treating pests and diseases - wk 8

Today in 'Recognising Pests and Diseases' the focus is learning about Anthropoda and their various classes. One of which is insects (class Insecta)

Marcus runs us through the characteristic features for each class. For example an Insect is characterised by having three separate parts to it's body - head, thorax and abdomen, a pair of antennae, three sets of legs and wings (one or two) or the absence of wings.

The three separate parts to an insect.

As Marcus points out - analysing and determining which pest or disease is that? is going to be a huge part of working in this industry as solutions to these problems are one of the most common requests for a horticulturalist.  Essentially...... "Which pest did this?" and "What disease has caused that?" will be the common theme. So with this in mind and also quite a healthy interest in this area I am starting to steadily build up my knowledge and reading.

A less than happy Viburnum tinus.

A good example this week occurred on my rotation day at Govt. house. I noticed a freestanding Viburnum tinus in the middle of a section of lawn looking particularly unhealthy, especially in one area that had quite a bit of dieback. After asking "what's wrong with this? we began searching for the culprits. Three things showed up quite obviously. The first was sooty mould all over the leaves which straightway made us think 'sapsucker'. The second was very small black thrips on the underside of the leaves. So our sapsucker was discovered! The last thing was a white creature living near the tip that Mick identifies as a woolly aphid. Not having heard of these before, I decide to look them up in my shiny & newly purchased "What Pest and Disease is That?" reference book. However woolly aphids are described as purply black so I quickly realise our white bug is not that. Searching through the only thing I think matches is a Mealy Bug - the oval shape of it's body and similar symptoms seem to match.


Our mystery white bug near the tip and two black thrips on the underside of the next leaf.

Mealy bugs are also sap suckers who have the ability to reproduce very well and can have multiple generations in one year! I read up on the main damage they cause to plants which is by feeding on the leaves either by direct removal of plant fluids and nutrients, and/or by the excretion of toxic salivary compounds into the plant tissue. They can be 'farmed' and given protection by ants who love to feed on the excreted honeydew they produce (and amazingly- can actually tickle their tummy to produce it on cue!) The honeydew then attracts the sooty mould which hinders the plants ability to photosynthesize, causing dieback. Parasitic wasps and ladybird beetles are an excellent biological control of Mealy Bugs.


Black sooty mould.



After checking with Marcus the next week, he confirms it is a Long Tailed Mealy Bug but feels the majority of the dieback damage will have been caused by the thrip and that is the area to focus on treating.

So......I research the best treatment for a Thrip invasion to find these suggestions:

• Remove diseased and dead growth as the thrips nest in these.
• They also nest in the dry soil and lay eggs in the ground so watering the plant heavily and keeping it thickly mulched with an organic compost will deter their nesting habits.
• Blast the plant with water in the early morning to wash off as many as possible. Do this for three continuous days.
• Spray with a homemade garlic or chili soap targeting underneath the leaves.
• Cultivate the soil to a depth of 6cm in Autumn and again in early Spring to deter them.
• Remove any affected flowers and buds but don't compost them.
• Concentrate on making the soil and plant as healthy as possible. Healthy plants are the most resistant to attack.
• Encourage ladybirds or lacewings into your garden.

A chemical solution is:

• Spray with Pyrethrum if unable to control with above methods.

The following week at Government House I spy some fungal looking mould on a leaf and Mick explains it is called downy mildew. This is a group of fungal diseases that is common in cool wet weather. Fungal spores are spread on the wind and through the soil up onto the plant. Commonly seen in plants growing on vines such as grapes and peas.

Downy Mildew



Prevention and treatment includes:

• Avoid overhead irrigation.
• Remove affected leaves as soon as possible.
• Improve air circulation around the plant.
• Spray with a seaweed based product to build vigor in the plant.
• Mulch to act as a barrier and help restrict the fungal spores spreading from the soil to the plant.
• Dispose of fallen leaves and prunings.

I noticed the area where the infected plant is at Govt. House does currently receive overhead watering so perhaps this is something simple that could be altered to prevent the infection getting worse or spreading.

Hmmm..... more interesting nasties will no doubt follow in weeks to come!