Introduction
Fungi, often overlooked and misunderstood, play a critical role in our natural ecosystem. These organisms can be both a blessing and a curse for plant life, especially in the unique climatic conditions of the United Arab Emirates (UAE). This post delves into the types of fungi that are commonly found in the UAE, the causes behind fungal infections in plants, and the preventive as well as curative measures that can be taken.
Types of Fungi: Beneficial and Parasitic
Beneficial Fungi
Mycorrhizal Fungi: These fungi form a symbiotic relationship with plant roots, aiding in nutrient absorption.
Trichoderma: Known for their biopesticide properties, they protect plants from harmful pathogens.
Saprophytic Fungi: These fungi decompose organic matter, aiding in soil fertility.
Parasitic Fungi
Common fungal diseases and their often-confused physiological conditions, please note that these are problems which are commonly encountered in the UAE, but by no least a definitive list.
Firstly, I need to point out one very often confused "fungal" problem. This is Mealy Bug, this is an insect, that covers its body with small white "hairs", this is often confused as a fungal problem.
Sooty Mold
Sooty mold is a secondary condition that is caused by various mold types growing on a sticky substrate; in this case, the substrate is caused by what is called "honeydew", essentially the sugar-rich excrement of scale or aphid insects. This falls onto the leaves below, and the molds grow over this. In itself the mold is not a danger to the plant, however it blocks light from reaching the leaves and reduces photosynthesis. In this case, you need to treat the cause of the problem, which is the insect infestation and not the mold. Once the insect problem has been treated the mold can be first loosened by applying a soap water solution to the leaves and then washing the plant off.
The real fungal problems are:
Powdery Mildew
Botanical Name: Erysiphales
Symptoms: White, powdery spots on leaves and stems; may cause leaves to curl or deform.
Likely to be found on: Roses, cucurbits (such as cucumbers and squash), and grapes
Often Confused With: Sun or wind burn, which can cause bleaching and scorching of leaf surfaces.
Downy Mildew
Botanical Name: Peronosporaceae
Symptoms: Yellow spots on the upper leaf surface and white to purple fuzz on the underside.
Likely to be found on: Commonly found on plants such as grapes, cucumbers, lettuce, spinach, and roses
Often Confused With Water stress, leading to yellowing and wilting of leaves.
Rust
Botanical Name: Pucciniales
Symptoms: Orange to brown pustules on leaves and stems; may cause premature leaf drop.
Likely to be found on: Turf grass, Plumeria, Roses, beans
Often Confused With Nutrient deficiency, particularly potassium, which can cause brown spots on leaves.
Black Spot
Botanical Name: Diplocarpon rosae
Symptoms: Black spots surrounded by yellow halos on leaves; this leads to leaf drop.
Likely to be found on: One of the main problems found on rose plants is when they are watered over the foliage, or if the ambient humidity level is too high.
Often Confused With: Leaf scorch, where leaf margins turn brown but without the black spots.
Leaf Spot
Botanical Name: Septoria, Cercospora, etc.
Symptoms: Brown or black spots on leaves, often with a halo; may cause leaves to drop.
Likely to be found on: Roses and Potato plants.
Often Confused With: Insect damage, which can also cause holes or spots on leaves.
Fusarium Wilt
Botanical Name: Fusarium oxysporum
Symptoms: Yellowing and wilting of lower leaves; may cause plant death.
Likely to be found on: Often found on the leaves of Tomato, Cucurbit, and Potato plants, especially if they are watered over the foliage.
Often Confused With: Overwatering, which can also lead to wilting and yellowing of leaves.
Botrytis Blight
Botanical Name: Botrytis cinerea
Symptoms: Gray, fuzzy mold on flowers, leaves, and stems; may cause rotting.
Likely to be found on: Seasonal plants and soft leaves plants in times of high humidity, or when the plants are watered over the foliage. A common problem on roses and grapes.
Often Confused With: Humidity-related disorders, which can also cause mold but are not pathogenic.
Anthracnose
Botanical Name: Colletotrichum spp.
Symptoms: Dark, sunken lesions on leaves, stems, and fruit.
Likely to be found on: Found on indoor plants with restricted air movement and high relative humidity.
Often Confused With: Physical damage, which can also cause lesions but without the sunken appearance.
Damping-off
Botanical Name: Pythium spp., Rhizoctonia spp.
Symptoms: Seedlings collapse and die soon after emerging from the soil.
