Onions - White Rot, Botrytis and Thrip
12th Aug 1998
Even though my exhibition onion bed has been ravaged by white rot disease , I was quite pleasantly surprised that I was able to harvest over a dozen onions from the four growing beds in the end. There are still a couple more to pull up once they arrive at the right size and hopefully will give me enough to select a decent set from them.I realised earlier on this year that I wasn't going to get really large bulbs so I concentrated my efforts on getting a matching set at around 21" in circumference and to do this, the bulbs are harvested at different times just as they arrive at that measurement. This means that you must have a tape measure close to hand on a daily basis and to monitor the onions progress, the measurement and the date is written down on the black and white polythene next to the onion. This gives you an indication on the growth rate and when other onions in the beds are likely to achieve whatever size you have set yourself.
From the end of June onwards, it was noticeable the a couple of tops on the onions had flopped over and this was a sure sign that growth had come to an end with no new leaves pushing through the centre. When I gently squeezed the onions neck, it was very soft with only the existing foliage now giving any added growth. From this point onwards, I lifted up any collapsed leaves and kept them upright using plastic plant support clips to canes and made a note of their circumference. They actually continued to swell out with most of them putting on an amazing inch a week.
Botrytis and Thrip
Although this summer has been dreadful in many ways, I was rather surprised that I had no sign of any botrytis affecting the onions even though the weather was damp and conducive to spores spreading around in an enclosed area such as under a polytunnel. The disease usually manifests itself around soil level as a dullish greyish blotch on the onion skin and a very close eye needs to be kept on the bulbs throughout their development. Another pest that has kept well away this year has been the thrip. I never saw any at all this season and I'm just wondering whether or not the cold weather has been conducive in keeping this pest under control.
I did get ants which just loved the dark environment underneath the polythene and I found that the best cure for them was a good soaking of Armillatox into the soil around each onion bulb. This has no harmful effect on the onions at all and, having carried out this treatment during the first week of July last year , my harvested onions had the most beautiful skin colour. Indeed they kept so well that I was able to take ten of those onions with me to stage on my stand in the USA after having been out of the ground for 9 months and kept in a cold store.
To get the best skin condition on your onions I personally feel it's necessary to remove any split skins a few days prior to lifting them as this will allow any slight ripples that you have in the onion to fill out so that when harvested, it will have a lovely sheen and be as smooth as silk. Once lifted, trim off the roots level with the base plate and give each onion a wash using some lukewarm water where a dash of washing up liquid has been added. Dry them up and powder them using talcum powder or better still, some zinc starch and talc (if you can still get hold of some) which leaves the onions in a lovely silky condition as well as allowing the bulbs to dry uniformly.
Where to store the onions is a regular question that I'm asked and usually mine are kept in the garage on a bed of fine hardwood saw dust. I have kept them in a spare bedroom as well as in the attic and in the potting shed; however one thing is important - don't keep them anywhere there is any dampness in the air as the spores of botrytis can still get at them.
It takes a minimum of three weeks before you can safely show them as by then the necks will have gone down sufficiently for you to tie them with raffia; they will also be starting to develop a lovely harvested colour. However the onions will improve again for a few weeks after which point the bulbs shrinks inside their skins and they begin to split which will cost you dearly, particularly at National level. One thing to remember if the onions are really large and heavy with good strong tops is to make sure you allow yourself at least a month to five weeks from pulling them from the beds to having them ready for staging at their first show in pristine condition.
Before tying the bulbs necks with raffia, make sure that you first soften the outer skin around the shoulders of the onion as failure to do this will inevitably lead to the paper thin skin cracking around and underneath the tied area, again leaving you vulnerable to be down-pointed by the judge. Hot water applied around the neck with some cotton wool and left on for a few minutes will do the trick as will Vaseline Intensive Care carefuly rubbed into the skin. However do make sure that, at the end of all the preparation work and prior to leaving home to stage them, they are well dried off from all the water, Vaseline and talcum powder!
As the show season is now slowly creeping upon us, may I wish the best of luck to all of you who are competing and don't worry unduly if it's your first time and you haven't won; losing can often be the gateway to success, provided you learn from your mistakes and go home determined to win the laurels on a future occasion.