Pests On Plants: How to Eliminate Plant Fungi & Other Pests

When it comes to gardening, winter can be a tough time of year. The cold weather can make it difficult to get out and tend to your garden, and the shorter days means there's less sunlight for your plants to grow. But there are ways to overcome these winter gardening woes and here are our top tips.

Certainly, your worst gardening nightmare is when you discover plant fungi and other pests on plants. Those unwelcome garden gremlins cause lots of frustration. This is especially true as we enter the winter months. With the season change, we, as gardeners, all experience winter gardening challenges. These challenges are not only due to the weather but also the pests on plants and plant fungi that become prevalent in the winter. We’re sharing some tips to help solve some of these problems. Remember, winter gardening problems cannot always be solved, and some fatalities in the garden are fairly normal. So don’t be too hard on yourself!

dealing with PESTS on plants


These small, pear-shaped, soft-bodied insects come in various colours and like to suck on plant sap from a broad spectrum of plants throughout the year. They are preferential to new and young plants. This activity sucks the energy from plants and weakens growth. Aphids are nasty pests on plants since they can also carry viruses that can be deadly to plants. 

How do you know that you have an Aphid infestation?

  • When you have an aphid infestation, you may notice an ant influx before seeing the small aphids. Ants will run up and down the infected plant. This is because they have a symbiotic relationship with aphids. The aphids secrete honeydew, which the ants eat. In return, the ants protect the aphids from natural predators. Unfortunately, your plant is the host to this alliance.
  • At this time of the year, one particular type of aphid is very active and destructive. They usually cause the complete dying-back and browning of whole branches. The cypress aphid, as the name says, attacks cypress and conifer plants. If left unattended, it can be fatal to your plant or tree. Treat the cypress aphid with a systemic insecticide like Insecticide Granules, which is very efficient.

DIY remedy for Aphids

Make a homemade pesticide spray for aphids by mixing 3 teaspoons of cornstarch with 1 tablespoon of cold water. Bring 250ml of water to a boil and then mix the cornstarch mix into the boiled water. Boil and let this mix thicken. To use your homemade pesticide spray for aphids, mix 125ml of the premix with 5 litres of cold water and spray it onto the affected plants.


At this time of year, we plant lots of winter-flowering seedlings and winter-bearing vegetables. Many of these veggies are in the brassica family. Unfortunately, this plant family is particularly susceptible to deadly attacks by caterpillars. There are many different types of these Larvae that can attack your garden. Caterpillars are certainly one of the worst pests on plants when it comes to your vegetables!

Please remember, that caterpillars are young moths and butterflies, which are all pollinatorsIf you have decided to treat the plants affected, opt for a shop-bought product like the Margaret Roberts biological caterpillar insecticide.

DIY remedy for Caterpillars

Make a homemade pesticide spray for caterpillars by crushing 4 hot chillies, 1 small onion, and 1 garlic clove. Add the crushed ingredients to 2L of water. Bring the mixture to a boil and then let the mix steep for 2 days. Strain the fluid and pour it into a spray bottle. Spray your homemade pesticide spray for caterpillars onto the affected plants. This spray is also effective for aphids and other soft-bodied insects.


Another one of the unwelcome pests on plants is the cutworm caterpillar. These worms, which are actually the early beginnings of a moth, vary in colour. They are smooth and hairless and curl up tightly when you disturb them. 

  • Cutworms can be problematic in the early winter months when we plant our winter annuals and veggie seedlings & seeds. Unfortunately, this garden pest targets young plants. 
  • The mature cutworm larvae are very destructive, cutting straight through young plant stems, immediately killing the plant. 
  • A great solution is to recycle toilet rolls and use them as plant collars when planting. 
  • You can also sprinkle cornmeal or bran around the affected areas, which they will eat and die from. 
  • Cutworms can also be controlled by placing matchsticks flush with the newly planted seedlings on either side. When the cutworm tries to curl around the seedling, the matches will get in the way.

Margaret Roberts’ biological caterpillar insecticide is very effective when you want to eliminate cutworms. It contains Bacillus thurengiensis (a bacteria). When caterpillars and worms eat this bacteria, it produces proteins that paralyze the caterpillar’s digestive system. This causes them to stop feeding and die. It is safe for use in organic gardens because it has a specific target and is nontoxic to humans, animals, and beneficial insects.


Soft and hard scales exist in many different colours and types. Scale can be present throughout the year. It likes to overwinter on larger shrubs, trees and fruit trees and this is where you are likely to find them hiding. 

