Page 13 - Simply Vegetables Spring 2022

wet summers and not hot dry ones. The sclerotia can only germinate once so if they can be tricked into germinating and there are no Allium plants present, they will die – more on this later.
Control – there is not one at present either for commercial or amateur growers, it is virtually impossible to eliminate the disease, so the main method of defence is prevention. Do not buy seedlings unless they are grown in sterilised compost and only buy sets from reliable companies.
Keep all tools, equipment and boots clean and clean between sites if you have a garden and allotment. If you know the disease is local take extra care, wash tools, boots, wheelbarrows, and machinery in a solution of 1 part bleach and 4 parts water.
If any plants get onion white rot carefully dig them up and put straight into a plastic sack and into the dustbin, remove as much of the surrounding soil as you can – do NOT compost.
If possible, grow your onions from seed as the disease is not seed borne, prick out into modules or pots into
sterilised compost and grow
on to transplant. If the soil is
infected raised beds could
be constructed but ensure
there is a break between the
bed soil and underlying soil.
derived from garlic and other related Allium plants. Along with diallyl trisulfide and diallyl tetrasulphide, it is one of the principal components of the distilled oil of garlic. It
is a yellowish liquid which is insoluble in water and has a strong garlic odour. This is likely to work similar to the above.
Using crushed garlic diluted in water could work similar to the above, a good use for garlic in my opinion!! The following have been tried experimentally and have worked reducing the infection by over 70%, garlic oil, onion oil, onion powder and garlic powder; also, onion waste also appeared to work.
CLUBROOT OF BRASSICAS
Clubroot is another serious soil borne disease that attacks Brassicas and other closely related plants including some flowering plants like wallflowers, Aubrieta and some stocks as well as weeds like shepherd’s purse, charlock, and hedge mustard. The disease is caused by a fungus like micro-organism called Plasmodiophora
plants as a gift unless you are very sure they are not infected.
Most of the Brassicas can be sown in seed trays or modules and then potted
up into small pots, grown on and potted
up into 15cm pots before planting out.
This produces a plant with a good root system which normally allows it to produce a decent crop even though it becomes infected with the disease.
Liming prior to growing Brassicas can help to prevent or reduce the disease, aim for a pH of 7.2 as this seems to give the best control. Do not go any higher as this can cause nutrient deficiencies. Trials have shown that raising the pH from 6.5 to 7.0 reduced clubroot infection from 70% to 40%. Improving the drainage or growing the plants in raised beds can help as there is les water in the soil for the zoospores to swim in so restricts the spread.
Good weed control is important especially of shepherd’s purse, charlock, wild radish, and hedge mustard. Also do not grow Brassica green manures as these will become infected and spread the disease.
Possible, the best control measure is to grow resistant cultivars, these include:
• Brussels Sprouts – Crytus and Crispus
• Calabrese – Monclano
• Cauliflower – Clapton and Clarify
• Cabbage – Kilaxy, Kilaton and Kilazol • Swede – Marian
There are likely to be other resistant
cultivars bred in the future so check the seed catalogues.
Ensure the soil is not deficient in Boron as this seems to have some effect on clubroot.
I have heard reports that the fertiliser Perlka gives some control of clubroot,
and the product publicity claims to if used correctly. Perlka is Calcium cyanamide
and supplies nitrogen, calcium and a little magnesium, the nitrogen is in a slow- release form which is useful for Brassicas. Use Perlka as a base dressing before planting at 50 to 100 gms /squ metre and apply 10 days before planting and then give a top dressing of 50gms /squ metre three to four weeks after planting keeping the fertiliser off the leaves.
Like onion white rot if the resting spores germinate and there are no Brassica
plants present the spores die, so if the
soil was watered with exudate and the spores germinated over a period of time
(4 to 5 years) the disease would reduce considerable. As a bit of a long shot it may be worth macerating old Brassica leaves (try using a blender, don’t tell the chef!) and watering it on the soil. I don’t know if this will work but is worth a try.
I am sorry I cannot give any cure for these two diseases but hopefully the above helps members to produce a reasonable crop.
If rotation is tried it needs
to be as long as possible to
allow the infection level to decline and a minimum is 10 years or longer.
Shallots and garlic and also sets can
be started in small pots or large modules in multipurpose compost, once they
are growing pot them into 15cm pots to grow on and then plant out once they are established. This should allow you to get a crop especially if the infection level is low.
Spring onions and the overwintering Japanese onions are very susceptible to the disease as the soil conditions are ideal for it, moist and cool. You could try growing them in polytunnels where it can be kept drier.
Resistant cultivars include Santero F1 and Golden Bear F1, I am not sure what level of resistance these have but should be worth a try.
A couple of log shots that may be worth a try are using materials that give off similar materials to the Alliums. Research has been carried out and this does seem to have some effect. The compounds cause the sclerotia to germinate but as there
are no Alliums present the fungal growth dies and eventually the spores die out. Garlic powder seems to work, apply it twice a year once in April and the second in September; if repeated for 3 to 4 years many of the sclerotia will have germinated and it may be possible to get a reasonable crop.
If you can get hold of Diallyl disulphide which is an organosulphur compound
If the soil is infected raised beds could be constructed
brassicae that are related to slime moulds. These cause swellings on the plants roots which reduces the plant’s ability to move water and nutrients within the roots. This causes stunting, leaf wilting and purplish tints on the leaves and in bad cases the eventual death of the
plant.
The disease survives in the soil as thick
walled long lived resting spores, some which can live for up to 20 years, although it is likely many die within 5 to 7 years. Therefore, short rotations are a waste of time. Once it is established it is nearly impossible to eradicate it. Infection occurs from mid-summer to late autumn.
When Brassicas are sown or planted into an infected area the roots give off an exudate that stimulates the clubroot resting spores to germinate and produce motile zoospores that can swim in the soil water (not Olympic champions though!). They infect the roots via the root hairs and once inside the roots produce galls that restrict the movement of water and nutrients. When the plant dies the galls, breakdown releasing more resting spores into the soil. For infection to occur the soil needs to be wet and above 16°C.
Control – there are no chemical controls for clubroot for either commercial or amateur growers and the best control is prevention; this starts with good hygiene and ensuring tools, equipment and boots are cleaned after use especially if using on different plots. Do NOT compost infected roots, place in a plastic sack, and dispose in the dustbin. When buying manure check that the animals have not been fed with clubroot infected crops like turnips. Only buy clean plants from reliable sources grown in sterilised compost. Do not accept
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