Citrus trees are fantastic. They’re beautiful, provide healthy and flavorful fruits, and the fragrance of the flowers is unmatched. Just the presence of an orange, grapefruit, lime, or lemon tree can bring joy to your garden. Pollinators love them, too.
Unfortunately, some pests love them as much as we do. Take citrus rust mites. These pests can ruin your harvest and are particularly common in humid regions.
Read on, and let’s explore this tiny but mighty pest and how you can control it.
What Are Citrus Rust Mites?
Citrus rust mites (Phyllocoptruta oleivora) are tiny arachnids in the family Eriophyidae that are native to southeast Asia that feed on citrus plants. They can also be referred to as silver mites and are often confused or found with pink citrus mites (Aculops pelekassi).
First recorded in Florida in 1879, they are recognized as a global threat to citrus trees and their highly valued produce.
They have a two-segmented body with a cephalothorax and an abdomen but do not have wings or antennae. But don’t worry about it if you don’t see them on your plants. They’re tiny. They’re hard to spot without a magnifying glass or microscopic lens.
If you can look at them, you’ll see the males have a more elongated body and are smaller than the females. Even the females are small at under 0.15 millimeters.
Adults are orange to red in color. That’s where they got the name citrus ‘rust’ mite, as they appear to be blobs of rust sitting on trunks, branches, and fruit. This pest changes to this color as it matures, with larvae and nymphs being a pale yellow or orange.
Habitat
These pests prefer to hang out on the bottom parts of trees and under leaves, as they aren’t fans of direct sunlight. They don’t like complete shade, either.
This pest likes to feed on young, tender citrus plant tissue. That means you’ll find them on new growth, tender shoots, flowers, buds, and young fruit.
Once they have obliterated one area, they will happily migrate to new growth in search of fresh resources and feeding opportunities.
They’re busiest in summer and early fall, and they do best in hot and humid conditions. The optimum temperature for all stages is above 80°F.
They like to cluster together in communal groups, making their ability to replicate swiftly and give rise to new generations in quick succession.
Citrus Rust Mites Lifecycle
With fast growth and a short lifecycle, citrus rust mites can reproduce rapidly in a short amount of time. Two or three can rapidly become thousands.
When conditions are favorable, this pest will complete its lifecycle in a matter of two weeks. A female citrus rust mite can lay between 20-30 eggs over a period of 20 days.
1. Egg Stage
The female generally lays the eggs on the underside of the citrus tree’s leaves, close to the midrib. This location offers the eggs some protection from detection or damage from the elements.
The eggs are oval-shaped and almost translucent, with a pale yellow to off-white tone. Typically, the eggs hatch within three days of being laid.
2. Larval Stage
As the larvae emerge from the eggs, they immediately start feeding on the plant tissue. They pierce the plant’s cells and suck out the nutrients.
Citrus rust mite larvae have six legs and are pale yellow or orange in color. The transformation from the larval to the nymph stage tends to occur after about two days.
3. Nymph Stage
Nymphs molt twice, and after the second molt, they resemble the adult form but in miniature. At this point, they are not yet mature enough to reproduce. They must metamorphosis through additional molts for this to be possible.
The citrus rust nymph develops two more legs, forming a total of eight legs in adulthood. Here, the coloring becomes more in line with the mature adult’s final orange and red rust appearance.
Nymphs feed on the host plant by attaching their mouth parts to leaves, trunks and fruit.
4. Adult Stage
Adult females can live up to three weeks and lay one to two eggs every day. Male citrus rust mites deposit what is referred to as spermatophores all around the host citrus tree foliage. These protein capsules contain spermatozoa, which the mature females use to fertilize the eggs.
Males often leave these capsules near emerging females who are transitioning from nymph to adult.
Adult citrus rust mites feed in much the same way as the larvae and nymphs. Thanks to this communal feeding, damage can be evident more quickly than it would if they stayed separate and fed far apart.
Signs and Symptoms
The seriousness of a citrus rust mite infestation can vary depending on the stages of the lifecycle, the degree of the infestation, and the type of citrus.
For grapefruit and lemon trees, citrus rust mites turn fruit skins slightly rough and silvery in color. With orange, tangelo, and mandarin trees, they turn the fruit skin blacky red.
