I had my first email of the year through from Blightwatch this morning telling me that in my area, Gloucester, we have had a Full Smith Period!
I am surprised to have this email so early in the year! I 7 years of allotmenting, this is the earliest in the year that I remember a Full Smith Period!
Blight is a fungus that is spread by spores, a Smith Period is where conditions are conducive for sporulation of the potato blight pathogen. on lesions – leaf wetness is also necessary for infection to occur.
“At least two consecutive days where min temperature is 10ºC or above and on each day at least 11 hours when the relative humidity is greater than 90%. “
So keep and eye on your plants!!!!
If affects Tomato as well as Potatoes and also other Solanum.
What to look for
At first it affects the leaves, look for black botches, its a fungus, so light spores on the underneath of leaf below the black spot.
The stalks then get black spots, become putrid and slimy and if it gets to the spuds, they will turn to liquid too.
On tomatoes, the fruit will have brown/black spots.
What to do
If you see the leaves have been affected, remove them and destroy them, check he plant at least every day!
If you see it on the stalk, best to dig up straight away.
Not to be confused with
Now we are in June the first Earlies will be starting to die back, some people confuse the blight with die back, as they have been waiting for the plants to flower and then they know they will be nearly ready for digging up. BUT not all potato plants seem to flower, or at least you may have missed it, I certainly have had earlies before now that I have not seen any flowers on, and they still produce perfect little spuds!
When they start to die back they may loose their colour, becoming yellow, they will have brown patches, as opposed to the dark brown/black that is the sign of blight. They will shrivel, whereas the blight usually makes the plant putrid and slimy.
Some people may now panic and spray their entire crop, I have never used spray, if you see a blue tinge to the plant, you know they have sprayed it! I always liked to grow organically, so was against using any chemicals. But if you look at the price of the spray, and the price of the potatoes in the shop, you might as well try the method above of picking off the infected leaves, rather than panic and spray!
Alternative prevention
My allotment neighbours did not approve of my recent method of growing potatoes, but it is something that my Dad mentioned to me a long time ago.
Last year I did not weed between the potatoes! The weeds grew higher than the potatoes! But, when all around me were suffering from Blight, even my most susceptible potato plants were blight free! Due to the dense weeds around the plant, I believe they acted as some sort of barrier in preventing the spores from finding my potato plants!! And yes, I know spores are very small, and they can probably get between the weeds, but it does seem to have worked!
Good luck!
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