Question: It appears that an islandwide disease is killing all impatiens. The plant division of Home Depot no longer carries this popular plant. I had 100 pots hanging from my monkeypod tree and on the ground, and they have all died. Can you find out what’s happening? Tourists would take photos of my yard, which is now a desert of impatiens.
Answer: Your concern points out what may be the unfortunate loss, at least for the time being, of the familiar plant with flowers in red, pink, white, purple, orange and other colors throughout the islands.
It turns out that a fast-spreading form of downy mildew disease (Plasmopara obducens), which targets common varieties of impatiens, has wiped out much of the plants across the mainland and is doing the same on Oahu.
The disease does not affect other plants.
It has also been found on Kauai and in the Hilo area, said Neil Reimers, administrator of the Plant Industry Branch of the state Department of Agriculture. So far, it has not been detected on Maui or the Kona area, “but it doesn’t mean it isn’t there,” he said.
“It’s a really bad disease for the impatiens — it wipes them out very rapidly. It looks like it just got here very recently, and it’s like a blight on impatiens.”
Local plant shops and nurseries were aware of a problem but did not notify state officials because they weren’t sure what the problem was, he said. Although the disease had decimated impatiens across the mainland, affected plants and “plugs” (seedlings) were still being shipped here without any kind of warning.
“We first got word of (the disease) about two weeks ago,” Reimers told us Friday. One of the Agriculture Department’s pathologists happened to be at a Walmart plant shop, noticed that the impatiens looked diseased and took samples to test.
“That’s the first time we discovered (the disease),” Reimers said.
Walmart immediately took the plants off the shelves. The plants were mainland-grown but obtained from a local nursery.
The impatiens at the nursery also were infested. “They were trying to deal with it but weren’t sure what it was,” Reimer said. “They thought they weren’t watering it enough.”
The nursery has since destroyed all the diseased plants and stopped bringing in more from the mainland.
From there, “we started looking at all the different garden shops and found out that Home Depot already knew about it,” Reimers said. “They didn’t know what it was, but they had stopped selling impatiens. … But no one had told us about it.”
Another nursery told agriculture officials it had begun noticing a problem about a month or two ago. It also hadn’t notified the state because workers thought that something had happened to the plants during shipment.
“Since then we’ve been doing surveys throughout Oahu, and we’re finding it everywhere,” Reimers said.
That’s not surprising, he said, because the powdery disease is spread by spores blown about easily by wind.
Is there a solution?
“That’s the problem — not much,” Reimers said.
There are sprays and fungicides that possibly can be used, “but we’re just starting to look into that now to see what’s available,” he said. “Any pesticide that’s used in Hawaii has to be licensed to be used.”
The varieties of impatiens affected are those that thrive under shady, moist conditions.
“What’s best for spreading the disease is rain, movement of water, sprinkling and wind,” Reimers said. So the affected varieties may do OK in drier areas.
Impatiens lovers can switch to varieties that are more resistant to the disease, notably “sun-loving ones,” such as New Guinea or SunPatiens, Reimers said. But how long they may be resistant is a question.
Asked about any prohibitions against importing impatiens, Reimers said, “It’s too late already. It’s so widespread now.”
Plant pathologists are trying to get more information about the disease, but “I think it’s a problem that we’re going to have to live with and look for ways to manage the disease. It’s not going to die out and go away.”
Mahalo
To the kind soul who came to my aid on Keeaumoku Street on Friday, April 12. I must have fainted as I was handing out pamphlets for my friend’s hairstyling business and woke as he tended to the cut on my head. It turned out to be minor, but his concern was truly felt. I’m sorry that I didn’t get his name. — Appreciative Volunteer
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