Exit pass for club root
Brassicas – cabbages, broccoli, cauliflower, brussels sprouts, radishes, turnips, stocks, wallflowers and other plants belonging to the family Brassicaceae ( Cruciferae) – are prone to club root.
The name derives from the damage the disease does to the roots of its host plants, deforming them into club-like lumps.
Primarily associated with warm, moist, acid soils, the disease spores can rest in the soil without any host plants for between 7 to 21 years, which makes it a real problem if anyone is unfortunate enough to have it in their gardens.
As club root is a soil borne disease, be careful about introducing soil from other areas including new top soil, soil on tools or boots, plants from other places grown in soil, including bundles of soil-grown plant seedlings.
When young brassica plants reach a certain stage, the infected roots restrict the amount of moisture or food available to the foliage. The leaves then turn yellow, droop and the plant dies.
There is no chemical treatment I am aware of that will eradicate the disease. The only known way to kill club root in infected soil is by using or applying steam – an unlikely option for most people.
As the disease prefers acid conditions, heavily treating the soil with soft garden lime will make it difficult for the spores to spread to the roots.
I have recommended using potassium permanganate (Condy’s crystals) as a soil drench to sterilise the soil in the planting area. Dissolve 3⁄ teaspoon of Condy’s
4 crystals into a litre of water along with three tablespoons of salt.
Once dissolved, add another 9 litres of water and apply one litre to each planting hole prior to planting. This appears to sterilise the soil, giving seedlings a good chance to establish, grow and hopefully reach maturity before the disease chokes off growth.
Planting quick maturing crops or planting crops after treating the soil in the early autumn can also work as the disease prefers a warm environment, not the cold soils of winter.
Unfortunately, Condy’s crystals also destroys beneficial microbes and fungi. An answer could be a product called Terracin which suppresses soil pathogens and helps increase beneficial soil life.
About a month before planting, drench the soil with Terracin according to the label instructions.
Ensure that the treated area extends a metre or more beyond where the seedlings will be planted.
Liming the area is advisable, keeping the soil moist, but not with chlorinated water as it kills beneficial microbes.
Three weeks later apply Mycorrcin (or Thatch Busta) to increase the beneficial microbe populations.
Plant the seedlings a further week after this.
The objective is to surround the roots with enough beneficial microbes and fungi to restrict the spread of the damaging spores.
Planting brassicas, other than the fast maturing bok choy, is not practical until after the shortest day, with August the preferred time for most areas, so there is plenty of time to plan an assault on club root.
Problems ring me at 0800 466 464 (Palmerston North 357 0606) Email email@example.com Web site www.gardenews.co.nz
Gardeners wanting to grow beautiful heads of broccoli first need to get on top of club root. Photo: FAIRFAX NZ