Do you panic when you see an insect you don’t recognise in your garden? Do you assume it’s a pest causing damage? If so, it may help to understand WHY insects attack plants. I also share a toolbox of natural and organic strategies to help prevent and control the damage.
Firstly, a reality check! Don’t expect a pest-free garden. Even the healthiest gardens still get pest insect visitors. It’s more important to focus on creating a healthy balanced ecosystem. Aim for a productive harvest rather than a zero-tolerance policy!
There will be more beneficial predatory insects and pest controllers in residence with the right elements in place, than those causing damage. You need both – in balance.
If your garden is new, has few flowering species or has poor quality soil, it may be a different story. If you have a horde of herbivores eating your plants, don’t give up! Give it a little time and nature will restore the natural equilibrium. Read on to learn how.
Let’s colour in the picture so you know why the pest insects are there and what to do about it.
How do Pest Insects Damage Plants?
Some insects suck the sap out of plants or chew leaves, while others bore into the roots, seeds or stems. You can tell if you have some unwanted visitors in your garden by the visual damage. You won’t see underground pest insects. However, you WILL be able to observe the evidence they’re in residence by the appearance of your plant aboveground.
Why do some Plants Attract Pest Insects?
Pest insects target plants that are minerally deficient. They are indicators of an imbalance. Weak malnourished plants are magnets for herbivorous insects. They are a CLUE you need to change something.
Professor Philip Callahan, the author of Tuning into Nature, observed that insect antennae enable them to sense a variety of environmental signals. He also found that plants emit infrared radiation (not visible to us). What’s really interesting is these signals vary depending on the nutrient levels inside the plant. He notes “A sick plant actually sends forth a beacon, carried in the infrared, attracting insects. It is then the insect’s role to dispose of this plant deemed unfit for life by nature.”
Survival of the Fittest
So, ‘pest’ insects are actually Nature’s ‘garbage collectors’. Their role is to remove ‘rubbish plants’ and help strong healthy plants survive! They leave plants with optimum nutrition levels alone. What can you learn from this? Grow nutrient-dense food and insect pests won’t bother your plants.
If you have a lot of pest insect problems in your garden, look at your soil health as a first step. Then, cultural practices like watering, feeding and position. It’s far easier to implement preventative strategies than deal with a big outbreak.
Pest insects select plants with a nutritional imbalance of one or more nutrients. They don’t have the pancreatic enzymes necessary to digest complex carbohydrates in healthy plants. Untouched plants are a clue you are meeting their needs.
Encourage Pest to Predator Balance
As gardeners, we tend to see things just through our lens rather than taking a ‘helicopter’ view of the big picture. So, let’s take a moment to explore ‘pest’ insects to get some perspective. If you’re just looking at bugs on one plant in your garden, you may be missing other characters in the story. Nothing exists in isolation, so take a wider view.
The pest insect problem may not be as bad as you think! Consider tolerating a few holey leaves unless there’s a significant amount of damage stopping you from enjoying a harvest. Homegrown food is certainly much healthier than perfect looking produce that’s been chemically grown.
Pest insects are not just there to ruin our day and destroy our favourite plants! Insects are food for many insect species, birds, lizards, frogs and other creatures that visit our gardens. Obviously, when some insects eat our favourite plants, we label them a ‘pest.’ However, they still provide a beneficial role as a food source for many living beings! They are part of an interconnected ‘food web.’
Predators actively seek out insect prey. Many predatory insects, including hoverflies and ladybirds, eat pest insects like aphids or scale as a major food source.
These natural enemies provide us with beneficial ‘ecosystem services’ including pest control and as pollination agents. As they visit flowers, pollen sticks to these insects and is transferred to other flowers, improving pollination and crop harvests. Many are primarily carnivorous predators. So, without the pest insect protein, they wouldn’t have sufficient energy to provide these benefits to us.
So, let’s get back to creating balance. Natural biological control agents are a vital part of a healthy garden. For example, spiders, parasitic wasps, tachinid flies, robber flies, ants, damsel bugs and lacewings. We need to encourage these species by growing diverse plants, avoiding any chemical use, and planting flowers.
Pest insect enemies save you wasting money on toxic sprays and losing edibles to herbivore damage.
Natural remedies like food grade diatomaceous earth, neem oil and eco-friendly horticultural oil sprays can help mitigate damage when used correctly without harming beneficial insects.
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Natural Plant Defenses
Research(1) shows some plants will put their survival ahead of reproduction. When pests such as caterpillars attack a plant, it puts its resources into immediate defence. Plants use their floral bouquet and leaf scents to either attract pollinators or repel herbivores. They release volatile organic compounds (VOCs) or plant chemical scents depending on what’s needed at the time.
According to one study, “Plants have evolved a high diversity of … induced responses to attack, including the systemic emission of herbivore-induced plant volatiles (HIPVs).”(2)
For example, in one study, when under attack, the white turnip(1) scent signals attracted mutually beneficial parasitic wasps. These insects laid eggs inside the caterpillars, ending their life cycle. When not under attack, the plant deployed its resources into stronger floral scents. The perfume attracted pollinators. So the flowers could develop seeds and complete the reproductive cycle.
