Hunger in the Countryside
One of the main concerns of the Việt Minh was the threat of hunger. In 1944-1945, a famine had resulted in the deaths of most likely over one million Vietnamese in the Red River Delta. The French and Japanese were blamed for this famine and the Việt Minh were able to harness popular discontent to gain valuable support in the countryside (Gunn).
Memories of the famine were still raw in the early 1950s, and the Việt Minh knew that they would lose valuable support and be held at least partially responsible if famines were to strike again (Lentz). Thus they were very concerned when they learned about charges that the United State's military was releasing crop-destroying insects as the French might similarly attack rice and vegetable crops in areas under Việt Minh control. Such actions would weaken their partisans and might encourage them to move to French controlled territory.
Below you can see a bird's eye view of part of Northern Vietnam showing the flat Red River Delta and surrounding hills. This map focuses on Bắc Ninh province, one of those reporting potential biological attacks between April 1952 and March 1953 as marked in a Google map showing the reported use of biological weapons. Hanoi and Thai Nguyen are also visible in this image.
Việt Minh reports note that farmers were initially quite concerned about biological weapons but that after initial exposures that did not result in crop damage or human illness, farmers grew less concerned about these weapons. Thus, Bắc Ninh only lists one reported incident. Other factors that seem to have played a role in number of reported incidents includes degree of French control of the region, with higher control resulting in fewer incidents, as well as strategic importance and accessibility, which resulted in more airplane flights.