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Spotlight on leaf spot diseases

by Theresa Friday

Plant diseases can significantly affect the aesthetic quality of many plants in the landscape. Interestingly, the weather greatly influences disease development on plants. When environmental factors favor the host plant, disease is unlikely. When environmental factors favor the pathogen, diseases are more likely to occur. High moisture and wind are two factors that favor the spread of plant pathogens and the incidents of diseases.

Foliar diseases were almost nonexistent during 2007 in the Florida Panhandle, because of the drought. But, the rainy spring of 2009 has increased the occurrence of several foliar diseases including oak leaf blister and Entomosporium leaf spot on Indian hawthorn. While these diseases are common problems, they appear to be wide spread this year.

Oak leaf blister is a common leaf disease among oaks in Florida and is caused by a fungus. Although infected trees may have unsightly leaves, serious damage is uncommon. The fungus which causes leaf blister attacks only the leaves, and does no damage to other parts of the tree. Spores of the pathogen infect young oak leaves. As the pathogen develops within the leaf, it causes a disruption of normal development of the leaf cells. The infected tissues appear swollen and lighter in color. Severe infections can cause the leaf to curl or twist. Over time the infected tissues die, leaving gray-brown areas scattered within the given leaf.

Leaf blisters first appear on the underside of leaves as small, slightly depressed gray areas. Over time the infection causes the leaf to become deformed, forming a blister. The blisters can grow to be 1/3 inch or larger and can be seen on both sides of the leaf. There may be several blisters on a leaf.  If blisters occur near the edge, leaf curl may result. Oak leaf blister is not usually noticed until many leaves have become heavily blistered or excessive leaf fall occurs. Any oak can be infected; however, live oak, water oak, and laurel oak are the preferred hosts.

Because oak leaf blister does not seriously affect the overall health of the tree, chemical control measures are usually not recommended. Just be sure to collect and dispose of the leaves as they drop to reduce the chance of the disease the following spring.

Entomosporium leaf spot is a common fungal disease on Indian hawthorn. Dark leaf spots with purple borders occur, causing distortion of new growth. The centers of older spots are often grey and may disintegrate. Infected leaves may drop from the plant.

New growth flushes are most susceptible. The optimum temperature for disease development is between 59 and 77 degrees F. Nine to 12 hours of leaf wetness or high humidity is required for new infections to develop.

To reduce the severity of the disease, avoid overhead irrigation, especially in the evening or night. Avoid tight plant spacing, which limits air circulation. Maintain a low fertility level to reduce new growth and pick up and dispose of infected leaves.

Fungicides may be necessary for disease management, rotating systemic and protectant type fungicides. Some recommended fungicides include chlorothalonil (Ortho® Max™ Garden Disease Control), myclobutanil (Spectricide® Immunox Multi-Purpose Fungicide) and thiophanate-methyl (Green Light Systemic Fungicide).

The best thing to do is avoid the problem by planting resistant cultivars. Resistant cultivars include: Olivia, Indian Princess, Janice, Eleanor Tabor and Dwarf Yedda. Moderately resistant cultivars include: Jack Evans, Snow White, Majestic Beauty, Rosalinda, Clara and Bay Breeze. Since it is often difficult to distinguish between cultivars, make sure you buy them from a reputable dealer that labels all cultivars clearly.

Spice up your landscape with ornamental peppers

by Theresa Friday

Looking for a hot landscape plant?  Try ornamental pepper.  Ornamental peppers are compact plants, reaching ten to twenty inches in height. Their size, interesting foliage, and attractive fruit make them ideal plants for a container garden or at the front of a border.  You can also use them as a groundcover.

Ornamental peppers produce colorful fruits from late spring through fall. The fruits come in a range of colors including red, purple, yellow, and orange. Many varieties also have interesting and attractive foliage, including variegated forms.

You can plant ornamental peppers several times during the year. Many people plant in mid-spring and enjoy the colorful foliage and fruit all the way through the fall until the first killing frost. It is also popular, and widely accepted, to plant ornamental peppers in mid- to late summer (July - September) for a nice color addition to the fall landscape.

