How can I separate the abundance factor of the incidence results?

I must calculate the incidence values for Watermelon Mosaic Virus in different seasons within of habitat.

This incidence data comes from infection detection of some plant sampled in different habitats (Oakwoods, Wastelands, Edges, Crops).
The plant sampled in these habitats were sampling in different seasons (Summer, Spring, Autumn)
The Crop habitat was sampled only in Summer, and the host sampled in Crops was in majority Cucumis melo species.

This virus have a preferred against Crop habitat, Cucumis melo hosts.
I calculated the incidence, and then I calculated the significant difference between them.
Fisher test, showed that the incidence is higher in summer and in Cucumis melo host.

Is it possible to separate the effects of Crop and Cucumis abundance (the unbalanced sampling of seasons across habitats) of my conclusion of significant seasonal variation?

I know that my conclusions are not really a seasonal effect. Because I sampled 10,000 melon plants for a short period in summer, and that is the preferred host.

How can I separate the abundance of the incidence results?
What statistical analysis may I perform?