From tomato blight to peach brown blight, home gardeners are all too familiar with how fungal diseases can affect the yield and appearance of their plants. In the pumpkin patch, a disease known as powdery mildew is often our biggest enemy. Whether you grow summer or winter varieties of squash, identifying and controlling powdery mildew can result in healthier, more productive plants. This article provides tips for detecting and preventing powdery mildew on squash, as well as a list of resistant varieties. You'll also find details on organic sprays you can use to control this disease in your garden.
What is powdery mildew?
Powdery mildew is caused by several types of fungi. Each species has its own preferred host plants. The type of powdery mildew that affects pumpkin leaves (Erysiphe-Radicchio) differs from those based on peas (Erysiphe pisi) or eggplants (Leveillula taurica). Interestingly, this fungus lives on the outside of the leaves and does not invade the internal tissues. It can only grow on the leaf surface.
No matter which plant is attacked by which species, powdery mildew looks the same. It is one of the most common plant diseases and because its appearance is so distinctive, it is quite easy to spot. Powdery mildew causes leaves to appear dusted with talcum powder. Mold is white to gray. Most of this white powder consists of spores, which are easily carried by the wind to other nearby leaves.
If left untreated, powdery mildew eventually forms small round structures that turn brown and eventually black. These structures produce the "dormant spores" that allow the disease to overwinter in the garden.
The final stage of powdery mildew infection causes squash leaves to turn yellow and crusty, causing them to wither and die.
Conditions that favor powdery mildew on pumpkin
Unlike many other fungal diseases, powdery mildew doesn't need moist or humid conditions to establish itself in your garden; It works well in hot, dry weather. This characteristic makes it a challenge even during dry growing seasons, when rust, white mold, and other diseases are not usually a problem. Mold spores can enter your garden from the wind, infected nursery plants, "dirty" tools, splashing raindrops, human hands, and spores that overwinter in the garden on plant debris. infected.
Although this fungus thrives in hot, dry conditions, a lot of moisture is required for powdery mildew spores to become established. This means crowded squash plants with poor air circulation are more likely to be attacked by powdery mildew. Young growth is more susceptible to developing powdery mildew than older leaves, which is why the first signs are often seen on the youngest leaves.
First signs of disease on pumpkin leaves
The first sign of powdery mildew on squash are small, white, powdery spots on the young leaves. At first there are only a few spots, but it spreads rapidly, eventually covering the entire leaf surface. Powdery mildew most often occurs on the tops of leaves, but it can also occur on the undersides of leaves, stems, and even fruit.
How to Tell Powdery Mildew from Natural Leaf Spot
Some pumpkin varieties naturally have white spots on their leaves. Therefore, it is difficult to say if the presence of white spots is just a physical trait of this variety or the start of a powdery mildew infestation. The easiest way to tell is by looking at the patterns of the white spots. If they are placed reasonably evenly on the leaf between the veins, it is probably a natural physical trait of this variety. If the spots are irregular and randomly placed, it's probably powdery mildew.
You can also easily clean the stains with your fingertip. If the dust comes off easily, it's mold. If not, it is part of the sheet. (Wash your hands afterwards so you don't accidentally transfer the spores to another leaf!)
How Fungus Affects Squash Plants
The good news is that powdery mildew is primarily an aesthetic problem, as these fungi live on the leaf surface and cannot invade the leaf tissue (meaning it doesn't make plants look as good). However, a thick layer of powdery mildew on squash leaves impairs their ability to photosynthesize and, over time, can hamper plant productivity and reduce yields. When printed, it causes the leaves to wither and die. These dead leaves can develop rot that can quickly spread into the plant's canopy.
Powdery mildew on squash can also affect plant resistance to other pests and diseases. When weakened by disease, squash plants are more susceptible to problems from insects, vine borers, botrytis, and other pests and diseases.
How can powdery mildew on pumpkins be prevented?
Prevention is very important when it comes to squash powdery mildew. Do what you can as soon as possible to prevent it from taking root in your garden.
Here are some important tips to prevent powdery mildew:
- Ensure good air circulation by placing the squash plants several feet apart.
- Do not touch infected leaves and then touch healthy leaves. You just spread spores!
