Winter Citrus Care

There are some pests and diseases which attack citrus trees that can betreated during winter. This helps to break the pest and disease life cycle, giving citrus trees a fresh start in spring.

White louse scale (Unaspis citri), is a type of hard scale that is a common insect pest that infests citrus trees, with infestations often starting on the trunk and main limbs and then spreading to the tips of the twigs. The scale may also move onto the leaves and fruit and there can be several generations produced each year. White louse scale can result in leaf fall, twig dieback, bark splitting, fruit blemishes and large limbs may even die. White louse scale looks like tiny fragments of dessicated coconut scattered over the bark. Female scale may be inconspicuous and similar in colour to the bark.
Citrus rust mite (Phyllocoptruta oleivora), attacks the outer exposed surface of the fruit. Slightly rough, greyish-brown blemishes on fruit occur due to huge numbers of mites infesting immature fruit in summer and autumn. When fruit colours and ripens, the blemishes become more prominent and become more severe the longer the fruit remains on the tree. Rust mites can also cause bronzing of leaves and green twigs.
Bud mite (Eriophyes sheldoni) are very tiny pests that are are difficult to spot with the naked eye. They target leaf and flower buds and result in leaves, flowers and fruit that can be misshapen and distorted
Sooty blotch is a fungal disease that results in fruit developing a sooty coloured blemish on the skin. It’s on the outer skin surface only and doesn’t affect the inside of the fruit.

Yates^® Lime Sulfur is a broad spectrum insecticide, fungicide and miticide that can be used at a higher ‘winter strength’ to control these citrus pests and diseases in July. Avoid spraying when freezing weather is expected.

Citrus Gall Wasp

Lumpy swellings along the stems of citrus trees are an indication of citrus gall wasp. Citrus gall wasp (Bruchophagus fellis) is native to warm coastal areas in New South Wales and Queensland but has also become an increasing problem in Victoria and also Western Australia. Its original host was the native Australian finger lime but can also seriously affect other citrus including lemons, grapefruit and oranges.

There are 3 main stages in the citrus gall wasp life cycle:

The small black adult wasp lays up to 100 eggs just underneath the bark on soft new spring growth.
Larvae hatch from the eggs, eat the stem tissue and the lumpy galls form around the developing larvae.
The larvae mature into the adult wasp which emerges from the gall the following spring, leaving small pin prick holes.

The galls not only look unattractive they can lead to poor plant health and reduced harvest. It’s important for home gardeners to be vigilant and look out for these galls and July is an ideal time to act to reduce this nasty pest, before the adult wasps emerge in spring. There are no sprays registered for controlling citrus gall wasp in home gardens and once galls are formed the damage is permanent.

Prune off affected stems and place these sections in a sealed plastic bag and put them in the garbage (don’t put gall infested stems in the compost bin). Disposing affected stems before the adult wasps have emerged stops the life cycle and helps to reduce new infestations in spring.