‘Late blight’ con­trol tac­tics

Amateur Gardening - - Your Letters -

I’M writ­ing about the ar­ti­cle ‘How can we beat blight’ (AG, 16 Septem­ber). It does give quite sound ad­vice but I thought I would add a lit­tle to it. Prop­erly known as ‘late blight’, the fun­gus af­fects both pota­toes and to­ma­toes with out­door to­ma­toes be­ing af­fected more than glasshouse crops. Con­trary to your ar­ti­cle, the blight spores are most un­likely to over­win­ter in soil or com­post in the UK. Spores will not over­win­ter in blighted fo­liage in the com­post heap. The fun­gus can over­win­ter, how­ever, in re­ject pota­toes left in the ground. I would de­stroy any blighted pota­toes and not al­low them to sur­vive over win­ter. If you no­tice rogue pota­toes ap­pear­ing next year, get rid of them.

The ad­vice re­gard­ing good ven­ti­la­tion is cru­cial to good blight man­age­ment but is eas­ier to do for to­ma­toes. In­fec­tion can of­ten start on the stems, dark brown patches be­ing seen fol­lowed by the rapidly spread­ing fo­liar black/brown rot if the weather is warm and wet/hu­mid. Keep­ing free air move­ment around the plants can do much to stem spread; re­move basal leaves as they be­gin to get old and even re­move younger leaves and side stems up the plant if by so do­ing you can cre­ate bet­ter ven­ti­la­tion around the stems. A cop­per based fungi­cide for ed­i­bles will help but a con­tact treat­ment will only pro­tect the plant sur­face it is sprayed on. It is im­per­a­tive to get your first spray on be­fore disease ap­pears. I ap­ply to my out­door to­ma­toes when they are 45cm high, mak­ing sure you treat the lower stems. When young fruits ap­pear I stop any chem­i­cal treat­ment and rely on ven­ti­la­tion to keep the fun­gus at bay. I still ex­pect some blight very late on, but by then I will have reaped the re­wards al­ready. Prof. P E Rus­sell via email

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