Is your Viburnum hedge suffering from sap-suckers? Perhaps you’ve noticed a general decrease in vigour and you’re trying to work out what’s going wrong and how to fix it? Sap-sucking insects, such as aphids, whiteflies, mealybugs, and scale, are a common threat to viburnum plants. These pests feed on the plant’s sap by piercing the leaves, stems, or branches with their mouthparts. This feeding weakens the plant, disrupts photosynthesis, and sometimes introduces pathogens.
In this article, we’re going to learn how to identify and control sap-suckers naturally, using the least harmful methods first.
Do you wish your Viburnum hedge looked like this? The sad truth is, if you’ve planted a low quality variety, it never will – even if you solve the pest issue. Opt for a high performer like Viburnum odoratissimum ‘VOQ1’ PBR Intended Trade Name Quick Fence™. https://www.ozbreed.com.au/plant-ranges/hardy-exotic-range/quick-fence/
How do we know that the plant is infested with sap-suckers?
Sap-suckers leave behind telltale signs on your viburnum plants, both in the form of visible pests and damage to the plants. By keeping an eye out for these indicators, you can detect an infestation early and take action to protect your plants.
Visible Signs of the Pests
- Presence of insects: Look closely at the underside of leaves and along stems for pests like aphids, mealybugs, whiteflies, or scale insects. These sap-suckers may appear as tiny dots, clusters, or even small cottony or waxy masses (in the case of mealybugs). Keep in mind that some insects are more active during the night, while others are more active during the day.
- Egg clusters or nymphs: Many sap-sucking pests lay eggs or have immature stages (nymphs) that can be spotted with close inspection. Check for tiny white or pale spots that may be grouped together on leaves or stems. You may also see signs of predator eggs, getting ready to hatch and feed upon the pests.
- Movement: Some pests, such as whiteflies, will quickly flutter away in a cloud when disturbed, making them easier to spot.
Symptoms on the Plant
- Leaf discoloration: Infested leaves often show signs of yellowing or pale mottling, as sap-sucking insects drain the plant of nutrients.
- Leaf curling or deformation: Feeding damage can cause leaves to curl, pucker, or distort, which is especially noticeable in heavy infestations.
- Stunted growth: Repeated feeding by sap-suckers can weaken the plant and slow its growth, leading to small, unevenly developed foliage or stems.
- Honeydew residue: Sap-sucking pests excrete a sticky, sugary substance known as honeydew, which can coat leaves, stems, and nearby surfaces like soil or garden furniture.
- Sooty mold: Black, powdery fungus often grows on honeydew, giving affected areas a sooty appearance. While the mold itself doesn’t harm the plant directly, it can block sunlight and interfere with photosynthesis.
Secondary Issues
- Weakening of the plant: Persistent infestations can leave viburnum vulnerable to secondary infections by bacteria or fungi, which may enter through feeding wounds.
- Lack of flowering: An infested viburnum may produce fewer flowers, or the flowers may fail to develop completely due to stress and nutrient loss.
Regular monitoring of your viburnum plants helps in spotting these early signs. By acting swiftly when you notice these symptoms, you can protect the health and vigour of your plants before damage becomes severe.
Without further ado, let’s explore some of our pest control options, prioritising the least harmful methods first.
Dark, moist parts of the garden tend to attract the most sap-suckers. This specimen seems to be doing just fine, regardless. Viburnum odoratissimum ‘VOC1’ PBR Trade Name Dense Fence™. https://www.ozbreed.com.au/plant-ranges/hardy-exotic-range/dense-fence-viburnum/
Cultural Controls
Maintaining a healthy and vigorous plant is the first line of defence against sap-sucker infestations.
- Proper planting site selection: Place viburnum in a location with adequate sunlight and good air circulation. Avoid shady, damp areas where pests thrive.
- Watering and feeding: Viburnums love soil that’s moist but not waterlogged. Over-fertilisation, especially with high-nitrogen fertilisers, can encourage excess tender new growth that attracts sap-suckers. Use a balanced fertiliser to promote overall health.
- Pruning: Regularly inspect and prune infested or weakened branches. This helps reduce the pest population already present and promotes healthy plant growth. Dispose of pruned material away from your garden to avoid spreading pests. Keep in mind that non-selective pruning (such as hedging) in the warmer months promotes excess fresh growth, potentially compounding the issue; try to remove badly infested branches early and cut back to a fork if you wish to minimise fresh growth.
