Common Plant Diseases
We all know how difficult it can seem at times just to keep your plants alive. If it’s not pests that destroy them then they get hit by various diseases. I this article I intend to discuss some of the most common diseases.
I will discuss how to recognize a disease and how to control it. But before I start on the list I just want to give you a word of advice on prevention measures you can take.
I have often been to gardens that have been ravaged by insects, rust, mold, black spot and so on. I have spoken to the owners of these gardens who have no idea why their plants seem to be picked on the most.
Well here’s a short list of some reasons that disease in particular will hit some gardens and not others.
1). Your soil is infertile.
Make sure you prepare your garden soil correctly, before planting. A healthy garden is a happy one, and it all starts with
Have you added fertilizer? Fertilizers come in many forms. I prefer the organic types. Particularly ones that are slow release and have added trace elements and minerals.
Have you added manures? Manures act as a soil conditioner as well as providing low levels of NPK.
Have you added compost? Compost also conditions the soil and provides certain levels of NPK.
Did you complete a soil test to check the Ph? Most soils require a ph from slightly acidic through to slightly alkaline. There are the exceptions where some plants like a high or low ph, but you can easy adjust the levels to cater for these plants specifically.
You can adjust soil Ph by using products such as Lime, Dolomite (to increase ph), and iron chelates (to decrease it)
When you add the manures,composts and ph adjusting products, you will need to incorporate them well into the soil structure.
2). Your plants aren’t getting enough light.
This is a common problem in well-established gardens. Far to often people over plant their gardens at the initial building stage. They put in far to many trees and bushes not realizing just how tall and wide these plants will grow.
When we first purchased our current property you couldn’t actually see the house. There were far to many large trees blocking out the sun. Most of the under story plants had died and only shade loving ones remained.
The house was moldy and damp and the garden was very sick. We removed about a dozen large trees and let in the light. It has taken us ten years but we finally have a healthy mostly disease free garden.
3). You have purchased plants that are really not suitable for your climate.
If you live in a wet, cold area then you need plants that are able to cope with the conditions. For example, most succulents and cacti prefer dry conditions. Other plants love the wet conditions and hate heat and dry.
Always ask questions at your local garden center when purchasing plants. Also, do some research on your PC or cell phone. Check out exactly what conditions plants thrive in before purchasing them.
4). You have purchased sick plants.
Make sure any plants you buy are healthy looking. Check the root ball in the pot. If the roots are heavily matted I would avoid purchasing them. They can be teased out before planting but if you don’t do this correctly they may struggle and become susceptible to diseases
Healthy plants can fight diseases better than unhealthy ones so give them the best possible start in life by implementing the methods I have mentioned above.
For further information on Manures and composts, soil preparation etc., click on any or all of the following links.
Now we Can Take a Look At the List of Common Plant Diseases.
1. Black Spot. (Diplocarpon rosae)
This is probably one of the most devastating of the fungal diseases that can affect Roses as well as other plants. It can start of as a small dark spot on a leaf and the leaf turns yellow and eventually falls off. It is always better to be diligent with inspecting roses for this disease and removing any infected leaves, placing them in a throwaway bag and disposing in the rubbish bin.
Don’t be tempted to place the leaves in your compost as this can spread the disease.
Black spot is worse in humid areas where it thrives in the moist conditions. Even though it is a fungal disease it is dependent on wet, damp, warm conditions to spread.
At one point in our lives we spent several years living in a dry arid, almost desert area. My wife planted a rose garden that absolutely flourished as long as it was watered every second day. We never saw any sign of black spot and the plants and blooms were magnificent.
Our current garden is located in the sub tropics some twenty miles (Thirty odd Kilometers from the coast.). Black spot and other fungal diseases are a constant issue on our Roses.
What can I do To help control the Black Spot Disease?
There are a number of steps you can take to help control black spot.
1). Remove any leaf that shows signs of the disease. As stated earlier, the first signs are a small dark brown to black spot which gradually is encircled by a yellowing of the leaf until, eventually the leaf drops off.
