According to one paper, about two decades ago, half of Hanoi province’s land was used for agriculture.¹ I don’t know the relation between the province and the city area. However, at table 4 there are supposedly 0.25 ha of agricultural land per household in the City Districts—more than in certain other areas in Hanoi province! A decline in the proportion of land dedicated to agriculture is likely to have occurred. But urban agriculture does not seem to have been eliminated. According to another (2010) article, the local government considers the growing of ‘modern’ vegetables (instead of less appealing rice—I don’t really understand this æsthetic preference) an important priority in preventing the city from looking outdated.² A reasonable number of farmers are interviewed. This suggests that a good number of urban farmers remained at least then. The most recent article I can find is from 2019, when the Asia Foundation published a post on their blog about a programme to assist local farmers.³

It’s very easy I think to forget that agriculture isn’t entirely squeezed out of highly urbanised Asian cities.I only realised recently that there were farms in Singapore: my relatives never mentioned them, even though they are always very eager to show me other parts of the city—possibly because they don’t know about them.

Returning to the original article, then, crops probably do pose a problem in controlling rat populations.

1: https://journals.sagepub.com/doi/pdf/10.1177/095624780301500...

2: https://journals.openedition.org/factsreports/464

3: https://asiafoundation.org/2019/07/17/going-green-urban-farm...