Garden Pests Series: D…

Thoughts and musings

Garden Pests Series: D…

Lewis | March 31, 2015 | 0 Comments

…is for Diaspididae.

In the fourth issue of our Garden Pests Series, we will be discussing scale insects; a group of high-profile pests of which Diaspididae is the largest ‘family’, in terms of biological classification. We understand that we are technically using the letter ‘D’ to discuss scale insects as a whole, which should ‘technically’ be saved for the ‘S’ edition. But we’ve got an equally important one saved for that one! So we might have bent our own rules – one garden pest for every letter of the alphabet – but scale insects like Diaspididae can really do some serious damage to the plant it chooses as its host, and as a result I think it’s pretty important you know about it! So sit back and give our latest instalment a read! It could just maintain your garden’s well-being…

There are a couple of early signs of potential scale insect infestation that you should keep an eye out for. Without physically checking leafs and stems for them, scale insects can cause plants to become distorted, discolour into a slight yellow and can slow their growth. A main visual indication of scale insect infestation, apart from seeing the insects themselves, is a dark and sooty mould on the foliage of the plant. This is also sticky to the touch, caused by the insects’ production of honeydew as they feed on the sap directly drawn from the plant’s vascular system.

These pests are rather troublesome, especially in greenhouses, and usually infect ornamental plants, where over 300 different species are targeted as hosts. They are very robust parasites, and firmly fix themselves on their hosts, so much so the scale can persist long after the insect itself has died. They can be difficult to detect, despite the telltale signs outlined above, as they are very small, appearing as flattened ‘discs’ that are white, yellow or brown in colour.

Scale insects are divided into two different families: soft scale, known as Coccidae, and hard scale, known as the aforementioned Diaspididae. They can breed all year round on protected crops, making them a constant menace! Diaspididae can also lay eggs under the scale which hatch into nymphs. Despite the fact they are entirely immobile despite some being able to move very short distances, if and when they find a good feeding site they can adversely affect a host plant to a high degree. Therefore, treatment to combat scale insects is very important.

As parasites, they can quite literally benefit at the expense of your garden. Luckily, both treatment and prevention strategies are widely available and well-known. Chemical treatments available are widespread and quite effective in ridding your garden of scale insects; these include pyrethrum, natural fatty acids and rape seed oil. We implore you that if you choose to use a chemical treatment, always take precaution and read the manufacturer’s instructions. Alternatively, if you choose to take an organic approach, there is also a number of options available to you, such as checking purchased plants thoroughly for early signs of infestation and purchasing natural biological control predators; Metaphycus helvolus, Chilocorus nigritus and lacewing larvae can parasitise, feed on, and control scale respectively.

In an ideal world, you won’t have to deal with these pests in the first place. So there are also a number of prevention exercises you can carry out. These include:

  • The regular checking of plants for signs of infestation;
  • Keeping your garden clear of weeds, as these can harbour them;
  • Looking for ants running up and down plants, as they ‘milk’ the produced honeydew;
  • Avoiding the use of insecticides designed to kill numerous species, as beneficial insects will perish as well; and,
  • The destruction of removed leaves from infected plants as these can harbour young scales.

The reality is that the majority of gardeners will have to deal with this common problem more than once in their travels. So do not let them ruin your enjoyment as use these tips to prevent them as much as possible.