It has been an unusually cool and damp spring here in Iowa, which may be the cause of the rusty jacks. I had never heard of arisaema rust, but today I noticed a large clump of native, black hooded jack in the pulpits whose leaves were crumpling, and looking closer saw numerous brown spots on the underside of the leaves and on the spathes (pulpits); obviously rust. A quick internet search showed that arisaema rust is a severe problem, and the only recommendation was to completely remove the plant; it is extremely contagious. Unfortunately a garden tour showed that about a third of the native jacks were infected, as were two of the Asian jacks, stately ringens and exotic iyoanum. I pulled all of them (flinching when I pulled up iyoanum), bagged and disposed of them… over a hundred plants, with the tubers on some of them being almost as big as a tennis ball.
There doesn’t seem to be any reliable treatment, but I am going to look into a couple of specific fungicides; Bayleton and Serenade, and keep my fingers crossed that the rest of the Asian jacks don’t develop this… if so, there will be much gloom in the garden here.
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