Plant Doctor Archive

Bugs on Hibiscus

Would you please help regards advice on bugs on hibiscus. Last year they chewed at the flowers and I have been told be very careful what you spray hibiscus with.

As you have not described the bug that is eating your plant, I will attempt to give you a general rundown of hibiscus pests, some of which are worse than others. Caterpillars, for example, will eat the leaves of the hibiscus plant, but their damage is mostly aesthetic. Simply pick them off and destroy them.

Other pests include beetles, which can also be picked off (except for the bronze beetle which is a quick mover), snails and slugs, which like the new leaves of mainly young hibiscus, and katydids and grasshoppers.

Katydids devour buds, leaves and flowers, but they are not often seen because they are nocturnal insects. During the day they hide out in long grass, so remove any overgrown grass that may be growing nearby.

Stick insects, whilst usually harmless to hibiscus, will lay their eggs on the plant. The eggs drop to the ground and nymphs emerge in spring. The nymphs will climb the hibiscus and eat the soft, new leaves. To deter this, apply a ring of Vaseline around the base of the trunk. This will also stop ants in their tracks.

Sucking and rasping insects include aphids, scale, mealy bugs, thrips and spider mites. If you are unsure which pest it is you have, click on the following link to determine which bug is doing what.

Bug detection

If you have mealy bugs, apply a mix of one part water to one part methylated spirits directly onto the bugs using a paintbrush.

Thrips like dry conditions, so frequent watering or misting will deter them.

Natural sprays for hibiscus include pyrethrum, garlic and onion sprays. All are short-lived, however, so regular spraying is necessary.

Garlic spray
Roughly chop 200 g garlic and soak in half a cup of mineral oil for 24 hours. Mix 20 g of pure soap into a litre of water, add to the garlic mixture and mix well. Strain, then use one part garlic mixture to 10 parts water. This mixture can be stored in a cool, dark place for several months.

Onion spray
Pour half a litre of boiling water over 1 kg roughly chopped onions, strain, then use one part onion mixture to 20 parts water.

Some people swear by Jeyes Fluid (a type of disinfectant) as a general insecticide. Mix together 1 dessertspoon of Jeyes Fluid, 1 tsp dishwashing liquid, 1 tsp baking soda and 1 litre water.

Systemic chemical insecticides such as Malathion or Maldison can cause defoliation, so milder, non-toxic systemics, such as neem oil, are better.

Horticultural oil mixed with water may be your best spray, but do not apply when the sun is at its hottest or you could damage the leaves. Similar to horticultural oil is insecticide soap, which is also good.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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