. Most established plants can tolerate some aphids, but all aphids produce honeydew, which can attract ants and sooty mold. Since milkweed is the sole food source for the Monarch butterfly caterpillar, pesticides are not recommended. Thus, using strong sprays of water every couple of days helps manage them. Based on previous experience, I know they will reach the end of their life and ultimately disappear. https://ipm.ucanr.edu/QT/aphidscard.html
Mealybugs (Pseudococcidae)
Paper wasps (Polistes gallicus)
Thanks to UC IPM, which provides information on garden issues and pests, along with giving scientifically researched options on how to deal with them, I have managed to either control or eliminate these pesky pests.
UC IPM Resources:
The above links are to Quick Tips, short, to-the-point cards on each topic. They are available for free at local UC Cooperative Extension offices. The references below are for Pest Notes, which may have multiple pages and offer more detailed information about each topic.
Ants: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7411.html
Pantry Pests: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7452.html
Aphids: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html; https://ipm.ucanr.edu/PMG/PESTNOTES/pn7410.html
Mealybugs: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74174.html
Wasps: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7450.html
Denise Godbout-Avant has been a UC Cooperative Extension Master Gardener with Stanislaus County since 2020.
/h3>/h4>/h4>/h4>/h3>/h4>/h4>/h3>- Author: Lauren Fordyce
It may be after Labor Day, but some of your plants may still be wearing white, breaking that long-standing fashion “rule”! While many of us don't adhere to this old rule for our wardrobes these days, you may care about white stuff on your plants this time of year.
There are several white colored pest insects and diseases that you could be noticing on your plants.
Scales
Several types of scale insects are white. Each has their own host preferences, or plants they feed on.
- Cochineal scales feed only on cacti, usually prickly pears. On the outside they are white and waxy but have bright red bodies. If you scrape them off, you'll notice a red stain left behind.
- Cottony cushion scale feeds on a variety of woody ornamental plants. Common hosts in California are citrus, cocculus, nandina, and pittosporum. Adult scales are elongated and fluted.
- Euonymus scale feeds on many different plants but can be a serious pest to Japanese Euonymus (Euonymus japonica). Immature males are white and elongated with a brownish-yellow area at one end.
See the UC IPM Pest Notes: Scales to learn more about these and other scales and how to manage them.
Mealybugs
Mealybugs are whiteish-gray, oval, wax-covered insects. They can be found on many different plants, from fruit trees to houseplants, often hiding in protected places like branch crotches.
Powdery mildew
Powdery mildew often appears as white powdery spots (fungal spores) primarily on the tops of leaves. It can infect fruits and fruit trees, vegetables, and landscape plants in shady conditions when temperatures are between 60 to 80 degrees.
Whiteflies
Whiteflies are tiny insects with white, waxy wings and yellow bodies. They feed in large colonies on the undersides of leaves and have a very wide host range, including trees, vegetables, houseplants, and flowers.
Hackberry wooly aphids
This introduced aphid species infests Chinese hackberry and other hackberry (Celtis) plants. Hackberry wooly aphid adults appear in white, fuzzy masses on shoot terminals and leaves.
Spittlebugs
Adult spittlebugs are often brown, but they produce a white, foamy excrement on plants that looks like spit. They are known to feed on just about any plant.
Mushrooms
Many fungi produce white fruiting bodies that may pop up in your lawn, mulched landscape beds, or on trees and stumps. Puffballs and other fungi in lawns are mostly just a nuisance. However fungi on trees can sometimes cause wood decay and harm trees.
For more help diagnosing a plant problem or identifying a pest, see the UC IPM Plant Problem Diagnostic Tool or contact your local UC Master Gardeners.
[From the UC IPM blog Pests in the Urban Landscape]
1. Aphids
These insects may be small, but they can quickly build up large populations. With many different species in California that feed on vegetables, flowers, fruit trees, and woody ornamentals, aphids are a common sight in landscapes and gardens. Year after year, aphids continue to hold the top spot. Learn more about aphids and their management in Pest Notes: Aphids.
2. Fungus Gnats
3. Thrips
Another tiny insect sometimes found on houseplants, thrips are slender insects about the size and shape of a dash printed in a newspaper. They suck out the cell contents, leaving a discolored speckling on leaves or stunting plant growth. For more about thrips monitoring and management, visit our Pest Notes: Thrips.
4. Mealybugs
If you've found soft, oval insects that are white in color with wax filaments on your indoor or outdoor plants, it is likely you have mealybugs. These wingless insects are often found in clustered colonies. In yards and gardens, handpicking, pruning, or high-pressure water sprays can reduce populations. For small infestations indoors, spot treatments may help reduce populations. For houseplants with severe infestations, consider disposing of the plant. Find additional information in Pest Notes: Mealybugs.
