Geranium Leaf Spot And Stem Rot: What Causes Bacterial Wilt Of Geraniums

Geranium Leaf Spot And Stem Rot: What Causes Bacterial Wilt Of Geraniums

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By: Mary Ellen Ellis

Bacterial wilt of geraniums causes spotting and wilting on leaves and rotting of stems. It is a damaging bacterial disease that is most often spread by using infected cuttings. This disease, also known as leaf spot and stem rot, can quickly destroy your geraniums.

Get to know the signs and how to prevent its spread in your indoor or garden.

Signs of Leaf Spot and Stem Rot on Geraniums

There are a few characteristic signs of this disease. Thefirst is the spot formation on leaves. Look for small spots that are circularand appear water soaked. These spots will quickly get larger and eventually theleaves will begin to wilt.

Other signs you may notice on geranium leaves areyellowish-brown spots. These emerge between veins and radiate outward making apie piece shape. This is followed by collapse of the leaf. Signs of the diseaseon leaves may emerge alone or with other symptoms of wilt.

Sometimes, the leaves on an otherwise vigorous geranium willjust simply wilt. You may also see signs of the disease in the stem. The stemsturn darker and ultimately turn black before collapsing completely.

Causes and Spread of Geranium Leaf Spot and Stem Rot

This is a bacterial geranium disease caused by Xanthomonaspelargonii. These bacteria can move through and infect an entire plant.Plant matter in the soil can carry viable bacteria for a few months. Thebacteria also survive on surfaces such as tools and benches.

Xanthomonas can spread and cause disease by water splashingup from the soil and onto leaves, through tools used on contaminated plants,and through whiteflies.

The best thing you can do to manage geranium leaf spot andstem rot is to use disease-free cuttings and transplants. Be careful whenpurchasing or sharing geraniums for this reason.

Avoid splashing water on geraniums and try to keep leavesfrom getting wet. This can prevent spread of the bacterial infection.

Also, keep all tools used on geraniums sterilized to preventdisease spread.

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Read more about Geraniums

Geranium and Pelargoniums

There are over 300 species of Geraniacaea. The best way to distinguish between Geraniums and Pelargoniums is the shape of the flowers and the colour of the leaves.

Pelargoniums have asymmetrical arrangements - 3 upper and 2 larger lower petals. They can be single or double. The leaves are lobed with colour in the leaves.

Pelargoniums are best treated as biennials and should be pruned regularly as they can get very woody. Use the prunings for cuttings.

Zonals – rounded leaves distinctively marked with a darker zone.

Ivy leafed – trailing plants that can be trained on a trellis, from hanging baskets, down a retainer wall or used as a ground cover. (This variety will grow under iron-bark trees with a little help from mulch and liquid fertiliser.)

Herb/scented leaf – have beautiful leaves with various scents: lemon, peppermint, nutmeg, spice, or rose, etc. They are often used in the perfume industry.

Geraniums, or Crane’s Bill, have circular (symmetrical) flower heads at the crown of the plant. The leaves are deeply dissected with no colour. These originated in the cooler climates of Europe and Asia. They have a low growing mound shape and come in a variety of colours.

Pests – caterpillars, aphis and white mite can be treated if detected early.

Rust – shows up as black on top of the leaves usually from watering on their leaves.

Bacterial leaf spot – is caused by watering the leaves and poorly drained soil.

Stem rot, leaf curl virus and mosaic virus

– these are hard to cure. The signs for stem rot are obvious as the name says. The two viruses show up as leaves curling in or going yellow. The best advice is to get rid of the plant (roots and all). Put in a plastic bag and place in your NORMAL rubbish bin. Never put diseased plants in for recycling. That only spreads the disease to other areas and other gardens.

Geranium Problems

Pelargonium peltatum. Source: Futureman1

There’s quite a few pests that geraniums have to contend with, as well as a number of diseases. While you’re not likely to experience these problems constantly, here’s how to handle them if and when you do!

Growing Problems

Geraniums are warmth-loving plants. If the weather gets too cold and the plant is not protected, it can cause yellowing or reddening of the leaves, wilting, and possibly even plant death.

To prevent these problems, be sure your geranium is kept warm during the winter. If it’s under 50 degrees, consider using a cold frame or other outdoor protection, place it in a greenhouse, or bring your plant indoors if it’s in a pot.

Oedema, also known as edema or corky scab, is another problem that primarily affects ivy geraniums. When the air is cooler than the soil temperature but humidity both in the soil and air are high, it can cause oedema.

This condition creates watery blisters on leaves that rupture and turn yellow or brown, and can be mistaken for forms of rust. To prevent oedema, keep the air humidity low and don’t overwater. Air temperature should be kept at or above the soil temperature as well.

