An accomplished gardener’s main task is to grow healthy plants, which are the best defense against plant diseases. Choosing a planting site and selecting plants that are resistant to disease is the best way to prevent and manage plant disease.
If a plant doesn’t look right, a gardener might think it’s sick and take steps to fix it. The gardener needs to have background knowledge about the plant, the current environment, and the typical diseases or other problems to which the plant is susceptible to properly diagnose plant problems. Having accurate information can help you avoid making a wrong diagnosis that would result in using pesticides unnecessarily, wasting time and money, and having the plant’s condition continue to deteriorate.
This publication provides gardeners with information on how to establish and maintain healthy plants, and describes a systematic approach to identifying and solving problems that may occur.
Disease is a Response
A plant disease is a problem that the plant has in response to being bothered by an infectious agent that causes illness. A plant disease can cause a plant to have problems yielding, reproducing, or growing properly.
Differentiating between a true disease and an abiotic disorder is crucial to developing an effective management plan. The agents that cause plant diseases are living things called pathogens. Abiotic disorders are caused by abiotic, or nonliving, factors. If you’re trying to figure out why your plant is dying, it’s important to understand the difference between the two possible causes.
Even if a disease is confirmed, the problems caused may be minor, making costly control measures not worth the expense or bother. In other situations, a disease might have less of an effect on older, well-established plants as opposed to younger plants.
The diseases that a plant suffers from can often give insights into the underlying issues that made the plant susceptible in the first place. Incorrect growing practices might cause problems such as choosing a bad location, not having the right mix of nutrients, not enough or too much water, or not pruning or mulching correctly. If you can figure out what is causing the plant’s problems, you can often stop the disease from continuing and the plant will be healthy again and able to resist such problems in the future.
When you need to implement control measures, you must choose which management techniques will work best. An IPM strategy is most effective when it involves a combination of management techniques. The first line of defense against plant pests are cultural practices and plant selection. In an IPM program, pesticides may be used as a last resort. If you’re just trying to solve a pest problem quickly, you might end up using too many pesticides. Try to understand why the problem Occurred. This document is a guide for the homeowner who is faced with the decision of selecting a pesticide for an isolated problem. When faced with the decision of selecting a pesticide for an isolated problem, choose the least toxic product that is designed for that specific plant and disease.
When pesticides are necessary, always follow the recommended application methods and rates described on the pesticide label. Since this will only increase your expenses and in some cases may decrease your overall crop yields You should not apply more than the recommended amount of the pesticide, as this will increase your expenses without necessarily increasing your crop yields. If a pesticide is used too often, the target organism may become resistant to it, making it less effective in the future. Pesticides can sometimes have negative impacts on human health, the environment, or organisms that are not the intended target, such as birds and helpful insects that could control other plant issues.
Plant Disease Triangle
The triangle is often used to show how plant diseases occur. A disease will only occur when three conditions are present:
- A pathogen, or disease-causing organism, such as a bacterium or a fungus, meets a…
- susceptible host plant, during…
- favorable environmental conditions for disease development.
A disease can only develop when all three conditions are met. The first condition for disease development is the presence of a pathogen, but there are many other factors involved. Resistant plants are much less likely to get sick, so choosing the right plants can be a key part of disease control. The disease will only occur if the environment is right for it. The conditions described allow pathogens to thrive while weakening the plant, making it more susceptible to infection. A plant that loves the sun but is grown in shade will be less vigorous and therefore more susceptible to attack. The shade will also extend the leaf wetness period, creating favorable conditions for foliar disease.
The best way to manage this is to make sure that none of the three conditions that form the triangle sides are present. Taking these conditions into account will give you a better understanding of plant diseases and how to control them.
Five Steps to Diagnose Plant Problems
To accurately diagnose a plant problem and find its remedy may seem like a daunting task, but with a little research it can be easily accomplished. If you cannot identify a plant, you may need help from a plant disease specialist. Try to diagnose the problem yourself before you ask for help from an expert. In order to be prepared, you should collect information on potential symptoms, signs, and sources of stress that could affect your plants. Even if the outcome is uncertain, the process can still be educational and provide useful insight.
When diagnosing plant problems, be sure to be as detailed as possible when collecting information, as though you were a detective trying to solve a crime. The following items will be most helpful on your journey: a hand lens with 10x magnification, a digital camera, a trowel, pruning shears, a pocketknife, a flashlight, and something to take notes with. Establish a location to keep records and reference materials.
Determine the most likely cause by following these five steps:
- Accurately identify the host plant.
- Determine what is normal for the plant.
- Learn common problems for the plant.
- Distinguish between biotic and abiotic causal factors.
- Examine the plant for symptoms and signs.
Confirming a Diagnosis
Troubleshooting plant problems using the five described steps is similar to assembling a puzzle. You will often see a logical picture emerge if you can find enough pieces and fit them together. Sometimes this process is called the guess-and-confirm method. With practice and experience, diagnosis becomes progressively easier.
Most noticeably, the labs observe the physical symptoms of the plant. To identify plant diseases and disorders, diagnostic labs use a variety of techniques, most noticeably observing the physical symptoms of the plant. In many cases, diagnosis will be relatively simple because the lab has seen many plants with the same disease.
