These are all contributing factors. Mono cultures mean a single problem with pests can rapidly spread. Using pesticides means you wipe out a lot of the local wild life; including any predators that might go after the insects that spread the pests. And if you grow the exact same variety of the same produce, they are all going to be vulnerable to the exact same thing at the exact same time. Using more pesticides just adds to the problem and eventually pests become resistant anyway.

A solution here could be growing a larger variety of produce, using organic farming practices, crop rotation, etc. Pests tend to specialize in specific things and most pests have natural predators. So, if you stop killing those they'll help keep outbreaks in check. And if you rotate crops, you take away the food source for the pests. And if you grown a variety of different things, it won't all get sick at the same time.

In the past, "monoculture" was used to describe things like "one particular variety of banana"[0] - e.g. the Gros Michel banana fell to fungus and was replaced by the Cavendish banana, which was not susceptible to the same fungus but is now also falling to a similar fungus, and will be replaced by another banana variety. In fact, they're not just the same species but closely related cultivars - both part of the AAA banana cultivar group (triploid cultivars of Musa acuminata).

The article in Time Magazine puts it succinctly:

> There’s a name for this situation: monoculture, the practice of fostering just one variety of something.

In the case of bananas (and many other crops, plants, decorative trees, etc), a diversity of varieties would have minimized the spread and impact of pathogens, while providing a more diverse selection of nutritional content and flavor for consumers. But that doesn't seem to be the case for citrus trees.

I don't think that "monoculture", as it has been used or the past 50+ years, is the appropriate concept to apply to this citrus greening. Perhaps we could criticize something else - like tree density? Or perhaps monoculture is the problem, but in a much broader sense - maybe a grove with 10% citrus trees, 10% corn, 10% soybeans, 10% berries, 10% apple trees, etc...would create a biome that was hostile to the citrus greening bacteria in such a way that it couldn't thrive and spread. We have no data to support that hypothesis at this time though.

0: "What We Can Learn From the Near-Death of the Banana" https://time.com/5730790/banana-panama-disease/