  • Scale-like aphids are sap-sucking insects that secrete honeydew and have the same symbiotic relationship with ants. Something not mentioned before is that black sooty mould is likely to form on top of the honeydew. This is a telltale sign of a serious problem. 
  • If you would like to purchase a pesticide product, you can opt for Oleum. – an environmentally friendly oil insecticide that works by suffocating insects and eggs.

DIY remedy for scale

A homemade pesticide for scale is to mix 30ml (1 tbsp) of methylated spirits or surgical alcohol with 250ml (1 cup) of water. Using cotton wool, wipe this homemade pesticide mixture over the scale.


In the winter rainfall area, these will become quite active and be a problem because of the damp and wet overcast weather in which they thrive.  

  • When checking if your garden has a slug & snail problem, don’t just think of seedlings planted, veggies, and plants commonly affected by these slimy critters. Remember that plants like succulents are also prone to pests on plants in the form of slugs and snails. They can cause severe damage to your succulents. Look at dense plantings in your gardens as well. They tend to hide in these during the day.
  • Mulching and using abrasive materials like eggshells acts as a deterrent to slugs and snails. 

If you don’t have pets, you can also place a saucer of beer near plants that tend to be attacked. They will drink the beer, become intoxicated, fall into the saucer and perish.

dealing with Plant fungi prevaent in winter


Black spot is a fungal disease and a common sight on rose leaves. Citrus fruits and quinces are also affected by a type of black spot.

  • On roses, this plant fungi is characterised by black spots on leaves where surrounding parts eventually turn yellow. The affected leaves eventually fall off. Almost the whole plant can be defoliated by this nasty plant fungi.
  • Black spot fungi become more prevalent now in winter rainfall areas when leaves stay wet for six to eight hours, allowing spores to germinate. 
  • Fungicides containing copper work very well to treat the problem.

DIY remedy for Black Spot plant fungi

You can also make a homemade fungicide by chopping up 500 grams of onions, garlic, and chives and adding this to 10L of water. Allow this mixture to ferment for seven days. Strain and dilute the mixture 1:10 with water. Spray your homemade fungicide onto affected plants to rid them of this unwanted plant fungi.


Downy mildew is a fungal disease that presents itself on roses, vegetables from the cucurbit (pumpkin, cucumber, and gem squash) and cabbage families, onions, peas, grapes and a variety of ornamental plants.  

  • Downy mildew develops when temperatures are low and heavy rain or dew occurs. This is why it is a problem in winter rainfall areas. 
  • The most common symptom is spotting accompanied by greyish mildew forming on the undersides of these spots. 
  • Again, fungicides containing copper work well to treat this problem. 
  • The above-mentioned homemade fungicide (onion, garlic, and chive) spray also works for downy mildew.


“Damping off”, is a horticultural disease or condition caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions. In winter rainfall areas this can become a problem. 

  • Planting fungicide-treated seeds directly into the garden can reduce “damping off” disease. Other preventative measures include using well-drained soil and avoiding plant overcrowding. Also, clean out all pots thoroughly before reuse and discard contaminated soil.
  • Cinnamon powder can also prevent “damping off” disease by sprinkling the powder onto the seedlings or the soil. 
  • There is no cure for “damping off” once plants are experiencing this fungus. Remove plants and discard. Remove affected soil and clean out pots if plants were in pots.


This is one of the most common of all the plant fungi found in the garden. It affects various plants including ornamental, vegetables, and fruit. 

  • The symptom is clear white powdery growth on leaves, stems and flowers, as well as fruit surfaces. Severe infestations can even cause the leaves to curl and yellow and flowers and fruits can become distorted and malformed. 
  • This plant fungus is more common in wet weather. 
  • Margaret Roberts’ organic fungicide is quite effective in treating this fungus. Alternatively, you can use the homemade fungicide recipe described above.


This fungal disease affects a wide range of woody and herbaceous plants. Even though it rarely kills plants, it reduces a plant’s health, vigour, and flower production.

  • Rust diseases occur most often in mild, moist conditions. Rust is spread by spores that are transferred from infected plants to healthy plants. These spores can be transferred either by the wind or by water, which is why rust disease often spreads after watering or heavy rains. Wet surfaces are also needed to cause infections.
  • Rust diseases come in different varieties and can affect a wide range of plants. People often struggle with rust on their roses. It is easy to remember the defining characteristics of this fungus, as it matches its name. Rust plant disease will look similar to the rust that appears on metal items. 
  • Rust is extremely difficult to treat and most times it is best to remove affected plants and put them into sealed rubbish bags and take them to the rubbish dump. You can try using a copper fungicide but this is not always effective.

