We all love having citrus growing in our backyards. There’s something to be said for being able to pop out and grab a fresh, sweet orange or lemon to add zest to our glass of water or herbal tea.
Sometimes, our citrus trees suffer from diseases that threaten the fruits of our labor. Citrus psorosis virus is one of these diseases, and it often goes undetected until it’s too late.
In this guide, we’ll talk about this disease, what causes it, how to identify it, and what to do about it. Here’s what’s on the roster:
What We’ll Cover
Get To Know Citrus Psorosis
It’s always smart to know your adversaries and how they operate so you know how to deal with them.
Citrus psorosis is considered one of the most economically impactful and important citrus diseases worldwide. If you’re growing citrus trees, this isn’t a disease you can ignore.
So, here’s a bit of citrus psorosis science knowledge stuff to start us off. Citrus psorosis is a serious viral disease caused by the Citrus Psorosis Virus (CPsV). CPsV is a type of virus in the Ophiovirus genus in the family of Aspiviridae (formerly Ophioviridae).
The significance of this genus is the segmented single-stranded RNA molecule. The virus structure is layered on a cellular level, with a protective outer membrane, so it can shift and adapt, replicating itself for optimal effect and attacking the connective tissues of its host.
Primarily, citrus psorosis targets sweet orange trees, but other citrus species can also be affected.
It was first identified in 1896 by citrus disease expert Walter Tennyson Swingle and fellow botanist Herbert John Webber. Since then, the disease has spread widely and has had a huge impact on citrus plants in the Mediterranean, the Americas, and Africa.
Over the years, it has adapted to navigate and infiltrate past plants’ natural defense systems. It’s a dynamic disease and many attempts to eradicate it have failed because it rapidly evolves past our control methods.
How Citrus Psorosis Spreads
Citrus psorosis is one of the most serious diseases associated with grafting oranges, lemons, and limes. Since many citrus trees are propagated through grafting, the disease can spread rapidly as diseased material is grafted to healthy material.
It’s transmitted primarily through grafting and propagation. Infected materials, such as budwood or scions, are introduced onto a healthy rootstock or section of a citrus tree, and it moves into the system of the host tree.
Though it can be deadly, it can take years to identify it in a plant. That means you might use that tree in grafting projects and unwittingly spread it to other trees.
It’s a slow-progressing disease due to the methodical way it manipulates the tree’s defenses and replicates itself.
Pests can also transmit this virus from host citrus plants to unsuspecting new ones through feeding. These vectors include:
- Citrus rust mites (Phyllocoptruta oleivora)
- Citrus snow scale (Unaspis citri)
- California red scale (Aonidiella aurantii)
- Citrus aphids (Toxoptera citricida)
Host Plants
Citrus psorosis can infect all members of the citrus (Rutaceae) family.
Non-citrus plants like lime berry (Triphasia trifolia), trifoliate orange (Poncirus trifoliata), and curry tree (Murraya koenigii) can be infected. Citruses like orange (C. × sinensis), lemon (C. × limon), grapefruit (C. × paradisi), and limes (C. aurantifolia, etc.) are all susceptible.
These plants can serve as hosts for the virus and can contribute to the spread of citrus psorosis within orchards, gardens, or homesteads.
Citrus growers must be aware of all potential hosts to implement proper management and control measures when planting and planning growing spaces.
Signs and Symptoms
Citrus psorosis virus can be exhibited in various ways in infected plants. The severity and combination of symptoms depend on the species, the age of the plant, and the environmental conditions.
Typically, the disease impacts citrus that are between 8 and 10 years old. Given the disease’s slow growth rate and manner of spread, infection may only become apparent later in the host’s lifespan.
Many of the symptoms present themselves as other citrus diseases. If in doubt and you don’t want to just rip it out, it’s best to get a confirmed diagnosis by a plant specialist or agricultural extension service.
Infected trees may develop bumpy, bubble–like or scaly nodules on the trunk and on branches. These scales can be grayish-white to silver in tone or light brown.
The bark of the infected citrus tree may develop vertical or horizontal cracks and fissures. These can be shallow or deep. Such open wounds leave the tree vulnerable to pest invasion from things like the lemon tree borer and other diseases.
This weakens the tree by interrupting nutrient uptake and hinders its natural first line of defense, the bark.
With the appearance of the cracks and fissures gummosis will follow. Trees will weep or ooze sap when damage occurs. The sap may be clear or amber in color and gummy in texture.