- Always plant the squash in full sun. Shady conditions are more humid and this encourages spore germination.
- Cut off leaves that show early signs of infection as soon as possible. Throw them away or burn the pile. Keep them away from the compost heap.
- Do not apply nitrogen fertilizer in the middle of the growing season. This leads to an influx of new growth that is more susceptible to disease.
- Remove and destroy infected plants at the end of the growing season to kill as many spores as possible. You did not compose them; Throw them away or bury or burn them.
- Prune half the leaves off each plant early in the season to reduce moisture levels around the plant and limit the chance of infection.
- Hayany evidence that milk sprays can help prevent powdery mildew, but they can also increase the likelihood of developing other fungal diseases. They also produce a very sour odor when decomposed.
- PLANT RESISTANT STRAINS (more on that in the next section).
Before I introduce you to our favorite mold-resistant squash, watch this short video to learn more about how to identify and combat this disease:
Mold Resistant Pumpkin Varieties
Your first line of defense in the pumpkin patch is always to plant varieties with known resistance to mold. It just makes sense. If you don't develop the infection in the first place, you don't need to worry about controlling it.
Fortunately, plant breeders have realized how annoying powdery mildew is to gardeners and farmers, so there are many powdery mildew resistant pumpkin varieties. In seed catalogs, look for the PM code in the description of each variety. This is code for resistance to powdery mildew. Here are some of my favourites:
Mold Resistant Zucchini Varieties
- 'Delta' - garganta amarga
- 'Yellowfin' – straight yellow
- 'Smooth operator' – straight yellow
- 'Mexicana' - light green challenge
- "Emerald Delight"– plain dark green
- "ATM" - medium green straight
- 'It is'– compact plant; medium green only
Mold Resistant Pumpkin Varieties
- 'Autumn Frost' - Butternut especialmente
- 'Butterbaby' - Pequeño Butternuss
- "Havana" - Butter
- 'Goldlöckchen' – yellow acorn
- 'honey bear- compact glans
- 'Zuckerbusch' – Compact ball
- 'Delicate Busch'- delicate type
If you think this disease is negatively affecting the production, yield, or aesthetics of your squash plants, you can intervene with a produce control. While all of the products I recommend below are organic and much greener than most synthetic chemical fungicides, they should be used with caution. Follow all label instructions and protect yourself accordingly. Do not spray when pollinators are active and only use when needed.
Der Cornell mix
Researchers at Cornell University found that combining sodium bicarbonate (baking soda) with light horticultural oil prevented and controlled powdery mildew on squash and other plants. To make Cornell's mixture, mix 1 tablespoon of baking soda with 2 ½ tablespoons of vegetable oil (I likeall Seasonsbrand) with 1 liter of water in apump sprayer. Spray every 14 days. It is best to use it preventively.
Bacillus subtilis aus B. amyloliquefaciens
These organic fungicides use a naturally occurring bacterium commonly found in soil to control powdery mildew on squash. In other words, they use a living organism to manage another living organism. based fungicidesB. subtilismiB. amyloliquefaciensThey are very useful and effective against powdery mildew. There are several different brands; are among the most commonComplete Monterey Disease Controlmirevitalize.
Derived from the seeds and fruits of the tropical neem tree, neem oil is often used as a pesticide. However, neem oil is also an effective fungicide against powdery mildew on pumpkin. It is best used preventatively before powdery mildew becomes severe. Common brands are, for example,Monterrey NeemölmiGarden Safe Neem Oil. Be careful when using neem-based products, as they are slightly toxic to fish and other aquatic life. Do not spray when bees are active.
cure powdery mildew
Unfortunately, there is no complete cure for powdery mildew on pumpkin or any other plant. Fortunately, you can still harvest plenty of pumpkins even if powdery mildew is present in your garden. Your first line of defense is always to plant resistant strains. Follow the prevention techniques outlined above and only use the products as a last resort. Even with powdery mildew in your yard, you're likely still lucky enough to have plenty of zucchini to share with your neighbors.
For more information on how to control garden diseases, see the following articles:
- Tomato diseases and how to combat them
- Organic Tips to Fight Plant Diseases
- Problems growing zucchini
- Problems with cucumber plants.