[Ivor Backache]

Ever since I have had the allotment (3 yr) I have been trying to eradicate white rot with some success.  The onion bed is fixed and filled with new soil and now I have extended it. (Last year i did not have any rot).  But this year,  there are 6 red onion sets with the problem and all the white (autumn and spring sown) are OK.

I have started a new area for shallots and there are some affected plants. All the affected plants are removed and destroyed and the location marked with the intention of removing the soil when I harvest the crop.

I am in the habit of checking all the plants and whilst weeding give them a tug. The tell tale white fluffy fungus is there but I never see any black scleroti.
1. By removing the affected plant before scleroti are formed,  am I then removing the infection from that place?  If so:-
2. If I rake over another part of the allotment and scatter spring onion seed as a sacrificial crop and remove the affected plants, will I then remove the fungus from that area?

[bigben]

You have my sympathy Ivor - I took over my allotment last year and around 40% of my onions got it. I turned the bed into a fruit bed and planted elswhere this year only to find the same problem with my garlic and winter onions. I have not harvested my summer onions - they look ok but so did my garlic till I tried to lift it.

Like you I am looking for a solution other than the dreaded "dont grow onions there for at least 8 years!". I found a suggestion involving garlic powder that is meant to trick the spores into germinating - they then die because there is no host. see http://westernfarmpress.com/aids-allium-crops-garlic-industry-develops-white-rot-control-program   for more info. I bought a big tub of garlic powder from amazon and plan on doing most of my beds at the end of the year and again in the spring. Good luck

[Salmo]

The good news in that article is that garlic powder appears to work.

The bad news is that they say white rot can remain in the soil for 40 years.

[Ivor Backache]

Thank you for your replies. Thank you Bigben for the link-I haven't seen that one.
I have read other articles about the garlic powder method which I understand has to be watered into the soil evenly and maintained. To me that is a lot of time and a lot of watering, and is probably the reason the commercial growers don't do it.  The idea is to cheat the scleroti into germination.

Wouldn't the sowing of spring onion seed do the same thing? I did try it last year and had an uninfected crop which I pickled. The roots on them were massive.

I cannot find any info as to when the sclerotia are formed. I am assuming they are formed after the white mould has finished (autumn?) and therefore removing the affected onions removes the white rot. I have marked the places and will remove the soil. The neighbouring plants remain unaffected which suggest to me that I have removed the problem in time.

Several members have mentioned the garlic powder method but i canot find any reports on their results.

 

[realfood]

I have previously posted about this method, and today I applied liquidised garlic to a bed that will be used for alliums next year. My alliums this year are being grown in a bed that was treated with liquidised garlic last year, while the soil was still warm. It works best where the soil temperature is about 15c, so do not leave it too late in the year.
The control method is to trick the dormant “sclerotia” into thinking that there is an allium growing beside it, by watering on a ground-up garlic bulb solution of 1 part garlic solution  to 1000 parts water, say one ground-up garlic bulb to a watering can of water. This should be watered onto 1 sq m of damp soil. It is best to be watered onto the ground when rain is expected, so as to take the garlic water deep into the soil to contact the maximum number of “sclerotia”.

Strip the garlic cloves of their papery wrapping and cut off the basal plates before you grind the cloves up, to cut down the danger of introducing any disease. You should be able to taste and smell the garlic in the solution. It should be applied when the ground temperature is between 10c and 20 c with an optimum temperature of 15c.

It should be watered onto the ground that you intend to use for alliums, during the preceding year while the ground is moist and warm.

It is also possible to use garlic powder which you can find in equestrian stores or on-line, as it is used for the treatment of horses. This should be applied at a rate of 250 lb to the acre. Roughly 125 Kg per 4000 sq m, or roughly 30 gm per sq m. This has the advantage of having been sterilised and unable to pass on any allium infections but is not so effective.
Interestingly, it seems that UK farmers are already successfully using a similar method of applying heat-treated onion waste to trick the dormant “sclerotia” to wake up, and subsequently die in the absence of the host allium crop. See http://www.farmersguardian.com/fighting-allium-white-rot-and-the-uk%E2%80%99s-waste-problems-with-composted-onions/23430.article (link no longer working )

[realfood]

I do not think that sowing spring onion seed would be effective as you are giving the sclerota something to feast on. You are most unlikely to see the sclerota as they are black and  smaller than a pin head.

[Yorkie]

You mention that the pathogen is spreading round the plot.  One reason for this is likely to be transfer on your boots and/or gloves, trowel etc. 

[bigben]

I fear Yorkie might be correct and you might need to do more than just the bed you plan on growing onions in next year. The other thing to watch is dont compost anything with whiterot or you really will be causing yourself problems.

[Ivor Backache]

I do not think that sowing spring onion seed would be effective as you are giving the sclerota something to feast on.

That is my point. I am sowing onions to make the sclerotia germinate, and then I remove the host plant and burn it. It has parallels with removing a weed before it can go to seed.

Thank you for the very detailed method of preparing the garlic solution. I will be lifting early potatoes in the next weeks and I shall treat the soil as you prescribe.