Topic: white rot in onions

[denis trundle]

For the last 2 years Ive had white rot in my onions and shallots is there anyway I can control this problem? Thanks :)

[BAK]

I have 2 half plots: I have given up after many years even attempting to grow onions on the first due to white rot; fortunately the second plot does not suffer from it (so far!).

I have heard of people replacing the soil or building up the soil on a bed (8-9 inches or more of uncontaminated soil), sometimes with a membrane between the two layers but I have never heard of anybody in the non-commercial world who has been really successful in combating the dreaded white rot I am afraid.

[Tee Gee]

I have been giving this one a lot of thought in recent years for the same reason, and sadly I have to agree with BAK.

I am going to conduct a little experiment next season and it is this;

In recent years I have used 100% setts, next year I am only going to grow only a few for comparison purposes.

I am going to grow the bulk of my onions from seed.

I have selected  'pear' shaped ones rather than 'flat bottomed' ones, my theory is; that there is less of the onion in contact with the soil so hopefully they won't succumb to the rot quite the same.

But most of all I am hoping the weather patterns are a bit more like of old e.g. a frosty Jan/Feb, March winds, April showers, Dry May, Flaming June.

But already it would seem my plans have been knocked for six what with the frosty spell in early Dec. now this very mild spell.

The only thing I am pleased with is my 'spring bulbs' ( I use them as a barometer) they are not as far on as I have seen them in the past two or three years so hopefully they are telling me something.

So its just a case (as always) of keeping my fingers crossed and hoping for a bit of 'normal' weather.

What do you think?

[Trevor_D]

On our site we suffer quite badly from white rot. Every single point raised by you, Tee Gee, has been mentioned by our more experienced plot-holders. Most of them have given up with setts & gone back to seed. And they all agree that weather plays an important part.

One of our older hands swears by a weekly dilute liquid feed to which he adds a touch of Jeyes Fluid.

Onion rot stays in the soil for something like 7 years! We've started marking problem areas on a plan so we don't re-plant in the same spot.

[saddad]

I have it on Plot 48, but as I have several Plots have not grown onions there for years, and don't intend to until 2012..
 :o

[Barnowl]

Armillatox has not been re-submitted for EU approval and so is no longer approved as a soil steriliser in the EU, and so I couldn't possibly recommend it as a course of action,  but has anyone in the past tried 'cleaning' their soil with this?

Curiously the international website even has a recommended dosage....

http://www.armillatox.com/onions.htm

Personally I've found it very effective at removing algae from paying stones.

[norfolklass]

Most of them have given up with setts & gone back to seed.

so you're more likely to get white rots in onion sets?
is that because you're introducing already infected plants to your soil, or are sets more susceptible than onions grown from seed?

as a newbie I know nothing about white rot and now it's right up there with clubroot (know nothing about this either) and all other things to be irrationally scared of!

[Trevor_D]

so you're more likely to get white rots in onion sets?
is that because you're introducing already infected plants to your soil, or are sets more susceptible than onions grown from seed?

I haven't a clue! I'm not sure they have either, but onion from seed does seem less susceptible. And thinking about club-root, seed sown in modules, then planted out seems less suceptible than either seed grown in situ & thinned, or plants brought in from elsewhere. Wish I'd paid more attention to science stuff when I was at school!

[Barnowl]

Presumably that's why some sets are sold as "heat treated" - the fungus dies above a certain temperature so the treatment should ensure they are rot free.

[Tee Gee]

Presumably that's why some sets are sold as "heat treated" - the fungus dies above a certain temperature so the treatment should ensure they are rot free.

You would have thought so but I always buy 'heat treated' and still suffer!!

In fact I even go to the extra expense of buying 'selected heat treated' setts and it doesn't seem to have made any difference.

I just don't know the answer other than to repeat what I have said before;

It must be related to the topsy turvy seasons rather than just wet & heat i.e.in the past few seasons it is wet when it was once dry, and warm when it was once cold and my guess the plants are not bred for such variables.

[redimp]

From what I read, it is about root length at certain times of the year (when rot is more prevalent)  Supposedly, the roots of seed sown onions are shorter when the rot is at its most prevalent.  Don't know how reliable this info is though.

[denis trundle]

Thanks for the replys, Ive been told you have to leave the ground for at least 5 yrs :( seems a shame really as I love growing onions.

[SteveJ]

I sow all my onions from seed.  Last year all my white onions (Bed. Champion) were infected, but I managed a reasonable crop from two different varieties of red onion (Red Baron & Long Red Florence)..   All were planted alongside each other in the same part of the plot.  Has anyone else noticed this, or do you think it was just a fluke?

This year I'm gonna sow a number of different varieties of white/yellow/red onions to see if I can repeat the results.

[davyW]

I don,t think it makes any difference what onions you plant, heat treated sets or from seed, the disease is in the soil and can be there for 15 years. At the moment there is no treatment for it so i think if you want to grow onions you have to find an alternative method.
I have always maintained that Garlic is the cause of it. I have never grown Garlic and so far never had white rot. ( Touch Wood )

[jennym]

Presumably that's why some sets are sold as "heat treated" - the fungus dies above a certain temperature so the treatment should ensure they are rot free.

I believe that the sets are heat treated to stop bolting, rather than to kill off any disease. If you consider the level of heat that would be required to kill off disease, that same level would kill the set too.

[jennym]

I know that a few folk including rc have spoken about the use of onion waste to control white rot, and although I've looked at a lot of papers on this subject, this link is relatively readable and may be of interest.
They seem to have better rates of control when onion waste composted at highish temperatures is incorporated into the soil, rather than raw onion waste:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TC7-45JGXNM-3&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=cd5827d590a6773d6807367c2bc728a4

There's also an abstract from some work done in New Zealand, where they increased the temperature of the soil by covering it with clear plastic for long  periods: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TC7-41YG2YJ-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bb437b33bf71b5f64c3573cbb0c4e094

[davyW]

I should have mentioned in my previous post is that i also give my onion bed a good liming a couple of weeks before planting. I think lime does a lot to control the virus

[BAK]

fyi - found a report on a trial done using garlic powder in an attempt to trick the fungus into growing and exhausting itself, as there are no alliums actually planted.

http://cdpr.ca.gov/docs/pestmgt/grants/97-98/finlrpts/97-0227.pdf

Version 2 of the report a year later was not quite as hopeful as the initial version

http://cdpr.ca.gov/docs/pestmgt/grants/98-99/finlrpts/98-0277.pdf

If you search on white rot garlic powder you will see that some commercial growers in the US have been using the technique.

[redimp]

Interesting to see what the results are once they have dug the garlic powder in a bit deeper.  Although, at Tesco's prices, I think, digging in garlic powder might be a tad expensive.

[tim]

Our only answer has been raised beds.