Source: http://www.abc.net.au/northcoast/stories/s2098285.htm?backyard

Sooty mold on your citrus tree

Last Update: Wednesday, December 5, 2007. 2:14pm AEDT

By Phil Dudman and Jonathan Atkins

The citrus tree is one of the most popular fruit trees across Australia.

For good reason too, they're great producers and very reliable but they don't come without their problems.

One of them is a black sooty fungal growth that's found on the leaf surface.

In fact it's called sooty mold and you will see it on many other plants such as gardenias, bottle brush and ixora.

So what causes it?

Sooty mold is caused by an insect and you need to look really close for little lumps under the leaves.

They are scale insects and what they do is suck the sap from the stems and leaves of the tree.

They leave behind a sticky, sugary residue and that's what causes the development of the sooty mold.

A plant can put up with the mold in small amounts but the constant feeding and breeding of the scale insects will weaken the tree over time and significantly reduce your crop.

The good news is, they are quite easy to control with an oil based spray and it's easy to make at home

All you need is a blender, a little vegetable oil and some liquid soap or dish-washing detergent.

In your blender, add 2 cups of vegetable oil (any cheap oil will do so don't use your best cold pressed extra virgin) as well as half a cup of liquid soap (or detergent) then blend it up until it's well mixed.

This mix is your concentrate... I suggest you store it in a jar. Good idea to put a label on it with the dilution rate on the label.

When you're preparing the concentrate for use, just dilute one tablespoon in a litre of water. Stick to that because if you use too much you can burn the foliage.

Give it a good shake then spray it all over the foliage and stems. Make sure you get the undersides as well and what the oil does is smother the pest and they eventually drop off.

A couple of things to remember.

Don't spray in the heat of the day because it can burn the foliage... late afternoon is best.

Also, when you have a bad infestation of scale, you'll need to follow up with a spray at least once a month for three or four months. And that will get your scale and sooty mold under control.

It's that easy, so why don't you have a go yourself?

This information is general in nature and should not be taken as personal professional advice. You should seek your own independent assessment from a qualified practitioner and not rely solely on the general nature of information in this site.