Overcoming Botrytis in Tomatoes

Overcoming Botrytis in Tomatoes

by Medwyn Williams, MBE FNVS National Chairman of the NVS

This article was originally published on 18th August 1999

The new wooden tomato box that I had constructed earlier on this year has worked a treat, the plants were strong and green with the tomatoes being of excellent size. However things went dramatically amiss from around early July as they succumbed to the dreaded botrytis disease. I try not to spray my tomatoes at all if I can help it so they'd had no fungicide protective spray applied prior to me noticing this serious problem.

Strain of Botrytis

The fact is that this year, particularly down in South Wales, there has been a lot of such problems and even Charles Maisey; who is well known for his brilliant dishes of tomatoes at national shows; has more or less lost most of his plant along one side of his greenhouse. This particular strain of Botrytis first shows itself as a brown patch on the leaf and if left untouched will progress right through that leaf into the stalk area and eventually it will work it"s way into the main stem itself rendering the plant useless, the dying leaf will have a crinkly appearance similar to Autumn leaves.

Fruit

Not only does it affect the leaves it also attacks the fruit via the calyx and if you see fruit dropped from the plant onto the ground you will notice a greyish soft area around the dying calyx leaf where the disease has taken hold. Having spoken to one of the countries top commercial growers it seems that the disease will always attack damaged or scorched leaves and never attacks healthy undamaged plants. Now none of us will deliberately damage our foliage and it doesn't matter how careful you may be, damage will occur through nature.

Leaf Scorch

After a few dull dark humid days followed by hot dry weather, leaf scorch occurs by the way of brown marks along the outside edges of the plant, this is caused by calcium deficiency and it"s these leaves that will be first attacked by the disease. Another awful thought is that very strong dark green plants will succumb to this problem easier than pale green medium sized stalk plants. The way apparently to ensure that your plant is growing correctly is to measure the diameter of the stalk 10 cm down from the growing tip early in the season, before you stop the leading shoot; it should measure 6 to 8 mm in diameter at this point.

Thickness of Stalk

If the stalk is much thicker than this then a leaf or two can be removed from the top of the plant, this will reduce vigour and in turn reward you with larger fruit. If however the stalk measurement is less than above then thin the fruit down on the top trusses. Well I couldn’t believe this, there I have been all these years trying hard to get a strong growing plant on the basis that it would be resistant to disease and produce a far superior crop of tomatoes; you most certainly live and learn!

Sap Flow

Unfortunately there isn’t a lot that the small amateur grower can do in a small greenhouse whereas the commercial grower will even things out during cold weather by having the heat switched on to increase the sap flow in the plants. The best thing to do according to this expert is to remove the stalk or even the whole leaf with a sharp knife or secateurs well back into clean flesh.

Acid

The alternative, believe it or not, is to spray the affected area with acid and that is best done with PLJ, pure lemon juice. Another type of acid that will do the trick is vinegar, both of these are to be used neat but not to spray the whole plant.

If it’s only in the leaf then cut it out and spray only the stalk or main stem area where the disease is noticeable. This is actually what they do on a commercial scale by applying the juice or vinegar directly onto the affected part and the plant monitored from that point on. There is no need to powder or spray the cut end of a stalk or leaf as it should heal naturally.

Potash

As the plants are now ripening up it will help to give them a really high potash feed such as Chempak N°10 which has a ratio of 13:0:45, in other words enough Nitrogen for continued growth, no Phosphate and a very high dose of Potash for good ripening. This was the feed that Frank Mercer from the Wirral used a few years ago on the tomatoes that he won with at the Welsh championships when staged at Wrexham. They were the variety Goldstar and probably that dish was one of the best that I have seen, top size with a bright red colour and still rock hard.

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