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Six methods for controlling Scale Insects on shrubs

As plant scientists we constantly get photos sent to us from friends and family who are having problems in their garden. Perhaps the most common picture sent in is a picture of a shrub infested with scale insect! These insects look ‘other worldly’, but in actual fact are related to aphids (greenfly), but the actual pest is hidden under a hard protective shell that it creates to ward off predators.

Scale insects are small, sap-sucking pests that can wreak havoc on plants if left unchecked. But fear not! In this blog post, we will explore six effective methods for controlling scale insects and protect your garden from their damaging effects.

Understanding Scale Insects

Scale insects belong to the superfamily Coccoidea and are known for their protective, scale-like coverings that shield them from predators and harsh environmental conditions. These tiny pests come in various shapes, sizes, and colors, but they all have one thing in common: they feed on plant sap. Scale insects attach themselves to the stems, leaves, and branches of plants, depriving them of vital nutrients and weakening their overall health.

The most important point to note about scale insects is; the newly hatched nymphs (AKA “crawlers”) hatch and crawl around your plants in mid-summer. It is at this point in their life cycle that they are easiest to control. Once they form their protective scale shell control becomes a lot more difficult to kill.

Identifying Scale Insect Infestation

Detecting scale insects can be challenging due to their small size and ability to camouflage. However, there are a few signs that can help you identify their presence:

Sticky residue: Scale insects excrete a sweet, sticky substance called honeydew, which may attract ants or promote the growth of black sooty mold.

Yellowing or wilting leaves: Infested plants often display symptoms of nutrient deficiency due to the feeding activity of scale insects.

Distorted growth: Affected branches or leaves may appear stunted, distorted, or discolored.

Presence of scales: Look closely for tiny, raised bumps or shells adhering to the plant’s surface. Scales can vary in color, ranging from brown and black to white or translucent.

Now that we understand what scale insects are and how to identify them, let’s explore some effective control methods:

1. Manual Removal

For light infestations, manually removing scale insects can be an effective control method. Gently scrape the scales off the plant using your fingernail, a toothbrush, or a soft brush. This approach is best suited for larger plants or those with fewer scales. Remember to dispose of the removed insects away from your garden to prevent reinfestation.

For larger shrubs, wait until the young nymphs are on the move and give the whole plant blast with a pressure washer. Just make sure the pressure isn’t too high or you could damage the foliage. Many pressure washers also come with an attachment/option for applying detergent at the same time. If this is the case, you can use it for applying insecticidal soap to large shrubs. 

2. Insecticidal soap

Insecticidal soaps work by disrupting the scale insects’ protective coverings. Dilute the soap according to the manufacturer’s instructions and apply it directly to the affected areas of the plant. Take care to cover all the scales thoroughly, as the oils and soaps need to come into contact with the insects to be effective. For best results, again, insecticidal soap should be applied when the nymphs are on the move.

3. Fumigate with Lime Sulphur

If you need to control scale when they are dormant and inside their hard shells then a good option is to apply diluted Lime Sulphur. This will act as a fumigant. Lime Sulphur works all year round, so can be applied when the plant is dormant and so there is no risk of scorch damage on the leaves.

4. Natural Predators

Encouraging natural predators of scale insects, such as ladybugs, lacewings, and parasitic wasps, can help keep their populations in check. These beneficial insects feed on scale insects and can significantly reduce their numbers. Create a welcoming environment for these predators by incorporating diverse plant species, providing water sources, and avoiding the use of broad-spectrum insecticides that may harm beneficial insects.

Earwigs have been found to be particularly important for eating scale insects and aphids on fruit trees. Although some gardeners believe earwigs to be a pest, earwigs are actively encouraged in commercial orchards, with growers attaching ‘earwig hotels’ to apple trees to protect the nocturnal earwigs when the trees are being sprayed with insecticides.

5. Systemic Insecticides

In severe infestations where manual removal and natural predators are insufficient, systemic insecticides can provide effective control. These products are absorbed by the plant and transported throughout its system, reaching the sap on which scale insects feed. However, exercise caution when using systemic insecticides, as they may also harm beneficial insects and pollinators. Follow the instructions carefully, and consider using them as a last resort when other methods for controlling scale insects have failed.

6. Regular Monitoring

Prevention is always better than cure, so incorporating regular monitoring and maintenance practices into your gardening routine is essential. Regularly inspect your plants for signs of scale insects or any other pests. Squash any scale you find by hand (you may want to wear gloves for this). Additionally, provide your plants with proper care, including adequate sunlight, watering, and fertilisation, to keep them healthy and less susceptible to scale insect infestations. Scale insects, and their relatives (greenfly, wooly aphid) thrive in shady locations.

Conclusion

Controlling scale insects in your garden requires a proactive approach and a combination of strategies. By understanding the signs of infestation and implementing the appropriate control methods, you can safeguard your plants and maintain a thriving garden. Remember, a healthy garden is a happy garden, and with the right knowledge and techniques, you can effectively manage scale insects and enjoy the beauty of your green oasis. Happy gardening!

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