A diagnostician may use a taxonomic approach to identify an unfamiliar disease, which includes isolating the suspect pathogen, identifying it, and confirming it is the causal agent of disease. This approach can take a lot of time and cost extra for testing. The lab may use other advanced testing methods, or send a sample to another plant clinic for retesting, if the original testing was inconclusive.
Even if you do everything correctly, diseases can still happen. Remember that most fungicides work best when used before the pathogen appears or soon after it first appears. It is very difficult to manage full-blown disease outbreaks once they have been established. You should be constantly looking for signs of disease during very wet springs and try to stop problems early on. To control plant diseases in the garden, it is important to do the following:
Effective Natural Fungicides for the Garden
Bicarbonates are commonly used in gardening as a fungicide to prevent plant diseases. Sodium bicarbonate (baking soda), potassium bicarbonate, and ammonium bicarbonate are all effective in preventing fungal growth. Many people believe that products containing potassium and ammonium bicarbonate are more effective than baking soda for fighting fungal pathogens. Baking soda needs to be mixed with horticultural oils to be effective, but this is not necessary with the other two bicarbonates.
The safety of these products for humans and beneficial insects is high. Be sure to look at the labels of these products before using them, as each type of bicarbonate is effective against different plant diseases. There are many products that use bicarbonate as their base, two of the most common being GreenCure® and Monterey Bi-Carb®.
This biological fungicide uses a naturally occurring bacterium found in soils and human gut to combat fungal organisms. It manages another living organism by inhibiting fungal spore germination and interfering with the fungi’s ability to penetrate into plant foliage. It also works against some bacterial pathogens.
Fungicides made from B. subtilis can prevent many different kinds of plant diseases in the garden, and they’re effective at doing so without harming birds, insects, or people. These products are helpful in fighting against black spot, powdery mildew, early blight, anthracnose, botrytis, and many other common fungal pathogens. There are many different brands of insecticides, some of the most common being Serenade®, Companion®, and Cease®.
Various fungal and bacterial pathogens, including the plant disease powdery mildew, anthracnose, leaf blights, bacterial leaf spots, and fire blight, can be prevented by using sprays based on copper. However, some plants cannot be treated with copper due to an adverse reaction. Copper-based fungicides are approved for use in organic farming because copper ions on the surface of plant leaves destroy pathogens before they can enter the plant’s tissue. However, once the disease is symptomatic, copper is ineffective. The purpose of these products is to prevent something from happening, not to treat it after it has already happened.
There are many products made with copper that are certified for use in organic agriculture, however ingestion or inhalation of copper by humans and other mammals is highly toxic. Additionally, copper is toxic to fish and other aquatic invertebrates and should not be used near waterways. Take care when using copper formulations around bees. If there is too much copper in the soil, it can be harmful to earthworms.
Brand names include Monterey Liqui-Cop® and Bonide Copper Fungicide®.
Sulfur-based fungicides have a long history, particularly when it comes to treating agricultural crops. For homeowners who want to prevent plant diseases like powdery mildew, leaf spot, and black spot, using fungicide is an effective way to do so. Sulfur prevents spores from taking hold and is most effective when used before disease establishment. Do not use sulfur-based products when temperatures are above 80 degrees F. Some brand names of products that contain sulfur are Bonide Sulfur and Safer Brand Garden Fungicide.
This oil is used as a natural pesticide and insecticide. Neem oil is an extract from the seeds and fruits of the tropical neem tree that is used as a natural pesticide and insecticide. Although it is most commonly known as a pesticide, neem oil can also be used as a fungicide to protect against many plant diseases, such as powdery mildew, black spot, rusts, leaf spots, and scabs. It is most effective when used as a preventative measure. Try to find Bonide Neem Oil Concentrate and Garden Safe Neem Oil. Be careful when using products that contain neem oil, as they can be harmful to fish and other aquatic creatures.
Using Garden Fungicides Safely
Look on the label of any product you want to spray on a plant to see if it is safe for that specific plant. Some plants can have a negative reaction to a particular product – a reaction called phytotoxicity. The product could cause phototoxicity, which would damage the leaves, stop the plant from growing, make it lose its leaves, and eventually kill the plant. You should check the label of each product to see if there is a list of plants that are not recommended to be used with that product. You should not use the product on these plants. There will also be instructions on how to avoid phytotoxicity that can occur from spraying when temperatures are too low or too high, or when the product is not mixed at the correct rates. Label instructions are there for a reason. Follow them carefully.
Growing a healthy, disease-free garden is within your grasp. The best way to control plant pathogens in the garden is to prevent them from occurring in the first place. Choose plants that are naturally resistant to disease and then follow good maintenance practices to further reduce the chances of disease. Consider spacing plants properly and paying attention to how you care for your garden. The products controls should only be used as a last resort.
Bicarbonate products are contact fungicides that can be used on many different plants to kill many different fungal pathogens, including powdery mildew, anthracnose, rusts, botrytis, and various blights and leaf spots. The drugs work by either inhibiting the growth of the mycelium or damaging the cell walls of the fungus. Fungicides are most effective when used before the pathogen takes hold of the plant.
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