Mary Lou Gripshover, Ohio

Hot Water Treatment

July 11, 2016

Categories: Diseases and Pests, Nematode

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I need to give bulbs from one area hot water treatment to control nematodes.  Since formalin is no longer allowed, what disinfectant do any of you use in the HWT?

Thanks for your help.

Mary Lou

15 responses to “Hot Water Treatment”

  1. Margaret Seconi, New Zealand Margaret Seconi, New Zealand says:

    Hi Mary Lou

    I’ve been asking this question for several years now and have yet to receive a satisfactory answer. I did manage to get a small bottle of Formalin from a vet which  allows me to HWT for next season. Good luck. I’ll be following  any replies with great interest.

    Margaret Seconi NZ

  2. Theo Sanders, Germany Theo Sanders, Germany says:

    Mary Lou,

    I use a product called Danchlorix in Germany which contains 2.8 g Nartriumhypochlorit per 100 g. Directly after the hot water treatment I give the bulbs for 15 minutes into a mixture of 3 l Danchlorix with 40 l water. With this procedure  I operated  successful during the last three years.




  3. David Adams, New Zealand says:

    Hi Mary Lou,

    I may be way out of line here but I ask the question ‘Why use anything with the HWT?’ I understood that the formalin was for fungal control. Some of us have proved that drying the bulbs properly is the best fungicide therefore the HWT is to kill insect and nematode pests. If we HWT at 113*F or 45*C for three hours then the beasties should be dead. Personally, when I HWT, I use hot water only then sun dry the bulbs. It seems to work.


  4. Kathleen Simpson, West Virginia says:

    Mary Lou – the 2007 June ADS Journal has a really nice article on HWT by Kathy Welsh.  She recommended either formalin or a 10% chlorox mix.  If memory serves, that’s what Tom Stettner mentioned a few years back when he gave a talk at the fall regional meeting on his experience with HWT.


  5. Ben Blake, California Ben Blake says:

    Having never HWT treated a bulb before, I find this discussion fascinating.

    I just reread the article by Kathy Welsh in the ADS June 2007 journal on  The article and the entire journal is at

    Kathy gave more details about how she does HWT of bulbs and also discusses 100 degrees for 1 hour to kill bulb fly and 112 degrees for 3 hours to kill bulb mite and nematodes.

    My question is about water temperature and how much control is needed.  If I put water in a large cooler and carefully measure the temperature to make sure it is 112 degrees, I could come back in 30 minutes and measure 90 degrees or certainly not 112.  Do I start with 150 degrees so the temperature will never fall below 112?

    Or do I only have to make sure the water feels hot, once I carefully measured the start?



  6. Mary Lou Gripshover, Ohio Mary Lou Gripshover, Ohio says:


    Thanks for your comments.  Since chlorine bleach was mentioned, I think I’ll add that to the water.  I washed the bulbs in a Clorox/water bath when they were dug, then dried them off.  Dave, I’ve been told that the formalin was added to kill any “nasties” that might be floating in the water.

    There’s a good article by Tom Stettner in the 2009 Fall Midwest Region Newsletter. Go to ADS Pubs, then ADS Regional and Local Newsletters, Midwest Region.

    Ben, you have to keep the temperature at 112 for the full three  hours to kill nematodes.  (Or for 1 hour to kill bulb fly larva.)  That’s why you need some kind of heat source.   The water should probably be hotter than that to start, as it will cool off as soon as you add the bulbs.  And if the water gets too cool, you need to add more hot water.  And you have to keep an eye on the thermometer to make sure the temperature is right.

    Mary Lou

  7. David Adams, New Zealand says:

    Yes Ben, I understand that if the water goes above 118 then you cook the bulbs and many of us have done that. If the water goes below 108 then you don’t kill the pathogens. The reason for the three hours is to ensure that the 113* heat gets right to the centre of the bulb.

    I need someone to convince me that additional chemicals are essential. Maybe its just folklore from the past with no scientific basis.