5. Carpet Beetles
6. Peach Leaf Curl
Peach leaf curl can affect the blossoms, fruit, leaves, and shoots of peach and nectarine trees. The symptoms of the disease first appear in spring, when distorted red foliage emerges. However, focus management for nonresistant varieties in the late fall and early winter, after leaves drop. Read more about this disease in our Pest Notes: Peach Leaf Curl.
7. Clothes Moths
New to the top ten list this year were clothes moths. These pests tend to hide when disturbed, so you may not realize you have an infestation until after the moths have already damaged fabric, fur, or feathered items. Some clothes moths make webs while others are casemaking moths. Regularly monitoring and cleaning clothing and storage areas can help prevent or reduce infestations. Find more identification and management information from Pest Notes: Clothes Moths.
8. Springtails
9. Whiteflies
Whiteflies are not actual flies but are tiny insects that are often found on the underside of leaves, feeding on the phloem of many different plants. Certain species can cause significant loss in vegetable gardens; other species found in fruit trees are less damaging. Both adult and immature whiteflies also attack houseplants. Management information can be found in Pest Notes: Whiteflies.
10. Scales
Scales are small, legless insects that look like tiny scabs on the stems, leaves, or fruit of plants. While some scale species can weaken a plant when abundant, other species do not appear to damage plants at all. Think you have a problem with these insects? Visit our Pest Notes: Scales for identification and management options.
/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h3>We all encounter pests in our homes, gardens, and landscapes, but which ones are most popular in California? While we can't say for certain, website traffic to UC IPM's Pest Notes gives us a glimpse of popular pests. Here are the top ten most frequently viewed publications in 2021.
1. Aphids
These insects may be small, but they can quickly build up large populations. With many different species in California that feed on vegetables, flowers, fruit trees, and woody ornamentals, aphids are a common sight in landscapes and gardens. Year after year, aphids continue to hold the top spot. Learn more about aphids and their management in Pest Notes: Aphids.
2. Fungus Gnats
This pest has become more popular in recent years, perhaps a result from growing numbers of houseplant enthusiasts. Fungus gnats are small flies that often infest soil and potting mix. They can be a common houseplant problem with larvae, or immatures, damaging roots and stunting plant growth when present in large numbers. More information on these frustrating flies can be found in our Pest Notes: Fungus Gnats.
3. Thrips
Another tiny insect sometimes found on houseplants, thrips are slender insects about the size and shape of a dash printed in a newspaper. They suck out the cell contents, leaving a discolored speckling on leaves or stunting plant growth. For more about thrips monitoring and management, visit our Pest Notes: Thrips.
4. Mealybugs
If you've found soft, oval insects that are white in color with wax filaments on your indoor or outdoor plants, it is likely you have mealybugs. These wingless insects are often found in clustered colonies. In yards and gardens, handpicking, pruning, or high-pressure water sprays can reduce populations. For small infestations indoors, spot treatments may help reduce populations. For houseplants with severe infestations, consider disposing of the plant. Find additional information in Pest Notes: Mealybugs.
5. Carpet Beetles
Immature carpet beetles feed on natural fibers such as wool, silk, or furs. The adults may be brought into the home on cut flowers or when they fly in through open doors, windows, or holes in screens. Regular cleaning of rugs, upholstered furniture and can prevent infestations or reduce damage. Check out the Pest Notes: Carpet Beetles for more information.
6. Peach Leaf Curl
Peach leaf curl can affect the blossoms, fruit, leaves, and shoots of peach and nectarine trees. The symptoms of the disease first appear in spring, when distorted red foliage emerges. However, focus management for nonresistant varieties in the late fall and early winter, after leaves drop. Read more about this disease in our Pest Notes: Peach Leaf Curl.
7. Clothes Moths
New to the top ten list this year were clothes moths. These pests tend to hide when disturbed, so you may not realize you have an infestation until after the moths have already damaged fabric, fur, or feathered items. Some clothes moths make webs while others are casemaking moths. Regularly monitoring and cleaning clothing and storage areas can help prevent or reduce infestations. Find more identification and management information from Pest Notes: Clothes Moths.
8. Springtails
Springtails made an unexpected appearance on this year's top ten list. These are small, jumping insects that can be found near kitchen sicks and bathtubs as well as in the soil of indoor houseplants. They often appear in the spring and early summer but can be found year-round in moist environments. They get their name because they jump when disturbed. Learn more about this pest in Pest Notes: Springtails.
9. Whiteflies
Whiteflies are not actual flies but are tiny insects that are often found on the underside of leaves, feeding on the phloem of many different plants. Certain species can cause significant loss in vegetable gardens; other species found in fruit trees are less damaging. Both adult and immature whiteflies also attack houseplants. Management information can be found in Pest Notes: Whiteflies.
10. Scales
Scales are small, legless insects that look like tiny scabs on the stems, leaves, or fruit of plants. While some scale species can weaken a plant when abundant, other species do not appear to damage plants at all. Think you have a problem with these insects? Visit our Pest Notes: Scales for identification and management options.
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