Palms   Pests and Diseases

Insect pests and a number of diseases can attack and damage palms and in extreme cases can kill them. If the growing point of a palm is invaded by insects or infected by disease the strength of the palm can be greatly reduced, and if it is destroyed, the palm will die. Cycads are less affected by pests and diseases, their tough leaves are most vulnerable only during the stage that they are emerging and before they have hardened up.

In the cool climates, attack on palms and cycads by pests and diseases is not as much a problem as it is in tropical climates where several generations of insects may breed within one year and where there are a large number of diseases that thrive in the warmth and humidity. This is especially the case with fungal diseases. The cool climates have the advantage in that during the cooler months many species of insects go into decline and in some climates are killed by cold. The marked separation of the seasons arrests the spread of some diseases and gives one the time to keep control.

Some pests and diseases are common to most countries, while each country has some that are common mainly to it Therefore mention of all of the types is not possible in this section.

Pests
Insects and mites can attack palms and damage the new growth causing the leaves to look unsightly. Older palms are not attacked to the same extent as younger ones, or if they are, the damage is less noticeable.

Insects generally fit into one of two catagories, those that cause damage by sucking sap from the leaves and those that cause damage by chewing at the leaves.

Mealy Bug:
These insects are oval in shape, about 2 mm in size, are grey, pale pink or pale yellow in colour and have a white wax covering their bodies. They multiply rapidly into large colonies that can often look like patches of white fungus and feed by sucking sap from the leaves and stems. They thrive in warm moist places and can live in the soil or on the plant. If they affect the bud of a palm, new leaves may emerge distorted They also have the tendency to colonise on the underside or in the crown of cycads, again sucking sap. Sometimes they may be associated with ants who feed on honeydew that they produce. Mealy bug infestations can be controlled by spraying with dimethoate.

Mites And Spider Mites:
These sucking insects are usually invisible to the eye and breed rapidly in warm dry conditions. They can tend to go unnoticed until signs of their damage are obvious. They colonize on the underside of palm leaves, withdrawing the sap causing the leaves to go brown and die. The European mite and the two-spotted mite are known to invade not only the leaves but also the bud and crownshaft of some palms, causing their growth to be arrested. Control is achieved by spraying with dicofol or other specific miticides often twice to break the insects breeding cycle.

Scale:
There are many species of these pests that suck sap from the leaves of palms and cycads. They can vary in shape and colour and commonly encountered types are oval in shape with armoured shells and sometimes waxy to touch, usually visible and do not seem to move about. While many of the types are specific to certain countries, some species, white palm scale (Phenacaspis eugeniae), palm scale (Parlatoria proteus), fern scale (Pinnaspis aspidistrae), soft brown scale (Coccus hesperidum) and pink wax scale (Ceroplastes rubens) are known to attack palms and cycads. Their damage is greatest on palms and can cause yellowing of the leaves with the infestation of sooty mould in shaded areas. Scale can be controlled by spraying with maldison or dimethoate.

Thrips:
A number of the species of thrips feed on dead leaves or decaying matter while some will attack palms causing considerable damage. They are small in size and colonize on the underside of palm leaves chewing by rasping and sucking the sap causing the leaves to develop silver-white patches. The adults fly from plant to plant, lay eggs and the young thrips feed on the plant then often move into leaf litter at the base of the plant, develop into adults then take flight to lay eggs again. They are particularly prevalent after warm dry weather. Control by spraying with dimethoate or maldison.

White Fly:
These insects resemble tiny white moths and some species attack palms infesting the underside of the leaves and sucking sap from the plant Small infestations can be controlled by hosing and if this is not effective it should be sprayed with dimethoate or demeton-S-methyl.

Caterpillars Of Butterflies And Moths:
Many butterflies and moths do not feed at all but lay eggs that develop into larvae and there are a large number of insect larvae referred to as caterpillars which cause damage to palm leaves or emergent cycad leaves by chewing or grazing on the foliage. Many can be picked off the leaves or controlled by spraying or dusting with carbaryl, maldison or pyrethrum.

Other Chewing Insects:
Grasshoppers, locusts, earwigs, beetles and their larvae can attack palms at certain times of the year. They can be controlled with an insecticide such as carbaryl or other types depending on the type of insect and the country. Snails and slugs will attack some species of palms, particularly Chamaedorea species , moving up the stems to feed on the leaves. They can be physically removed or prevented by the use of metaldehyde or methiocarb pellets.

Borers And Termites:
These insects are known to cause damage to palms and cycads. Borers can bore holes in the trunks of palms causing visible damage but do not threaten palms particularly if they are healthy. Termites can cause major damage to palms, attacking from below the ground and are difficult to control In areas where they are prevalent, prevention by destroying their nests is the best means before they affect a plant They will also invade cycads that are unhealthy, attacking the roots and trunks. Slaters behave similarly, attacking unhealthy cycads, feeding on their stems and any rot that may have developed.

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