The fungus spreads quickly to the other leaves and plants, infecting the plant and eventually reducing the plants vigour
2.) Always wet the ground and not the plant. If you are putting in an irrigation system, stick to drip lines that water the base of the plant and don’t touch the leaves.
3).Keep the plant healthy by fertilizing on a regular basis. We supply our Roses with some type of slow release organic fertilizer once a month. As our plants in the sub-tropics flower all year we like to add Sulfur of pot ash to the mix twice a year. This not only helps to flower but strengthens the stems and helps fight disease.
4). Purchase only those plants that are strong and healthy and are breed for disease resistance.
5). Use a natural fungal spray once a week. (see below for a recipe). Another natural spray is a ‘Bordeaux mixture’, which is a mixture of lime and copper sulfate. Neem Oil is also a good natural product to use for any fungicide related disease and will also help control certain insects.
6). Use a Chemical solution. If you have an extreme situation then you can think about using a chemical fungicide such as Mancozeb or
A Natural Recipe for Black Spot:
Fill a five liter ( or approx 1 gallon ) sprayer with water.
Add 1 heaped tablespoon of Bicarbonate soda (baking soda).
Add 1/3 rd of a teaspoon of dish washing liquid.
Mix well and spray over leaves and stems. Make sure you cover the whole plant. Both sides of the leaves, and the soil at the base of the plant to the drip zone
You will need to spray the leaves twice a week while the weather is wet or humid. Diplocarpon Rosae thrives in wet, damp, moist conditions, particularly when the daytime temperature fall below 80 degrees (27 c).
If you can keep the sprays up to the plant during this type weather you will find that you can reduce the spraying once the climate becomes warmer and drier.
Make No Mistake!
Black spot can be debilitating to Roses in particular. It can, and will, kill Rose plants. Black spot is also known to mutate meaning that even so called resistant Rose varieties can succumb to this terrible disease. All the more reason why you need to be diligent.
. Keep your Roses as healthy as you can.
. Use some form of control, preferably an organic one, regularly.
. Wet the soil when watering, not the plant.
. Never plant a new Rose in a spot where an old one has died. I have been successful in doing this myself, however, I removed about two square feet of soil and replaced it with new healthy soil.
2. RUST ( Pucciniales )
Rust is caused by a pathogenic fungi that comes in many diverse forms that are specific to different plant species.
Rust is another disease that can completely destroy a plant. It is probably one of the best known among common disease terms and can be described as being a fungi that produces red, brown or black spores in Pustules.
These Fungi, as mentioned, are specific to certain plant species and each type may only affect one to two plant varieties.
About twenty years ago I operated a Daylily (hemerocallis) nursery, daylilies are an extremely tough, hardy, fiber rooted perennial. They had very little disease or pest issues and came in thousands of colors and types.
Our nursery was thriving, until rust disease arrived. It decimated our plants and made our business unprofitable. Eventually people discovered organic ways to control the fungi, sadly this came too late for us and we were forced to close our nursery.
Most Daylilies can outgrow the disease if you use control methods. However, the control has to be diligent as the rust will reappear during times of high humidity and rain.
If you have Daylilies that look like they might be struggling, check under the leaves. The rust will show as an orange powder. Should you notice this powder, carefully remove all leaves, cutting the plant back close to ground level.
Place the leaves in a plastic bag and throw away into the rubbish bin. Do not compost as the spores can survive the composting treatment.
This is one disease that I would suggest you bring out the heavy artillery. Using fungicides such as Zineb, mancozeb, lime sulfur or copper can control it.
Also, when cutting up clumps and moving them to a new location, I like to dip the plants for one hour in a mixture 0f 1:20 Chlorine and water, that being one part Chlorine and 20 parts of water.
Household bleach works well for this. Make sure the plants are completely submerged for the length of time mentioned.
Other plants that can suffer from Rust include:
A). Gerberas: This shows up as a creamy-colored pustule under the leaves.
