Powdery Mildew is a type of crop disease which affects crops like carrot, cucumber, okro, tomato, hot pepper, sweet pepper, etc. When it comes to diseases that may befall your plants, powdery mildew tops the list as one of the most common culprits.
While almost no type of plant is immune, certain species are more susceptible than others, including lilacs, flowering crab apple trees, phlox, red bee balm plants, roses, squash, cucumbers, and more.
Powdery mildew fungi can be found anywhere but it thrives particularly well in climates where there are extended periods of warm temperatures paired with dry conditions.
The fungi spores first appear in plant debris throughout the winter and are then carried to your plants via wind, insects, and splashing water.
Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant.
Powdery mildew thrives in conditions opposite those where you would find ordinary mildew. Instead of liking wet and damp conditions, powdery mildew actually prefers warm and dry environments.
When it shows up, it’s often first thought to be dust or dirt and can be swept away with your finger – then it returns. It appears as light white or gray spots on the tops and bottoms of the leaves, stems, new growth, flowers and even fruit or vegetables.
This fungus brings out a white powder on older leaves from the bottom lower and elder leaves through the youngest at the top of the plant. It is favored by a very high relative humidity and large temperatures variations between day and night and is spread by the wind.
How to Identify Powdery Mildew Damage
- Plants infected with powdery mildew look as if they have been dusted with flour.
- Powdery mildew usually starts off as circular, powdery white spots, which can appear on leaves, stems, and sometimes fruit.
- Powdery mildew usually covers the upper part of the leaves, but may grow on the undersides as well.
- Young foliage is most susceptible to damage. Leaves turn yellow and dry out.
- The fungus might cause some leaves to twist, break, or become disfigured.
- The white spots of powdery mildew will spread to cover most of the leaves or affected areas.
- The leaves, buds, and growing tips will become disfigured as well. These symptoms usually appear late in the growing season.
Symptoms and Damage
Symptoms usually appear later in the growing season on outdoor plants. Powdery mildew starts on young leaves as raised blister-like areas that cause leaves to curl, exposing the lower leaf surface.
Infected leaves become covered with a white to gray powdery growth, usually on the upper surface; unopened flower buds may be white with mildew and may never open.
Leaves of severely infected plants turn brown and drop. The disease prefers young, succulent growth; mature leaves are usually not affected.
Powdery mildew forms when plant foliage is dry, lighting is low, temperatures are moderate and there is high humidity. Ideal conditions for powdery mildew growth is often during the late spring or early summer when evenings are still cool and somewhat humid, but the days are beginning to get warm.
Some of its symptoms include the following:
- Formation of a white powdery film on the leaves. Leaves can dry and become brittle.
- On solanaceae, Leveillula induces yellow then brown spots on leaves and a white powdery apparition on the underside of leaves.
Some of the major ways or measures by which damage can be prevented or controlled include the following:
- Remove weeds and plant residues from the previous crop.
- Practice overhead watering
- Apply preventive sprays with sulfurs and fungicides on the underside of old leaves.
- Sow on raised and well-drained ridges.
- Plant resistant cultivars in sunny locations whenever possible.
- Prune or stake plants to improve air circulation. Make sure to disinfect your pruning tools (one part bleach to 4 parts water) after each cut.
- Remove diseased foliage from the plant and clean up fallen debris on the ground.
- Use a thick layer of mulch or organic compost to cover the soil after you have raked and cleaned it well. Mulch will prevent the disease spores from splashing back up onto the leaves.
- Milk sprays, made with 40% milk and 60% water, are an effective home remedy for use on a wide range of plants. For best results, spray plant leaves as a preventative measure every 10-14 days.
- Wash foliage occasionally to disrupt the daily spore-releasing cycle. Neem oil and PM Wash, used on a 7 day schedule, will prevent fungal attack on plants grown indoors.
- Water in the morning, so plants have a chance to dry during the day. Drip irrigation and soaker hoses will help keep the foliage dry.
- Use a slow-release, organic fertilizer on crops and avoid excess nitrogen. Soft, leafy, new growth is most susceptible.
- Destroy all plant debris after harvest.
Some Varietal solutions include:
Carrot: carrot varieties like: Bahia, Amazonia, F1 Louxor, F1 Japan Cross, Pamela, F1 Talena.
Cucumber: some cucumber varieties like: F1 Antilla (IR), F1 Mondial, F1 Olympic (HR), F1 Tokyo (HR), F1 Tropical, F1 Lina, F1 Nagano, F1 Sirana, F1 Murano.