Geranium Blackleg Disease: Why Geranium Cuttings Are Turning Black

Geranium Blackleg Disease: Why Geranium Cuttings Are Turning Black

By: Bonnie L. Grant, Certified Urban Agriculturist

Blackleg of geraniums sounds like something straight out of a horror story. What is geranium blackleg? It is a very grave disease that most often occurs in a greenhouse during any stage of the plant’s growth. Geranium blackleg disease spreads rapidly in close quarters and can mean doom to the whole crop.

Keep reading to find out if there is any prevention or treatment for this serious geranium disease.

What is Geranium Blackleg?

By the time you discover your plant has blacklegdisease, it is usually too late to save it. This is because the pathogenattacks the root, where it is impossible to observe. Once it creeps up the stem,it has already affected the plant badly enough that nothing can be done. Ifthis sounds harsh, there are things you can do to prevent it and keep it fromspreading.

If you notice your geraniumcuttings are turning black, they are likely victims of some species of Pythium.The problem starts in the soil where the fungus attacks the roots. The firstabove ground observations are limp, yellow leaves. Under the soil, the rootshave black, shiny lesions.

Fungusgnat larvae are generally present. Due to the semi-wood stem of the plant,it won’t completely wilt and fall over, but the dark fungus will go up thecrown to the new shoots. In a greenhouse, it most often affects new cuttings.

Contributing Factors of Geranium Blackleg Disease

Pythium is a naturally occurring soil fungus. It lives andoverwinters in soil and garden debris. Excessively wet soil or high humiditycan encourage the growth of the fungus. Damaged roots allow easy entry todisease.

Other factors that promote the disease are poor cuttingquality, low oxygen content in soil, and excess soluble salts from too muchfertilizing. Frequent leachingof the soil can help prevent the latter and avoid damage to the roots.

Treating Geranium Blackleg

Sadly, there is no treatment for the fungus. Prior toinstalling your geraniumplants, soil can be treated with a fungicideregistered for use against Pythium; however, it doesn’t always work.

Using sterilesoil is effective, as is developing good sanitation rituals. These includewashing containers and utensils in a 10% solution of bleach and water. It iseven suggested that hose ends be kept off the ground.

When geranium cuttings are turning black, it is too late todo anything. The plants must be removed and destroyed.

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Wilting Geraniums

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Geraniums (Pelargonium spp.) owe their enduring popularity to several factors, including their constant bloom, long-lasting flowers, reliability and variety of cultivars, noted by their many leaf, growth and bloom characteristics. Grown in gardens and as potted plants, geraniums produce brightly colored flowers in many hues, mostly commonly pink, red and white. Although typically easy to grow, geraniums are susceptible to diseases and environmental problems that may result in wilting.


Symptoms and Life History

The bacterium reproduces and moves systemically in the water conducting cells of the plant resulting in wilt. Leaf spot and stem rot may or may not occur. The stem rot phase is occasionally referred to as black rot and can be confused with the black leg disease caused by the fungus Pythium. In greenhouses, the most common symptom is a wilting of one or more leaves even though the root system appears healthy and the soil is moist. However, if root rot is evident, that does not rule out the presence of bacterial blight. Excessive fertilizer can also mimic these symptoms.

Leaf spot is less common than wilt but may occur if plants in advanced stages of disease are present. For leaf spot to develop, the bacterium has to be splashed from one plant to another or be underneath hanging baskets that are contaminated. Leaf spots are fairly diagnostic. When leaves are held up to the light, the spots will have dark centers with translucent borders. They may be circular or they may run together resulting in a blighted appearance. Leaf spots are soon accompanied by yellowing, often in a V-shaped pattern. The bacterium will move into the vascular system of the leaf and then into the stem. Other bacteria may cause similar spots but do not result in wilt.

Symptoms on ivy geraniums are much less obvious than those that occur on seed and zonal types. The thick waxy leaves do not wilt. In general, the foliage becomes dull and grayish, ultimately resulting in scorched or dried leaves. The symptoms are easily confused with nutrient imbalances or insect infestation.

A laboratory diagnosis is necessary to confirm the presence of the bacterium.

Cuttings taken from systemically colonized stock plants may fail to root, turn gray-brown to black, and develop a dry rot. Other pathogens may cause similar symptoms. Cuttings with low levels of bacteria may root and not develop wilt symptoms for 10 weeks or longer.

