Knowing your climate zone will help you decide the best time to sow the vegetables, herbs and flowers you want to grow, and which varieties should perform well in your garden. Growing plants that are suited to your climate zone will usually give you the best results in your garden.
The cucurbit family offers some of the veggie gardeners most generous friends. Zucchini, pumpkin, cucumber and squashes are easy to grow and extremely productive, racing away to provide lush foliage, striking flowers, and masses of fruit.
However, all the species in this family can fall prey to a common fungal infection known as powdery mildew. This first shows up as white spots on the leaves, which if left untreated eventually spread across the entire plant.
Faced with a full-blown mildew infection for the first time, its natural for a cucurbit grower to feel worried. The good news is that the problem is rarely fatal for the plant, although it usually reduces yields.
Its also fairly easy to discourage the infection from taking hold. And if it does, there are several reliable ways to reduce its impact.
As a gardener, nothing is more frustrating than seeing your cucumber plants suddenly covered in a white, powdery substance This dreaded powdery mildew can quickly damage leaves and limit your cucumber harvest But don’t worry – with some TLC and preventative care, you can get your cukes back to their happy, healthy selves. In this article, we’ll walk through the causes of powdery mildew, how to treat active infections, and tips to prevent future outbreaks. Let’s get started!
What Causes Powdery Mildew on Cucumbers?
Powdery mildew is a fungal disease that affects cucumbers and other cucurbits like melons, squash, and pumpkins. It thrives in warm, humid environments. The main culprits are the fungi Podosphaera xanthii and Erysiphe cichoracearum.
Spores from these fungi can overwinter in plant debris in your garden. Then, when conditions are right in spring and summer – typically when temperatures are between 68-80°F and humidity is moderate to high – the spores activate and infect your plants.
Powdery mildew spreads easily via wind water splashes, garden tools, and pests like aphids. It often starts on older lower leaves with limited sunlight and air circulation. These areas tend to have higher humidity which the fungi love.
How to Identify Powdery Mildew
The most obvious symptom of powdery mildew is white powdery spots on leaves and stems. It often starts as individual patches, then spreads to coat the entire plant.
You may also see speckled spots on fruits However, powdery mildew mainly affects the foliage and not the cucumbers themselves. Downy mildew is another disease that can affect cucumbers. It has similar symptoms but a bluish cast on leaf undersides.
Check all sides of leaves thoroughly to determine if you have powdery or downy mildew. Proper identification is key for treatment.
How to Treat Active Powdery Mildew
If you catch powdery mildew early, there are organic and chemical treatment options available:
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Prune infected leaves – Remove and destroy any leaves showing white fungal spots. Sterilize pruners in rubbing alcohol between each cut. Pruning helps stop spore spread.
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Increase airflow – Powdery mildew hates wind and direct sunlight. Prune dense interior foliage to allow better air circulation.
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Water at the base – Water with a soaker hose or drip irrigation. Avoid getting leaves wet as this encourages mildew growth.
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Apply neem oil – Neem oil disrupts the fungus’ reproductive cycle and is approved for organic growing. Mix with water and spray leaves weekly.
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Use fungicides – Chemical options like copper, chlorothalonil, and Daconil are effective against powdery mildew. Follow label instructions carefully.
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Try milk spray – Surprisingly, diluted milk sprayed on leaves can inhibit powdery mildew. Mix 1 part milk and 10 parts water and apply weekly.
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Consider plant invigorators – These products contain pesticides and nutrients to strengthen plants against diseases. They are often OMRI listed for organic use.
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Remove debris – Clear all dead leaves and plants around your garden to eliminate spore sources.
Catching infestations early and using a combination of these methods can help eliminate powdery mildew and save your cukes!
How to Prevent Powdery Mildew
An ounce of prevention is truly worth a pound of cure when it comes to plant diseases. Here are organic tips to prevent powdery mildew from ever taking hold:
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Choose resistant varieties – Some cucumber varieties have genetic resistance against powdery mildew. Look for ‘Marketmore 76’, ‘Salad Bush’, or ‘Fanfare’ types.
