Wednesday, October 19, 2016

Downy mildew on viburnum - a disturbing mess

'Awabuki' viburnum is a favored ornamental hedge or shrub noted for its large shiny green leaves useful for screens and formal hedges.  The last few years have seen a new disease organism move into our area and infect these beautiful landscape plants.  The disease known as downy mildew on viburnum, a species specific water mold disease, can make a disturbing mess of these plants.  There are some management techniques for the home landscape that can help lessen the damage.

The 'Awabuki' viburnum is really different than any other viburnum with very large glistening, almost mirror-like leaves.  Homeowners often use 'Awabuki' as a screen around pools or just as an impressive tall hedge.  Downy mildew is a water mold organism that develops when nighttime temperatures range from fifty to seventy-two degrees F.  Mostly occurring from November to March, this downy mildew needs a cool, foggy and humid environment, typical of some nights in our area, to develop.  Most of the damage appears on the newest leaves with yellow specks and reddish brown blotches – almost a bronze appearance on the leaf surface.   On the underside of the leaf, you will notice whitish-grey downy growths.  Soon after, the leaves will often drop with some portions of the plant becoming defoliated – near eighty percent defoliation in severe cases.  The disease can spread rapidly and can be moved about with rain, wind and irrigation.

While you have no control on environmental conditions like high humidity and cool temperatures, you can reduce overcrowding of plants so that there is good air movement.  Remove the fallen leaves which can re-infest plants next year.  Do not provide overhead watering if at all possible – micro-irrigation at the soil level is more efficient and does not wet the leaves.  Do not water at night.  Also, do not over-fertilize as this makes the leaves much more succulent and open to infection.

Chemical treatments can be made with the use of fungicides, but work best when used as a preventative.  Rotating chemical families will help reduce the possibility of fungicide resistance – a real problem if one type of fungicide is used all the time.  Fungicides to use would include copper octanoate, chlorithalonil, and extracts of neem oil, as examples.  Always read the pesticide label as the label is the law.

The 'Awabuki' viburnum is worth protecting from downy mildew.  A bit of cultural practices, possibly augmented with some properly timed fungicides, can help reduce this disfiguring disease.  For more information on the suppression of all types of fungal disease in our area, 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 -

Palmateer, A. J. (2016) Viburnum Downy Mildew.  The University of Florida Extension Service, IFAS.
Caldwell, D. (2011) Viburnum Downy Mildew Disease on Awabuki (Mirror leaf) Viburnum.  The University of Florida Extension Service, IFAS – Collier County

Monday, October 17, 2016

Africanized honeybees are in Charlotte County

Africanized honeybees have been in Charlotte County for years and a recent rash of calls to our office for information have spurred me to write about them again. Domesticated European honeybees are present in commercial beehives that pollinate our crops, visit our flower beds and make our honey. Unfortunately, almost all feral (wild) hives in our area are now probably Africanized. Living and working safely among these bees is something that everybody needs to understand.

Knowing the difference in the behavior and habits of these visually indistinguishable types of bees is critical. At a glance, both the European honeybee and the Africanized honeybee look the same. However, when we examine the behavior of these two, there are some stark differences. The domesticated European honeybees for example are relatively “gentle” due to years of breeding by beekeepers. They will still defend their hive if an invader comes within 20 feet, but will only send out ten to twenty guard bees to potentially sting an invader.  They remain upset for one to two hours only. Europeans will chase you for only about 30 yards before breaking off the attack. On the other hand, Africanized honeybees may send out hundreds of guard bees to attack an invader as close as 40 yards away. An Africanized hive is capable of stinging up to 10 times more than Europeans and remains defensive for several days. Keep in mind that Africanized honeybees can chase you for up to 300 yards! All honeybees can only sting once. Africanized honeybee stings are not more toxic than Europeans; they simply are more aggressive increasing the chance of more individual stings. European honeybees are also known to only swarm one or two times a year. Swarming is a process when a hive divides and splits off to form a new hive elsewhere. European swarms are large and they rarely all leave the hive, just a portion. Africanized honeybees can swarm 10 or more times a year.  Their swarms are smaller (the size of a softball) and are known to abscond which means that they abandon their original hive and relocate the whole colony to a new site.

European and Africanized honeybees also have different nesting site preferences. Europeans make large hives comparable to 10 gallons in size. Europeans also prefer nest cavities well above ground in a clean and dry location. On the other hand, Africanized honeybee hives are much smaller - around two gallons in volume. They are known to select underground sites such as water meter and valve boxes. Other sites may include abandoned tires, stored building materials, birdhouses and debris. Their nests may also be completely exposed hanging from a tree branch. If you discover a feral Africanized honeybee hive on your property, never try to control it yourself! Not only could you get seriously injured, but neighbors and passersby may also be attacked by a disturbed hive. Studies have shown that wasp and hornet sprays actually magnify the honeybee’s aggression and intensifies the attack. Have them removed or eradicated professionally by a Registered Beekeeper or a Certified Pest Control Operator who has had been trained in African honeybee control – please see this link for a list assembled by FDACS - . If you accidentally disturb an Africanized honeybees hive, run! Get into your car or house. Don’t try to elude them by jumping into water as they will wait for you.

Keeping things in perspective, honeybees are crucial pollinators and honey producers  that benefit us all and need our protection. However, Africanized honeybees are aggressively dangerous and that deserves our respect and awareness. Just like any potentially dangerous wildlife whether it is a venomous snake or spider, knowing the characteristics of Africanized honeybees and how to deal with them will pay off with a safer community environment.   For more information on insects of all types, 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 -

O’Malley, M. K.,  Ellis, J. D. & Zettel Nalen, C. M. (2015) The Differences between European and African Honeybees, The University of Florida Extension Service, IFAS.
O'Malley, M.K. & Ellis, J.D. (2014) - Living with African Bees in Florida's Outdoor. The University of Florida Extension Service, IFAS.