Lalambchop1 said:Someone told me that plants can respond to rust differently in different years. Has anyone found this to be true? I hate to get rid of something because it was rusty one year if it wasn't going to be consistently so.
Plant fungal diseases are dependent on the environment and since different years can have different weather patterns, this will affect the incidence and severity of diseases such as rust. As an example, if you have a susceptible daylily in your house where there is no dew, fog, rain etc. so the leaves are never wet, you can totally cover it with rust spores but it will not get the disease. This is because rust spores need a minimum number of hours of leaf wetness at the same time as suitable temperatures in order to germinate. Of course this scenario won't happen outdoors, but some years and seasons are wetter, drier, cooler, hotter, windier etc. than others and this directly impacts such diseases.
This is why it is usually recommended to avoid overhead watering or, if you cannot avoid it, don't water in the evening or overnight because that prolongs the time that there is water on the leaves allowing spores to germinate.
One of the concepts in plant pathology is what is called the "disease triangle", where one side of the triangle represents the host plant, another side represents the pathogen, and the third side represents the environmental conditions. If any one of these factors is missing, e.g. the host plant is not susceptible, the pathogen is not present, OR the environment does not favour the disease, it will not occur. If any are limited, a small amount of disease may occur. If the host is very susceptible, there is plenty of the pathogen, and the environment is very conducive to the disease, then you'll have a bad case of rust.
There's an example diagram of the disease triangle on this page:
http://www.gocorn.net/v2006/In...