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Allow proper spacing – Give cucumber vines enough room to encourage airflow between plants. Overcrowding creates the humid conditions mildew loves.
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Use trellises – Trellising vines keeps fruits and leaves off the ground and improves air circulation.
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Test soil pH – Powdery mildews thrive in overly acidic soil. Test pH yearly and amend with lime if needed to reach proper cucumber pH of 6.0-6.8.
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Water early – Water at the roots early in the morning so leaves have time to dry out during the day. Avoid wet nighttime conditions.
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Use drip irrigation – Drip systems and soaker hoses prevent moisture on leaves while still watering roots effectively.
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Rotate crops – Don’t plant cucumbers in the same spot as last year. Crop rotation limits the buildup of fungus in the soil.
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Scout regularly – Inspect under leaves frequently and remove any showing early powdery mildew signs. Early removal limits spore spread.
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Clean up debris – Remove all dead vines and leaves at the end of each season to eliminate overwintering spores.
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Apply compost tea – Compost teas introduce beneficial microbes that can outcompete and prevent fungal growth. Spray leaves monthly as a preventative.
With vigilance and preventative care, you can avoid powdery mildew heartache and enjoy a thriving, productive cucumber patch. Don’t be afraid to take action at the first sign of trouble on your vines. Catching it early makes treatment much more effective. Here’s to a bountiful, mildew-free cucumber harvest!
What Causes Powdery Mildew?
Powdery mildew appears when fungal spores settle on a plant and start to reproduce. These spores are always present in the air, but whether they spark off a serious infection or not depends mainly on growing conditions.
Here are the main ways to prevent a major infection from developing.
Careful Watering – The spores prefer to reproduce in humid air. However, to complicate matters, they also thrive on drier, weaker leaves. This means getting your cucurbit watering technique correct.
Water your plants generously at the soil level rather than from above, so they stay fully hydrated without liquid misting around the leaves. Adding a good layer of organic mulch will help the process along, channelling water to the roots rather than letting it evaporate into the air.
Air Circulation – Also make sure theres adequate air circulation around your plants to stop humidity from building up. Dont plant cucurbits too close together, and keep them out of enclosed, highly sheltered areas.
Pick a Sunny Spot – Growing your plants in a sunny location is perhaps the most important point. The heat of the sun burns away humidity, while also raising temperatures above the moderate level that mildew spores prefer.
Also, plenty of sun will help give your plants extra vigour to withstand an infections damage.
Soil Quality – Adding plenty of rich organic matter to your soil will also help your plants grow strongly and cope with infection. However, avoid using too much nitrogen-rich fertiliser. This can prompt fast growth of tender foliage thats less able to withstand the mildews advance.
If youre growing cucurbits in containers, be scrupulous about cleaning them properly and using fresh compost for each sowing. Spores are hardy enough to survive most winters, and so problems can quickly build up from year to year if theyre allowed to settle.
How to Use Climate Zones
First, find your climate zone using the map or descriptions below. Next, refer to our sowing chart, which provides approximate sowing times for our most popular seeds for each climate zone.
While knowing your climate zone is helpful when planning your garden, there are many other factors that may affect how your plants grow, including unseasonal weather conditions, the specific microclimate of your garden and how you care for your plants. You know your garden better than us, so if a different climate zone seems to ‘fit’ your garden better, go ahead and use it as a guide.
Our climate zones cover huge areas of Australia, so we recommend gardeners also consider their local conditions when planning what and when to plant. For example, gardeners in alpine areas have shorter growing seasons than gardeners in cool coastal areas, even though both alpine and coastal areas are included in our ‘Cool Temperate’ climate zone. We recommend gardeners in cool regions look at the ‘days to maturity’ information provided for each variety and choose those that will mature in a short (6-12 week) growing season.