Garden issues specific to WINTER-RAINFALL AREAS

Apart from pests on plants and plant fungi, there are some other nasty gardening problems which become prevalent in winter. Most of South Africa experiences summer rainfall but a small part, being the southwest and the Western Cape area, experience winter rainfall and therefore have a different climate and unique winter gardening problems.

Garden issues: Drainage problems

If your garden has a heavy clay content in a winter rainfall area, you may experience drainage problems and, therefore, experience rotting of plants. It is said that this can be remedied over time by adding agricultural lime to clay soils, which helps break this type of soil up. Most don’t realise that agricultural lime also has the potential to alter the PH of your soil, which can be harmful (Fynbos, for example, cannot handle alkaline products).

Gypsum is another product used to break up clay soils, but there are varying opinions as to whether Gypsum is actually an effective product for this purpose. Our recommendation is to apply and work large amounts of organic matter like compost and well-rotted manure into heavy clay soils as this will over time improve the structure of the soil and help with drainage. When the organic matter breaks down, it will also feed the plants. 

Garden issues: Plants washed away

Another problem in winter rainfall areas is when heavy rains occur, some young plants are often washed away. You can prevent this by mulching in your flower beds. Take special care around the younglings.

Garden issues: Plant rotting

Plants from more naturally arid areas can experience rotting when there are consistent heavy rains. Examples of these are succulents, cacti, and aloes. If plants are in pots, it is a fairly easy problem to prevent or remedy. Use gravel or grit as a mulch around the plants as a collar (Prevent stem from being constantly wet). Also, apply this method in garden beds. 

Garden issues: Mulching too thick

When mulching, be careful not to apply too thick a layer and ensure the mulch is not piled high around plants or tree trunks. This is because mulch can hold moisture, which in turn can cause rotting and lead to fungal growth when there is lots of rain. Once plants start rotting, there is not much you can do to remedy the organic decomposition process. Do a spot check on your mulching level during the rainy season to ensure it is not piled up too high.

Garden issues specific to Frost-prone AREAS

Some South African summer rainfall areas experience extremely cold winters and frost. You can do a few things to minimise frost damage to your plants. 

  • When plants are damaged by frost, do not cut back frost damage as these parts can protect the plant from further harm. Cut it back once all cold weather has passed. 
  • If you see that certain shrubs or small trees suffer quite heavily from frost damage, transplant them into more protected and appropriate areas. This is the correct time to transplant trees and shrubs that may have originally been planted in inappropriate areas, as plants are fairly dormant in winter. When transplanting, ensure you water the plant well the day before and try to limit damage to the plant’s root ball. 
  • If you know you have susceptible plants in your garden that don’t naturally cope with frosty conditions, protect them with some form of frost cover to minimise damage. Examples of frost cover are grass wigwams, frost fleece and hessian. 
  • A lesser-known fact is that frost-prone gardens must get adequate watering. This is because frozen soils do not yield water. Make sure, though, that this watering takes place in the morning. Morning watering is important so plants and roots can dry out throughout the day and not stay wet at night.  
  • In frost-prone areas, the freezing and thawing of soils occur naturally, and this churning and heaving can damage the roots of plants. Adding mulch to the garden regulates the soil temperature and moisture, easing the transition into winter. Mulching creates a buffer against hard weather.

winter gardening, Next steps

In conclusion, the above information we at Contours Landscapes provided should help you solve some of your biggest winter gardening problems. But please remember to be kind to yourself. You cannot always solve every problem in your garden. If your problems persist or you need further advice, ask for a horticulturist’s advice at your local retailer. They should be able to shed some more light. Alternatively, send us a direct message if you have a question for Jessica Ruger, our horticulturist partner.

Now let’s try to keep those critters at bay!

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We plan, install and maintain award-winning landscapes for our commercial clients and project partners. Clients who wish to add function, value and inspiration to their outdoor spaces and properties.

Our roots are in Cape Town, but our footprint stretches deep into southern Africa.


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Let’s plan your landscaping project together!

We plan, install and maintain award-winning landscapes for our commercial clients and project partners. Clients who wish to add function, value and inspiration to their outdoor spaces and properties.

Our roots are in Cape Town, but our footprint stretches deep into southern Africa.

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