Plant Problems in the Keys

Learn about the effects of hurricanes and pests on plants in the Florida Keys.

Hurricanes and the Landscape

by Susan McGarry

Once a hurricane watch is announced, you’ll have a very lengthy “to do” list. Below are some hints to help you get a jumpstart on yard-related activities. Also presented are some tips for your use in the critical time after a hurricane based upon local storm recovery experience.

Pre-storm tasks include:

  • During the winter months, prune to prevent future hurricane damage by: 1) Thin branches to reduce wind resistance, and 2) Severely pruning back to major framework limbs to dramatically cut wind resistance and tree toppling.
  • Harvest all coconuts and dead palm tree leaves.
  • Dispose all clippings that would act as missiles in high winds.
  • Clear gutters of debris to allow free passage of rain water.
  • Move container plants, furniture, trashcans, and other equipment inside.

Then hope for the best, and rest up to prepare yourself for an extensive post-storm cleanup.

After the storm, you’ll want to employ “triage” techniques to rescue your yard. For example, damaged trees already declining in health should be taken out while defoliated trees should be saved, as most will resume growth with proper care.

For toppled trees and palms, exposed roots should be covered immediately with moist dirt, sphagnum moss, or burlap to prevent drying. Once reset at ground level, they should be held in position with stakes or guy wires. Then soil should be filled around the root area and watered in to eliminate air pockets. Reset trees should be watered twice a week and then less frequently as they become reestablished. DO NOT FERTILIZE for two months, as it may injure the tree.

For single stemmed palms, bent, splintered or severed trunk damage cannot be repaired so the palm should be removed. Broken stems of clustering or clumping palms should be removed as close as possible to the base to allow fill in with new growth.

For trees split at a crotch, remove the smaller branch if damage is severe, or ask a certified arborist for help in saving both branches. Meanwhile, support and stabilize the split.

Foliage plants and shrubs should be pruned of broken branches, and some species can be cut to the ground to induce re-sprouting.

If the landscape was flooded with saltwater, all plant parts should be washed with clean water to remove salt and silt (provided there are no restrictions on water use). Rake silt away from the plant while still wet, and then apply three inches of mulch around the plant. (Silt will eventually harden, preventing air movement.)

For lawn grass, all leaves, silt, mud and debris should be removed to allow essential light penetration and airflow. Grass should recover and resume growth if the length of the flooding was less than 36 hours. If flooding lasted for a longer period, water must be drained from the area or the vegetation will die. In this case, trenches can be dug to encourage water movement to lower land areas.

Remember that plants damaged by a hurricane or tropical storm will be more susceptible to other problems and will need your TLC throughout the next year, including extra watering and mulching during drought periods.

Pests and Least Toxic Pest Control

by Edward Bouton & Katie Davis

Major pest problems include weeds, insects, nematodes, and diseases caused by fungi, bacteria, viruses, and phytoplasmas. Most problems can be controlled using least toxic pesticides if you understand the life cycle and/or growth habit of the pest. Highly toxic and persistent hard chemicals should be avoided because they can harm humans, pets, and wildlife.

The first step in pest control is to grow healthy plants adapted to the area. Plants native to the Keys have adapted to the environment and are more resistant to disease and insect attacks. Also, water and fertilizer need to be tailored to the particular plant, but in general, improper watering, improper fertilizing, improper pruning, and mowing grass too short are the greatest contributors to poor plant health.

The second step in pest control is to monitor plants. Walking around the yard twice per week allows for early detection of plant problems. Keep in mind that for successful gardening you do not need to kill all the pests, just control them. Also, the well-informed gardeners remember that correctly identifying the problem will make fixing it much, much easier! Many plant problems are not caused by diseases or insects, but by poor growing practices or environmental conditions.

The third step in pest control is to decide what to do when there is a problem. Whenever using a chemical on plants, read the label for the following: 1) check that the chemical will control your problem, 2) check that the chemical can be applied to your specific plant, and 3) understand and follow the directions carefully. Least toxic pest control practices for plant pests are listed below.

