Bud drop and other hibiscus horror stories

By Ralph E. Mitchell

A landscape without a hibiscus is like a day without a sunrise!  These beautiful, well-developed flowering shrubs are readily available and in great demand across the gardening spectrum.  Hibiscus have their share of problems – nutrient deficiencies, mealy bugs, thrips, nematodes, etc.  But perhaps one of the most vexing newer problems is bud drop.  This can be caused by several factors including tiny insects.  What is the scoop on hibiscus bud drop?

I have seen numerous simple reasons for hibiscus bud drop such as too much nitrogen applied.  Too much nitrogen can spur leaf growth and cause unopened buds to drop.  Nematodes – those microscopic worms that are plant parasites – can infest hibiscus roots and cause buds to drop as well.  Too much or too little water and high (alkaline) soil pH can also trigger this problem.  Excessive heat can cause buds to abort as well.  Actually, some types of hibiscus, especially double-flowering types, are known to drop buds more than single-flowering types.

When you have eliminated all of the above factors, it could be a one of two insect pests – a hibiscus bud midge and one of several  tiny caterpillars.  The midge is a tiny fly that lays eggs in the developing hibiscus bud .  This tiny insect was first detected in Florida in 1992 attacking certain orchid buds.  By the late 1990’s this pest was found in hibiscus buds.  Mature bud midge larvae (maggots) are only one-twelve  of an inch long, but are visible to the naked eye inside a dissected bud.  The feeding damage they cause makes the bud drop off before opening.  As these midge larvae are safely inside the bud, chemical control measures are difficult.  A systemic insecticide such as imidacloprid could be tried for suppression of this pest.  Perhaps the best cultural practice is removal and destruction of fallen buds to decrease the population of midges.  This plant sanitation practice does help.

Another problem insect is a group of unspecified tiny caterpillars that feed inside the developing bud.  Their activities also cause premature bud drop and management can be the same as is recommended for bud midges.

Hibiscus are beautiful horticultural treasures worthy of our time and effort.  They can be troubled from time to time with pest issues.  To know the pest and/or properly identify the problem, is the beginning of finding a solution.  Take heart, bud drop on hibiscus can be suppressed with proper management techniques.  For more information on all types of plant pest controls, please call our Master Gardener volunteers on the Plant Lifeline on Mondays, Wednesdays and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer.  Don’t forget to visit our other County Plant Clinics in the area.  Please check this link for a complete list of site locations, dates and times – http://charlotte.ifas.ufl.edu/horticulture/Plant%20Clinics%20Schedule.pdf .

(Photos by Paul Schumaker)

Resources:
Caldwell, D. (2017) Hibiscus Buds Dropping? The University of Florida Extension Service, IFAS – Collier County.
Mannion, C., Hunsberger, A., Gabel, K., Buss, E. & Buss, L. (2006) Hibiscus Bud Midge – Contarinia maculipennis. The University of Florida Extension Service, IFAS – TREC.
Osborne, L.S., Duke, E.R., Weissling, T.J. , Pena J.E. & Armstrong, D.W. (2015) A Serious New Pest is Causing Significant Problems for Dendrobium and Hibiscus Growers . The University of Florida Extension Service, IFAS – MREC.
Lamb, P. (2008) My hibiscus is dropping buds. The University of Florida Extension Service, IFAS – Duval County.

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