When it comes to bacterial and fungal diseases in the garden, there is not much that can be done to treat them other than discarding the affected parts of the plant. Luckily, gardeners can take preventive measures to stop a disease before it gets out of control. One of the products you can use is copper fungicide. It is safe to use for organic gardening, but there are some precautions you need to take when using it.
Copper fungicides won't solve all your problems, such as: B. Tomato late blight, but they will slow or at least stop the spread of diseases such as powdery mildew, downy mildew, black spot, rust, fire blight and anthracnose many other listed diseases that you might find in your garden.
There are many different types of copper fungicides, although there are a few types of liquid copper fungicides that are readily available to home gardeners. The other forms can usually only be purchased from commercial growers.
Let's take a look at how you can use copper fungicide in your garden, along with the potential problems it can cause.
What is copper fungicide?
Copper fungicide is a useful tool in the gardener's arsenal. Source: Lorin Nielsen
Copper fungicide is not just a single product. It is a category of products with copper as an active ingredient, used to prevent bacterial and fungal diseases to save your garden. The active ingredient is the positively charged copper ion Cu+2. Bacteria and fungi are sensitive to this copper ion, which stops spreading when you apply the fungicide.
Copper is a metal that comes from the earth. So if you prefer organic methods it is safe to use and most brands of copper fungicide are OMRI assessed and as such approved for use in organic environments. However, moderation is key. For example, sugar is organic, but consuming it in large quantities is bad for you. Copper is the same when it comes to applying it to your garden. Copper products do not break down in the ground in the same way or at the same rate as many other products. As a result, they can eventually contaminate the soil and harm your plants if you apply too much at once.
How does copper fungicide work?
Every living organism needs trace amounts of copper to survive. One of the reasons people need it is for red blood cell formation. But too much copper is a bad thing, and that's how copper fungicides came about.
Organisms that infect your garden include algae, bacteria, mold and fungi. They're tiny organisms, so only trace amounts of copper are needed to kill them. The copper penetrates the membranes and disrupts enzymes, causing the microorganisms to die.
Luckily, the amount of copper fungicide you apply to your garden isn't enough to kill your plants or harm you or your pets, just the bacterial or fungal disease you're trying to treat. There is a limit, but you probably won't find it anytime soon. Still, you should be sure you have protections such as masks, eye protection, and long sleeves during use.
If you use copper fungicides in your garden, you may find that new growth is negatively affected. This is because mature leaves have a protective waxy layer that prevents copper ions from penetrating the leaf. New growth doesn't have this layer yet, so it's more likely to be damaged. However, new growth also comes with a higher risk of spreading disease, so you'll want to treat it anyway, just to be safe.
Copper ions are released when the residue on the plants gets wet. Plants treated with copper products and exposed to wet conditions are also more likely to suffer damage. This is why it is so important that it is applied in warm weather and sunshine.
Types of copper fungicides
Bordeaux mixture (copper sulphate and lime) on grape leaves in a vineyard. Source: p. 1945
Liquid copper fungicide is the most readily available form for home gardeners. Most of these products come ready to use (RTU) or as a concentrate that you need to mix with water.
There are also granules that you can mix in water, but these are usually only available to commercial growers. RTUs and concentrates contain small amounts of copper, while granules usually contain higher amounts that are generally more toxic and risky to use.
The two liquid forms you will see in stores are copper ammonia diacetate complexes or Bordeaux mixtures.
copper ammonia diacetate complexes
These copper fungicides contain about 30% copper ammonia diacetate complex. Percentages may vary between brands and are usually significantly lower in a ready-to-use format due to the addition of water. Popular ready-to-use brands are Southern Ag and Copper-Count-N.
copper octanoate
Another common blend of copper fungicides for residential use is copper octanoate. In diluted or ready-to-use forms, the solution usually contains less than 1% of the active ingredient, but concentrated versions contain up to 10%. Popular ready-to-use brands are Monterey and Bonide.
Bordeaux blends
Bordeaux mixtures consist of copper sulphate, lime and water. They usually contain less copper than copper-ammonia diacetate complexes with around 25% copper. This type of copper fungicide was the first ever used, dating back to the 19th century. It can leave a blue-green stain, but it can stay in place much longer after rain than other copper fungicide types.
Other copper fungicides
A few other copper fungicides are available, but these types usually cannot be used for residential purposes. We'll list them so you can learn more about them if you'd like, but you'll probably only use the types mentioned earlier.
The other forms are in water-dispersible granules. Granules are mixed in water and then sprayed on the plants. There are copper hydroxide, copper oxide and copper oxychloride. Each species has a different copper content. Copper oxide is the most concentrated type available, containing about 83% copper.
Benefits of using copper fungicides
While there are many things to look out for when using copper fungicides, there are many benefits that make their use worthwhile. For starters, they can be used to treat almost any plant. They are great for vegetables, roses, fruits, nuts, herbs and other plants.
Copper fungicides are approved for use in organic horticulture. So if you prefer to stick to natural gardening methods that don't involve the use of chemicals, copper fungicide is your friend.
