This is one of our Top 10 most popular articles based on customer feedback and engagement. Originally published in July 2016, it has been updated with new information and product links. As always, please leave us your comments below!
The hot and humid days of July and August are prime time for fungal infections to start popping up on your trees, vegetables, and landscaping plants. Some of the most common infections are powdery mildew, rust, leaf spot, and blight. Preventative treatments, and acting quickly to treat fungal infections when you first notice them are crucial to keeping your plants healthy and prevent annually recurring infections in trees and perennials. Luckily, a myriad of organic products exist to prevent and treat fungal infections. We know that the options can sometimes be confusing or overwhelming, so here’s a helpful primer!
Sulfur comes in either a powder or a concentrated liquid. It works better as a preventative than a treatment or cure. This is because the sulfur prevents fungal spores from germinating. It can be effective in slowing down an existing infection by keeping the fungus from multiplying rapidly, but sulfur is most effective when applied at the beginning of the season, and before you notice signs of a fungal disease. Sulfur should never be applied within 4-6 weeks of using an oil spray. It will have a phytotoxic reaction with the oil, and result in plant death. Some plants are especially sensitive to sulfur products, so definitely avoid using it on gooseberries, apricots, raspberries, currants, and anything in the cucurbit family (cucumbers, squash, melons). It’s also important to consider that with continued application, sulfur can lower the pH of the soil and start to affect plant health.
Our available products: Bonide Copper Fungicide
Copper is a good choice of fungicide because it essentially kills the fungus. It is very successful for treating and preventing tomato blight and can be applied once a week. It’s important to follow the dilution instructions very carefully as too strong a mixture can burn leaves. Young plants, and new growth are often very sensitive to copper, so applying an extra diluted mix is a good idea. It’s also important to apply copper during cooler times of the day when the sun is not too bright, so evening applications are preferred. Azaleas and Rhododendron are sensitive to copper. With long term use, copper can accumulate in the soil and eventually make it to streams as runoff. Large accumulations of copper can reduce the diversity of naturally occurring plant life. It’s unlikely that home gardeners will contribute to this problem, but it is a factor to consider.
Oil Based Fungicide
Neem oil is going to be the most effective oil for controlling fungal infections. It is a good choice for mild to moderate powdery mildew infections, but doesn’t do much good for blight, leaf spot, or rust. Oils are mostly used to control insects, but since many fungal infections are spread by insects, keeping pests at bay is a good practice for maintaining plant health.
Our available products: Monterey Disease Control
Bacterial fungicides, also called biofungicides are an exciting, newer development that works with bacteria and other microbes as the active ingredient. Some bacteria actually prey on and consume the fungus infecting the plant. Others trigger a defensive response in the plant that helps it prevent the fungus from further invasion. Some bacteria even produce a toxin or antibiotic that acts against the fungus. Biofungicides work best as a preventative spray, but an application after disease is present can also be very effective at preventing the spread of the pathogen. Unfortunately, spraying a biofungicide after you notice an infection will not likely cure the plant of the disease, except in the case of mild to moderate powdery mildew infections. Since these sprays contain living organisms, it’s important to store them at a consistent temperature. In other words, leaving them outside or in a shed or garage where temperatures fluctuate daily and seasonally, can reduce the number of live microbes and decrease its effectiveness.
Other Fungal Prevention Pro-tips: Preventing and controlling fungal issues in the garden goes beyond waiting for a problem and then treating it. By keeping in mind these simple tips, you’ll be more likely to avoid issues later on.
- Space Out: Overcrowding creates issues with airflow and allows the foliage to dry out. Follow recommendations for spacing and know that as plants grow they will fill out.
- Prune and Thin: Of course, as plants fill out, proper thinning will also help ensure that there’s enough airflow and that any problematic leaves (i.e. those perhaps showing early signs of disease) are removed to help stop any spread.
- Proper Watering: Both how and when you water your plants factor into the health of your plants. Water the soil around the roots of the plants versus watering overhead and wetting the foliage. Also, watering in the morning is ideal so that the sun can dry out the foliage throughout the day. Someone once asked, “Do you like to go to bed with wet feet?” Good point!
- Healthy Plant Stock: Choose disease-resistant varieties as much as possible and know if you do rescue a sick plant, keep it isolated from the rest of your plants until its health and vitality is fully restored. Weak plants are more susceptible to disease.
- Balanced Soil: Plants thrive in healthy soil. Deficient soil = sad plants. Ensure your soil has the right balance of compost and amendments and is well-draining to keep roots from rotting.
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