Powdery Mildew of Cucumber

By Andy Wilson
Extension Specialist

Fall is a good time for vegetable gardening in Pinellas County and cucumbers are one of the many vegetables that can be grown now. Cucumbers are not difficult to grow but, as with other vegetable crops, some problems can occur. One of the most common disease problems of cucumbers is powdery mildew. We usually receive many samples of this disease during the fall through spring vegetable gardening seasons at our Lawn and Garden Help Desk.

Powdery mildew is one of the easier to diagnose diseases due to the distinctive white fungal growth it produces. This growth resembles a fine dusting of talcum powder over the leaves. Heavily infected leaves turn brown, shrivel and die.

Where possible, select cucumber varieties that are known to be resistant to powdery mildew. Also, keep the plants adequately fertilized. Cucumber plants that are suffering from nutrient deficiencies tend to be more vulnerable to attack by powdery mildew than healthy plants.

Among the fungicides that can be applied to cucumbers in the home garden to control powdery mildew are copper fungicides and neem oil. Neem oil may harm bees and other beneficial insects. Be sure to read and follow all label directions. For more information on disease control on cucumber see this fact sheet: http://edis.ifas.ufl.edu/PG046

Take-all Root Rot of St. Augustine lawn

In August and September we saw many Take-all Root Rot samples brought in to our Diagnostic Desk by frustrated homeowners. Periods of heavy rainfall and a stressed lawn trigger this disease which appears in summer and early fall.

Yellow and light green patches of St. Augustine lawn that eventually thin and die are the symptoms our walk-in customers described. Roots show the symptoms before the leaves do. By the time the leaves turn yellow, the disease has been destroying the roots for weeks or even months.

This disease is more easily prevented than controlled. Reducing stress on the lawn in the areas of mowing, fertilizing and herbicide applications is important. Proper watering, with a Rain Sensor Shutoff for sprinkler systems, helps in prevention.

There is no chemical control for Take-all Root Rot unless you are treating preventatively.
For more information, please see this University of Florida link: http://edis.ifas.ufl.edu/pdffiles/LH/LH07900.pdf

Hickory Horned Devil

This imposing larva (caterpillar), known as the hickory horned devil, is most often observed when it is full grown and comes down from the trees to wander in search of a site for pupation. It can beome as large as a hot dog.

This large caterpillar will eventually become the regal or royal walnut moth, one of our largest and most spectacular moths. Like most other moths, it is nocturnal but is sometimes observed around lights at night.
The regal moth typically has only a single generation per year. In Florida adults have been collected in May, but are more common during the summer.

The larvae live about 35 days and have been reported from a variety of host tree species. They are commonly found on species of the family (Juglandaceae) including walnut (Juglans nigra), butternut or white walnut (Juglans cinerea), and a variety of hickories (Carya spp.) including pecan. In Florida, larvae are frequently found on sweetgum (Liquidambar styraciflua). Other hosts commonly listed are persimmon (Diospyros virginiana) and sumacs (Rhus spp.).

In central Florida, larvae are usually found from late July to mid-August while they are wandering on the ground searching for a suitable location to burrow into the soil for pupation. The pupa is the overwintering stage.

The regal moth is a beautiful and fascinating member of our native fauna, and its larvae should NOT be killed. If a larva is found crawling on pavement or in an area of thick turf grass where it would have difficulty burrowing, it should be moved to an area of soft soil or a mulched area where it can burrow for pupation.

For more information see this website: http://entomology.ifas.ufl.edu/creatures/bfly/regal_moth.htm

Cicada Killer

This giant ground wasp, the Cicada Killer, hunts cicadas as a food source for their young. This giant wasp can dig a 4-foot burrow in the ground with several branches and cells. One to four cicadas are placed in each cell for the larvae to eat.

The female paralyzes the host (cicada) by stinging it, then carries the cicada by dragging or flying to the nest. One egg is placed on the last cicada in each nest.

Cicada killers are usually considered beneficial insects since they destroy plant feeding cicadas. Also, they rarely sting except when the females are handled. However, under certain circumstances such as when elderly persons or young children are present in the breeding areas one may want to discourage their presence. This can be done by eliminating or reducing the breeding area which usually consists of exposed, sandy soil. This area can be mulched or covered with grass. Labeled insecticides can be applied to the nesting sites to kill the wasps.

For more information see this site: http://www.entnemdept.ufl.edu/creatures/beneficial/cicada_killers.htm

New Weevil In Town

A new exotic insect has recently been seen in the landscape and brought into our Horticulture Help Desk for identification. This is a new exotic invasive weevil called the Sri Lanka weevil. It does leaf and root damage to several fruit trees, palms, ornamental plants and citrus.

There are no pesticides registered for homeowners to use on fruit trees. For landscape trees, severe infestations can be controlled using insecticides which include carbaryl (Sevin), acephate (Orthene) or a pyrethroid labeled for leaf-feeding insects.

They can be removed from ornamental or fruit trees by holding an open, inverted umbrella under a branch and shaking it vigorously to knock the weevils into the umbrella. The weevils can then be dumped into a bucket of soapy water and they will drown.

For more information see this University of Florida publication: http://trec.ifas.ufl.edu/mannion/pdfs/SriLankaWeevil.pdf or google: Sri Lanka Weevil IFAS.

This notching of the leaf edge is typical damage caused by this pest. Be aware that other types of insect pests can cause similar damage. Many times this damage is cosmetic and the plant recovers. Small plants and young trees may need protection.