Speaking of overwatering, improper irrigation is a regular issue for geraniums. Overwatering can cause leaf yellowing, but so can underwatering. Check the soil if your plant starts developing yellowed leaves, and if it’s too wet, reduce your watering frequency.

Underwatering can cause reddening of leaves, or crisped edges of leaves. Again, check the soil and if it’s dry, water your plant.

Some nutrient disorders or deficiencies may also cause reddening or yellowing of leaves, but checking your irrigation status first is usually the best choice. If your irrigation level is good, then move on to having the soil analyzed and checking for signs of plant disease.

Sucking Pests

Geranium phaeum flower closeup. Source: Joan Simon

There are a number of sucking-type pests that go after geraniums for their inner juices.

Aphids are quite common in gardens, and they like geraniums almost as much as they like our edible plants. They group on the underside of leaves and along stems.

Scale insects, especially two types of mealybug (the citrus mealybug and Mexican mealybug) and the cottony cushion scale, are also prone to attack your geranium plants. These can create little fluffy, cottony masses on the leaves and are easy to identify.

The twospotted spider mite will also attack geraniums, although they typically only go after plants in drier conditions. These can create web-like masses on the leaves.

Thrips, especially western flower thrips, can often be found on the flowers or buds of geraniums. These may also be found on the leaves.

And finally, there’s whiteflies. You may find clouds of tiny white bugs flying above your plants, and that’s a sure sign that they’re present. Their larvae will be hiding on the underside of leaves, sucking the juices out of them.

On the bright side, there’s a couple things you can do to conquer all of these pests. Spray your geraniums regularly with neem oil to keep them at bay and to smother their eggs. Release ladybugs and lacewings around your garden during spring and summer to help kill them off.

You can also use insecticidal soaps like Safer Soap against these pests, if neem oil isn’t available. But I honestly recommend keeping neem oil at hand for the sucking pests at all times! A weekly or biweekly application of neem keeps them at bay.

Caterpillar Pests

A huge list of moth larvae feast upon geraniums, too. And unless we want a plant’s leaves to look like Swiss cheese, they need to be controlled quickly and effectively.

Armyworms, particularly the beet armyworm, are quite fond of geraniums. While they’ll go towards edible plants first, they’re more than willing to feast upon your geraniums next if they’re not dealt with.

The bollworm may be more of a curse to cotton growers than to home gardeners, but if you live anywhere near cotton farms, you’re susceptible. These hungry little caterpillars will chew through your leaves.

Cabbage loopers are common throughout the United States and in many other countries. Like armyworms, geraniums are not their primary choice, but they’re certainly not unwilling to chew huge holes in your leaves.

The geranium or tobacco budworm is a moth larvae who specifically targets both geraniums and tobacco, along with petunias and other common flowering plants. Widespread through the western United States, it’s found in lesser numbers worldwide.

Another larval pest that targets geraniums is the geranium plume moth, which is also widespread throughout the western USA. The adult moth has frilled wings and looks like a cross between a moth and a butterfly. Their caterpillar form is particularly destructive to flowering plants.

The oblique-banded leafroller is a moth that’s native to North America. Its larvae feed on an extensive range of plants. While geraniums are one of their targets, so are roses, rhododendrons, strawberries, carnations, honeysuckle, and azaleas. These also attack trees like willow and pine!

The omnivorous leaftier is sometimes called strawberry fruitworm because it attacks strawberries. But it will happily consume geraniums as well, and it’s best to keep a watchful eye out for this moth and its caterpillars.

And finally, there is the variegated cutworm. Like all caterpillars, these small larvae feed on plants. However, they’ve earned their name by eating through stems, causing the stem to topple over as if it were cut. These can be absolutely deadly to young geranium plants.

Like the sucking insects, there’s one primary control method that I recommend for all of these. Spraying or powdering your plants with bacillus thurigiensis, also known as BT, will eradicate a couple hundred species of caterpillars.

I recommend Monterey BT as a spray, or Garden Dust as a powdered form. Both will work quite effectively without harming beneficial insects.

Other Pests

Geranium maculatum. Source: amy_buthod

The Fuller rose beetle, aka the rose weevil, is as inclined to consume geranium plant matter as it is to go after roses. The adults will eat the plant’s leaves, where larvae go after the plant’s roots. A bad infestation can easily kill your geranium plants.

It’s important to control these beetles in their adult form, before they can lay eggs. Neem oil is considered to be an effective deterrent against the Fuller rose beetle, and can smother their eggs.

Once larvae form, beneficial nematodes in the soil will also attack the weevils, as will parasitic wasps.

And at the end of this long pest list, we have the sciarid fly, known as the dark-winged fungus gnat. While the adults are mostly just an irritant, their larvae will live within your soil and do root damage to your geranium plants.

Using the common household version of hydrogen peroxide as a soil drench is quite effective at killing the larvae of fungus gnats, as is neem oil.

