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Hi all, this weather is making me panic! We didn't actually have potato blight last year on our site for the first year ever! There doesn't seem to be any signs yet, but I am thinking about spraying with bordeaux. Can I do this in the drizzle or does it have to be dry? Thanks

Bordeaux dooesn't stick to wet leaves and washes off fairly quicklyonce it starts raining...all you'll be doing is spraying lime on your potatoes (and spuds hate lime) and pouring copper on your soil (which the worms won't like much)...

Quote from: chriscross1966 on July 01, 2012, 11:39:43
Bordeaux dooesn't stick to wet leaves and washes off fairly quicklyonce it starts raining...all you'll be doing is spraying lime on your potatoes (and spuds hate lime) and pouring copper on your soil (which the worms won't like much)...

yes..and what is able to stick will be diluted from the effective ratio with the excess moisture.

Thanks guys! They are looking quite healthy at the moment so will keep my fingers crossed.

If you keep an eye on the weather forecast and try to spray them a day or two before rain, then the stuff will be on the leaves at the right time, though its effectiveness depends on how heavy the rain is when it arrives.

I've got to get up to the plot early tomorrow as I noticed something on my Highland Burgundy Red's that looked a bit like blight.... and I'm not some squawking newbie running around screaming "Blight" whenever a bit of potato leaf dies..... that worries me as I've had no reports of confirmed infection and none of the other potatoes look affected (and I grow some classically susceptible varieties like Lumper and PFA). Hoping it's just a side-effect of weedkiller contamination.... but I'll be out there tomorrow morning with a sprayer....

Quote from: chriscross1966 on July 01, 2012, 11:39:43
Bordeaux dooesn't stick to wet leaves and washes off fairly quicklyonce it starts raining...all you'll be doing is spraying lime on your potatoes (and spuds hate lime) and pouring copper on your soil (which the worms won't like much)...

True, bordeaux only sticks after it has dried on, but then it sticks quite well through subsequent rain.

It's far from being copper and lime though...

Actually bordeaux mixture in its traditional recipe makes a new chemical when the lime and copper mix and 'change partners' - becoming nearly-neutral (amphoteric) copper hydroxide... If it is mixed on the spot this is generated as a colloidal precipitate which is much finer than any pre-mixed powder you buy in the shops - and probably more effective.

The old DIY ways may require more knowledge and skill, but those that can hold their own with modern ways (unlike lead arsenate!) are usually the best, safest and most reliable method - not to mention cheaper.

BTW - copper hydroxide is most likely to change to carbonate - which isn't very soluble in the kind of pH recommended for growing veg. and even if it did end up on your blueberry bed, anything like the recommended humus content would 'lock' it away pretty sharpish.

In any case the amounts are trivial compared to the volume of soil involved.

Cheers.

Don't know where you are Chriscross but definitely blight here and potatoes going down like ninepins.

Swindon't