Waiting patiently for your citrus to ripen only makes it all the more exciting when you can finally enjoy your bounty. And all the more devastating when the fruits fail to ripen or they fall off the tree way too early.
If this happens, your tree might have citrus greening disease.
Learn about this devastating disease that has upended citrus growing in North America and what you can do about it in this guide.
What We’ll Cover:
What Is Citrus Greening Disease?
Citrus greening disease, also known as huánglóngbìng (HLB) and yellow dragon disease, is a devastating bacterial disease that affects citrus trees worldwide.
The disease is caused by the bacterium Candidatus Liberibactor asiaticus. This bacterium infects the phloem tissues of citrus trees, disrupting the flow of nutrients.
Infected citrus trees suffer from poor health, failed seasonal growth, dieback, and death.
In the US, citrus greening disease was first detected in Florida in 2005 and has since spread to other citrus-growing states such as Georgia, Louisiana, Arizona, California, and Texas.
There are no resistant species or cultivars. All citruses are susceptible to the disease, making it even more challenging to deal with. It’s down to early identification and prompt action to prevent a bigger problem.
Since 2020, there have been significant efforts made to breed resistant trees, but they aren’t there yet. For now, prevention is our only option.
This disease is primarily carried by the Asian citrus psyllid (Diaphorina citri). Wherever citrus trees and Asian citrus psyllids co-exist, you’ll find citrus greening disease.
This disease has devastated the citrus industry in the US, reducing production by up to 75 percent in some areas.
How Citrus Greening Disease Spreads
This disease primarily spreads via the Asian citrus psyllid, which is a small insect that feeds on citrus trees using its sap-sucking mouthparts. As it does, it transmits the bacterium from one plant to another.
The bacterium responsible for citrus greening disease can also be spread through infected plant material and grafting. You absolutely can’t avoid this disease without preventing psyllid from visiting, so let’s talk about those first.
Asian Citrus Psyllids
It’s worth knowing the lifecycle of the Asian citrus psyllid so you can understand how to stop it. This pest has a seven-stage lifecycle that extends over a period of 15-47 days. In the right conditions, this pest will continue its cycle throughout the year.
The adult females lay an average of 800 yellow-orange eggs in their lifetime on tender shoots and leaves. These eggs are shaped like small almonds. They hatch in about four days at 75-85°F. These eggs are generally laid in new shoot folds.
Nymphs, referred to as crawlers, pass through five instar stages. They are yellow-orange in color and feed on the sap of the citrus tree. They are often found on new growth and move slowly and steadily if disturbed. They produce a waxy tube that extends out of their rear.
Of course, the pupae are immobile at this stage, encased in a protective covering as they metamorphose into their adult stage.
Adult psyllids are small at about 1/16 to 1/8 long and can fly or jump short distances. They are elongated and have a fawn and brownish-mottled body pattern with transparent wings. You might mistake them for a tiny moth.
Because they’re so tiny, it’s difficult to make a positive identification. But look for their distinctive way of feeding. They attach their mouth to the plant and lift the rest of their body away from the plant at a 45-degree angle.
Depending on the season, adults may live for months. They’re most active on the plant when new growth is developing.
Infected Plant Material
The bacterium can also be spread if proper garden hygiene isn’t followed.
It’s not an airborne pathogen, but the disease can be carried from citrus tree to citrus tree via human activity.
The use of infected budwood, nursery stock, or grafting material can spread the disease from infected to uninfected trees.
Signs and Symptoms
Citrus greening disease affects all parts of the citrus tree, including leaves, fruit, and roots. The most obvious symptoms will appear on the leaves, so let’s talk about what that looks like.
A distinct sign of citrus greening disease is the asymmetrical distribution of symptoms within the host tree.
1. Yellowing of Leaves
One of the most characteristic symptoms of citrus greening disease is the yellowing of leaves, known as chlorosis. The yellowing typically begins on one side of the leaf and may appear as a blotchy pattern.
The veins of the leaf may remain green. Giving the foliage a mottled or “blotchy” appearance.
This yellowing typically starts on one branch or section before spreading further.
Don’t rely on leaf discoloration to tell you that the disease is present, though. Chlorosis is a common symptom of many problems.
2. Misshapen and Stunted Growth
Infected citrus trees may exhibit stunted growth and produce smaller, misshapen leaves. The leaves that do develop might grow up rather than out. The host tree’s overall growth may be reduced, and its branches may become sparse or die back.
