Root and Leaf Nematodes

Foliar Nematode Research Program

The American Hosta Society, in keeping with our mission statement to further the education and understanding of the genus Hosta, wishes to pursue additional nematode research with the stated goal of developing an Integrated Pest Management (IPM) solution.

Foliar Nematode Research Program Funding (1-9-2013)

OSU Matching Grant Proposal (1-9-2013)

Foliar Nematodes

Stages of infection go up from A to D. A - Initial signs, barely visible. D - dead (necrotic) tissue essentially caused by dehydration.

Many different problems can result in very similar symptoms in plants. For example, sun scorch, fungal disease, bacterial disease, nutrient deficiency may all result in interveinal chlorosis and later necrosis. It is very important to take additional steps to determine the primary cause. Secondary fungi could move into almost any damaged tissue so confirmation steps are critical for an effective pest and disease management strategy.

To diagnose foliar nematodes, first, realize that you can see them. The best way to confirm their presence is to break or cut open the leaves showing symptoms (necrosis and/ or chlorosis between the veins). Put some water on a piece of clear glass or a clear glass dinner plate (or Petri dish). Let the cut edges of the leaves stay in contact with the water for 10- 30 minutes. Then back light it (hold the glass over a lamp so the light shines through the water and leaves). You will see the very tiny nematode snaking and swimming out of the leaf tissue. If you have a dissecting scope, focus on the bottom of the water because the nematodes will "settle out". Foliar nematodes are a serious problem and require much more extreme measures than a foliar fungal disease. For this reason it is very important to CONFIRM their presence in your

hosta by actually seeing the creatures. A good pair of reading glasses or a magnifying lens will help if you can't quite make them out with the light alone.

These worms live and over-winter in the plant and not in the soil. They are short lived outside the plant tissues. Yes, they are spread from plant to plant by rain and irrigation, thus over head watering spreads them faster and farther than drip irrigation. They have been found to be present in every area of the country and probably world where hostas are grown and are not killed by winter's cold unless the plant is killed. Hostas are not their only host as they are found on many shade perennials, ferns, bulbs and even some woody plants.

If you have a large collection of hostas you probably have some infected plants. In the garden, the symptomatic brown area of dead tissue between the leaf veins occurs after the worms have reached the leaf surface and have probably been carried by water to the hosta next door. The brown color is actually a secondary fungus infection. Symptoms begin to appear in mid to late June in the Southeast US (about 3 months after emergence) in August in the Midwest and maybe as late as September in Michigan and Minnesota. If you stress your hostas in the summer, you will stress the worms and their population will be reduced and symptoms may not appear. If your hostas are all fed and watered throughout the summer and are actively producing new foliage then the nematode population will also increase at a high rate all summer.

If you find nematode damage in the garden...

1. Remove all plants, hostas and others, which show symptoms from the garden. We put them in black plastic bags and take them to the dump. Also, remove their next door neighbors up to a 6 foot radius away since they are probably infected especially if they were touching the infected plant. There is no need to treat the soil since the worms are in the plants not in the environment!!! In two to three years your garden could be virtually nematode free.

2. If this is too extreme, you can "cook" the hosta clump or a piece of the plant. This will kill the nematode eggs in the plant. To cook, use only dormant hostas, I do this in February, about a month before emergence. You can do this in the kitchen sink with tap water and a good thermometer. The proper cooking time is somewhere between 120 oF for 20-25 minutes to 130 oF for 10 minutes. Try doing different pieces of the same hosta at several bracketed temps and times. The lethal temps and times for hostas are very close to these "recommended" ones, thus you will kill all the roots on the hostas and maybe the whole plant. So pot them up and re-grow the roots and put the plant in the ground in August.

3. If you do not want to throw infected hostas away or heat treat them then you can choose to live with them. (Pesticides are not really an option. They kill worms but not eggs thus they must be used continuously over a long period of time to exhaust the eggs in the plant. A few may be effective but are not currently labeled for homeowner use.) If you choose to have an infected garden then please do not bring any of your plants to auctions and do not give them away with out cautioning, "These hostas may have nematodes."

One final word: There is a difference in acceptable nematode tolerance between the home gardener and the nurseryman. Hosta nurseries should guarantee their hostas to be "pest free". That means no hostas that "may have nematodes" should be sold. Most hosta nurseries work very hard at this.

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