The biggest benefit that will make you want to use copper fungicides is that although they are not effective against late blight in potatoes and tomatoes, they can be used to treat symptoms of almost any bacterial or fungal disease. Many if not all diseases have no single true cure, instead utilizing an integrated crop management system to control the spread. The only way to get rid of infections is to remove the infected plant tissue, or in severe cases the entire plant, and try to prevent them from spreading and developing to other nearby crops. Copper fungicides can help prevent bacterial and fungal diseases if you coat the entire plant. Be sure to coat all plant tissues evenly, as uncoated portions are still vulnerable.
Bacterial and fungal diseases can spread with consistently wet weather or stubborn pests. Applying copper fungicides before pests and wet weather hit will help and protect your plants. Timing is essential with this prevention method, but it's worth it in the end if you get it just right.
Disadvantages of using copper fungicides
Copper sulfate powder is the active ingredient in Bordeaux mix. Source: Chemical Interest
Many will agree that chocolate is delicious, but too much will leave you with stomach ache and regret. Copper fungicide works similarly: it's good until you overdo it!
As we have already discussed, copper fungicide is effective because it is toxic to the microorganisms that make up a bacterial or fungal disease. The amount needed to kill these microorganisms is tiny and not enough to harm you or your plants. However, medium or large amounts can harm you, plants, animals and the environment. Strictly follow the instructions on the product label and you will not encounter any problems.
Copper fungicides can contaminate soils that are rich in organic matter but leach into groundwater in mineral soils. Typically they are not degraded in soil like other products. Because of this, you should always be very careful about where you apply the spray. Spray only stems and foliage to limit how much fungicide comes in contact with the soil. If you plan to use copper fungicides regularly, consider crop rotation to alternate between susceptible and resistant species so you're not applying the sprays to the same beds every year. If you're concerned about metal buildup in the floor, a lab floor test can help determine if you've applied too much. On the bright side, your garden will also use small amounts of copper as a micronutrient over time, so if you're careful you shouldn't have any major problems.
Sometimes plants can be damaged by copper. The leaves' waxy surface usually protects them from injury, but some fungicides use surfactants or spread stickers to help the fungicide adhere better to the plants (more on this in the next section). Surfactants allow the copper to spread throughout plant tissues and enter through their stomata or pores. In excess, this can cause damage to the plant. Make sure that if you use concentrated forms, they are limited to the manufacturer's recommended dose, dissolved in a gallon or half-gallon of liquid (according to directions), as this limited amount is helpful and not harmful.
Finally, some copper fungicides can be harmful to bees, something every gardener tries to avoid. To protect the bees, avoid spraying directly on flowers or other places where you often see bees landing. Bees don't usually stop at leaves and stems, so following label directions will help protect them. Copper sulfate is the most harmful to bees, but this is one of those forms of fungicide that isn't readily available to home gardeners, so you don't have to worry about it too much. Most ready-to-use or concentrated copper fungicide formulations in the United States are either copper octanoates or copper ammonia diacetates.
Use of copper fungicides
When using a copper fungicide, always follow label directions for best results. While small amounts of copper are not harmful to humans and pets, you should still wear protective clothing and equipment and keep children and pets out of the area while applying the product and while it is wet.
The best time to apply copper fungicides is during dry weather, before you see any signs of disease or when you first see them. Don't put it on top of new growth as it is more prone to injury as it doesn't have a protective layer of wax on the leaves.
If you have a ready-to-use product, all you have to do is spray the fungicide on your plants.
If you have a liquid concentrate product, you must mix it with water before you can spray it. The ratio may vary between brands, but you'll likely need 1-2 tablespoons per gallon of water.
It can take up to 12 hours for the spray to dry. So be sure to wait for a clear, dry day before applying it, otherwise it won't be as effective. In dry weather and moderate to low humidity, it dries within a few hours. You will most likely need to reapply the fungicide every 1-2 weeks during dry weather if there is a continued risk of infection. Be sure to read the instructions before reapplying.
If possible, cut off material showing visible signs of serious bacterial or fungal disease before use. Spray only the stems and leaves of plants, taking care to avoid soil and flowers, to avoid soil contamination and harm to bees. If you are concerned about how much copper is in your soil, you can buy test kits online and test your soil regularly. Annual testing allows you to continuously record copper levels in the soil so you can plan your garden accordingly.
frequently asked Questions
Q: When should I use copper fungicides?
A: Apply the fungicide to mature plants in dry, clear weather before you see the disease or when you see the first signs of disease incipient.
Q: How fast does copper fungicide work?
A: Copper fungicide works best when dry, which can take up to 12 hours. When the sun is out and the weather is warm, it can dry much faster. Cloudy or cool days or high humidity will slow down the drying process after the plant has been treated. Remember that in itself it is not a cure, but a treatment of the disease or prevention if applied in advance.
Q: Is copper fungicide safe for all plants?
A: When used as directed, copper fungicide is safe for all plant species. Too much can harm them, which is why it's so important to only use as much as directed.
Q: Is copper fungicide safe for humans?
A: The small amount you use on your plants will not be enough to harm you, but large amounts can harm you. Never drink copper fungicide and wash thoroughly after application. Wear masks, gloves and protective clothing while applying to stay safe. It is best to keep children away from the area until the product is completely dry.
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