So basically, plants are mini-chemical factories. They manufacture aromas to help defend themselves from destructive insects or attract pollinator insect ‘partners’ to aid reproduction.
Grow Resilient Plants
The next step is understanding the link between soil health and pest-resistant plants. Plants that have all their dietary needs met are more likely to have a robust ‘immune system’. Their cell walls are stronger, making them harder to penetrate. Weak, minerally-deficient plants are missing vital nutrients for healthy growth. So they’re a sitting target for nature’s insect ‘clean up crew’!
Moist, well-drained, nutrient-rich, pH balanced, covered soils with a diverse microorganism community provide most plants with the environment needed for optimum resilience. If you sow seeds and plants into healthy soil, they have the best chance of strong early development, minimizing the chance of pest insect attack.
Resistant Plant Varieties
If possible, select varieties that are bred to be naturally resistant to specific pests. Some varieties are highly attractive to pest insects whereas others either negatively affect them or are not their preference. Plant tags and seed catalogues will provide more information about each species.
Choose cultivars that grow well locally rather than buying from another area that may not be acclimatised to your conditions. These plants may still grow well but may take several seasons or generations to fully adapt to your soil and microclimates.
If you have a great season with a crop that sailed through without problems, save seeds or take cuttings to cultivate more of this species. Those beneficial genetic characteristics will be inbuilt into the next generation.
Choose the Right Plant for your Climate and Season
This is an important and often overlooked factor in plant failure and pest attacks. Know what to plant when and try to meet your plant needs in terms of location.
Firstly, research the ideal growing conditions. Will the plant species grow best in full or partial sun or shady conditions? Can it handle an exposed spot or need a protected position? How much water, drainage and nutrients does it prefer? If you put a plant in an unsuitable position, you could be setting it up for pest attack. Give your plant babies a fighting chance!
Secondly, don’t just plant them and leave them to their own devices. Plants need your care to establish and through their lives.
- Pay attention to reinvigorating your soil seasonally or refreshing potting mix with nutrients.
- Provide sufficient soil moisture to minimise water stress. Don’t put a bullseye on your plants!
- Practice good hygiene with your tools, supplies, pots and greenhouse. Avoid spreading pest insects (including eggs) from one part of the garden to another.
- What if a plant has been severely damaged by insect pests? Consider binning it rather than composting. This may help stop the life cycle of the pest.
Weed out Weeds
Some common weeds are hosts to pest insects that can spread to nearby vegetables in your garden. Some flowering weeds can provide habitat, nectar and pollen for beneficial predatory insects and pollinators. However, the risks generally outweigh the benefits. Observation is key!
Regular weeding is important to:
- Minimise competition for nutrients and moisture, which can create stress in your edible plants.
- Make sure weeds don’t build up in density. Keep them under control. Otherwise, when you eventually remove them, any pest insects in the host weed can migrate to your edible plants in significant numbers.
Natural Enemies of Pest Insects
Keep a garden journal. Note down observations of insects visiting your garden each season. Always record plant damage you notice. e.g. Holes in leaves, caterpillars on fruits, webbing or slimy trails. Which insects didn’t cause damage? Did you notice any friendly predatory species controlling pest insects?
Take photos of the culprits! Remember insects have a life cycle. The same insect species changes its appearance in different stages of its life. e.g. egg, larva, pupa, caterpillar or adult.
Many pest insects prefer specific host plants. Which plant(s) did you find them on? Like us, insects have their favourite foods too! For example, the large Cabbage white butterfly (Pieris brassicae), small cabbage white butterfly (Pieris rapae) and cabbage moth (Plutella xylostella) target the Brassica (cabbage) family of plants. However, many pest insects like aphids, have a broad range of plants they will attack.
Learn to identify common pest insects. What do they look like? Don’t assume insects you see at the ‘scene of the crime’ are automatically the guilty culprit! They may be, but it takes a while to get to know who the ‘usual suspects’ are versus the good bugs that may have just ‘disposed of the evidence’! Don’t accidentally kill the heroes! Or the eggs or larva of beneficial predators.
Assassin bugs, Ichneumon wasps and lacewings, for example, are innocent biological control agents doing the dirty work for you! So take time to identify who’s who before taking action.
Online Identification Tools
There are many resources to help you. These include:
- Online ID tools and apps.
- What Bug Is That? The Guide to Australian Insect Families – A visual resource to help identify insects. An overview and description of each insect order are presented with photos. More in-depth information is included to identify insects to the family level.
- Brisbane insects– A great photo guide with information about a variety of insects in Brisbane and southeast Queensland.
- Discover Life — Insect orders identification– Visual keys are used to help identify insects to order. Each order has detailed information, photos and links.
- Visit your library and locate books on local insect species.
