Powdery mildew is a huge challenge for both global food producers and indoor/outdoor gardeners We’re going to explore some ways to keep this fungus from ruining your plants.
First and foremost, prevention is key. As the saying goes, “an ounce of prevention is worth a pound of cure”. Once it is in your environment it is very difficult to eradicate. The spores are very hardy and can survive winter. Carefully screen any plants before you bring them in to your garden – both sides of the leaves, fruits, and stems. If you have the space, consider creating a ‘quarantine’ area where you can put new plants for the first few weeks. This may seem like a drastic step, but killing powdery mildew can be a significant amount of work.
It’s also generally a good idea to use a quality anti-fungal treatment as a preventative measure. Once you start to see the visible signs of powdery mildew – fluffy white spots – the infection will be spreading at a rapid pace. Silica is known to have anti-fungal properties and also helps to create a barrier that makes it more difficult for pests to attack plants – in addition to many other benefits. Some of our favorite anti-mildew sprays are Serenade, PM Wash, and No Powdery Mildew. Make sure to coat the entire plant, including the undersides of the leaves, and apply regularly. If you’re not seeing any signs of mildew, once a week should be fine.
If you do start to see signs of infection, move quickly. Trim off any infected areas, making sure not to shake or disturb the plants. You want to minimize spore release! Put the pieces you trimmed off in a sealed bag and remove them from the garden. Then immediately apply a foliar spray as described above. You will want to increase the frequency of spraying to once every 3-4 days. Keep a very close eye on the plants. Powdery mildew thrives in shady areas, so check every branch and leaf. For some plants, spraying is difficult due to flowering or fruiting, as excess moisture can cause mold to grow in the flowers. Make sure you have good air circulation and ventilation to reduce the chance of mold.
Many powdery mildew treatments work by raising the pH of the plant surfaces – this is an effective measure as above a pH of 8 or so powdery mildew can’t survive. Using a dilution of baking soda as a “DIY” cure can be effective for small outbreaks, but can cause problems if not mixed and applied properly. If you’re in an indoor area, you can consider using a sulfur burner to cure powdery mildew, but this can impart a poor taste to food crops and is generally kind of difficult to deal with.
One thing to keep in mind is that powdery mildew is host-specific – you could have a tomato plant with powdery mildew directly touching a strawberry plant and the strawberry plant would be unaffected. Put in another tomato plant and it would get infected but the strawberry plant would be fine.
Larger infections may require additional measures. A future post will cover more advanced control methods.
As usual, keep your garden clean at all times.