Organic control of plant diseases in the garden.

Even the healthiest gardens sometimes fall victim to plant diseases. While giving your plants plenty of room to grow and caring for them properly can help cut down on disease prevalence, there are times when a gardener will need to step in with a product control. To help prevent and manage plant diseases in the garden, we’ve compiled a list of the best products for the job.

Plant disease prevention

As with all ailments — whether human or plant — prevention is key. Maintain a healthy garden environment through proper maintenance. Keep pruning equipment clean and in good repair. Don’t over-fertilize, and because fungal diseases love wet environments, always water in the morning so foliage has time to dry before nightfall.

But, even when you do everything “right,” diseases can still strike. It’s important to remember that nearly all fungicides are protectants, meaning they’re best used before, or very soon after, the pathogen first strikes. Full-blown disease outbreaks are very difficult to manage once they’re established. During very wet springs, be on constant lookout for signs of disease, early and often, and do your best to nip problems in the bud early in their development. This is key to controlling plant diseases in the garden, especially if you’re going to use one of the products described below.

Foliar diseases of tomatoes can be managed with the right organic products.
They key to managing plant diseases, like this tomato blight, is keeping a keen eye out for early signs of disease and tackling the problem quickly.

When to apply a plant disease control product

If you feel a pathogen is affecting the production, yield, or aesthetics of your garden in a negative way, it’s okay to step in with a product control. But, it’s important to choose the products you use wisely as not all are effective against every disease. For example, using a fungicide on a bacterial disease will get you nowhere, and using a pesticide on a foliar disease is nothing but a waste of time and money. It’s absolutely essential that you properly identify the disease affecting your plant before stepping in with a product control. There are many online and printed guides to identifying plant diseases, including two of our favorite books, What’s Wrong With My Plant? and The Organic Gardeners Handbook of Natural Pest and Disease Control.

Though all of the products we recommend below are far more environmentally friendly than most synthetic chemical-based products on today’s market, they still should be used with care. Follow all label instructions and protect yourself appropriately. Do not spray when pollinators are active, and be smart about using them only when necessary.

Maple tar spot is a fungal disease of trees.
Fungal diseases, such as this maple tar spot, can create unsightly aesthetic issues, but issues like this one don’t necessarily cause significant harm to a plant’s health. It’s important to properly identify pathogens before determining if control measures are necessary.

Effective natural fungicides for the garden

Bicarbonates:
Sodium bicarbonate (baking soda), potassium bicarbonate, and ammonium bicarbonate have been used as fungicides for preventing plant diseases in the garden for years. However, potassium and ammonium bicarbonate-based products are considered by many to be more useful than baking soda (sodium bicarbonate) because in order to effectively combat fungal pathogens, baking soda must be mixed with horticultural oils, whereas the other two bicarbonates do not.

Bicarbonate products are used as contact fungicides, and they’re labeled for use on many different plants against many different fungal pathogens, including the plant disease powdery mildew, anthracnose, rusts, botrytis, and various blights and leaf spots, to name just a few. They work by inhibiting the growth of the thread-like mycelium of various fungi and/or damaging the cell walls of the fungus. Like most fungicides, they’re best used as a preventative, before the pathogen takes hold.

Powdery mildew is one of many plant diseases in the garden.
Bicarbonate-based fungicides are great for managing a broad range of fungal diseases, including the powdery mildew affecting this zucchini crop.

The toxicity of these products to humans and beneficial insects is almost non-existent. Pay careful attention to the label of these products as each different kind of bicarbonate is effective against different plant diseases in the garden. There are many different brand…