You can prevent pest insects from doing too much damage. Simply spend a few minutes daily visually checking your plants. Obviously, take a closer look as soon as you notice a problem,
One or two tiny holes in a leaf may indicate a small caterpillar has recently hatched and is hiding underneath. If you leave it a week, that caterpillar will grow considerably fast. The leaf holes will be much bigger! Unfortunately, its brothers and sisters may also be in residence. Smear the underside of the leaf with your finger to squash them when small. Cut your losses early!
Visually check for predatory insects. Don’t assume all bugs are bad! Quite the opposite. Many beneficial insects dine out on common pest bugs. If they are already taking care of business, leave well alone. Nature in ecological balance will self-regulate.
Not all plant damage may be a problem! For example, you can use trap crops like nasturtiums as a sacrificial target plant to attract pests away from your edibles.
Early maturing vegetable varieties are a good choice. They will be ready to harvest before many pest insects arrive. Select those with short maturity dates.
Generally, harvest your vegetables and fruit early. When possible, allow them to ripen indoors. The longer they stay in your garden, the greater the risk of being exposed to insect attack. Over ripe vegetables often become more attractive to some pest insects. So, pick your produce frequently!
Handpick Pest Insects
Handpicking is an easy way to maintain quick control over small numbers of pest insects like grasshoppers and caterpillars. I’ve found the best time to easily squish docile slow-moving insects is early morning. Before they have had time to warm up and get moving!
8 Protective Strategies to Control Pest Insects
Strategy 1: Flowers
Grow diverse flowering plants with nectar and pollen throughout the year or growing season in your climate. These attract pest insect enemies as a supplementary food source and a wide variety of nectar and insect-eating birds.
Strategy 2: Herb Companions
Plant herbs with strongly scented foliage to confuse and repel pest insects naturally. Lavender, rosemary, scented geraniums, basil, mints, nasturtiums and dogbane are just a few that help mask the scent of nearby crops.
Strategy 3: Timing and Preparation
Learn about the common insect pests in your garden. Understand the timing of their life cycles. Importantly, know when pest insects are likely to be in residence. Prepare ahead of time. Refer to the most common pests in the Subtropical Planting Guide if you’re a SE Queensland gardener.
Strategy 4: Not too much Nitrogen
Avoid high-nitrogen fertilisers. Quick-release of nitrogen often causes a flush of sappy new growth. Chemical and synthetic fertilisers are the most common culprits. Oversupply of nitrogen can cause the plant to become a magnet for aphids and other sapsuckers to fly in and dine out! Use slow-release organic soil conditioners. Compost, worm castings, aged manures, blood and bone, soft rock minerals, liquid seaweed/kelp or fish-based micro-nutrients are bioavailable. Mulch also feeds the soil slowly.
Strategy 5: Install suitable crop protection
Exclusion nets, bags, barriers and traps minimise plant loss. Make it hard for pest insects to gain access by excluding or trapping them!
Strategy 6: Crop rotate
After you harvest, avoid planting species from the same plant family in that location. They are usually vulnerable to the same pest insects. Keep plants moving so you break the pest insect life cycle. This is a fundamental practice to minimise damage from pests and diseases.
Strategy 7: Enhance biodiversity
Interplant with a variety of flowering edibles and perennials. You can create biodiversity even in a tiny space in pots. The greater plant species diversity, the more abundant predatory beneficial insect populations will be. The more habitat your garden provides for other creatures in the food web, the fewer pest insect problems you will have.
Strategy 8: Allow spiders to set up web nets
Spiders only put the effort into building webs where they know there’s a good source of food! I’ve seen this countless times in my gardens. Spider webs are quickly filled with grasshoppers, night-flying moths, flies, aphids and many other pests that save me from dealing with them. Spiders are your best friends in the garden!
I hope these tips help give you some preventative strategies and natural ways to control pest insects in your garden.
Related Articles and Videos:
- How to Protect Seedlings from Pests
- Why are Ants in my Plants, Pots and Soil?
- 5 Simple Secrets to Building Healthy Soil
- Imitate Nature for Higher Yields and Less Pests
- Organic Fruit Fly Control Strategies
- Coping with Caterpillars Part 1
- Coping with Caterpillars Part 2
- 13 Benefits of Growing Flowers in your Vegetable Garden
Want to dig deeper? Article References:
- Herbivory and ﬂoral signalling: phenotypic plasticity and tradeoffs between reproduction and indirect defence, Florian P. Schiestl, Heather Kirk, Laurent Bigler, Salvatore Cozzolino, Gaylord A. Desurmont. New Phytologist, 2014.
- The effects of herbivore-induced plant volatiles on interactions between plants and flower-visiting insects, Dani Lucas-Barbosa, Joop J.A. van Loon, Marcel Dicke, Phytochemistry, Volume 72, Issue 13, 2011, p1647-1654.
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© Copyright Anne Gibson, The Micro Gardener 2021. https://themicrogardener.com. All rights reserved.
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