A species of BT that’s not in most commercial sprays or powders, Bacillus thurigiensis var. israelensis, can also be used to kill fungus gnat larvae. You can find this in Microbe-Lift BMC Fertilizer if you need to fertilize your plants. Alternately, water in some Mosquito Bits to get it in your soil.

Fungal Diseases

Fungal issues like Armillaria root rot, botrytis blight, Alternaria leaf spot and other leaf spots, pelargonium wilt, and verticillium wilt are common problems for geraniums.

Armillaria root rot is caused by the fungus Armillaria mellea. It causes stunted growth and wilting on geraniums, as well as leaf drop. Honey-colored mushrooms may form at the base of infected plants, although that’s more common on trees. Destroy infected plants and remove all root material.

Botrytis cinerea creates greyish, mold-looking spore infestation across leaves and can be fatal to plants over time. Treatment is a bit complex, so I recommend you read my article on how to handle botrytis cinerea infestation.

A variety of leaf spots tend to be caused by fungal growths, and many of them cause damage to geraniums. The worst of these is alternaria leaf spot, which causes brown spots with a yellowish halo around them. Use a liquid copper fungicide to treat these conditions.

Geranium rust, occasionally referred to as pelargonium rust, can cause yellow spotting with dark brown pustules filled with fungal spores. Neem oil can help protect your plants’ foliage from developing this disease.

Finally, we come to the last fungal issue for geraniums, verticillium wilt. Wedge-shaped yellow patches on leaves will form. Quickly thereafter, the entire leaf may yellow, wilt, or simply fall off. Plants will become stunted and may have limp branches.

Geraniums showing the symptoms of verticillium wilt should be removed completely and destroyed. This fungus lives in the soil, so new plants susceptible to verticillium should not be placed in that soil unless it’s fully heat-sterilized.

Bacterial Diseases

Geranium pratense. Source: CameliaTWU

Bacterial infection for geraniums tends to be uncurable. Prevention is your best defense.

Bacterial leaf spot or bacterial blight are some of the most common diseases of geraniums. There are multiple bacteria, but the most prevalent are Xanthomonas campestris pv. pelargoni, the Psuedomonas species Pseudomonas cichorii and Pseudomonas syringae pv. syringae, and Ralstonia solanacearum.

Most of the bacterial leaf spots and blights are spread by water splashing onto the leaves or through infected soil. While there are some chemical bactericides which may be partially effective, these bacteria are notoriously hard to wipe out. Destroy infected plants.

Blackleg is a common infection for geraniums which turns the stems a distinctive black color and causes them to wilt, as well as causing root rot. Plants infected with blackleg will not recover, and should be destroyed.

A pair of gall types also tend to strike geraniums.

Leafy gall causes a cluster of strangely-shaped leaves to appear right at the soil line. This bacteria is transmitted through the soil, and infected plants should be destroyed. Avoid planting new geraniums in that spot.

Crown gall causes distorted growths or galls directly on the plant’s stem. These galls make it difficult for the plant to take up water or nutrients. Plants with galls should also be destroyed, and again, avoid planting geraniums in that spot.

Viral Diseases

There is also a long list of viral diseases which can affect geraniums. Like the bacterial diseases, these have no known remedy. Infected plants should be destroyed to prevent viral spread.

Two mosaic viruses, the cucumber mosaic virus and tobacco mosaic virus, can spread via aphids, virally-infected seed, or via human hand on tools. These cause mottling and streaking of the geranium leaves, as well as blistering or crinkling of the leaves.

Curly top, also referred to as beet curly top virus, causes thickening of the leaves and twisting and deformation. Leaves may yellow, as well. Younger plants often will die off quickly, while older plants may hold on for a while.

Impatiens necrotic spot virus and tomato spotted wilt virus were originally considered different strains of the same virus, but now are viewed separately. Both cause a wide variety of symptoms including yellowing, spotting, discoloration, stunting, wilting, and stem death among others.

Pelargonium flower break causes stippled yellowing of leaves, leaf edge browning, and yellow veining. This disease is widespread in greenhouse environments.

Finally, there is the tobacco ringspot virus. Transmitted by everything from nematodes to honeybees, this virus causes irregular yellow splotches on leaves, crook-shaped stems with drooping flower heads, browning and rolling of leaves, and other symptoms.

Most of these viruses are transmitted by pest populations. If you keep your plants free of pests, you will greatly reduce your chances of plants developing these viral infections. Destroy any plants which are infected to prevent spread of the diseases.

Whether you’re growing them for their luscious scent or their showy blooms, geraniums are definitely worth growing! What’s your favorite variety of geranium? Let me know in the comment section!

Watch the video: 2018 02 28 12 00 New England Greenhouse Webinar Series Growing Healthy Roots


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