  8. Kirby Fong, California Kirby Fong, California says:

    As Dave points out, the purpose of formalin (formaldehyde) is to kill fungus (like basal rot). Until it was banned, it was used by commercial growers and some hobbyist growers (presumably because they didn’t have the space or sun to sun dry the hot water treated bulbs).  Hot water is not particularly effective in killing basal rot fungus and can disperse the fungus in the solution to all the bulbs. Commercial growers can use a compound that has to be formulated just before use.  I forgot what it is, but I remember it being described at a conference of the Northwest Bulb Growers Association.  Laundry bleach can be used in lieu of formalin, but it breaks down more rapidly (i.e. loses effectiveness) in the presence of organic matter.  This just means you shouldn’t do multiple batches of bulbs in the same solution; mix up a new bleach solution for each batch of bulbs you treat.  I believe Clive Postles used something with the trade name Jet 5.  In the U.S. this is sold as peracetic acid.  As its name suggests, it is related to acetic acid, and it smells like strong vinegar. In the U.S. its purpose is to disinfect food processing equipment — i.e. kill anything that might contaminate food.  You do not need a permit or anything special to buy it.  I’d have to look up the proper dilution, but I have dipped bulbs in the solution (at room temperature) and then laid the bulbs to dry in the sun.  So I don’t know whether it’s sun drying or peracetic acid that does more (or any) good.  Gary Chastagner at the Washington State University agricultural research extension told me that I should break off any black tissue at the top of the neck before replanting a bulb in case it still harbors dormant fungal spores that were hiding too deep to be killed by the fungicide.  Healthy dried tissue is  brown or tan in color.


  9. Margaret Seconi, New Zealand Margaret Seconi, New Zealand says:

    Hi Kirby
    You’re a Honey. Your explanation is exactly what I’ve been waiting for. I’ll try Your ideas out when I lift my bulbs next season. My thanks to you and everyone else who contributed to this discussion.

    Margaret Seconi, Wellington, NZ.

  10. Mary Lou Gripshover, Ohio Mary Lou Gripshover, Ohio says:

    Kirby, thanks for your post.  I would have used the same water for multiple batches of bulbs.  Thanks to you, I know better.

    Mary Lou

  11. Becky Fox Matthews, Tennessee Becky Fox Matthews, Tennessee says:

    Mary Lou, I have not tried it yet, but I have purchased an Anova Culinary Precision Cooker (under $200 US) that I believe might be a solution to the non-commercial daffodil gardener’s dilemma on how to easily hot water treat bulbs.  A little background: I was introduced by a gourmet friend to the sous vie method of precooking meats (and other foods) in a sealed bag to make them (after the Sous Vie treatment) cook tender on a grill and to be safe at rare temperatures.  Anova’s newest introduction is not an enclosed container as sous vie devices have been in the past, but a wand that can be inserted into various containers, including boiler pots and small coolers that can be adapted for the wand to fit in.  It supposedly can keep the water bath at a steady temperature and the Wifi version can send the temperatures to your smart phone so you can monitor the timing and the temperature of the food (or daffodil bulbs) remotely.  I am hoping this works as I think it will, as I have read that it is important that the temperature of a hot water bath remains at the optimum temperature of 112 degrees.  Wish me luck!

  12. Mary Lou Gripshover, Ohio Mary Lou Gripshover, Ohio says:

    Becky, the temperature is 112 degrees, NOT 212 degrees.  A typo on your part?  I hope!

    Mary Lou

  13. Lesley Ramsay, New Zealand Peter Ramsay says:

    Hi Becky I would check on the temperature  – 212 degrees! Peter always did his HWT at 40 – 42 degrees celcius ie.  110 – 114 degrees F. Wouldn’t want you to cook them. Cheers Lesley

  14. Becky Fox Matthews, Tennessee Becky Fox Matthews, Tennessee says:

    Yes, a typo.  Thanks, all!  I corrected the temperature in the above post from 212 F to 112 F!

  15. Faith and Graeme Miller says:

    Hi Becky and other readers The Journal of Nematology 1993 (I think that was the date) which I once read, says that less than 44 degrees C will not kill nematodes and that for larger bulbs 2 1/2 hours is necessary. For small bulbs (e.g. miniatures) 1 hour is enough. The critical factor is for the bulbs to be in the water for long enough for the centre of the bulb to be able to reach a temperature of 44 degrees C.