Weeds

Weeds can be pulled or held down by excluding light. Organic mulch, not counting its other benefits is ideal when applied thickly. Also, spot treat weeds with herbicide when necessary, rather than spraying large areas with herbicide.

Disease

Use disease resistant plant varieties when available. Avoid long wet periods by watering in the morning. Learn to identify the disease and prune out the infected parts. Copper sprays can help many fungus and bacterial diseases. Viral diseases cannot be cured with chemicals.

Nematodes

Choose plants resistant to the most common (root knot) nematode. Sterilize garden soil with soil solarization, using clear plastic during the hot summer months.

Insects

Some of the most common insects of concern are aphids, mealybugs, scales, whiteflies, spider mites, chinch bugs, and chewing caterpillars. Some can be removed by hand. There are least toxic pesticides available that are effective for control. Insecticidal soap helps control aphids, whiteflies, spider mites (alternate with oil) and fleas. Horticultural oil helps control mealybugs, scale, thrips, whiteflies (alternate with soap), and spider mites (alternate with soap). Bacillus thuringinsis (BT), helps control destructive caterpillars, but remember that these may be the larvae of butterflies. Natural beneficial insects such as lady beetles (both adult and larvae), lacewing larvae, and parasitic wasps help control aphids, mealybugs, scale, and spider mites. Birds, stinkbugs, big eye bug, lizards, red eye fly, and earwigs help control caterpillar, mole crickets and chinch bugs. If beneficial insects are on the plant, they are doing the work for you!

Lethal Yellowing of Palms

by Susan McGarry

Lethal yellow (LY) is a disease that attacks and eventually kills coconut palms and many other palm species. By 1965 a Key West LY epidemic killed 65% of the island’s coconut palms. In the early 1980’s, South Florida lost an estimated 100,000 coconut palms and thousands of other palm species. Recently, LY has again been reported in the Keys, though its presence is less significant due to the use of numerous LY-resistant palms that have been made available.

LY symptoms appear in three stages: 1) pre­mature dropping of most or all coconuts at any stage of maturity, 2) darkening of the inflorescence to a blackish color, having a dry and gnarled appearance, and 3) yellowing or browning of fronds, beginning with the older and advancing to the young ones of the crown. The final stage is death of the bud, which causes the youngest unfolded leaf (spear) to collapse. This whole process takes about 3 to 6 months to occur.

The cause of LY is a phytoplasma not much larger than a virus. It is sensitive to tetracycline antibiotics, which when injected to trunks of palms in the early stages of LY, causes a remission of symptoms. However, the injection must be continued multiple times per year for the rest of the palm’s life. Over time palms will die due to the holes made for the antibiotic injection.

LY is spread by a planthopper and other insects when feeding on a susceptible palm. Over 30 palm species have been shown to be susceptible to LY. Reference lists are now available indicating susceptibly ratings of low, moderate or high for different palms.

How can you help control this disease? First, be aware that antibiotic treatments (described above) cannot cure the problem and must be repeated every 3-4 months to keep the disease under control. Second, since immature planthoppers develop on turf grasses popular in the Keys (such as St. Augustine), limiting grass areas can be a management tool in conjunction with other methods-- primarily the use of LY-resistant palms. Third, buy palms grown from certified seed only. Do not plant the nuts of resistant palms because they probably will not have the same resistance as the parent, since the pollen source is unknown.

Native palms are good choices for landscaping her since LY has not been reported in palms species native to Florida. Coconut palm cultivars that show resistance include the Panama or Pacific tall, the Malayan dwarf, and a hybrid of these called Maypan. Here are some exotic palms that are not known to contact LY: Alexandra, Carpentaria, Yellow Cane, Miniature Date, MacAuthur, Solitare, Royal, Mexican Washingtonia, Foxtail, and Queen.

Although LY continues to be a problem in the Keys, the risk of palms contracting the disease can be greatly reduced by planting only LY-resistance palm species.

Cycad Scale on Sagos

by Shelly Martin-Vegue

In 1996, Aulacasp yasumatsui, an armored scale specific to Cycad trees, especially the King and Queen Sagos, was discovered in South Miami. Within two years, the infestation had spread to Monroe County.