- Sanitation: Remove plant debris and weeds nearby which could serve as alternative hosts or shelter for sap-suckers. Some sap-suckers are fussy with their hosts, while others have a wider palette.
The natural growth habits of different Viburnum species can differ greatly, and there’s even more variety to be found with countless cultivated varieties of popular species like Viburnum odoratissimum. This cultivar has a narrow, upright growth habit, perfect for natural fences, driveway hedges and large feature trees with a small footprint in courtyards and suburban gardens. Viburnum odoratissimum ‘VOT1’ PBR Intended Trade Name Thin Fence™.
Physical Controls
Physical methods can help reduce the presence of sap-suckers on viburnum plants.
- Water sprays: Use a strong jet of water to dislodge pests like aphids, whiteflies, or spider mites from the leaves. Repeat every few days to keep populations under control, particularly when populations rise drastically.
- Sticky traps: Place yellow or blue sticky traps near the plant to attract and capture flying sap-suckers such as whiteflies. These traps help monitor pest activity, though I don’t know any professionals that use them to reduce pest populations. They can also look a bit ugly for ornamental applications
- Barrier methods: For young or small plants, use fine mesh or horticultural fleece to physically block access to pests, especially during peak activity seasons.
Biological Controls
Encouraging and introducing natural enemies of sap-sucking insects is a sustainable way to manage populations. You can either purchase them as a short-term pesticide alternative, or you can facilitate an environment that attracts them naturally for more long-term benefits.
Introduced Beneficial Organisms
- Ladybugs (ladybird beetles) and their larvae are voracious consumers of aphids, mealybugs, and whiteflies. Purchase live ladybugs and release them directly onto infested plants in the evening to reduce the risk of them flying away immediately.
- Lacewing larvae (commonly known as “aphid lions”) feed on a wide range of sap-sucking pests. Release them near problem areas for targeted control.
- Encarsia formosa, a parasitic wasp, is an effective option for controlling whitefly. Purchase and release in areas with confirmed whitefly infestations.
Viburnums provide flowers with nectar that are fantastic attractors for the predators and parasitoids of their pests, such as beneficial hoverflies and micro wasps. Viburnum odoratissimum ‘VOQ1’ PBR Intended Trade Name Quick Fence™. https://www.ozbreed.com.au/plant-ranges/hardy-exotic-range/quick-fence/
Enhancing Biodiversity to Attract Predators
- Planting companion flowers: Attract beneficial insects by planting pollinator-friendly flowers, such as Callistemon, Chrysocephalum, Lomandra, or Rhaphiolepis, near the viburnum plants. These provide nectar and pollen for predatory insects. In fact, Viburnum flowers are quite attractive to beneficial insects themselves.
- Provide habitat and water: Leave some areas of the garden untidy with logs or perennial grasses where predatory beetles and wasps can shelter. A fish pond or bird path will provide flying insects with a source of moisture, a very important element of any eco garden.
- Avoid broad-spectrum insecticides: These can kill beneficial insects and disrupt natural predator-prey dynamics. Minimise chemical intervention to encourage the population of natural enemies. If you must resort to chemical controls, opt for the least harmful option possible.
Chemical Controls
Use chemical interventions only after cultural, physical, and biological methods have proven insufficient. Always opt for the least toxic methods first and follow label instructions to minimise harm to beneficial insects and the environment.
Least-Harmful Options
- Horticultural oils (e.g., white oil or horticulture oil): Apply to smother and kill small pests like aphids, mealybugs, or whiteflies. These are generally safe for beneficial insects when applied directly to pests at the right time of day (evening or early morning), although any beneficials contacted will be killed as well. Keep in mind that neem oil is different as it is actually absorbed by the plant and acts as a broad spectrum poison; don’t be tricked by its reputation as a “natural” or “organic” insecticide, I personally treat it as just another nasty chemical.
- Insecticidal soaps: Effective against soft-bodied sap-suckers, these soaps disrupt the pests’ cell membranes and kill them on contact. Use when you observe clusters of pests, ensuring thorough coverage of leaves and stems.
- Chemical insecticides As a last resort, sometimes a chemical option is required. To minimise harm to beneficial predators, parasitoids and other insects, we want to use the least harmful method (that will actually work) first. This means choosing between systemic vs non systemic chemicals, and also selective vs non-selective chemicals.
