Brown Spots on Rubber Plant (Causes and Treatment)

The rubber plant (Ficus elastica) has been a favorite classic garden plant and houseplant way back from the Victorian era. Nothing disrupts the lush, vibrant, glossy green look of your rubber plant, quite like the presence of unsightly brown spots. 

No matter how you rationalize it, ‘brown’ is not the ‘new green.’ Thankfully, I am here to help you diagnose the issue and show you how to nurse your rubber plant back to health.

How to Get Rid of Brown Spots on Rubber Plant leaves: Prune away diseased or heavily affected leaves so that green, healthy foliage can thrive. Use pruning shears or scissors and disinfect with alcohol between trims. You should also remedy watering, light, humidity, temperature, pests/diseases, and other conditions that caused brown spots. 

Before I walk you through the various potential causes and treatment options, let’s talk about where these spots are found and how they appear.

What Portions of the Plant Are Infected?

Rubber plants are currently hot and trendy for their charming personality, character, and beauty. That’s why it can be nerve-wracking to see them freckled with brown spots.

These are dark brown patches or blotches, prominently on the leaves. The browning usually starts from the leaf tips and edges. And depending on the cause, they can start as small brown spots on the center or near the edges.

Some pests and diseases may attack the base of the leaf. Some may appear where the leaf meets the stem. In either case, you may see brown spots on the leaf underside and stems.

If the issue isn’t dealt with in the early stages, brown spots will appear on new leaves, shoots, and new stems.

What Causes Brown Spots on Rubber Plants?

Rubber Plant Algal Leaf Spot

The rubber plant algal leaf spot is caused by parasitic algae called Cephaleuros virescens. It thrives in warm, humid conditions. It’s sometimes known as green scurf.

Symptoms

The leaf spot disease is characterized by small rough, mesh-like brown spots on the leaves of your rubber plant. They can be pale green, gray, or orange. These small spots can expand and merge into larger brown blotches.

• Stunted growth and appearance
• Reddish-brown lesions on twigs or branches (on large plants)
• Leaf yellowing and falling off prematurely

Control and Management

Luckily, algal leaf spot is rarely a lethal disease. Instead, the damage is usually cosmetic, and organic control methods should be enough.

Encourage dry leaves by pruning excess foliage, improving aeration, and spacing out your houseplants. Also, avoid overhead watering – instead, water at the base or use self-watering pots.

Remove and discard diseased or dead parts of your rubber plant

Ensure your plant is healthy so that it can fend off infections. Water, fertilize and provide light as needed. Ensure the soil is well-drained, aerated, and fertile.

If the infection is too severe, apply copper-based fungicide or Bordeaux mixture biweekly until you get rid of the algal leaf spots.

Alternaria

Alternaria is a fungal disease that leaves plaque-like spots on the leaves of your rubber plant.

Symptoms

Alternaria is a fungal disease that leaves plaque-like spots on the leaves of your rubber plant. They often start as small (around half-inch in diameter) dark circular brown spots. They may change in color as they spread from dark brown or black to gray or tan, usually encircled by yellow halos around the outside.

• A stunted or weak plant
• Sunburned, wilted, and dropping leaves
• Fuzzy-textured spots

Control and Management

• Start by isolating your infected rubber plant.
• Prune away and discard diseased, dead, or heavily affected plant materials
• Treat your rubber plant by spraying with copper-based fungicides
• Keep your plant as healthy as possible.

Anthracnose

Anthracnose is one of the most severe fungal diseases that can affect your rubber plant. It’s caused by Colletotrichum, which blooms in damp conditions.

