Tom Jaszewski wrote:
There is a link between roundup use and fusarium disease in spring
wheat. No or minimal til using roundup seems to lead to accumulation
and overwintering of fusarium in the crop debris. There is a similar
effect related to roundup and fusarium sudden death syndrome in soy.
[...]

Very interesting.

I suspect that Roundup kills a plant that contains a natural fungicide,
or else is food for some critter that eats the fungus or its spores or
else is a preferred host for the fungus, which in the absence of this
host colonises the next best thing. Or the critter that eats the fungus
also needs some other critter that feeds on a plant that's killed by the
Roundup. Or maybe the fungus has adapted to be more infectious to wheat
in the absence of its other host plants. Or maybe the "crop debris"
provides a better climate for overwintering when it contains no weeds.
Or some other subtle effect of disturbing the diversity of the
wheatfield (which is not very diverse in any case.) My reading around
these issues indicates that the cause-effect connection is very rarely a
simple one, which explains why such effects are rarely if ever caught in
the so-called testing stage of new products.