As the virus develops and multiplies, necrosis in woody tissue can develop. The first indicators of this will, obviously, be discoloration and decay.
This symptom leads to premature leaf or fruit dropping, disformed fruit formation, and the tree will lose overall vitality.
The citrus tree will struggle with nutrient uptake, lose vital minerals, can’t take up water, and will weaken.
Results are poor growth, naked branches that don’t recover, dramatically reduced vigor, and an overall decline in tree health.
Citrus trees and plants affected by citrus psorosis can produce fewer fruits, and the quality of the fruit may also be compromised. Fruits could be smaller, misshapen, or even show signs of internal disorders like discoloration and rot.
Foliage might discolor from vibrant green to yellow and finally brown before dropping to the ground. Mottling of the leaves where the veins run may also occur prior to the early shedding.
Loss of foliage and leaves means photosynthesis and cellular renewal will be difficult, if not impossible, depending upon how much is lost. Thus, the citrus tree or plant will struggle and eventually die.
Prevention and Management
Prevention is a key factor when dealing with citrus psorosis. If you suspect the virus has infiltrated your plants, then management will make the difference as to how much impact it has.
It can lie undetected for years, making it difficult to manage. Once established, it’s extremely hard to control or eradicate.
While complete prevention is challenging, there are several steps that can be taken to minimize the risk of citrus psorosis virus transmission and infection.
Hygiene
Implement strict sanitation practices to prevent disease transmission. This includes cleaning and disinfecting tools, equipment, and containers between use with a 10% bleach solution or hot, soapy water. You can also buy equipment cleaning solution at Amazon.
Deter pets, such as dogs, from removing and carrying infected debris from the area. Speaking of, you should always clean up fallen fruit, leaves, or limbs.
Sterilize all gloves and footwear before moving around between plants, trees, and areas of the orchard or garden.
Maintain Plant Health
Promote overall tree or plant health through proper fertilization, irrigation, weeding, and pest control. A healthy tree is better able to withstand a viral infection.
Here’s a list of how to keep your citrus comfortable and happy, but remember, this can vary depending on the species. Be sure you know what your specific species needs.
- Maintain the right soil acidity, which should be acidic to neutral.
- Grow in free-draining soil.
- Maintain soil health by adding well-drained organic compost each growing season.
- If growing in pots, make sure roots do not get restricted as the citrus plant grows. Re-pot into larger containers regularly to prevent this.
- Routinely prune to promote new, healthy growth.
- Immediately treat any diseases or pest problems that pop up.
- Feed with a balanced fertilizer with added copper, manganese, iron, zinc, and boron, according to a soil test. Find one that is slow-release to prolong the nutrients available.
- Control potential vectors by using integrated pest management practices and organic sprays.
Source and Quarantine New Trees
Always purchase from reputable sellers. Look at reviews of previous customers on any sites or companies you are looking to buy citrus from. What is their track record for selling healthy, disease-free stock?
Go local and ask community groups or nurseries where to obtain verified CPsV-free trees and plants.
If you’re planning on grafting or propagating your trees, use only certified virus-free citrus planting materials from reputable sources. Again, do your research.
Then, quarantine new trees for a few weeks before planting so you can watch for any signs of disease.
Monitor
Get to know your land, plants, and trees so you know what is normal and can act fast when signs pop up that something is wrong. Monitor plants regularly for any signs or symptoms that would indicate citrus psorosis.
Monitoring is an essential part of growing and something you should do every day. Don’t just look at your trees. Lift up the leaves and examine the underneath. Inspect the trunk and stems. Be sure you know how your trees should look and how they actually look.
It’s possible for the disease to spread beyond your home boundary and risk others, so confirmation is important.
Sign up for alerts and information regarding diseases like citrus psorosis via your local extension service.
As important as knowing what’s going on in your own garden is, knowing what is happening over your garden wall is also essential for management, prevention, and protection from CPsV.
Remove the Plant
Act immediately if one or more symptoms of CPsV show up. You might need to seek confirmation and advice from citrus disease experts, agricultural extension services, or plant specialists.
While there is, at present, no cure for this destructive disease once a citrus tree or plant is infected, there’s still one step to take: the complete removal of the plants. The entire thing needs to be removed, roots and all. Make sure all debris is removed, too.
Dispose of all removed parts hygienically and within your region’s guidelines. The threat to other orchards and citrus businesses is high if you don’t dispose of the plant appropriately.
