HIBISCUS - Queen of the Flowers
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CHAPTERS EIGHT & NINE
Pests and Diseases of Hibiscus
by F.D. Hockings. Brisbane, Old. Aust.
Hibiscus are attacked by a number of pests and diseases. Some are not very important but others require treatment to prevent the leaves and flowers from being destroyed.
Correct diagnosis of problems is of utmost importance because fungicides are effective against fungal diseases only and pesticides are usually even more specific. Each pesticide is effective against only a particular class or group of pest. If you use the wrong chemical you are wasting your time and money and your plants will continue to be damaged.
Always carefully read the label on garden chemicals. Be aware of what the actual chemical is (the active ingredient) and not just the trade name. Carefully follow the recommended dilution rate stated on the label; too weak may not control the problem and too strong may harm the plants or you. Metricated measuring receptacles are inexpensive, so do not guess quantities. Addition of a non ionic wetting agent such as Agral or X77 will improve the effectiveness of sprays, but, of course, thorough coverage of both sides of leaves is the key to successful pest and disease control.
Spray materials should be mixed fresh for each spraying operation; do not use solutions that have been mixed overnight. If plants are drought affected or if the temperature at the time of spraying is too high (32°C or 90°F or higher) plants may be damaged by sprays. Water plants thoroughly a day or two before spraying and apply sprays in the early morning or late afternoon. Wettable powder forms of chemicals are safer for plants than emulsifiable concentrates and furthermore, two or three wettable powders may be mixed with relative safety. Malathion and Lannate sometimes cause injury to hibiscus plants. In general, plants that are grown in clean surroundings and are properly fertilized and regularly (but not too frequently) watered, are less likely to be attacked by diseases and pests.
Some caterpillars combine their chewing with leaf rolling or with the binding of leaves, shoots or buds with silken threads.
A number of fungal and viral diseases commonly infect hibiscus plants. In addition, physiological disorders also occur.
Leaf Spots. Several species of fungi may cause brown to black circular or irregular shaped spots on the leaves. Infected leaves should be removed and burnt and plants sprayed with a fungicide such as mancozeb (Dithane M45, Manzion, Manzate).
Sooty Mould. The black sooty substance that sometimes coats leaves and shoots is a fungal growth. It indicates the presence of sap sucking insects such as aphids or scales which excrete a sticky, sugary substance on which the fungus grows. Ants are often associated with sooty mould because they too are attracted to the sugar. Treatment involves eradication of the sap sucking insect followed by application of a fungicide such as mancozeb to kill the fungus.
Root Rots and Collar Rots. Several species of fungi may cause soft rotting of roots and sometimes also stems. Infected plants will often wilt as though they are short of water. In general, root rots are associated with over wet soil conditions brought about by overwatering or poor draining. Treatment involves watering less frequently and improvement of soil drainage as well as soil drenches with fungicides such as Terrazole (Terrazole WP) or Fongarid (Fongarid).
Plants infected with virus diseases may bear deformed or cupped leaves or leaves with mottle patterns. Infection may be carried by insects or on secateurs or by propagation of infected plants. Infected plants generally lack vigour. Leaf symptoms are more obvious at some times during the year than at other times. There is no cure or treatment.
These disorders resemble the symptoms caused by a disease but are not associated with infection by a fungus, bacteria or virus. Physiological disorders are the result of some unsuitable factor in the growing conditions such as over fertilizing, trace element deficiency, over or under watering, soil too acid or alkaline, position too hot or too shady, etc.
Bud Drop. This is one of the most common physiological disorders of hybrid hibiscus. The problem is more severe in some seasons than in others and some varieties are more severely and more regularly affected than others. Sometimes an improvement can be effected by shifting the plant to another part of the garden. If a variety is severely and continually affected by bud drop, it is better removed and replaced with another variety.
Spraying Safety Measures and Equipment
When spraying on a regular basis, it is advisable to cover every part of your body for self-protection. Cover-alls or overalls, boots or shoes, safety gloves, respirator, safety glasses are adequate protective apparel.
Do not smoke while handling poisons or spraying. Shower well after spraying, wash clothes separately from normal washing.
Obtain a poison and antidotes' list from your Department of Primary Industries. It's a must to have this on hand. Make sure your spraying equipment is in good working condition at all times, thoroughly washing after use so it is ready for its next use.
Do not use this spraying equipment for any weedicides at all, particularly herbicides containing hormone 24-D and 245-T. Have a separate unit for this as these herbicides particularly, have disastrous effects on hibiscus and other plants, causing malformed leaves and flowers. It will take your plant a long time to get over this type of damage which can sometimes cause the death of your plant or plants. Any slight drift can cause severe damage.
Never use White Oil sprays and fungicide sprays mixed together as this will have toxic effects.
Never use pre-mixed sprays from the day before.
It is desirable not to pour excess sprays down drains where they can be washed into creeks, streams and rivers. Burying this waste is one safe method of disposal.
Index | Chapter 1 | Ch 2 | Ch 3 | Ch 4 | Ch 5 | Ch 6 | Ch 7 | Ch 8 | Ch 9 | Ch 10 | Ch 11 | Ch 12 | Appendix
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