Powdery mildew spores reside in the soil. But yes, that would kill the spores on the trellis.

Good to know. Won't have to bother then. :0)

I believe fungal spores can be dormant on a dry surface. Moisture and warmth is required for germination, however. Killing those spores on a trellis, however, is like catching raindrops before they can wet the ocean. Interestingly, there are videos of people proudly spraying trellises with bleach.

Some fungal spores can. PM spores cannot. They only overwinter in soils on plant debris, which is why they stress good garden clean up at the end of the season with a case of PM.

there are a lot of species of powdery mildew. one that affects tomato for example, does not affect squash. it is one of the reasons crop rotation is recommended. if you plan to grow the same type of vegetables in the same spot, i always recommend preventives maintenance.. in other words, start treating plants before they show signs of diseases.. i recommend spraying some potassium bicarbonate diluted in water every 1-2 weeks, because if you had it last year, the chance of having it again the following are very high.

Not sure about PM spores needing soil or plant debris to survive. For commercial greenhouse gardens, cleanliness is next to godliness with regard to PM. Indoor tools live inside, outdoor tools live outside, and if done carefully, there should even be separate indoor and outdoor clothing. That's precisely to prevent PM infection. So the spores can certainly be carried on things other than soil and plant debris. It is possible, however, that they just don't last that long on these other carriers.

It is certainly true that Erysiphales are obligate parasites, in that they can't grow without a living host.

I always though PM spores just blow in and start up regardless of you cleaning up or trying to clean tools/supports/etc.

We have a very long growing period, usually lasting into late October, early November. I seem to always get PM....maybe early October. Time to pull! I haven't had PM earlier except a couple of cool falls

West coast summers are ideal for plant mildews in general because of the combination of dry soils (= drought stressed plantings) and dews or fog (= dampened, but not washed leaves). Otherwise in addition to site conditions genetic susceptibility of host plants is a big factor in the occurrence of plant mildews in all geographic locations.

There are many, many different types of powdery mildew and they differ by plant hosts. So you cannot make uniform assumptions about how they survive off the plants, how the infestation is usually spread or how best to treat.

For the most part, the vast majority of PM strains are highly climate related and only sporate when temperatures and humidity levels are appropriate......with cucurbits, this is late summer into early fall. And the spores are wind borne and do travel through the air.

Same with greenhouse crops. While good sanitation in a greenhouse setting is always a concern, cleaning surfaces will not eliminate all potential for the pathogen to return, if it even exists at all in spore form on any surfaces. PM in a greenhouse setting is far more dependent on the cultural factors involved than it is on any old spores hanging around....ideal temps, high humidity, crowded growing conditions and inadequate air circulation.