3. Fruit Drop and Deformation
If this disease is the problem, any forming or developing fruit may fall from the tree before reaching maturity. Any remaining fruit could be lopsided, smaller than normal for that tree, and have a bitter, almost rotten flavor.
4. Root Decline
As citrus greening disease progresses, it can affect the tree’s roots leading to decay and a decline in overall tree health. Once this occurs, the infected tree will have significant problems absorbing nutrients and water from the soil.
Once the roots are involved, things take a real downhill turn.
5. Loss of Vitality
A thinning of the tree’s canopy and increased susceptibility to other diseases and pests will be noticeable once the roots are involved.
As the disease continues to develop, you will see twig and limb dieback the tree will be unable to recover. The end result will be the death of the entire tree.
A healthy tree can die in a matter of just five years.
Prevention and Solutions
Before we dive in, we’ll give you the bad news. There is no cure for this disease. The only strategy to deal with citrus greening disease is prevention. Prevention hinges around keeping Asian citrus psyllid away.
1. Early Detection
As with preventative action quick detection and diagnosis of citrus greening disease is crucial for effective management in the orchard. While you can’t cure the diseased tree, you might be able to save the rest of your citrus trees.
Look out for any of the signs and symptoms we’ve mentioned, then act with a combination of other measures
2. Good Garden Hygiene
One of the most important preventative tools for avoiding this disease, beyond psyllid control, is practicing good hygiene.
Prune regularly to remove any infected branches that leave the plant exposed to invaders. When you prune, use clean, sanitized tools. Remove fallen leaves and fruit, and dispose of debris properly.
Control weeds in the garden as they can harbor pests like the Asian citrus psyllid.
Clean all tools and equipment used in the care of each citrus tree.
Only purchase from reputable sellers, and don’t bring in trees or material from a quarantined area.
3. Nutrient Management
Nutrient deficiencies weaken citrus trees’ immune systems, making them more susceptible to pests and diseases.
By ensuring your citrus trees get the right amounts of essential nutrients, you automatically help them combat issues such as citrus greening disease. You also don’t want to overfeed nitrogen, as this causes leafy growth that attracts psyllids.
Test your soil before feeding your plants. If you already have lots of nitrogen in the soil and you add a balanced food, you risk over-feeding your trees.
Research your particular species and its food requirements and then feed accordingly after your soil test.
4. Notify
Due to the threat this disease and its carrier pest buddy pose to citrus orchards, both home and commercial, as well as the citrus productivity on a national scale. US authorities are continually monitoring outbreaks.
If you suspect or identify citrus greening disease has infected your trees then the local agricultural governing body needs to know.
Similarly for monitoring this disease in your local area the agricultural commissioners website will advise on what’s happening.
A report can be filed via the USDA Website.
Vector Control
You won’t stop citrus greening disease if you don’t control the Asian citrus psyllid. The first step is to hang yellow sticky traps so you can determine immediately when the adults arrive in your garden. You should also inspect your trees regularly.
Once you confirm their presence, you’ll need to act fast. First, report your sighting to the USDA as described above. In most areas, they will guide you through treatment and may even come to spray your trees.
One common method of vector control is the use of insecticides, but keep in mind that any insecticides need to be applied carefully so as not to harm beneficial insect populations in the garden. You also need to apply multiple products to control the vectors.
Sprays need to be applied every 10 days and whenever any new growth appears on the host tree.
First, you’ll need to spray the tree with a pyrethroid. Southern Ag makes a good option, which is available at Amazon. This will kill the adults and young nymphs. You can also use a spray that contains malathion.
Then, you’ll need to apply a soil-drench systemic insecticide to target the nymphs and eggs. Use a product that contains imidacloprid, like ImidaPro 2SC, which you can also find at Amazon.
Maintaining a good biological balance and encouraging equilibrium in the garden, orchard is vital on so many levels.
Introducing and encouraging predatory animals that feed on the Asian citrus psyllid can be both a deterrent and a form of population control. The following will feed on various stages of the psyllid:
- Lacewing larvae
- Ladybugs
- Parasitic wasps, particularly Tamarixia radiata
- Pirate bugs
- Birds
- Spiders
- Syrphid larvae
- Ants
Organic sprays like insecticidal soap and neem oil can also be used preventatively or in addition to chemical sprays. You need everything available in your toolbelt to tackle this awful disease.
Sadly, once your tree is infected, all you can do is remove it. To leave it is to allow the disease to spread to other plants both in your garden and outside of it.
