On 18 Sep 2019 16:18, Jeff Layman wrote:
I pulled up my tomato plants yesterday (growing outside) as blight hit
them with a vengeance, taking only a couple of days to spread. The
interesting thing is that this blight hadn't read the books stating that
it is supposed to spread most readily in warm and humid weather. Or,
again, is that correct? Wikipedia says it is favoured by cool, moist
environments: "The pathogen is favored by moist, cool environments:
sporulation is optimal at 12-18 °C in water-saturated or nearly
saturated environments, and zoospore production is favored at
temperatures below 15 °C. Lesion growth rates are typically optimal at a
slightly warmer temperature range of 20 to 24 °C". But I guess it
depends on what you think is "cool".

Down here in south central Hampshire it has been a bit warmer the past
few days (around 20 - 21 deg C or so), but it has also been very dry,
with no rain for at least a fortnight, and precious little for a few
months before that. At the time of posting this, RH is apparently 45/
55% outside (depending on which humidity meter you believe).

So have the books got it wrong? Is it all down to luck and wind
direction? Out of interest, Phytophthora infestans is always associated
with potatoes and tomatoes, but does it have much effect on other,
particularly solanaceous, plants? There is some very limited information
he
https://www.cabi.org/isc/datasheet/40970#tohostsOrSpeciesAffected, but
that's all I've been able to find (and I don't have access to the
reference quoted).

We have had some heavy dews over the last week or so, could that be it
coupled with the cooler nights.
I sprayed mine with Bordeaux Mixture and not had any rain to wash it
off.
--
Regards
Bob Hobden