These plants are easy to maintain.  They do best in full sun.  Soil pH is not critical, but slightly acid conditions (5.5-6.0) are most preferable. Chose a spot with well drained soil and irrigate during dry spells. Space plants according to the mature size for the variety chosen.  When planting in the spring, fertilize at planting and again at a half rate in early to mid-summer. When planting in mid- or late summer, a fertilization at planting will normally last through the fall.

A few of my favorite varieties include Chilly Chili (an All-America Selection in 2002), Medusa and Black Pearl. There are, however, many new and exciting varieties to try.

Chilly Chili is a compact ornamental pepper that produces a heavy load of mild, two-inch long, erect chilies. The chilies start green, and then change through chartreuse and orange on their way to a deep, waxy red. Because the plant is indeterminate in its growth habit, it has fruit in all stages of development and gives a handsome blend of colors throughout the summer and fall. The indeterminate growth habit means that plants will have fruit on display from July until frost, with the plant gaining beauty as the season progresses.

Medusa is a consistent performer and unique with the 'snaky Medusa hairdo' peppers in colors ranging and changing from ivory to yellow to orange to bright red. I've had this pepper return each year in my garden from seed that fell the previous season.

Black Pearl is famous for its deep purple, almost black leaves. The compact, upright plants bear distinctive semi-glossy, deep purple to black leaves, complemented with scores of shiny round black-purple "pearls" of fruit that mature to bright red. Like most peppers, it's edible, though VERY hot. This plant withstands high heat and humidity.

All ornamental peppers are very heat-tolerant and will make a great addition to the late-summer and fall landscape along the Gulf Coast.

Despite their name, many ornamental peppers are edible and tasty. But many are very spicy and very hot. People without a sturdy palate will enjoy just looking at them. Medusa and Chilly Chili bear non-burning, "child-safe" fruit, making them ideal for indoor and outdoor use in both public and residential areas once thought unsuitable for the traditional "too-hot-to-handle" ornamental peppers.

Using ground covers in the landscape

by Theresa Friday    

Ground covers are low-growing plants used to cover an area in the landscape. Typically, they are perennial, evergreen plants with sprawling or spreading habits. They generally are 1 foot or shorter, but taller plants are used occasionally.

In addition to the beauty they provide, ground covers have practical uses. They can guide traffic movement through a site. They lower the ground temperature and reduce glare. Some are effective in erosion control. They are especially useful in problem areas such as steep slopes, under low-branching trees and shrubs, places where large tree roots protrude and confined areas where mowing is difficult.

The most widely planted ground cover in today's landscape is turfgrass. While many people may avoid the use of turf as a ground cover, on the practical side, no other plant can withstand as much foot traffic as turf. Most of the time it succeeds in providing a suitable cover. Sometimes however, unsuitable growing conditions like too much shade, prevents its continued success. Other ground covers may provide solutions to a landscaping challenge or just add a bit of much needed texture and color.

Following are some tips to consider when adding ground covers to your landscape.

• Use low ground covers for a transition between the lawn area and taller plants in the garden bed. 
• Select ground covers based upon their ability to add year-round beauty to the landscape. Herbaceous ground covers die back to the ground in the winter, exposing bare soil. If this is not the look you want, choose evergreen ground covers. 
• Select ground covers, according to your site's conditions: Sun or shade? Clay soil or sand? Moist or dry? Select ground covers that will survive and thrive under your conditions and not require heroic measures to keep them alive! 
• Moss as a ground cover? Sure! While heavy, dense shade is often considered a curse, it is a blessing when it comes to moss. The color and texture of moss can add great interest. And, it's virtually maintenance free. 
• Consider the height of the ground cover. Will you choose a six-inch ajuga or a four-foot fern? 
• Before planting, always prepare the soil as you would for any other permanent type of planting. Remember, ground covers are capable of giving long lasting beauty and function, but their performance is only as good as the effort one puts into soil preparation. 
• Beware of ground covers that state, "Easy, rapid coverage in either sun, shade, wet or dry." They may be horticultural nightmares due to their aggressive nature. If you need fast coverage, closer planting of better behaved ground covers may be the better answer. 
• Ground covers are not the "bottom feeders" of the landscape. They add interest, and bring unity to the garden making them the unsung heroes among the more horticulturally prominent members of the garden.

