Foliar Nematodes in Hosta

I'm sure nematodes have been around forever.  I had never heard of them, until a few years ago when I attended the American Hosta Society convention in Indianapolis, Indiana.  It was a hot spring there, so even though the signs on nematodes usually come later in summer, they had shown up early just in time for the convention.  Foliar nematodes are microscopic roundworms that love to live in hostas and other perennials.  One of the reasons I had never heard of them was before global warming nematodes could not survive Wisconsin winters.  But that is not true anymore, and nematodes have been shown to survive temperatures of -80.

How do you know if your hostas have nematodes?  Signs of nematode damage come to Wisconsin in later summer through fall.  You will start to notice brown streaks in the hosta leaves that stay between veins.  You can also cut up the leaf you believe is infected, place the cut up leaf in a glass of water, wait an hour or so, hold the glass up to the light, and look at it with a magnifying glass.  If you see something swimming around in the glass, your plant has nematodes.

Not best picture, but example of hosta infected with nematodes.

How does a plant get nematodes?  I have one plant in my garden that is infected with nematodes.  I am guessing that the plant had them already when I bought it from the nursery.  Plants often become infected with nematodes in nurseries and greenhouses through their watering methods and from cuttings.  This is why it's important to buy from reputable nurseries.  Be leery of people who try to sell you hostas with all of the leaves cut off in fall, if you have never bought anything from them before.  They may have cut all the leaves off so you cannot see the nematode damage on the plant.

How can you get rid of nematodes?  There is not a lot you can do, besides destroy the plant.  There have been some experiments done, but nothing has been clear cut as to how to rid a plant of nematodes.  One of the suggestions is to heat treat the plant.  Submerged plants in water that is 124 degrees Fahrenheit for 10 minutes.  Or you can just throw them in the washing machine like my friend Andrea did;)  Another suggestion is to cut off all of the leaves and soak the plants in a 10% bleach treatment  overnight.  Just be aware that both of these treatments may kill your hosta.  So while there are no 100% effective ways to get rid of nematodes, you can prevent the spread of nematodes by not watering plants from overhead and buying from reputable sellers.