Symptoms

When Anthracnose infects your rubber plant, you will see reddish-brown or tan lesions along the veins. The infect areas will die and sink in, leading to the following symptoms:

• New, younger leaves to curl up
• Distorted growth
• Some parts of the leaves die rather than the whole leaf
• Greasy yellow halos encircling the brown spots
• Leaves drop prematurely

Control and Management

• Isolate your affected rubber plant.
• Make sure to remove and discard any diseased parts, debris, and fallen leaves.
• Stay away from overhead watering.
• Spray your Ficus elastica with copper-based fungicides. If the case is too severe, consider using chemical fungicides, such as those containing chlorothalonil.

Septoria Leaf Spot

If you leave your Ficus elastica in wet, humid conditions for long, it may develop Septoria leaf spots. This is a fungal disease characterized by small, irregular (about 1/8-1/4-inch in diameter) brown spots on both leaf tops and undersides. (Source: Iowa State University)

Symptoms

• Black or dark brown edged lesions on the leaves
• Mold-like growth on the leaves
• It affects mostly older or lower leaves
• Affected leaves turn yellow and brown. Eventually, they’ll wither and die.
• Leaves may shrivel, blacken, and drop off.

Control and Management

• Poor aeration and overcrowding act as a fan for the spread of septoria leaf spot disease. That’s why it’s crucial that you quarantine affected houseplants immediately.
• Prune and destroy diseased, dropped, or dead parts
• Space out your houseplants to improve aeration
• Spray using captan, copper, or sulfur-based fungicide

Downy Mildew

Downy mildew usually inflicts rubber plants in cool, humid conditions. It shouldn’t be confused with powdery mildew. You’ll rarely see the disease during sunny weather.

Symptoms

Downy mildew often emerges as colonies on the underside of your rubber plant leaves. As such, you will see spots covered with bluish-gray, purplish, whitish, or bluish cotton-like fungi.

As the mildew spores dig lock into the leaf from beneath, the top of the leaves will appear yellowish or whitish. With time, they will form a fuzzy coating on the leaves. Further damage will result in brown spots.

Control and Management

There are a lot of unknowns when it comes to controlling downy mildew. Your best bet is to isolate the affected rubber plant to prevent the spread.

You can use horticultural oil like neem oil to prevent the spread and colonization of other leaves in the early stages. Use a copper-based fungicide to battle any colonies; spray once every seven to ten days.

For severe cases, use stronger chemical fungicides.

Powdery Mildew

Although hardy, rubber plants sometimes attract powdery mildew. The fungal pathogen that causes the disease loves warm, humid environments.

Symptoms

The first and obvious sign of powdery mildew is the spotting of dusty light gray or white growths on the stem and leaves of your rubber plant. These powdery splotches actually start budding from the underside of the leaves.

• They start out as tiny patches or spots that expand until they cover the whole foliage. While younger leaves are more prone, both new and old foliage is affected.
• Infected leaves usually dry and turn brown or yellow because the mildew leach away nutrients and cause tissue damage.
• Affected leaves dry, die, and drop off prematurely
• Stunted, twisted, and distorted growth

Control and Management

• Use cultural methods that reduce humidity levels around your rubber tree. Space out your plants, avoid overhead watering, and improve air circulation.
• Prune out and destroyed affected parts
• For organic methods, use biological fungicides (like those that contain Bacillus subtilis), horticultural oils, or neem oil. Repeat the spray application every 7-10 days until you get rid of powdery mildew.

Bacterial Blight of Ficus Elastica

Bacterial blight on most Ficus elastic plants is caused by Xanthomonas sp. It usually affects younger plants and newer growths. The disease oftentimes in summer temperatures of 78-86 °F (26-30°C)

Symptoms

The bacterial blight starts out on near leaf edges as tiny, watery, circular lesions surrounded by irregular borders. This is a systemic disease that will spread over one to two weeks. During this time, the lesions will expand and coalesce into large blotches.

Ultimately, the lesions will become necrotic and turn brown. The leaves will then wither and fall off prematurely. These symptoms are usually visible in tender, newer, and older foliage.