There are many ground covers to choose from for North Florida growing conditions.  Some to consider are ajuga, perennial peanut, cast iron plant, holly fern, autumn fern, English ivy, shore juniper, creeping juniper, liriope, mondo grass and confederate jasmine.  For more information on ground covers, visit the Florida-Friendly Landscape website at http://www.floridayards.org/index.php or call your local Extension Office.

Generally, ground covers are established in two years, although some require slightly more or less time. During this period, a regular program of irrigation, fertilization and weed control insures strong, rapid growth. Mulch aids water retention in new plantings and helps the spread of ground covers that root along their stems. Once established, many ground covers need only an occasional trimming to keep them tidy and within their designated area.

Invite butterflies to your garden

by Theresa Friday

     A butterfly garden is an easy way to see more butterflies and to contribute toward their conservation.  Conservation efforts are important since many natural butterfly habitats have been lost to urbanization and other development.

    To begin, select a site for your butterfly garden that will receive sun for most of the day. Although full sun is desirable for the garden, butterflies will benefit from having a windbreak nearby for those days with gusty winds. The same windbreak can provide shade on those very hot days in north Florida. If the windbreak includes shrubs, the butterflies may also use the plants as a roosting area at night.

     Once a sunny location is selected and before planting, take a soil sample. Contact your local Cooperative Extension Office for soil testing information.  Apply lime and fertilizer according to the recommendations from the soil test. Keep in mind that once established it will be difficult to improve the soil in the butterfly garden, particularly if perennial plants are involved.

     When choosing a site for your butterfly garden remember to place it close to a water supply so that the plants in the garden can be watered if necessary.

     Be sure to plant both host plants and nectar plants.  Host plants are those where the adult butterfly lays her eggs and the caterpillar will feed.  Several good host plants include milkweed for the monarch butterfly, passionvine for the gulf fritillary, cassia for the cloudless sulphur, wild lime for the giant swallowtail and pawpaw for the zebra swallowtail.

       Nectar plants are also needed in the butterfly garden.  These plants provide the food for the adult butterflies.  Several good nectar plants include zinnias, goldenrod, butterfly bush, plumbago, verbena, firebush, pentas and porterweed.

     Remember to add an artificial puddle or two. Several species of butterflies are attracted to free-standing puddles. They not only benefit from a drink but also utilize salts and breakdown products of decaying vegetation which is present in most puddles.

     To keep your puddles from becoming a source of mosquitoes, bury a shallow potted plant saucer to its rim in an area receiving full sun in the butterfly garden. Fill the saucer with coarse pine bark or stones and fill to overflowing with water. The butterflies are able to drink from the cracks between the pine bark pieces or the stones while the mosquito larvae have a difficult time becoming established. Occasionally adding a small piece of over-ripe fruit, some stale beer, or a tablespoonful of composted cow manure or leaf compost to the puddle will provide the salts and amino acids that the butterflies need.

     To keep the plants in your butterfly garden productive, scatter a slow release fertilizer two to three times during the summer. Do not over fertilize. Excessive nitrogen may reduce flowering.

     Avoid the use of broad-spectrum pesticides. Alternatives are oils, soaps and microbial insecticides. But keep in mind that oils and insecticidal soaps can kill caterpillars if sprayed directly on them. A good side effect of decreased pesticide use is the increase of natural enemies.

Theresa Friday is the Residential Horticulture Extension Agent for Santa Rosa County.  The use of trade names, if used in this article, is solely for the purpose of providing specific information. It is not a guarantee, warranty, or endorsement of the product name(s) and does not signify that they are approved to the exclusion of others.

For additional information about all of the county extension services and other articles of interest go to: http://santarosa.ifas.ufl.edu.