Conventional growers control the life of the vineyard with a series of toxic sprays. Their aim is to keep the vine healthy by killing anything that might be harmful to it.
In the short term, this can give the grower what he wants : large yields and little risk of a blighted crop. In the longer term, there are problems.
Contrary to what the names suggest, insecticides, fungicides, herbicides, and the rest, are not very well targetted.
They also kill much that is beneficial or necessary to the vine, including the natural predators of the pests they are designed to control.
The most significant casualty is the microbes that live around the roots of the vine. These help the plant to fix nutrients from the soil. Without them, it is unable to feed itself properly.
The solution, of course, is further spraying, this time of nutrients in the form of soluble fertilizers.
Very soon you have a weak vine with shallow roots in a dead soil.
The roots are shallow because there is no need for them to push down in search of nutrients. Everything is provided from above. The soil is for structural support only.
By this point it is extremely difficult to return to more natural viticulture. The microbial life of the soil will take years to recover, and the plant is in any case incapable of exploiting it properly.
The grower is caught. If he withdraws chemical assistance now, he will be much worse off than before he started.
Nor is this situation stable.
The short life-cycles of many of the vine's enemies mean they are quickly selected for tolerance to whatever chemical the grower is using to eradicate them.
So he has to use larger quantities, or newer chemicals, in order to achieve the same effect.
Everything the grower sprays onto his vineyard will have to be paid for out of what he makes from the land.
And the company that sells it to him has no interest in solving the problem. Their aim is to keep selling him short term fixes, because he will keep having to come back for more.
Some of what is sprayed onto the vineyard will be present in the harvested grapes, and still present in the finished wine.
How much, and how much this matters, is hotly contested.