Wilson died when a "catapulting" cedar branch fell and hit her while walking in the gardens nearly two years ago.
At the inquest, held at West London Coroners Court. John McLindon, acting for the Wilson family said the Wilson family believed Kew arboretum head Tony Kirkham should have said in the family-commissioned Jeremy Barrell report on the incident, and in interviews with investigating body the Health and Safety Executive, that summer branch drop could have caused the accident.
Kirkham said he had not mentioned it because "I didn't attribute" the accident to summer branch drop. Kirkham said: "The trigger was a squally wind from a northerly direction, an unusual direction, and heavy rain."
He had told the court 50km/hour gusts and 5mm of rain in the previous hour had caused the branch to fall.
McLindon said the phenomenon was identified in 1979 by Rushforth and that Professor Richard Harris had given a lecture in 1982 in which he said Kew had entrance signs warning of branch shed.
Kirkham said he could not remember the signs and neither could his predecessors but they may have referred to branches dropping after 1976's drought and because of Dutch Elm Disease.
McLinden argued that potentially hazardous areas should be roped off and there should be website warnings and signs.
He cited an interview in Horticulture Week given in July 2012, two months before the accident, in which Kirkham said cedars were among the trees that have suffered from summer branch drop because of "fantastic" growth during that year.
Kirkham said of summer branch drop incidents that year he had "no particular knowledge from Kew but generally across colleagues in other gardens and in arboriculture".
He said his statement was made "for people to be wary".
McLinden questioned Kirkham about tree maintenance record keeping and Kirkham admitted some errors. The tree was last pruned in 2000 and was on a 10-year cycle but Kirkham said Kew had a prescriptive policy for pruning rather than the regular "haircuts" McLindon suggested were necessary.
But he said: "You can't totally mitigate the risk of branch failure even from pruning."
Kirkham said Kew had improved record keeping to add more comments boxes since 2012.
He added: "I still believe what we did was right and following inspections we carried out to that tree it was deemed no further pruning was warranted."
The court heard there was a fatality at Kew in 1951 caused by a tree and that an empty pushchair had been hit by a falling branch in recent years, as referenced by a Tree Advisory Trust note on summer branch drop.
Kirkham said there were two recorded summer branch drop instances in 2013 at Kew and "about 20 incidents in the last 25 years".
McLindon cited a letter from a regular Kew visitor which said they had seen three branches fall from the cedar in 13 years.
McLindon said Kew's approach to warnings was "outdated" because it was a "doctor knows best" approach. He added that Dorset County Council warned about summer branch drop on its website.
Kirkham said: "I still don't believe that signage would deter people from walking under trees and prevent something like this accident from happening."
An external audit of Kew reported staff saying "tree inspections at Kew suffered from a lack of resources". McLindon suggested it was a matter of luck that the cedar was inspected but Kirkham denied this.
Kirkham said of 10 secondary characteristics of summer branch drop, the cedar displayed just three.
He told Patrick Blakesley, acting for Kew: "I don't think any other organisation in the UK is doing tree management to the detail we do."
Independent court-appointed tree report writer Dr David Lonsdale said the failure was "not completely typical of what might be regarded as summer branch drop", when questioned by coroner Elizabeth Pygott.
He added: "It was akin to summer branch drop but could not be attributed specifically to that cause."
He said when asked if Kew could have prevented the accident: "I don't think in the case of this particular tree there were actions that could really have been taken."
He added: "There was something about that branch that caused it to fail but that can only be seen with hindsight."
McLindon questioned Lonsdale about the risk of summer branch drop, which Lonsdale said was poorly defined in science, and Lonsdale said warning signs were not necessary under Health and Safety Executive guidelines of one in a million chance of death being a "tolerable" risk, because the phenomenon is so rare.
Kew has had one tree fatality since a death in 1951, in which time it had had about 60m visitors. McLinden cited the family-commissioned report by tree expert Jeremy Barrell on the case, which suggested a "subtle" pruning method could have prevented the branch failure. Lonsdale said that was "possible" rather than "probable".
Blakesley established Lonsdale was an independent expert, selected by Kirkham and Barrell as "the expert's expert" and established different arboriculturists would have different ideas on how to manage a tree "but if they were good arboriculturists they wouldn't be that far apart".
He said on general Kew had "very well-managed trees".
Yesterday, Wilson's friend, Tessa Marshall, who was with her when the accident happened described how it was lucky she and her three-year old daughter were not killed by the falling branch too.
The inquest continues