The best disease prevention measure you can take with ornamental plants, fruits and vegetables is to start with healthy or disease-resistant plants. A common fungus referred to as plumeria rust is showing up on many garden plumeria now. Symptoms show up as a rusty appearance on the underside of leaves. This causes premature yellowing and dying of leaves.
According to University of Hawaii plant pathologists, once a plant becomes badly diseased, it is difficult to nurse it back to health. For this reason, every effort should be made to prevent introduction of disease-causing organisms on plant material or in soil. Many common plant diseases are caused by fungus organisms. Others are caused by virus and bacteria. Identifying the cause is vital to knowing the proper cure.
Plants in poor growth are usually more susceptible to these diseases. Good cultural and sanitation practices will help prevent trouble, such as removing diseased parts like leaves or branches as soon as they appear affected. Treat pruning wounds with a specially prepared material to stop entrance of wood decaying organisms and wood feeding insects.
For treatment of fungus diseased plants, fungicide applications should begin when disease development first appears and should continue as recommended by the manufacturer.
Other fungus organisms that cause disease on plants, people and even buildings are not diseases but are bothersome. Two types found throughout the tropical world, including Hawaii, are house mildew and green algae.
Mildew flourishes in damp places. Hawaii’s high humidity often creates conditions favorable to the growth of this unsightly problem.
UH home economists suggest where mildew is already established on walls, remove as much as possible by scrubbing the discolored surfaces with a strong detergent in warm water. The remaining mold spores should then be killed with a treatment of household bleach, applied at the rate of 1 pint per gallon of water. Of course, you should be sure the bleach you select will not seriously fade the paint. If the infected surfaces need repainting, then the use of a mildew-resistant paint is recommended or a standard paint to which a mildew inhibitor has been added. They also point out that paints that provide a hard surface will discourage the lodging of mold spores. For more advice concerning the control of mildew on painted surfaces, check with a paint dealer.
Algae commonly grow on the surface of soil that is moist for periods of time. This is very common during the rainy season. These minute green plants often develop in such profusion that it forms a rather thick, greenish to blackish mat. Growth of such magnitude in a turf planting is detrimental to the grass because algae actively competes with the grass for both space and nutrients. In addition, if the algae mat dries, it forms a crust that retards or prevents the movement of water into the soil. If this occurs, the grass is subjected to a moisture stress directly because of the presence of the algae.
The same conditions that favor the growth of algae also favor the growth of fungi that cause turf grass diseases. In fact, a close association has been noted between frequent disease outbreaks and the presence of algae. Therefore, it’s desirable to control both of these problems with one practice. Reducing the moisture level would be the ideal method, however, in many situations, this is not possible. Other control measures must be used. The use of fungicides that are effective against both turf diseases and algae is an efficient method of control. A garden supply store or nursery can assist you on the correct material to use. You may also call the Master Gardener hotline at the UH College of Tropical Agriculture. In Hilo, the main number is 981-5199. In Kona, the main number is 322-4892. You may then be directed to Extension staff or master gardeners to assist you.
Bacteria, fungus and algae are not always doing harm. Our edible limu is an algae, yogurt is the result of a certain type of bacteria, and those delicious mushrooms on your steak are a fungus. These beneficial organisms are important to a healthy soil, and to healthy nutrition. Many that are yet to be discovered may be key in developing new drugs to fight disease in plants, animals and man.
However, prevention of disease organisms is vital and also includes keeping it out of Hawaii.
Some folks get unhappy when they find they can’t bring certain plants or seeds into Hawaii, or if they can, they have to go through all kinds of red tape, fumigation or extended quarantines to get the plants through.
A few of these folks figure it is a bother to get permits and go through the proper procedure to bring plants to Hawaii. They smuggle a few plants thinking it won’t make any difference. This attitude couldn’t be further from the truth or more dangerous. If it weren’t for people bringing in disease- and insect-infested plant materials, our island would not be plagued with such creatures as fruit flies, burrowing nematodes and many other pests that damage food crops, as well as ornamentals. Just the fact that we are plagued by fruit flies means that the potential export of mangoes and other tropical fruits is nipped in the bud. So we lose millions of dollars of potential income just because of some careless person who didn’t think it would hurt to smuggle in some fruit. Now there are serious fines and even imprisonment for plant smuggling. This should discourage potential pest introductions.
Florida has one of the best examples of what happens when folks get careless about clean plant introductions. Lethal yellowing, a disease of palms, killed palms by the tens of thousands there and is a threat to other areas like Hawaii. The disease affects coconut palms, manila palms, Veitchia merrilii, and Hawaiian fan palm, Pritchardia species. The disease is attacking other types of palms also.
According to the University of Florida, it has been reported in the Dominican Republic, Bahamas, Cuba, other Caribbean Islands, Venezuela, Panama and West Africa. It was identified in Key West in 1955. The disease was probably brought into the area by folks smuggling contaminated plants.
The disease, similar to a virus, is a mycoplasma that infects the plant. Taking palms from infested areas to an area free of lethal yellowing is extremely dangerous. A leafhopper is involved in spreading this palm plague over the last 30 years. Florida lost at least 90 percent of its coconut palms.
There is no control at present except avoiding carrying this disease to unaffected areas.
This, again, shows we should support our state and federal agricultural quarantines. Importing plants illegally could bring a devastating disease like this to Hawaii.
There are ways to bring new plants to Hawaii legally. The state Department of Agriculture and U.S. Department of Agriculture Plant Quarantine Office can give you the details.
By following the law, hundreds of new plant introductions are being made each year. These can enrich our lives without bringing with them unwanted insects and diseases that could bring disaster to our economy.
This information is supplied by the University of Hawaii College of Tropical Agriculture and Human Resources. For further information, contact the nearest office.