beckygardener said:
In all honesty, the plants in my yard that get the most rust also seem to be the ones that get the most sun. I have a lot of daylilies that receive some shade during the day and most all of them look pretty good. Not an overwhelming amount of rust. Could rust infestation be dependent on the stress of the plant? If my daylilies get too hot and dry because of too much sun, they appear to be more prone to rust?
It may depend if the soil analysis (amount of nitrogen and potassium) is different between the two places or there is some other environmental factor. Rust spore germination is inhibited by high light - infection is most likely to happen between evening and early morning when the leaves may be wet, the temperature optimal and the light low according to Mueller and Buck's paper Effects of Light, Temperature and Leaf Wetness Duration on Daylily Rust. Plant Disease. 2002 Vol 87 No. 4 442-445.
The environment is not as much of a factor once the infection is established. Having said that, other people say rust is worst where it is shady which is what one would typically expect. It may depend on what's causing the shade and where the bed is in relation to it. Shade would keep the light lower and the leaves wet longer, things rust likes.
Stress is a controversial aspect. Some experts say it actually reduces rust others say it depends on the stage in the lifecycle. There was a lengthy article years ago about how stress from insects etc. can reduce rust on other plants, but I'd have to find it again. The idea is that since rust needs living tissue to survive then it will do better on a healthy plant. If you think about when daylilies are shipped, that's a huge stress, yet often they can be carrying rust that doesn't develop for several weeks after they arrive.
We only see the rust once it has produced spores, we don't see it when it's happily feeding away inside the leaf and stealing nutrients before it sporulates.
