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 )