- Includes: Darwin, Cairns, Townsville, Exmouth
- High humidity summers with most rainfall in summer and dry, warm winters. Includes northern Australia from Exmouth (WA) across to south of Townsville (Qld).
- Set as my climate My climate
- Includes: Alice Springs, Mildura, Albury-Wodonga, Shepparton, Wagga Wagga, Dubbo
- Hot dry summers, winters can be warm or cool depending on the region. Includes a large area of central Australia from the WA coast to Charleville (Qld), Tamworth (NSW) and Albury-Wodonga (NSW/Vic).
- Set as my climate My climate
- Includes: Brisbane, Bundaberg, Coffs Harbour, Gold Coast, Hervey Bay, Mackay, Rockhampton, Sunshine Coast
- Warm humid summers with high summer rainfall and mild winters. Includes coastal Queensland and northern NSW from north of Mackay to just south of Coffs Harbour.
- Set as my climate My climate
- Includes: Sydney, Perth, Adelaide, Newcastle, Toowoomba, Central Coast NSW, Wollongong, Bunbury
- Moderate humidity and reliable rainfall, with four distinct seasons. Includes coastal areas from north of Port Macquarie to south of Woollongong in NSW, coastal SA and the southeastern coast of WA.
- Set as my climate My climate
- Includes: Melbourne, Canberra, Hobart, Launceston, Ballarat, Bendigo, Geelong, Mt Gambier
- Low humidity with most rainfall in winter; hot dry summers and cold winters. Some regions will experience frosts and snow. Includes coastal areas of south-eastern Australia and alpine areas of Victoria, NSW and Tasmania.
- Set as my climate My climate
What if I can’t find my climate zone? If you can’t locate your zone from looking at the map or the descriptions on this page, we suggest that you think of an area that has a climate that’s similar to yours and use the zone for that area as a guide.
What if I live on the border of two zones? If you live near the border between two zones we suggest you read the descriptions for both zones and decide which best describes the climate where you live. Depending on the microclimate in your garden, you may be able to grow a wider range of plants over a longer season than others in your zone. Lucky you!
What is a microclimate? A microclimate is a small area where the temperature or humidity differs to the climate of the surrounding area. For example, if you live in a climate zone where frosts are common but your garden is protected by buildings or large trees, your garden may be frost-free. Similarly, if you live in a warm temperate zone but your garden is at a high altitude your microclimate may have more in common with the cool temperate zone, so use this as a guide when deciding which zone is relevant to you.
Can I grow varieties not listed for my climate zone? While our climate zones and sowing chart will help you decide what is suitable to plant in your garden, they provide general guidance only. We recommend you start by sowing seed that’s recommended for your climate zone; once you get a few successes under your belt you can experiment with varieties in neighbouring zones and see how you go – gardening is all about experimenting after all!
The cucurbit family offers some of the veggie gardeners most generous friends. Zucchini, pumpkin, cucumber and squashes are easy to grow and extremely productive, racing away to provide lush foliage, striking flowers, and masses of fruit.
However, all the species in this family can fall prey to a common fungal infection known as powdery mildew. This first shows up as white spots on the leaves, which if left untreated eventually spread across the entire plant.
Faced with a full-blown mildew infection for the first time, its natural for a cucurbit grower to feel worried. The good news is that the problem is rarely fatal for the plant, although it usually reduces yields.
Its also fairly easy to discourage the infection from taking hold. And if it does, there are several reliable ways to reduce its impact.
Easy, Inexpensive Powdery Mildew Spray for Squash & Cucumbers, Prune Leaves to Keep Production Going
FAQ
What kills powdery mildew on cucumbers?
Research has shown that diluted milk applied to cucurbits can help control powdery mildew. The dilution recommended is 40% milk, 60% water.
What is the most effective treatment for powdery mildew?
… use a horticultural oil such as Saf-T-Side Spray Oil, Sunspray Ultra-Fine Spray Oil, or one of the plant-based oils such as neem oil or jojoba oil (e.g., …