Tomatoville® Gardening Forums - View Single Post

bower · May 10, 2018

Well I did a hunt through my files as well as google and couldn't find that reference to spore timing, which I read maybe 3 years ago or 4 when we had a humid summer and the mildew turned up in greenhouse. At the time they were talking about two different species of mildew on tomato, and now they are talking about three.

There's quite a bit out there if you google "diurnal cycle mildew" or something of the kind, but involving the mildews on all kinds of plants - however there is cross infectivity to tomato from eg onion mildews and others. Weeds (vetch, clover, forgetmenot here) are often hosts. One of the key IPM strategies for greenhouse is also to remove weeds that host the mildew from the area, where they can blow into the greenhouse.

Anyway I may have got it wrong about spores being released at dusk. From what I'm reading now, it looks like the "conidia" (infective particles equivalent to spores) are germinating and developing during the night.

There's a general ref to mildew cycles in
https://www.annualreviews.org/doi/fu....081407.104740
The Powdery Mildews: A Review of the World's Most Familiar (Yet Poorly Known) Plant Pathogens Glawe,2008
"Conidial production and release frequently follows a diurnal pattern, with most spores becoming airborne in the period extending from mid-morning to early afternoon.."

Here's another study, looking at relative humidity, light levels and temperature. This one reports germination occuring in darkness - spore release conversely is prompted by daylight and by rapidly changing temp/light/humidity conditions at the leaf surface as happens on a sunny day.
https://apsjournals.apsnet.org/doi/p...HYTO-98-3-0270

Another study trapping spores in the wild: in dry weather, Erysiphe (one of the mildews), Alternaria, smuts and rusts were most abundant afternoon
Phytophthora infestans max concentration before noon
https://www.sciencedirect.com/scienc...07153653800343

I guess the take home message about the diurnal cycle is that they do land, germinate and produce a new batch of infective particles within the 24 hours. So the worst thing you can do is wait a day.

Some other treatments:
https://www.tandfonline.com/doi/abs/...nalCode=tcjp20
fermented milk byproduct + surfactant
citrus oil + borax
potassium bicarbonate

Some genetic resistance identified here:
http://ipm.uconn.edu/documents/raw2/...ato.php?aid=39

May 10, 2018	#16
bower Tomatovillian™ Join Date: Feb 2012 Location: Newfoundland, Canada Posts: 6,793	Well I did a hunt through my files as well as google and couldn't find that reference to spore timing, which I read maybe 3 years ago or 4 when we had a humid summer and the mildew turned up in greenhouse. At the time they were talking about two different species of mildew on tomato, and now they are talking about three. There's quite a bit out there if you google "diurnal cycle mildew" or something of the kind, but involving the mildews on all kinds of plants - however there is cross infectivity to tomato from eg onion mildews and others. Weeds (vetch, clover, forgetmenot here) are often hosts. One of the key IPM strategies for greenhouse is also to remove weeds that host the mildew from the area, where they can blow into the greenhouse. Anyway I may have got it wrong about spores being released at dusk. From what I'm reading now, it looks like the "conidia" (infective particles equivalent to spores) are germinating and developing during the night. There's a general ref to mildew cycles in https://www.annualreviews.org/doi/fu....081407.104740 The Powdery Mildews: A Review of the World's Most Familiar (Yet Poorly Known) Plant Pathogens Glawe,2008 "Conidial production and release frequently follows a diurnal pattern, with most spores becoming airborne in the period extending from mid-morning to early afternoon.." Here's another study, looking at relative humidity, light levels and temperature. This one reports germination occuring in darkness - spore release conversely is prompted by daylight and by rapidly changing temp/light/humidity conditions at the leaf surface as happens on a sunny day. https://apsjournals.apsnet.org/doi/p...HYTO-98-3-0270 Another study trapping spores in the wild: in dry weather, Erysiphe (one of the mildews), Alternaria, smuts and rusts were most abundant afternoon Phytophthora infestans max concentration before noon https://www.sciencedirect.com/scienc...07153653800343 I guess the take home message about the diurnal cycle is that they do land, germinate and produce a new batch of infective particles within the 24 hours. So the worst thing you can do is wait a day. Some other treatments: https://www.tandfonline.com/doi/abs/...nalCode=tcjp20 fermented milk byproduct + surfactant citrus oil + borax potassium bicarbonate Some genetic resistance identified here: http://ipm.uconn.edu/documents/raw2/...ato.php?aid=39