The prohibition will primarily affect shipments to Hawaii florists, who rely on imported flowers and greenery in bouquets and floral displays.

At Kihei-Wailea Flowers by Cora, Manager Thelma Garso said about 40 percent of their products used in displays may be affected by the ban.

At the smaller A Special Touch shop in Lahaina, florist Leann Lum said she hoped she can purchase more of what she needs from local growers.

"I think local is always better anyway. It's always fresher," she told The Maui News.

The order approved at a board meeting on Aug. 28 takes effect Friday on shipments of any plants of the Myrtaceae or Myrtle family, which includes eucalyptus and guava as well as ohia, which are endemic to Hawaii, and ohia-ai or mountain apple, which is Polynesian introduced.

According to Department of Agriculture information officer Janelle Saneishi, the state Plant Quarantine Division has notified Hawaii florists that any Myrtaceae family plants or plant products from the three regions will not be allowed without proper documentation that the plants are not infested with ohia rust, known in other regions as eucalyptus rust.

The disease is caused by a fungus, Puccinia psidii, that develops as a yellow powdery growth on leaves and stems of infected plants. As the fungus spreads, leaves and stems are deformed and can die. The department reports the disease has its most severe effects on young growing shoots.

It was first reported in Brazil infecting common guava, but spread to nurseries that were growing eucalyptus. It has been found in Florida since the 1970s, while the rust was reported infecting a San Diego nursery in 2005.

In April 2005, a strain of the rust was observed on plants in an Oahu nursery. The same strain was later found to have spread through the islands, according to a report to the Board of Agriculture. The disease has been found infecting three native ohia species, including an ohia, Eugenia koolauensis, found only on Oahu and listed as an endangered species.

But the agriculture report said the strain of ohia rust found in the islands is "found sparingly on ohia with little damage detected." It is causing significant damage to an introduced species, the rose apple, which is of less concern. The primary fear is that other strains could be introduced from infested areas.

In issuing its order, the board found that a rule was needed to restrict importation of plants that may be carrying other strains of the fungus or its spores.

A spokeswoman for the Hawaii Coordinating Group on Alien Pest Species, Christy Martin, said the board's decision will help to protect Hawaii's native forests, in which the ohia is a primary species.

"We are very pleased the ohia has gained this protection," she said. "As it is, we are at risk of losing one of the main forest plants in the islands and stopping this halfway is very important. We've been talking about it since 2005.

"At least, we don't think it's too late," she said.

The board's interim order is for one year, during which time the department will be gathering data on the status of the spread of ohia rust and on the economic effects of the ban.

"Because rust fungus spores are very tiny, Puccinia psidii is difficult to detect by visual inspection and visual inspection cannot be relied on to prevent introduction of this pest," the board staff reported.

The report also noted that ohia make up 80 percent of the remaining native forests in Hawaii, which are habitat to a large number of endangered endemic plants birds, insects and mollusks.

"In addition, this rust can affect many plants of economic importance in the Myrtle family, such as eucalyptus. This could lead to trade restrictions or quarantine on Hawaii products," the report said.

Saneishi said plant quarantine inspectors have been rejecting shipments of plants found with evidence of a rust infection all along. Under the new interim rule, the inspectors will reject any shipments from the affected regions without documentation.

A letter to florists from state plant import specialist Leslie Iseke said plants from South America, Florida and California are prohibited unless there is documentation that the plants have been treated against the fungus, are tissue cultures grown in completely enclosed containers or are from an area certified free of the fungus.

Lum at A Special Touch said it was still too early to say how much of an impact the restrictions will have on her business.

"Most of the greens, we try to buy locally. I think this affects those with high volume," she said.

At Kihei-Wailea Flowers, Garso said she will be contacting all her local growers to determine what they can supply. But her business uses a number of plants on the restricted list in displays and bouquets including wax flowers, leaves and seed capsules of the tea tree and other eucalyptus greenery.

"We do use a lot in our spring flowers arrangements. A lot of the arrangements are ordered from the Mainland for people here or for weddings. Weddings are big business," she said. "We need a lot of flowers, wax flowers and roses."

Martin said the ban is needed to protect the island's native forests, noting that the ohia rust was discovered just a month after the discovery of the Erythrina gall wasp infesting native and introduced wiliwili trees. Gall wasp infestations have killed thousands of trees used as windbreaks and in landscaping, and are still a threat to the native wiliwili that is a mainstay in dryland forests.

"We got the one-two hit back in 2005. We noticed the gall wasp in March 2005, which got everybody out in the forests looking for where it was infesting. The very next month, we found this ohia rust," she said.

"Unfortunately, the rust didn't draw as much attention as the gall wasp because it was not front and center in your front yard. It was infesting the forests. That's why it took us so much longer to get this passed."