Impatiens downy mildew

by Adam Pasco

Impatiens downy mildew was first discovered in the UK in about 2003. I've never come across it, and can't recall seeing any letters from Gardeners' World readers about it...

Foliage affected by impatiens downy mildew

During an enjoyable day scouring for new plants at a horticultural trade show last week, several growers told me about a devastating new fungal disease killing off busy Lizzies in parks and gardens up and down the country.

Impatiens downy mildew was first discovered in the UK in about 2003. I've never come across it, and can't recall seeing any letters from Gardeners' World readers about it. But growers I spoke to at the show told me vast bedding displays had been killed off completely by the disease. Symptoms appear to be stunted growth, yellowing and wilting leaves, followed by plants collapsing and dying. This is worrying growers, as there doesn't appear to be a cure.

If impatiens downy mildew is now established in the UK then gardeners may have to consider switching to alternative bedding plants. Clearly this also worries the plant breeders and growers who make a living out of developing and raising busy Lizzies.

At present it appears that impatiens downy mildew only infects varieties of Impatiens walleriana, the common bedding varieties most gardeners are familiar with. However, some varieties appear to be more susceptible to infection than others.

Thankfully there is some good news: New Guinea busy Lizzies are not prone to attack.

The wonderful variegated New Guinea Busy Lizzy called SunPatiens Spreading Salmon Variegated was one of the highlights of the Four Oaks Trade Show for me. Hopefully it will stay disease free for gardeners across the country to enjoy when it goes on sale next year.

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Gardeners' World Web User 13/09/2008 at 00:22

Will garden centres continue to sell these to the unsuspecting public next year and if so will there be refunds available if mildew reoccurs? The new guinea impatiens is much more expensive to buy and I CAN'T SEE HOW i could afford to use these plants on a large scale Ruth harris

Gardeners' World Web User 13/09/2008 at 19:30

Hi Guys, this has happened in Lowestoft too. I am a retired commercial grower, and when this happened to my Busies I was so upset - and my pride was hurt! The weird thing was that there were no obvious signs. I looked for mildew (any) but nothing was visible. Normally if Busies take a bad shock you can trim them right back and they will grow back, bless 'em. Dead is dead! If this problem becomes embedded (no pun intended) it will be a major blow for growers and gardeners alike. Does anyone know if they problem is due to our odd Spring weather or how downy mildew is spread please. All the best, Penny

Gardeners' World Web User 13/09/2008 at 21:33

Like Kathleen I too have lost some busy lizzies in 2 pots on the patio. These were some I bought early July for a bit more colour,the ones I bought at the start of the season are all fine,so I don't know what has caused it.At first I thought of slugs or snails or even vine weevil but there is no sign of any of these pests.

Gardeners' World Web User 19/09/2008 at 17:20

Hi, Exactly the same problem here in N.Derbyshire. 200 impatiens planted from a very large grower in early July. All ok till late August when the first began to die. Now they are all gone. Normally they last till November. Symptoms are gradual defoliation leaving bare stalks. No sign of mildew on the back of leaves. The stalks then die also. Root structures look normal.

Gardeners' World Web User 19/09/2008 at 21:13

we bought 160 from a well known supplier and all have died, they were all in tubs round the garden. We thought at first that it was due to slugs or snails, but it started with spots on the leaves, which then turned yellow and fell off. We have left them in situ at the moment hoping they would come back. This is in Staffordshire.

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