Systemic vs Non-Systemic Insecticides
Understanding the difference between systemic and non-systemic insecticides is key in choosing the right control method for pests while minimising environmental impact.
What Are Systemic Insecticides?
Systemic insecticides are absorbed by plants, typically through their roots or foliage, and distributed throughout the plant’s tissues. When sap-sucking pests, such as aphids or whiteflies, feed on the plant, they ingest the insecticide and are killed.
How They Work
After application, systemic insecticides travel through the plant’s vascular system, targeting pests that feed on internal plant fluids.
Application Methods
- Applied to the soil as granules or drenches. The plant absorbs the chemical through its roots.
- Sprayed directly onto leaves as a foliar application, where it penetrates the plant tissue.
Examples
- Imidacloprid (commonly available in products like Confidor) is widely used for pests such as aphids and psyllids.
- Dinotefuran is another popular option for systemic pest control.
Advantages
- Targeted action: Effective against pests that live within plant tissues and are difficult to reach with contact insecticides.
- Long-lasting control: Systemics provide residual protection, sometimes for weeks or months, reducing the need for frequent applications.
- Weather resistance: Rain or irrigation doesn’t wash away systemic treatments, as they work internally.
Disadvantages
- Potential for harm to pollinators: Systemic insecticides may affect pollinators like bees if applied to flowering plants, as the chemicals can reach nectar and pollen.
- Environmental concerns: Some systemics can remain active in the soil or water for long periods, potentially impacting non-target organisms.
- Higher risk of resistance: Prolonged use of the same systemic insecticides can lead to pest resistance.
What Are Non-Systemic Insecticides?
Non-systemic (contact) insecticides act on pests externally. The insect must come into direct contact with the chemical or consume it while feeding on treated surfaces.
How They Work
Non-systemic insecticides remain on the surface of plants. They kill pests either by direct contact (disrupting their nervous system or cell membranes) or ingestion. These insecticides do not move within the plant.
Application Methods
- Sprayed on leaves, stems, or the soil surface.
- Direct application to visible pests for immediate results.
Examples
- Pyrethrins, insecticidal soaps, and horticultural oils (except neem oil) are common non-systemic options.
Advantages
- Reduced systemic spread: Chemicals stay localized, posing less risk to non-target areas or soil.
- Safer for pollinators (if applied at the right times): Non-systemic sprays can be used sparingly and on non-flowering parts to protect beneficial insects.
- Immediate results: Non-systemics work quickly, often killing pests upon contact.
Disadvantages
- Short residual activity: Non-systemics degrade quickly and require more frequent applications, especially after rain or watering.
- Limited reach: They cannot target hidden pests living inside stems or on undersides of leaves effectively.
- Potential for non-selective harm: May kill beneficial insects like ladybugs or lacewings if used indiscriminately.
Summary of Key Differences
| Feature | Systemic | Non-Systemic |
| Mode of Action | Absorbed by plant, targeting internal feeders | Acts externally on pests through contact or ingestion |
| Application | Soil drench, foliar spray | Foliar spray, direct pest targeting |
| Residual Effect | Long-lasting, often weeks or months | Short-lasting, may need reapplication |
| Weather Resistance | Resistant to washing off | Can be washed away by rain or irrigation |
| Effectiveness | Great for sap feeders (e.g., aphids, whiteflies) | Best for surface pests visible on the plant |
| Impact on Beneficials | High if not used carefully | Moderate, depending on timing and method |
Both systemic and non-systemic insecticides have their place in integrated pest management. Systemics offer long-term protection but come with broader environmental concerns, while non-systemics are ideal for quick, targeted treatments with lower ecological impact. Careful consideration of the pest type, plant health, and environmental factors will guide the best choice for pest control.
Monitor your Viburnum closely for signs of pests so that you can control them culturally and physically before they warrant chemical pesticides. These red tones are totally healthy, and something we actively selected for during the breeding process. They add some seasonal colour during spring as the plants put on a growth spurt. Viburnum odoratissimum ‘VOC1’ PBR Trade Name Dense Fence™. https://www.ozbreed.com.au/plant-ranges/hardy-exotic-range/dense-fence-viburnum/
Selective vs Non-Selective Pesticides for Sap-Suckers on Viburnum
Every good horticulturist has an understanding of the difference between selective and non-selective options. Each type has specific characteristics that influence its effectiveness, safety, and environmental impact.
