Cucurbit Downy Mildew is one of the most common diseases that can affect widely grown plants in the home garden. We’re talking about crops such as zucchinis, cucumbers, pumpkins, melons, and watermelons. It’s a fungal disease that requires specific weather conditions and if not treated promptly, it can destroy the entire cultivation.
In this article, we will introduce you to the signs and effects of this downy mildew. We will also explore how to prevent and treat it using organic products.
Identifying Cucurbit Downy Mildew
Attack of downy mildew of cucurbits on leaf
Cucurbit Downy Mildew, scientifically known as Pseudoperonospora cubensis, is a fungal disease of plants. It falls under the pathogenic agent category in the division Eumycota, class Oomycetes. As the name suggests, it affects plants from the botanical family Cucurbitaceae, which are grown in open fields and greenhouses. Along with powdery mildew, it is the most serious disease for these crops. It’s a summer disease, favored by hot and humid climates. The leaves of affected plants exhibit visible polygonal “spots”. Initially, these spots discolor the natural green of the vegetation, then turn yellow-brown and eventually become completely dry. On the undersides of the leaves, a slight mold of gray-violet color can also be observed. The damage to the crops is due to the drying out of the leaves, which compromises lymphatic exchanges. In the case of severe attacks, the affected plants die.
Biological Life Cycle of the Disease
Cucurbit Downy Mildew persists in the form of oospores in the remains of previous crop cycles. It can also be transmitted through seeds taken from plants with early infection, which unfortunately is not uncommon in the nursery industry.
The pathogenic agent has a type of asexual reproduction, which involves the differentiation of zoosporangia containing zoospores. These are mainly dispersed on vegetation by the wind. Zoospore germination occurs with high air humidity and a temperature around 20 °C (which is possible during summer nights). The pathogen enters the vegetation passively through the stomata. It has a rapid incubation period of about 5 days, making it easy for a field to be destroyed in a short period.
Preventing Cucurbit Downy Mildew
Agronomic Prevention
To prevent Cucurbit Downy Mildew, agronomic prevention actions should be taken:
- Firstly, destroy all infected remains from previous crops. As we’ve seen, the pathogenic agent persists on plant debris. Therefore, their complete removal is the first step to prevent the disease from recurring. They can be burned, provided that legal conditions are respected.
- Cultivate with wide spacing to facilitate air circulation and prevent moisture formation. Planting the crops too closely is never a good idea.
- Finally, avoid foliar wetting. Therefore, it’s advisable to set up a drip irrigation system rather than overhead irrigation.
Biological Defense
Cucurbit Downy Mildew can also be eliminated using products allowed in organic farming. In general, these biological treatments should be carried out during the cooler hours of the day when direct sunlight isn’t intense.
Copper Salts
Firstly, you can use copper salts, similarly to what we’ve seen for tomato downy mildew and the use of copper in organic farming. Copper should be applied preventively once, at the beginning of the crop cycle. This provides a certain level of protection against this cryptogamic disease. You can find a good copper-based product. Alternatively, you can follow our guidance on preparing Bordeaux mixture at home.
Sulfur Powder
Another solution is the use of sulfur powder, which is commonly used on Cucurbitaceae to eliminate powdery mildew. Sulfur, due to its characteristics, generally protects against fungal diseases, including downy mildew. Here’s the sulfur powder. Use it carefully, following the instructions on the label.
Baking Soda
However, our preferred solution is the use of baking soda. This simple product makes plants inhospitable for the pathogenic agent. The recommended dosage for plants is 10g per liter of water.
Further Reading
Disease Control and Pest Management – A Quantitative Review of Fungicide Efficacy for Managing Downy Mildew in Cucurbits
Plant Management Network – Cucurbit Downy Mildew ipmPIPE: A Next Generation Web-based Interactive Tool for Disease Management and Extension Outreach