B). Snapdragons: Spray these with a fungicide every ten days. Alternate between different spray types. Make sure you commence the spray program from the time you plant the seedlings.
Once the plants have finished flowering pull them out and either dispose of them by placing into a plastic bag and into the rubbish bin, or burn them
C). Beans: Bean rust attacks the whole plant, the beans included, but it can be first seen on the leaves which become covered in red, yellow and / or brown pustules. If you notice this disease in your beans my advice would be to remove and dispose of the plants immediately as mentioned above. Fumigate the soil with a relevant fungicide and don’t plant any other related legume in that particular spot.
There are many other plants such as Hostas and members of the myrtle family, that are affected by rust. In some cases the spores can completely kill of the plant or tree and in others the plants seem to fight back and survive.
Unfortunately, rust is a growing world problem that is affecting more and more plant species every year.
Powder Mildew. (Erysiphe polygoni and E. cruciferarum)
Downey Mildew. (Peronospora sparsa)
There are two main types of Mildew that affect the garden.
A). Downy Mildew.
B) Powdery Mildew.
Both these can be debilitating to plants. In most cases they will cause the plant infected to die and they will also spread to other plants.
How Do you recognize these mildews?
When a plant is infected with Downy the mildew the upper surfaces (or top of) of the leaves) will become blotched. If you turn the leaf upside down you will clearly notice the formation and origin of the blotchy patches.
Eventually the whole leaf will turn yellow and drop of.
Powdery mildew reveals itself as a light gray coating on young leaves, buds and shoots.
These are not diseases you want to ignore as they can destroy most garden plants, in particular vegetable plants and annual flowers.
THE BEST THING TO DO IS TO DESTROY THE PLANTS INFECTED.
If you find this to be far to drastic, and it is a measure I would undertake, then you will need to use a fungicide such as Mancozeb or an Eco based fungicide.
Other preventative measures you can take are:
A). Make sure you don’t plant seedlings to thickly. If you have, then thin them out, It’s far better to lose a few this way then to find you have lost the lot. Plants require good air circulation and over planting can cause a host of different issues.
B). Don’t use overhead sprinklers or water the plants on top with a hand held sprayer. Always try to water plants at the base. This helps minimize any spread of the mildews. It’s also better to use a good drip system.
C). I also suggest that you water your plants in the morning and not the afternoon.
4). Root rot. (Phytophera – or Armillaria(Honey fungus)
The two most common forms of root rot are Phytophera and Armillaria, the later is known as Honey Fungus and is prevalent in many countries around the world.
Root rots are one of the most serious of all plant diseases. It’s above ground. symptoms include a sudden stunting of growth and a tendency for the plant to wilt, and in severe cases, to die back completely.
Root rot is carried by a fungus in the soil, and it affects all plants from annual flowers to large trees. I have personally seen many avocado orchids decimated by Phytophera.
When the plants stems rot at ground level it is known as crown rot.
The fungus is most active in moist damp soils and those soils that have bad drainage. It can also develop during periods of extended heavy rainfall, even on well drained soil
Some Preventative Measures to stop it spreading Include:
A). Soil Sterilization. This can be an expensive option and would need to be carried out by experts. The downside of sterilization is that you will have to rebuild your soil structure and health from the ground up. excuse the pun.
B). Drench the soil with an organic fungicide or fungicides such as aluminium tris (O-ethyl phosphonate)
C). Remove all infected plants and replace with those resistant to this disease. If you live in humid areas, such as the tropics or subtropics, then I would stick to growing those plants that come from these areas.
There You Have It. Part One of: Common Plant Diseases.
You need to remember that the most basic measure to prevent or control any fungal disease is to plant either disease resistant species or those that belong to the environment you live in. If you live in the sub tropics or tropics then an intense wet season can kill off most cool climate annuals.
You must also prepare your soil diligently. A good garden will require a healthy, friable and well draining soil.
The old saying ‘prevention is better than the cure’, is mandatory within any garden environment.
Happy Gardening. Jim
Look out for the next installment in this gardening series.