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Powdery mildew is a group of diseases caused by several closely related fungi that can affect many plants. The common symptom of powdery mildew is white or grayish-white, powder-like patches visible on the surface of leaves, stems, and flower petals. The disease can also appear as blotchy, felt-like mats or cobweb-like formations. Leaves commonly turn yellow and wither, flowers are distorted or fewer in number, and fruit yield and quality are reduced. Tissues sometimes become stunted or distorted.
Powdery mildew can affect a wide range of crops, including grapes, cucurbits (such as cucumbers and squash), apples, pears, strawberries, and roses. The disease can cause significant yield losses if left untreated. In some cases, the entire crop can be lost due to severe infection. The amount of crop harvest lost due to powdery mildew can vary depending on the severity of the infection and the type of crop. In general, yield losses of up to 50% have been reported in some crops. Powdery mildew can kill an entire crop relatively quickly if left untreated. In some cases, the disease can cause significant damage within a matter of weeks.
Powdery mildew can be difficult to control because it is caused by a fungus that can reproduce rapidly and spread easily. The fungus produces spores that can be carried by the wind or on insects to other plants, making it difficult to contain the disease. Another reason why powdery mildew can be difficult to control is that the fungus can develop resistance to fungicides over time. Fungi that are not killed by the fungicide can survive and reproduce, passing on their resistance to their offspring. Over time, the population of resistant fungi can increase. This means that the same fungicide that was effective at controlling the disease in the past may no longer work. In addition, powdery mildew can be difficult to control because it thrives in conditions that are favorable for plant growth. High humidity and warm temperatures can create an environment that is ideal for the growth of the fungus. A good integrated pest management (IPM) program that includes insecticides can help prevent powdery mildew by reducing the number of insects that can spread the disease.
In addition to insecticides, cultural practices such as crop rotation and sanitation can also help prevent powdery mildew. Crop rotation can help reduce the incidence of disease by reducing the amount of inoculum in the soil. Sanitation practices such as removing infected plant material from the field can also help reduce the spread of disease.
Fungicides that can be used to treat powdery mildew include myclobutanil, propiconazole, and thiophanate-methyl which have systemic properties and can be sprayed less often than chlorothalonil, sulfur, or copper-based fungicides. Systemic fungicides are absorbed by the plant and transported throughout its tissues, including the fruit or vegetable that is produced. This means that humans may ingest small amounts of the fungicide if they consume the produce. The toxicity of systemic fungicides will depend on the specific chemical being used. In general, most systemic fungicides are considered to be safe when used according to the label instructions. However, overuse or misuse of these chemicals can lead to residues in the produce that exceed safe levels.
Effective, High-efficacy Powdery Mildew Fungicides include:
- Protection PlusTM – This natural, non-systemic fungicide works by inhibiting the respiration of the fungus. It is a 25(b) exempt fungicide made of food-grade ingredients that are non-toxic.
- Azoxystrobin – This fungicide works by inhibiting the respiration of the fungus, leading to its death. It is considered to be moderately toxic and can cause skin irritation and eye damage if it comes in contact with the skin or eyes.
- Myclobutanil – This fungicide works by inhibiting the growth of the fungus. Is considered to be moderately toxic and can cause skin irritation, eye damage, and respiratory problems if it is inhaled.
- Propiconazole – This fungicide works by inhibiting the synthesis of ergosterol, which is an essential component of the fungal cell membrane. This fungicide is considered to be slightly toxic and has low acute toxicity.
- Trifloxystrobin – This fungicide works by inhibiting the respiration of the fungus. This fungicide is considered to be slightly toxic and has low acute toxicity.
It is important to note that not all fungicides for powdery mildew work in the same way and that some may be more effective than others depending on the type of powdery mildew and the stage of infection. A fungicide that kills powdery mildew directly will cause the fungal cells to rupture and die. This can be observed by examining the leaves of the plant after treatment. If the white powdery spots have disappeared or turned brown, this is an indication that the fungicide has been effective at killing the fungus. Using a high-efficacy fungicide for white powdery mildew can help prevent the development of resistance in fungi. By killing the fungus effectively, the population of resistant fungi is reduced, making it easier to control the disease.
For more detailed information about powdery mildew and its impact on various plants, you can refer to this external resource on powdery mildew.