The Wolbachia method is primarily associated with the control of the spread of viral diseases by mosquitoes. Wolbachia is a genus of bacteria that infects arthropod species, including a high proportion of insects. When present in mosquitoes, these bacteria can reduce the ability of viruses like dengue, Zika, and chikungunya to be transmitted, hence the association with disease control.

Option 2, conversion of crop residues into packing material, is primarily a procedure connected to waste management and recycling, having no relation with Wolbachia.

Option 3, producing biodegradable plastics, typically involves chemical processes or the use of other bacteria, not Wolbachia.

Option 4, producing biochar from thermochemical conversion of biomass, is a technique associated with sustainable agriculture and carbon sequestration, again without any relation to Wolbachia.

Therefore, the correct option in the context of the Wolbachia method is option 1: `Controlling the viral diseases spread by mosquitoes.`