Brown Spots on Orange Tree Leaves

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To the untrained eye, gardening may seem like a relaxing hobby. In reality, gardening requires a lot of effort. Gardeners, professional or amateur alike, deal with different challenges to keep their plants alive —never knowing which issue will ruin their hard work.

To present solutions to some of these problems, this article covers everything from an immediate cause to a far-fetched possibility that leads to brown spots in orange trees, a condition prevalent in most citrus plants.  

Keep reading for some insightful realizations!

Reasons Behind Brown Spots On Orange Tree Leaves

The following diseases, infections, and environmental repercussions can lead to brown spots on orange tree leaves either in the initial or final stages.

Scroll down to know the specifics of each condition and how you can combat them:

Nutrient Toxicity

If supplied in excess, certain nutrients can damage orange tree leaves in more ways than one. Sodium, chlorine, and boron toxicity are fatal to orange trees as it onsets heavy leaf drop and leaf damage. In case of boron toxicity, your tree might even suffer from excessive shoot dieback.

The initial stage of nutrient toxicity is often characterized by yellow and brown spotting, spiraling into irregular discoloring. Spots caused by Boron toxicity first appear on the underside of leaves and might remain undetected unless the leaves start mottling. Sodium toxicity gives way to draught-inspired stunted growth shortly after taking root.

Treatment:

Ensure that you provide your orange trees with a balanced fertilizer instead of those rich in one or two nutrients. You can supply them with specific nutrients if you notice signs of nutrient deficiency; otherwise, a balanced fertilizer should work just fine.

Also, avoid using saline water to water your orange trees if they are not suffering from sodium deficiency. Saline water is mostly only suitable for plants meant for beach areas like coconut trees and does not abide by the dietary preferences of citrus plants.

Anthracnose

Anthracnose is a citrus plant disease of fungal origins that often runs rampant in old wood canopies. The disease first develops as small reddish spots, then matures into unseemly dark brown spots on fruits and leaves. They attack frail and unhealthy stems and spindles more severely because of their weak defense mechanism.

This contractive fungal disease uses rain for its spread but can also be caused by overhead watering. The worst case of Anthracnose can lead to premature leaf fall and damage to the rind tissue of orange fruits. Some extreme cases even cause untimely stem dieback, leading to stunted growth in young plants.

Treatment:

The easiest way to combat Anthracnose is through periodic fungicide application. Fungicides of sulfate combination like zinc and copper sulfate are potent against Anthracnose progression. Azoxystrobin and hydrated lime have a chemical composition that has been proven deadly against Anthracnose.

Unlike most causes of brown spots on orange tree leaves, this fungal disease can be managed by regular pruning and trimming. Conversely, you can’t do anything to revive the damaged leaves, so they need to be cut off and swept into a trash bag.

Citrus Canker

Citrus Canker is a contagious bacterial infection prompted by the pervasive Xanthomonas citri pathogen. It can be transmitted from one host to another via wind, rain, gardening equipment, insects, and clothes. Prolonged exposure to moisture makes orange tree leaves the perfect breeding ground for the leading pathogen.  

The initial symptoms of Citrus Canker include yellow scabs, which later transform into brown spots on leaves, trunk, spindles, and fruits. If left unchecked, this bacterial disease leads to early fruit drop, dieback, and scarred fruit.

Treatment:

Unfortunately, there is no cure to treat brown spots on orange tree leaves caused by Citrus Canker. Still, as a preventative measure, or in the early stage, you can use Liquid Copper Fungicide to keep its progression at bay. A severely damaged orange tree cannot be saved and must be destroyed in due time to prevent its spread to the surrounding trees.

Melanose

Brown spots on orange tree leaves are the early signs of Melanose, a fungal infection prevalent in citrus plants. In severe cases of Melnaose, brown spots on foliage develop a reddish hue and mime the otherwise radiant appearance of orange fruit.

Melnaose spots are set apart from other brown spots because of their rough feel. They have raised bumps, are coarse to touch, and can be scratched off for inspection. Wet dead foliage, overhead watering, and rain enable the unsightly progression of Melanose. Young plants are more prone to developing Melanose compared to mature ones.

Treatment:

There is not much you can do once the infection has taken root except cut out the damaged tree parts to stop the spread. Additionally, you can regularly remove dead foliage from your orange trees to discourage Melanose development.

Alternaria Brown Spots

Alternaria Brown Spots is a wind-blown fungal infection spread by spores. Water damage like wilting leaves provides them with the perfect venue to settle and propagate. In the early days of the disease, the spots are brown, sometimes with a black tint, but as it matures, the brown spots develop a yellow halo.

Damaged and young orange plants fall prey to Alternia Brown Spots easily, whereas the older ones can build immunity over time. Alternia’s toxins are harmful and eventually lead to tissue death in the secondary veins of leaves and fruit rot.

Treatment

Although tangerine varieties are more susceptible to Alternia Brown Spots, orange trees have had their fair share of unfortunate run-ins with the disease. Strobulirin and Copper Fungicide are effective against the infection, eliminating brown spots on orange tree leaves.

Citrus Blast

Citrus Blast is a bacterial disease that first appears on orange tree petioles as black spots. Eventually, as the condition matures, the black spots turn brown and cover all tree parts, including the leaves. Citrus Blast can further damage twigs and stems if not contained in time.

The extent of the Citrus Blast damage depends on the wind exposure. Higher wind exposure means rapid bacterial growth. Therefore, trees growing in strong winded areas are more likely to contract Citrus Blast.