Control and Management

• Prevention is usually the best strategy because it can be tricky to control an outbreak of bacterial blight on your rubber plant.
• Water your Ficus early in the morning so that leaves can dry during the day
• Seek out early signs to control before the damage is done
• Space out your houseplants to improve aeration

Root Rot

Symptoms

If you notice brown spots trimmed in a yellow halo, the issue with your rubber plant is root rot due to overwatering. Even if the topsoil is bone dry, the roots may be sitting in waterlogged or soggy soil.

The brown spots will persist even if you’ve improved lighting, humidity, temperature, and other growth conditions. A Sulky-looking appearance and stunted growth may be present. The brown-spotted leaves will turn yellow, wilt, and drop.

Check the root ball for signs of decay. If root rot is present, the otherwise glistening white roots will be soft, mushy, and dark brown or black in color. They will also give off a stinking smell.

Control and Management

• Check the drainage holes. They shouldn’t be blocked by sticky soil. Make sure they’re enough to ensure proper drainage.
• To save your plant from root rot, wash off soil from the root ball, and prune away diseased roots. Prune back some foliage to offset root loss.
• Treat the remaining roots using fungicide or hydrogen peroxide.
• Repot with fresh soil and provide adequate growing conditions.

Nutrient Deficiency

If you notice brown spots on your Ficus elastica, it could be lacking major nutrients like nitrogen, phosphorus, magnesium, or potassium. They’re required for robust health and growth.

Symptoms

• Chlorosis (decoloration) is among the earliest signs of nutrient deficiency. It’s often seen as the yellowing of leaf margins and paling of leaves.
• In severe cases, you’ll notice browning or speckling of the leaves.
• Leaf scorch or burns may also appear.
• For potassium deficiency, for instance, you’ll note dead brown or black spots on the foliage.
• Stunted growth
• Pests and diseases are among signs of weak or malnourished rubber plants
• Older/lower leaves turn yellow, wilt, and fall off

Control and Management

• Test the soil for fertility. If the potting mix has been spent, repot with fresh, fertile, and well-draining soil.
• Check the root system. Damage roots may cause nutrient deficiency. Propagate if the root system is severely damaged.
• Ideally, you should feed your rubber plant every four to six weeks during spring and summer.

Edema On Rubber Plant Leaves

A physiological condition, edema, happens when your rubber plant absorbs too much water faster than it can use. At first, you will notice water-soaked raised spots on the leaf underside. However, the cells will eventually rupture, leading to coarse-texture brown spots.

Symptoms

The water-soaked spots can take a black, yellow, or reddish-brown hue with a cork-like texture.

The characteristic rubber tree milky sap may leak out. When it dries, it will leave more brown spots.

Control and Management

Usually, the effects of edema can’t be reversed or cured. However, you can prevent your rubber plant from further effects of edema by:

• Stop overhead watering; prefer watering in the early morning
• Don’t get leaves wet
• Improve air circulation
• Improve light conditions

Excess Light/Scorching

Rubber plants prefer bright (not hot), indirect light. However, too much light, especially direct sunlight, will cause your Ficus to sunburn and develop brown spots. 

Sunburns can also result from seasonal changes in light intensity. For example, your rubber tree may have been thriving in a south-facing window in colder weather. But when the spring or summer sun kicks in, they can easily scorch.

Symptoms

Generally, scorched rubber plants will manifest as burned brownish spots. However, look out for other symptoms of scorching.

• Brown edges or tips on the ficus leaves
• Yellowed or pale leaves
• The leaves will be dry, crispy, and wilted

Control and Management

Move your ficus elastica away from the source of scorching light. It’ll do well in a spot that receives plenty of bright, indirect, or filtered light, preferably an east-facing window.

Perhaps you can place it near a west-facing or south-facing window with a sheer curtain to filter out intense UV rays.

Frost Damage

As a tropical plant, Ficus elastica isn’t too keen on exposure to temperatures below 40°F (4°C). Cold injury is detrimental to your rubber plant’s health and growth.

