Dying river lupins mystery solved

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Philip Brown and some of the dead lupin.

On one of his regular trips crossing the Rakaia River bridge Philip Brown noticed the usually abundant lupin plant on the Rakaia River bank had gone brown.

Philip, who owns land bordering the river, has a naturally inquisitive streak and took a closer look at the plants.

He found they were dead, while other plants right next to them were still ok.

As someone who is on riverbank regularly this seemed unusual to Philip and piqued his interest.

“I’ve got consent to do work out the back of my place here and also maintain an irrigation intake further down, so I am out on the riverbed quite a bit so I see what’s going on,” he said.

Philip who grew up on his property said it was the first time he had seen the plant die off like this.

“I was trying to figure out what it was, thought maybe a high flood might have flooded them out, I did a bit of research on it and thought I’d take a bit of the plant to this plant diagnostics place so they can do a test.

“It’s the best way to find out I think.

“I’m the scientific type with my engineering background, it’s good to know what’s going on,” Philip said.

He sent a sample to Plant Diagnostics in Christchurch who sent a report back identifying two fungus Colletotrichum gloeosporioides and Fusarium had colonised the plants.

Colletotrichum produces spores which are dispersed in water-splash such as that of rain.

Humid conditions also encourage disease infection and development.

The report concluded “it is likely that the wet conditions experienced this season have contributed to the disease being so prevalent.”

An Environment Canterbury (ECan) document about the plant states it is under a sustained control programme, with the objective to control lupin within specified distances from waterways to prevent its establishment to protect biodiversity and biosecurity values.

An ECan spokesperson said “Lupins are an introduced pest plant, so aren’t important for the ecology of riverbeds.”

-By Daniel Tobin