When plants are in advanced stages of disease or when leaf spots are present, the bacterium is easily spread by splashing irrigation water and by physically handling plants, especially when they are wet. The use of cutting knives is an efficient way to spread the disease therefore cuttings should be snapped off of the plant. If cuttings are rooted together in a flat, bacteria are easily spread to adjacent cuttings. Capillary mats under pots also provide an efficient means for spread. It has been reported that whiteflies can transmit the bacterium.


13 Geranium Essential Oil Uses and Benefits

If you have Geranium essential oil in your collection (or are thinking about it!), let me tell you that Geranium oil has many beautiful uses.

  1. Infection Fighter: Geranium can help in protecting the body from infection. It has shown the ability to stop 22 different types of bacteria and 12 types of fungi fungi from growing on the skin ². For example in patients suffering athlete’s foot, adding 4-5 drops of geranium oil to a foot bath with a warm water and sea salt may help fight the infection. For best results, use it twice daily.
  2. Wound Healer: Geranium could help heal wounds and incisions. With its powerful cicatrisant (=skin healing) properties, it helps in blood circulation below the surface of skin. It also fades away the look of scars and spots of acne in your skin.
  3. Urination Promoter: Geranium essential oil promotes urination. It helps release toxins, sugar and sodium from the body.
  4. Body Odor Eliminator: This could be your next deodorant, protecting your body from perspiration. When you sweat you could smell like flowers. With Geranium’s antibacterial properties, it can eliminate body odors. Add 5 drops of oil to a spray bottle and mix it with 5 tablespoons of water.
  5. Pain Killer: Geranium can reduce nerve pain. Mix a tablespoon of coconut oil to three drops of this essential oil then massage it to area where you feel the pain.
  6. Muscle Toner: Due to its astringent properties, Geranium helps in tightening and contracting the muscles. It prevents the muscle and skin from sagging, and can help untimely loosening of teeth by tightens the gums. Geranium essential oil also reduces wrinkles and tightens the facial skin. Therefore it delays the effects of premature aging. Mix a tablespoon of jojoba oil to 5 teaspoons of geranium oil and massage into the affected areas.
  7. Mental Health Support: Geranium essential oil has the power to improve the function of your mind that uplifts your spirit and helps people suffering from depression and anxiety.
  8. Possible Prevention of Dementia and Alzheimer’s Disease: To prevent the formation of neuro-degenerative diseases, this oil can work with the chemistry of the brain to prevent these conditions that lead to memory loss ³.
  9. Hemorrhage Prevention: The essential oil speeds up blood clotting that aids wound healing and it prevents the toxins to enter to the blood stream through unclotted wounds. 4
  10. Relaxant: Need a break? Geranium oil gives off a calming aroma similar to the scent of Rose. Put a few drops of this oil to a cotton or wool and set beside your lamp. Make sure to take deep breaths once in a while to let the oil enter your senses and calm your mind.
  11. Cell Growth Support: This helps in recycling the dead cells as well as the regeneration of new cells to promote cell growth. It allows the metabolism to work more effectively.
  12. Add Aroma to Perfumes: Geranium leaves provide scent and flavoring in the incredible scent similar to orange, rose, lemon, chocolate and peppermint.
  13. Insect Repellent: Applying geranium oil mixed with Soya oil can be a good insect repellent. You may repeat applying the oil several times a day if you have been bitten by an insect. To keep insects away at night, add a few drops of this essential oil to a cotton or wool ball and set it beside your night light.


Dependable, Disease-Resistant, and Decorative

Whether you cultivate it in a meandering border or a decorative vessel suspended from a pergola rafter, you can be sure that your Pelargonium × hortorum will be noticed.

With full sun, well-draining soil, and a little bit of maintenance you can enjoy this dependable, disease-resistant classic as an evergreen perennial in Zones 10 and 11, and as an annual in all temperate zones.

Are you growing geraniums in your garden? Let us know in the comments section below, and feel free to share a picture!

And to learn more about growing flowers in your garden, check out these guides next:

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About Nan Schiller

Nan Schiller is a writer with deep roots in the soil of southeastern Pennsylvania. Her background includes landscape and floral design, a BS in business from Villanova University, and a Certificate of Merit in floral design from Longwood Gardens. An advocate of organic gardening with native plants, she’s always got dirt under her nails and freckles on her nose. With wit and hopefully some wisdom, she shares what she’s learned and is always ready to dig into a new project!


Watch the video: Processing Geranium Cuttings