Symptoms

Damage from cold drafts and frosts will cause young and tender foliage to look puckered or distorted at first. Over time, large brown spots will develop on both older and newer leaves.

The bark of your tree may also start to peel or crack due to cold damage.

Control and Management

Move your Ficus elastica away from floor vents, air conditioners, opened windows, and other sources of frosty drafts. Also, don’t leave it outside when the temp is likely to drop below 40°F (4°C). Remove and discard any heavily frosted-damaged parts.

Low Humidity

Symptoms

If your rubber plant leaves have become browned, crispy, and dry, you may want to check the humidity leaves in your room. This is especially noticed during winter when our homes are drier and hotter.

Apart from brown spots, other signs of low humidity include:

• Leaf Edges Dry Out
• Leaves dropping
• Dry brown leaf tips
• Sunburned appearance on the surface of the leaves

Control and Management

The best answer is to ensure relative humidity of 40% to 50%. For the best results, invest in a reliable digital hygrometer (or a multipurpose meter) and place it close to your plants.

Adjust humidity levels using a water tray with pebbles, misting, or a humidifier

Insect Infestation

Symptoms

• Rubber plants are often vulnerable to spider mites that leave small brown speckles on the leaves. If they’re present, you will find delicate webbing on the underneath of the foliage. Leaf mottling and yellowing are also common.
• Other pests like aphids, scales, and thrips also attack rubber plants and cause brown spots. Aphids are small, pear-shaped bugs that form colonies on the underside of the leaves and stems.
• Scales, like aphids, are sap-suckers and attach themselves anywhere to the rubber plant. Aside from black spots, you’ll notice waxy, cotton-like scabs on the leaf surface.
• Thrips are winged bugs that fly or jump when disturbed. They’re either straw-colored or black.
• Some of these insects leave a sticky, sugary substance on the leaves, which attracts fungus gnats and ants. As such, you may spot sooty molds on the foliage.

Control and Management

A strong blast of water usually can wash these insects off your rubber plant. Be sure to rub affected areas with an alcohol-containing cotton ball.

Spray with neem oil, insecticidal soaps, or any other non-toxic horticultural oils.

Watering Problems

Symptoms

If you see brown spots and tips on your rubber tree, the problem is most likely due to improper watering. If the soil is bone-dry, the leaf tips and edges turn brown and wilt. The rest of the foliage will also follow with wilting, drying, and browning.

When overwatered, Ficus elastica will develop yellow, brown, or pale green leaves. Eventually, they will develop large watery blotches, wilt, and fall off prematurely. Dropping, stunted growth, and soggy soil are other signs of overwatering.

Control and Management

• You must water your rubber tree when the top inch of the soil has dried out.
• Check an overwatered ficus elastica for root rot and treat as explained above.
• Water an underwatered rubber plant thoroughly until liquid comes out of the drainage holes.
• Avoid overhead irrigations and consider using a terracotta pot with proper drainage holes.

Fertilizer Burn

Overfertilizing will result in a salt build-up in the soil. The salts will hinder root function and cause leaf damage, causing leaves to develop brown spots.

Symptoms

• You’ll find white salt scabs or spots on the surface of the soil
• Brown spots on the margins and tips of the leaves

Control and Management

• Flush your rubber plant with water to remove excess salt from the soil
• Reduce the amount of fertilizer and increase frequency accordingly
• Avoid high-nitrogen fertilizer
• Repot with a fresh potting mix if the salt build-up is too much
• Avoid using chlorine/fluoride-containing water like tap water as it’ll cause salt deposits

How to Prevent Brown Spots on Rubber Plant

• Avoid overcrowding of houseplants
• Improve air circulation by pruning and spacing out your plants
• Avoid overhead irrigation; consider watering in the morning or using a self-watering pot
• Desist from overfeeding your rubber plant with fertilizer
• Isolate any diseased plants at first sight
• Stick to proper watering habits

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