Hibiscus Pests and Diseases
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Pests and Diseases
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The prevalent Pests and Diseases for hibiscus growers vary from place to place around the world. This justifies the various quarantine laws in the different countries.
Treatment varies too as different governments authorize chemicals for use in their areas.
I'll attempt to list as many problems as possible with suggested solutions, treatments you will need to check with your appropriate authority. Some will be the safer organic alternatives where possible. Always remember to read and follow the directions supplied with chemicals, and particularly the advice on protective clothing, goggles, etc.
Oh yes, and there's always the two brick treatment - one red and one blue. Put the bug on the blue brick and hit it with the red brick! Most treatments won't be quite so elementary.
If you have a pest or disease not listed, email me the details for adding to this section. Supply the appropriate treatment too if known. Any queries, with pictures where available, should also be emailed to me. Here is an old Pests page I made some time ago. Here too is a hurriedly re-located Erinose Mite article.
I recommend the hibiscus mail lists where a response to any query can often be obtained from someone in your own locality.
The identification of most pests and diseases can also be obtained at Chris Noble's Bug Identification site.
|THE GOOD GUYS
Beware: there are many beneficial insects, etc. in your garden. I have lots of little green frogs and the work of he Assassin Bug, the Praying Mantis, the Spider and the Lady Beetle amaze me as they (and their progeny in many cases) consume the pests.
Unfortunately, the build-up of bad guys just forces me to use chemicals from time to time and I know I deplete the good guys when I do that.
Carbaryl was always a good spray for caterpillars and hoppers and most beetles. Chlorpyrifos is now my spray of choice, mainly because, for the time being, it gets those pesky pollen beetles which now seem to be resistant to sprays like Folimat which used to control "everything" until the resistant few bred up into the hordes we see today.
For those with a manageable number of hibiscus, it is better to pick off your old flowers and dispose of them in a bin bag. This breaks the beetle breeding cycle where the young feed in the mushy old flower, then bore into the ground to pupate and later emerge as beetles to repeat the process. White containers with just a little water and a drop of detergent to break the surface tension also attract beetle to the trap where they sink and drown.
The monolepta beetles swarm in spring here attacking Tipuana and Cassia trees, shredding the flowers. They then drop to the hibiscus and turn flowers into lace and shred buds and young leaves. Chlorpyrifos or Carbaryl works wonders and creates a carpet of dead beetles under the bushes very quickly.
There is a problem with white oil on hibiscus leaves - that's why only one part in 200 is recommended as the leaves will otherwise damage in sunlight. Spraying early before 9 am or late after 3 pm also allows the oil effect to dissipate before the midday sun can cause damage.
The main reason for using oil is to dissolve waxy secretions that insects like scale use for protection so the insecticide can then do its work Home made white oil is now used much more. Canola oil, mixed with a little washing up detergent and shaken vigorously to emulsify it, is suitable.
Aphids and Mealy Bug: A sharp blast with a hose will remove most. The chemical, Imidacloprid (Confidor, here) is the spray of choice for good control. It may be necessary to treat the surrounds for ants as they manage the "herd" of suckers often moving them from place to place.
Bugs in general - I combine Confidor (imidacloprid) and Lorsban (chlorpyrifos) for good results.
White Fly - I had a nasty experience the first time I found this pest, brought home on some abutilons. Months later when I noticed the swarms of tiny insects, I bagged some and took to the local Department of Primary Industries office - and they were sent to their Brisbane based entomologist who just happened to be away for six weeks. On his return and recovering my sample from his freezer, he identified the white fly, but didn't know which one! He referred me to an Experimental Station supervisor who gave these instructions which worked - I've never had them since. I also used this to clear up huge infestations on other hibiscus properties.
The chemical is Imidacloprid (Confidor) used 3 times in seven days, every 3 days - to break the breeding cycle. You need a very weak white oil solution as well - and this acts as a spreader and also sticks the pests to the leaf - which must be sprayed fully, front and back, over the whole plant.
The oil mix I used effectively was 250 mL of Canola Oil and 150 mL of concentrated washing up detergent. This I put in a litre Coke bottle, added water, little by little, shaking in between to emulsify (aerate) the mixture. After the froth settled, I made this up to the litre and used 250 mL per 100 L of my spray tank (effectively 100 mL of the actual white oil to 100 L spray pack - 1:1000, much less than the normal 1:200 recommended for scale insects).
For small quantities, that's about 6 mL ( a little over a teaspoon) of oil mixed with half a teaspoon of detergent in a bucket with Imidacloprid according to label directions. Of course, put the oil mix in a small shakeable container with a little water first. The white oil mix must always be mixed slowly with a little water and shaken, the rest of the water then being added - otherwise, the oil will just float on top.
In the U.S., I believe there are granular forms of Imidacloprid which are added to the potting soil and the chemical taken up by the roots, the white fly being dosed systemically when it sucks the sap. Correct me if that is incorrect.
Scale (in particular white louse scale or snow scale): This needs the oil and Confidor mix, but with a stronger oil concentration. Oil alone works for many scales. Spraying the stems with cooking oil (often Canola) aerosols is effective but must not be sprayed on the foliage. It won't kill the plant but will cause the leaves to die and recovery with new growth will take a while.
MITES: Red spider or two-spotted mite becomes a real pest after insecticide sprays in spring wipe out the good guys who are their predators. Those yellow leaf blotches with dark webbing patches at the back followed by a big leaf drop leaving many bare stems is a sure sign you are late getting to the problem. Me included.
As spring advances, there is a need for a spray for mite - the foliage must be covered front and back for an effective kill. Vertimec (abamectin) is the spray I use. Even that is supposed to be somewhat ineffective now as the resistant mites are believed to be breeding up in large numbers, Strawberry growers were forced to use a different chemical this year. However, my garden still responds to this spray.
FUNGAL Diseases include black spot, mildew, bottrytis and the like.
A spray with copper oxychloride, compatible with most insecticides, is an excellent preventative. Remember that a black spot appearance is common on many varieties in autumn as new growth starts and the spotted leaves are soon shed. It is not worth a panic. Bottrytis is most evident when buds get that greyed dead area on the side and then abort. Copper is usually effective but chemicals like Rovral (iprodione) are specifically recommended.
In damp wintry weather, the old flowers hang on and get mildew which spreads to the developing buds. Here's a case for removing old blooms - or starting a copper spray routine. I usually do a copper spray combined with my insecticide and fertilizer, during autumn. I generally ignore black spot as the plants grow out of it in spring. I don't believe that it is a true black spot disease but just a symptom of old leaves.
Here is an excellent article I found - great advice!
PESTICIDES AND HOW TO USE