There are also some other general tell-tell signs that citrus rust mites are congregating. These include:
Leaf Damage
One of the most noticeable signs is damage to the leaves, particularly on new leaves growing towards the trunk or at the base of the citrus tree.
Citrus rust mites feed on the underside of the leaves, causing them to become distorted, curled, and wrinkled.
The affected leaves may develop a bronzed or rust-colored appearance on their surface. This is caused by a film that sticks to the foliage due to the citrus rust mites’ secretions and feeding habits.
Silvering or Stippling
In addition to distortion and discoloration, citrus rust mites can also cause a silvering or stippling effect on the upper surface of the leaves.
This is caused by the mites feeding on the plant tissue and disrupting the normal chlorophyll production. Leading to a mottled or speckled appearance on the leaves.
Fruit Damage
When citrus rust mites migrate to the fruit and suck on the outer layers, they cause blemishes, scarring, and deformities to develop.
Infested fruits generally exhibit pitted skin, discolored areas, and reduced quality.
Any fruit harvested doesn’t store well. This is due to the interruption in nutrient uptake by the tree, and damage to any citrus fruit’s protective outer skin allows pathogens to activate decomposition.
Reduced Growth and Yield
When infestations are severe, citrus trees can be stunted and fail to produce any usable fruit. The fruit may also be smaller than usual, as the tree will be unable to hold on to nutrients, suffer from reduced photosynthesis, and become significantly weakened.
The damage this pest does can affect the tree’s overall health and threaten its ability to ward off other pests and diseases.
Presence of Mites
In some cases, citrus rust mites may be visible when they congregate in large numbers or during periods of high activity.
It’s definitely worth having a magnifying glass or similar item in your gardening toolbox. If citrus rust mites are suspected, take a closer look.
Prevention
Tackling this pest involves a combination of cultural, biological, and chemical control methods. Applications of treatments and good gardening protocols must be consistently implemented for success.
Monitoring
Know the plants in your garden and take time to study and observe them throughout the year. Doing this will help you better realize there is a problem before the citrus rust mite population becomes an epidemic.
Look for distortion in the leaves early on in the summer and act promptly should mites appear.
Keep Trees Healthy
Healthy trees are better equipped to withstand some pest attention.
Using proper irrigation, fertilization, and mulching will promote good overall health of citrus trees.
Citrus trees ideally need to be fed monthly from early spring to fall. A good N-P-K fertilizer of equal levels of nitrogen, phosphorus and potassium is a good place to start, or you can use a food formulated for citrus trees. Down to Earth makes a good option.
You should also test your soil regularly to determine what your soil lacks and what it has too much of.
When mulching, always use organic materials that enhance the soil’s microbiological strength. Instead of plastic mulch, use straw, leaf litter, or bark.
Encourage Beneficial Bugs
Encourage the presence of natural enemies of citrus rust mites. This can easily be done with a good companion planting plan and by maintaining a healthy environment by avoiding commercial pesticides.
Ladybugs (Novius cardinalis, Hippodamia convergens, Coccinella trifasciata, Strethorus punctillum), predatory mites (Amblyseius spp.), lacewings, and predatory thrips (Scolothrips sexmaculatus, Franklinothrips vespiformis).
Plant sweet alyssum, buckwheat, calendula, sunflowers, dill, and nasturtiums to build a positive environment for natural pest control.
Treatment
Avoid the use of broad-spectrum insecticides, which can harm beneficial insects that can otherwise help keep pest numbers in check.
Apply horticultural oils or insecticidal soaps to the foliage of citrus trees. These will suffocate and kill the mites at all stages of it’s lifecycle. Utilizing these types of treatments is a less harmful way for the predatory insects you want to keep around.
You can purchase predatory mites that will feed on citrus rust mites. Talk to your local extension office for options.
If an infestation of citrus rust mites is so severe chemical pesticides may be necessary to save the tree. Speak to your local extension to learn what works on the populations in your area, since citrus rust mites can develop resistance to chemicals.
Pruning
Prune and remove infested plant material, including heavily infested leaves and branches.
To reduce citrus rust populations and prevent their spread to other trees, destroy all infected parts.