What Are Selective Pesticides?
Selective pesticides are designed to target specific types of pests while minimising harm to non-target organisms, including beneficial insects or other garden biodiversity. For sap-suckers, selective pesticides often act against their particular physiology while sparing other species.
How They Work
Selective pesticides disrupt biological processes unique to targeted pests. For example, they may interfere with sap-suckers’ growth cycles or inhibit feeding mechanisms.
Application Methods
- Applied via targeted sprays on affected viburnum foliage where the sap-suckers are active.
- Best used during early stages of infestation for maximum effectiveness.
Examples in Australia
- Pymetrozine, found in products like Chess, disrupts aphids and whiteflies’ feeding behaviour without significantly affecting beneficial insects.
- Spirotetramat, available in products such as Movento, is a systemic selective pesticide effective against sap-sucking insects like scale and mealybugs.
Advantages
- Pest-specific action reduces risk of harm to pollinators and other beneficial insects.
- Integrated Pest Management (IPM) compatibility supports biodiversity and sustainable gardening practices, as we’re outlining in this article.
- Lower environmental impact when used as directed, as it spares most non-target species.
Disadvantages
- Limited scope restricts efficacy to specific pests, requiring accurate pest identification. (This is actually a good thing – hopefully we aren’t trying to wipe out every living thing in the garden.)
- Persistence risk: If overused, targeted pests may develop resistance. This is less likely in smaller urban gardens than it is in larger agricultural operations.
What Are Non-Selective Pesticides?
Non-selective pesticides serve a broader purpose by killing multiple types of insects, including but not limited to sap-suckers. They do not discriminate between targeted pests and other insects, making them useful for severe or uncontrolled infestations but potentially hazardous to garden biodiversity.
I can’t imagine a scenario in which I would personally recommend a systemic non-selective herbicide in a landscape maintenance setting, after more than a decade’s professional experience.
How They Work
Non-selective pesticides act through mechanisms such as nerve disruption or suffocation, affecting a broad range of insects that come into direct contact or consume treated foliage.
Application Methods
- Sprayed evenly across viburnum plants to reach all affected areas, particularly with non-systemic options. Care should be taken to avoid contact with nearby plants or pollinators.
Examples in Australia
- Pyrethroids, found in products like Yates Baythroid Advanced, provide broad control of sap-suckers but also kill non-target insects.
- Neem oil, an ‘organic’ non-selective option disrupts insect growth and feeding for pests such as aphids and whiteflies.
Advantages
- Broad efficacy makes these pesticides a quick solution for mixed pest infestations.
- Fast results, with many pests affected almost immediately after application (particularly with contact sprays).
Disadvantages
- Non-target harm poses risks to beneficial insects like ladybirds and bees.
- Environmental concerns arise if chemicals run off into waterways or disrupt ecosystems.
- Short-term approach, as broad elimination can disturb natural pest predators, potentially leading to further infestations.
Key Differences for Viburnum Pest Management
| Feature | Selective Pesticides | Non-Selective Pesticides |
| Target Scope | Specific pests (e.g., sap-suckers like aphids) | Multiple insects, including beneficial species |
| Application Focus | Directed at infested parts of viburnum | Broadly applied to all affected areas |
| Examples in Australia | Pymetrozine (Chess), Spirotetramat (Movento) | Pyrethroids (Baythroid), Neem oil (Eco-Neem) |
| Impact on Beneficials | Low when applied carefully | High, affecting pollinators or predatory insects |
| Environmental Impact | Reduced due to specificity | Increased risk of ecosystem disruption |
| Effectiveness | Ideal for sap-feeder control when pests are identified | Useful for large-scale, mixed infestations |
With their lush green light to semi-dark tones, Viburnum hedges provide a wonderful contrast of colour and texture to plants with other colours. Viburnum odoratissimum ‘VOC1’ PBR Trade Name Dense Fence™. https://www.ozbreed.com.au/plant-ranges/hardy-exotic-range/dense-fence-viburnum/
Conclusion
By integrating these strategies and prioritising prevention, you can manage sap-suckers on viburnum while supporting a healthy and biodiverse garden environment. Regular monitoring and early intervention are essential to long-term success.
As a gardener, it’s your job to decide between systemic vs non systemic, and selective vs non selective pesticide choices if you aren’t able to control the pests naturally. These can be used in the short-term, but a wise gardener plans to make chemical controls obsolete in the future.
