On 24 July, PSD ordered the suspension of products containing aminopyralid after reports that residues of the chemical can affect peas, beans and other legumes, carrots and parsnips, potatoes and tomatoes, and lettuce crops.
Amateur gardeners first reported that the herbicide - used by farmers to control broadleaf weeds on grassland - was distorting crops in their gardens and allotments. This is because the chemical can be passed into the manure they use when it is consumed by livestock - either directly or as hay or silage.
Earlier this month the Organic Growers' Alliance (OGA) reported that commercial growers, both organic and conventional, were also at risk of being affected.
The OGA wrote to the PSD, the Food Standards Agency and the Health & Safety Executive calling for an immediate ban of the use of the product, which had not been cleared for use on crops for human consumption.
PSD, before it decided to ban the product, confirmed that the highest aminopyralid residues would not be a concern for health, so vegetables "should" be safe to eat.
However, the OGA questioned whether this meant that commercial crops affected by the herbicide would be safe to sell and asked each of the agencies for a public comment on the safety of contaminated crops - and how land that manure has been spread on should be treated.
A week after the OGA's request, PSD banned the product.
PSD said in a statement: "PSD has already confirmed that using manure, which may contain residues of aminopyralid, does not have implications for human health.
"However, in response to the concerns ... about damage believed to result from these residues, PSD has been in contact with Dow AgroSciences, the approval holder and data owner for the majority of aminopyralid products approved in the UK."
It added: "Dow AgroSciences has asked for its approvals to be modified while the situation is under investigation.
"PSD has accepted this and amended the approval of all products containing aminopyralid to suspend the approval for sale, supply and use with immediate effect while further investigations are undertaken."
OGA chairman Alan Schofield, who has been a vegetable grower for 26 years, welcomed PSD's decision on the chemical.
He told Grower: "This is excellent news and I am glad that the PSD has listened to the mounting evidence against aminopyralid.
"I welcome (PSD's) caution in this matter and hope that a review of this (and related compounds) leads to their permanent withdrawal from use."