August 11, 2008

Timely Gardening Tips for Midsummer

Andy Wilson, Departmental Training Specialist/Horticulturist

Twig Borers- A common and often alarming sight to homeowners is the appearance of dead branch tips, about one to three feet long on trees such as oaks, red maples, magnolias and others at this time of year. Close inspection of branch at about the point where the dead wood begins sometimes reveals a clue to the problem: a small round hole about the diameter of a pin. This is evidence of twig borers. These small beetles bore into the twigs or smaller branches to feed and reproduce. The beetles introduce a fungus commonly called ambrosial fungus which grows inside the twig and on which the beetles feed. They also feed on some of the tissues of the twig or branch itself. The fungus and the feeding damage cause the twig to wilt and die. Fortunately, the damage is usually not life threatening to healthy, established trees. Where possible, prune out the dead or dying branches back to healthy wood. When small dying branches appear without any evidence to twig borers, other possible causes, including root rots and fungal dieback diseases, may need to be investigated.

Gray Leaf Spot of St. Augustinegrass- One of the most common diseases of St. Augustinegrass during the summer months is gray leaf spot. As the name implies, the most visible symptom of the disease is the appearance spots on the grass blades, initially olive-green to brown, later growing in size and becoming tan to brown with dark brown margins. When many spots develop on a single blade it may wither and die. The grass may appear thin due to this damage. Conditions that encourage the development of gray leaf spot include warm temperatures, frequent rainfall or irrigation, applications of quickly available nitrogen and compacted soils. St. Augustinegrass that has been treated with atrazine herbicide is more likely to be attacked by gray leaf spot.

To manage gray leaf spot, don’t provide the conditions, as mentioned above, that favor it. Avoid applications of quickly available nitrogen. Keep in mind that often in the summer the less green than normal color of an otherwise healthy lawn can often be improved by applying iron. One way to supply iron is by spraying a solution of iron sulfate (2 ounces in 3 to 5 gallons of water per 1000 square feet of lawn area). Chelated iron (applied at the label rate) is another option. For serious outbreaks of gray leaf spot it may necessary to apply a fungicide. Products containing azoxystrobin, propiconazole, thiophanate methyl or trifloxystrobin are usually effective against this disease. More information on gray leaf spot can be found here:

Summer Care of Christmas Cactus- Christmas cactus is one of the most rewarding cacti to grow, producing beautiful flowers at the ends of pendant stems usually sometime between Thanksgiving and Easter. They can be grown outdoors in pots or hanging baskets in our climate most of the year. However, these cacti are susceptible to root and stem rot diseases if they are over-watered and during the summer rainy season it is a good idea to either move them to an area with overhead protection from the rain or to remove the saucers from the pots so that water does not stand in them and keep the soil waterlogged.

Drought Tolerant Bedding Plants- For summer color that is also drought tolerant consider these:

Globe amaranth produces round, clover-like flower heads that feel like crepe paper. Purple is the most common color but there are also varieties with red, pink or white flowers. Height varies from about one to 2 feet depending on the variety. Glove amaranth prefers full sun and is nematode tolerant.

Purslane is low growing with fleshy stems and small fleshy leaves. It produces showy single or double flowers in a range of colors from white and pastel pinks to sunny yellows to intense oranges, reds, maroons and other colors. It blooms best in full sun and thrives on heat. It is easy to propagate from cuttings. The flowers usually close during the intense heat of mid-afternoon. Barring a significant freeze event during the winter, purslane will often live over for more than one year.

Moss rose or portulaca is a close relative of purslane. It has long, cylindrical leaves but flowers that are similar to those of purslane in shape and in color range. Like purslane, the flowers usually close in the afternoon.

Vinca or periwinkle is a traditional favorite for summer planting in Florida. Breeding work in recent years has broadened the flower color range available and has improved the growth habit with some smaller, fuller branching varieties. Vinca does best in full sun. It can be prone to root and stem rots and fungal blights if overwatered or if planted in poorly drained soil.

More information on bedding plants can be found here:

Trees and Potential Storm Damage- If you are concerned about the health of trees in your landscape and about the possible susceptibility to storm damage it’s a good idea to consult a certified arborist. To obtain this certification an arborist must pass an exam to demonstrate their knowledge of trees and tree care practices. The arborist certification program is conducted by the International Society of Arboriculture (ISA) and the organization’s website includes a search engine that can be used to find certified arborists by city or zip code:

Snowbush Spanworms- Snowbush spanworms have become a fairly common sight on snowbush plants (Breynia disticha) in our area. The small caterpillars are colorful with black markings on a yellow background. They feed on the leaves, sometimes completely defoliating the plants. Usually the plants will regrow following this damage. If populations of the caterpillars are high and food is limited they may even feed on the twigs and bark. There have been some reports of snowbushes being killed by this more serious damage. Sprays of products containing spinosad or Bt (Bacillus thuringiensis) will usually control them.

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