The label actually recommends rotating Indar with a different class of fungicide, or mixing it with a different class for resistance management. Indar is what’s called a DMI (aka SI) fungicide, with a single mode of action. DMI’s are highly susc. to selection of resistant strains of fungi. In other words, fungi can develop field resistance to DMI’s in a fairly short amount of time.
Agriculture has been using DMI’s for about 45 years and some fungi have developed resistance along the way. The development of newer more powerful DMI’s have pushed the resistance curves back, so far. The active ingredient in Indar, even though 25 years since it’s introduction, is still considered a powerful DMI.
Immunox/myclobutanil is also a DMI, so there would be no advantage mixing or rotating it with Indar, from a resistance management standpoint. You’ll note that Blueberry above is tank mixing Rally (commercial equivalent of Immunox) with Manzate or Captan. This not only increases the activity of the fungicide spray, it also helps prevent resistance buildup because they have different modes of action than a class 3 DMI fungicide.
All that said, backyard growers really don’t have to worry about creating disease/insect resistance, imo. But if you notice your Immunox is not doing the job by itself, you might want to add a little Captan in the mix.
I sometimes tank mix Captan at the half rate with some Indar, if rains have been non-stop torrential.