Likely to be found on: Very prevalent on germinating seedlings, this causes the seedling to bend or "break" just above the soil level, the common term for this is "damping off"
Often Confused With: Poor germination conditions (or low seed germination), such as too much or too little moisture.
Phytophthora
Botanical Name: Phytophthora infestans
Symptoms: Phytophthora infection in plants can cause wilting, root rot, and leaf yellowing due to damage to the root system and impaired water and nutrient uptake. Phytophthora is very prevalent in the UAE, particularly in the coastal areas.
Likely to be found on: This is the fungus that caused the Great Potato Famine in Ireland. Phytophthora can affect a wide range of plants, including trees, shrubs, ornamental plants, and crops such as citrus, tomatoes, grapes, and potatoes.
Often Confused With: Physical symptoms such as wilting, yellowing leaves, and root damage can sometimes be mistaken for Phytophthora infection, but these symptoms can also be caused by other factors like drought stress, nutrient deficiencies, or different pathogens.
Causes of Fungi
Environmental Conditions: High humidity and temperatures are breeding grounds for fungi.
Poor Drainage: Excessive water in the soil can lead to fungal growth.
Infected Plant Material: Always ensure that the plants or seeds you are introducing are disease-free.
How to Avoid Fungal Problems
Proper Spacing: Adequate space between plants ensures good air circulation, reducing fungal risk.
Well-Drained Soil: Make sure your planting area has excellent drainage.
Pruning: Regularly prune dead or diseased branches and leaves to prevent fungal spread.
Regular Monitoring: Keep an eye out for the early signs of fungal infections to act swiftly.
Sterilize old soil if you intend to reuse it, this applies to soil for indoor containers as well as in the landscape.
Fungus and cuttings
When propagating plants from cuttings, it is always imperative to sterilize the entire cutting before planting it. The environment around us is filled with millions of fungal spores; when you propagate cuttings you normally cover them to increase the humidity around the cutting - this increases the likelihood that some of these fungal spores will germinate, including some of the "bad" types of fungi, which can then start attacking your new cuttings. The easiest method is to use a household bleach and water solution (no more than 10% bleach), immerse the cutting into the solution for about 10 seconds, and then plant immediately.
Fungus in indoor plant containers
This is a fairly common problem, finding a "mushroom" growing out of the soil of one of your container plants; these are saprophytic fungi and are busy decomposing something in the soil and do not affect the live plant tissue. These normally grow when the soil and ambient conditions are right for the spore to germinate. Fungi require humidity, warmth, and a source of nutrition. Often they will be "breaking down" a large piece of un-decomposed material in the container - like a small piece of wood or bark. This situation is normally associated with soil that is too wet or damp and may be an early indication of overwatering. They will normally wither away after a few days but can be removed manually with a pair of gloves and disposed of. You should never assume that fungi or mushrooms are edible.
Treating Fungal Issues
Chemical Means
Fungicides: Products like Mancozeb and Copper oxychloride are effective.
Systemic Fungicides: Absorbed by the plant, these offer internal protection.
Home Remedies
Baking Soda: A solution can act as a preventative spray. Changes the pH on the leaf surface making it more difficult for fungal spores to germinate.
Application: Mix 10 grams of baking soda with 1 liter of water. Spray on plant leaves.
Garlic Extract: Known for its antifungal properties. Often used in tissue culture to suppress fungal infections in in-vitro cultures.
Application: Crush 5 garlic cloves and mix with 1 liter of water. Let it sit for 24 hours and then spray.
Apple Cider Vinegar: A mild antifungal agent. Changes the pH on the leaf surface making it more difficult for fungal spores to germinate.
Application: Dilute 10 ml of apple cider vinegar in 1 liter of water. Spray sparingly to avoid leaf burn.
Lemon juice: A mild antifungal agent. Citric acid changes the pH on the leaf surface making it more difficult for fungal spores to germinate.
Application: Dilute 10 ml - 15m of strained lemon juice in 1 liter of water. Spray sparingly to avoid leaf burn.
Chamomile Tea: Offers mild protection against fungi. Contains natural compounds which have anti-fungal properties.
Application: Brew chamomile tea and let it cool. Use it as a spray without dilution.
Milk: Effective against powdery mildew. Lactic acid alters the pH on the leaf surface making it more difficult for fungal spores to germinate.
Application: Mix 100 ml of milk with 900 ml of water. Spray on plants early in the morning.
Conclusion
Fungi in the landscape can be both beneficial and detrimental. While they contribute to soil fertility and plant health, they can also be the cause of plant diseases that can be devastating if not managed properly.
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