What is a Leafminer?
Technically the Citrus leafminer, Phyllocnistis citrella, is a small moth pest of citrus.

How do they Damage Citrus Plants?
Damage is caused by the larvae as they mine immature foliage. Twisted and curled leaves are generally the first symptoms noticed. Severe infestations, (an average of two or more mines per leaf) can retard the growth and yield of nursery and newly planted trees.

Such infestations usually only occur in late summer and autumn, and are often related to low natural enemy activity. They rarely occur in spring because the production of new growth is prolific and synchronised, and quickly becomes immune to attack.

The History and Spread of Leafminer in Australia
The moth was first recorded in Australia in and around Darwin in the Northern Territory in 1912. It was probably present several or more years earlier and was apparently eliminated in 1922 after a five-year campaign to eradicate citrus canker. During the campaign all citrus trees north of the nineteenth parallel in the territory were destroyed. Since then rigorous quarantine measures have been in force to prevent establishment of the disease in Australia.

However in 1940 citrus leafminer was again found in Darwin and in 1965 it was recorded at Cairns in Queensland. Between 1965 and 1985 it spread slowly southwards along the east coast of the continent to the NSW south coast. And by April 1995 it had spread across the continent to south-western Western Australia.

Control Methods…
Because infestations are restricted to flush growth, particularly in late summer and autumn, their severity can be reduced by:

• Fertilising in winter to promote flush growth in spring when the pest is either absent or relatively scarce, and 
• Limiting flush growth in late summer and autumn by not fertilising and irrigating during summer and autumn in excess of the amount needed for normal growth. 
• Pruning of late summer and autumn flush growth can also be used to limit and remove unsightly infestations on home garden trees.

Recommended Products…
Horticultural mineral oils (HMOs) and agricultural mineral oils (AMOs) are generally as effective as insect growth regulators and broad-spectrum organophosphates and carbamates. They are the only products recommended for general use in nurseries, home gardens, and orchards.

Options -
White Oil
Confidor
White Oil and Malathion together

Spraying
Spraying should commence as soon as the summer flush commences in mid to late January, before the first flushes produced by trees attain a length of 10 mm. This strategy will prevent rapid growth of leafminer populations and reduce the risk of heavy infestations during peak periods of flush growth later in the season.

Sprays should be applied thoroughly to the upper and lower surfaces of susceptible leaves. They should generally be applied at 7-day intervals during warm to hot weather, and every 10 to 14 days during cooler periods. The number of sprays required depends on the citrus cultivar being treated and the duration of flushing. Lemon trees will generally require more sprays than orange, mandarin or grapefruit trees.

Oils…
Oils are effective because adult female moths avoid sprayed surfaces and this leads to reduced egg laying. Broad-spectrum insecticides and growth regulators are generally used to kill adults and immature stages, or to disrupt the development of some immature stages.

In addition to their effectiveness, the major advantages of using HMOs and AMOs are:

• They can be handled with minimum protective clothing such as overalls, goggles and a facemask.
• They have low toxicity to vertebrate animals— they are almost as pure as the products used for baby and hair oils, skin lotions and creams.
• They have little detrimental effect on beneficial insects and mites.
• They do not stimulate outbreaks of pests.
• Pests have not developed resistance.
• Spray deposits are broken down within weeks by microbes, oxidisation and ultraviolet light to form simple molecules that do not pose a threat to the environment.

Coffs Harbour Produce currently stocks a range of the products listed to help you prevent your Citrus Trees being ravaged by Leafminer. Pop in store to talk to our friendly team about the best product and spray unit for you.

Information sourced from www.dpi.nsw.gov.au - Get the Complete Article HERE

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