The white, oval-shaped insects are the size of a pencil point cause damage by sucking the juices from the plants. It secretes a white, very waxy coating that resembles powdered sugar and is usually found near the base of the leaves and on the trunk. In severe infestations, the entire leaf may be covered. When the plant begins to decline, the scales crowd to the leaf tips for wind dispersal to the neighboring trees.

Early treatment may prevent plant death. Begin by clipping off the most severely infected leaves. If the entire plant is covered, leave the top 1/3 of the leaves. To avoid spreading the infestation, throw clipped leaves in the garbage, not in your yard waste to be recycled.

Wash the plant with water using a garden hose. DO NOT BLAST WITH HIGH-PRESSURE WATER. This can damage the plant. After the plant dries, mix a fish- or petroleum- based horticulture oil as described by the manufacturer’s instructions and spray the plant to the point of run-off. Be especially diligent about spraying the undersides of the leaves. Spraying in the evening is recommended to avoid the heat and the sun of the day. Repeat the washing/spraying procedure once a week for five weeks.

The University of Florida/IFAS/Monroe County Extension Service has initiated a biological control program used throughout South Florida. The program involved releasing Coccobius fulvus, a beneficial parasitic wasp, which lays its eggs inside the body of the scale. The young wasp larvae then feed on the scale as they develop inside. You’ll know the wasp has laid its eggs if you find small holes, as if stuck by a strait pin, in the scales.

The beneficial wasp was released at 35 locations throughout the Keys. Over time, the population will build up, reducing the need for spraying. The horticultural and fish oils do not hurt the wasp. However, insecticides will. There are a few stronger pesticides available, but research shows that they are not as consistently effective as the oil.

The scale on Cycads is not easy to control. Spraying will need to be repeated occasionally throughout the year. Keep in mind that dead scale stays on the tree-they don’t disappear. You will know you have control when new leaves are scale free.

Citrus Canker

by Susan McGarry

The recent outbreak of citrus canker, a highly contagious bacterial plant disease, has prompted the establishment of quarantine areas in Miami-Dade, Collier, Hendry, Hillsborough, and Manatee Counties. To date, citrus canker has not been found in the Keys (as of July 2000). However, we should all be aware of it, take some precautionary measures, and stay on the look-out.

Citrus canker can infect limes, oranges, sour oranges, grapefruit, tangerines and lemons. There is no human health risk from citrus canker. There are many diseases that infect citrus, so proper disease identification is essential. The Division of Plant Industry, which is part of the Florida Department of Agriculture and Consumer Services, sends survey crews to infected trees for free. To request a visit to your tree, call (305) 275-1900.

Look for brown, raised lesions surrounded by an oily, water-soaked margin and a yellow ring or “halo.” Symptoms can be seen on leaves, stems and fruit. Old lesions may drop off, leaving a shot-hole appearance. Citrus canker also causes weakened trees to be vulnerable to other, often fatal diseases and pests. In severe causes, leaves will drop, branches will die back, and immature fruit will drop.

Citrus Canker can spread to Monroe County in several ways. Wind-driven rain, birds, and animals are vectors that we cannot control. However, people can spread canker by carrying the bacteria on their hands or clothing, using contaminated equipment, or moving infected trees, plant parts and fruit. It would be wise to postpone buying citrus trees from the mainland. Let’s all practice “safe citrus gardening” and cross our fingers that this devastating disease does not travel south to the Keys!

There is no chemical cure for canker that will kill the bacteria in leaf tissue. This is the reason the state Department of Agriculture and Consumer Services Division of Plant Industry, along with the U.S. Department of Agriculture has launched a tough citrus canker eradication program. Scientific studies show that citrus trees within 1900 feet of an infected tree are highly likely to contract the disease, and that infected trees may not show symptoms for 90 days or more. Therefore, it is necessary to remove all citrus trees within 1900 feet of an infected tree in order to stop the spread of the disease. This applies to homeowners as well as commercial growers.

For more information about the Citrus Eradication Program, call (800) 850-3781 or visit the Citrus Canker web site.