Treatment:

Citrus Blast can be contained by snipping off the damaged parts in spring or spraying them with a cultural control antidote. Adding windbreakers around orange trees can also discourage the growth of the bacteria.

Citrus Leprosis

Citrus Leprosis is a mite-transmitted virus with alternative names like Nailhead Spot, Rust, and Scaly Bark. Brevipalpus, a spider mite, carries the virus from one tree to another, facilitating its widespread transmission. The virus doesn’t need the tree to grow or reproduce and treats the mite’s body as its primary host.

Orange tree leaves develop Leprosis spots with dark brown centers when the mite feeds on them and injects the plant with the virus. The virus transmission continues as long as the mite is alive and on the move.

Treatment:

Leprosis spots appear on both sides of orange tree leaves and sometimes even have a yellow halo around them. The most efficient way to treat this viral mite infestation is through a potent yet chemically sound miticide.

Greasy Spots

Greasy Spots is the name of a fungal infection that relies on wind, rain, and dead foliage for its transmission. Brown spots on orange tree leaves are the first sign of infection, which snowballs into oily blisters. The disease is further characterized by yellow spots on leaves and black imprints on fruit.

This fungal infection breeds in the heap of fallen leaves, wet and left to discompose for an extended period. Once mature, it moves towards healthy foliage to feast. Their persistent progression triggers an early and excessive leaf fall for an infected orange tree.

Treatment:

Liquid Copper fungicides can be sprayed on premature brown spots to stop them from transforming into blisters. You can avoid the development of Greasy Spot altogether by clearing dead foliage around your orange trees regularly and not letting the moisture rest.

Citrus Scab

Just as the name suggests, Citrus Scab produces brown scabs on the fruit and leaves of almost all citrus plants. The disease starts with brown or pink spots on the leaves, progressing to a wart-like ugly scabbing. At its worst, it looks like a grey infestation and is primarily clustered in fruits.

The brown scabbing of Citrus Scab is often mistaken for other blotting and lumpy infections. The scabbing spores are spread through wind and rain splashes and multiply rapidly in a wet environment. The disease dies a natural death in unfavorable conditions.

Treatment:

Ideally, copper sprays should be able to cure the early signs of citrus scabbing, i.e., brown spots on orange tree leaves. Furthermore, damaged leaves and fruits should be eliminated for new and healthy outgrowths.

Citrus Variegated Chlorosis (CVC)

Citrus Variegated Chlorosis (CVC) is instigated by Xylella fastidiosa, a bacteria, and its subspecies. This bacterial disease is transmitted by many insects hopping from one leaf to another, carrying the bacteria on their bodies or fluids. Grafting is also a transmissible hazard for orange trees and can result in a haggard appearance.

The CVC is often mistaken for nutrient deficiency because of its symptoms on young leaves. The yellowing between leaves can lead to a misdiagnosed zinc deficiency and eventually to mistreatment. You can differentiate between the two by checking the underside of the mature leaves. If you see brown spots there, your orange tree is like suffering from CVC than a zinc deficiency.

Treatment:

Citrus Variegated Chlorosis (CVC) can be controlled by regular pruning and trimming of dead foliage. The affected parts can hardly be resurrected, so it’s better to cut them off and allow new and healthier outgrowths to grow in there instead.

Common Solutions to Prevent Brown Spots on Orange Tree Leaves:

Although the diseases mentioned above show themselves as brown spots on orange tree leaves, fruits, and leaves at varying stages, they stem from more or less the same environmental circumstances. If you can control these conditions now, there will be no room for abnormalities in the future.

Water Requirements:

Ensure that your orange tree gets optimal water, especially during long, dry summer spells. Over-watering and under-watering can lead to the development of brown spots on orange tree leaves through lateral means. Imbalanced water input can weaken plants, making them more susceptible to dangerous bacterial, fungal, and viral diseases.

You should only water your orange tree on root level when the soil is dry up to 4 inches. Overhead watering enables moisture accumulation on leaves, making for an ideal breeding ground for many foes.

Balanced Nutrients:

Excessive use of fertilizer can lead to nutrient toxicity primarily when you don’t drain the soil of the last feed. Feed your orange trees after watering them, or else each new feed will pile on the older one, amassing one nutrient or many nutrients in excess.

Proper Sunlight:

Orange trees need adequate sunlight; therefore, they should be planted in areas aligning with their nature. Scorching heat with insufficient water input can cause sunburn, further characterized by brown spots that turn blotchy and irregular in the long run.

Admittedly, you can’t control sunlight reaching your orange trees, but you can increase their tolerance level to heat by increasing their water input.

Regular Trimming & Pruning:

It’s essential to snip off dead, weak, or damaged leaves, stems, fruits, and twigs regularly as they are susceptible to fungal or bacterial attacks. The best time to do this is late in the season after the seasonal leaf and fruit drop.

Soil Maintenance:

Dead and wet foliage around your orange trees can trigger many kinds of infestations. Don’t let any litter accumulate in the soil; clean the ground regularly, especially after rain. Moreover, mulch the soil bed at least twice a week or just after feeding it fertilizer thrice a week.

Takeaways:

Sometimes, brown spots on orange tree leaves appear as symptoms, hinting at a bigger problem, while other times, they embody severity themselves! From the minor environmental infraction to dangerous viral infestations, we have discussed every possibility that can cause this deplorable condition in orange trees in this article.