More than a quarter of maize plantations in Embu County have been destroyed by the armyworm.
County Director of Agriculture John Ndwiga said 5,500 out of 20,000 hectares of the crop had been affected.
He said the infestation is mainly in Ugweri and parts of Mbeere.
The official spoke during the launch of a programme to mitigate the impact of the worm.
Food and Agriculture Organisation (Fao) Embu County programme officer Patrick Marangu said the situation poses a threat to food security.
"We have embarked on a pilot programme involving 300 farmers in Kagaari, Runyenjes Sub-County, to assess the modality of control," he said.
Some 50 scouts have been selected for a two-day training on a mechanical control of the worm.
The 50, who will be paid by Fao, will then train farmers at the local level on this method, which involves manual destruction of egg masses and larvae.
It is considered a simple and inexpensive option for affected farmers to curb the damage to their crop.
Mr Ndwiga said there could be massive crop failure in the region due to the infestation.
In Turima Location, Tharaka Sub-County, farmers told Nation on Tuesday that they had lost hope of any maize harvest and asked the county government to intervene.
Ms Lucy Kagendo, a resident, said they had sprayed the pest using various pesticides without success.
"We urge the county government to help us get rid of the dangerous pest before it clears our maize farms," said Ms Kagendo.
Another farmer, Mr James Kinoti, said despite Governor Muthomi Njuki having launched a campaign against the worm and directing extension officers to help growers control the pest, nothing had happened.
Mr Kinoti added that farmers in the area were not familiar with the worm and had no idea of the appropriate pesticide to use.
At the same time, more than 5,000 acres of the maize crop in Isiolo County have been destroyed by the worm.
Livestock Chief Officer Adan Jaldesa said farmers in Burat and Ngaremara have been affected by the infestation, sparking fears of losses among them.
He said the deadly pest, spotted this week, had already caused a lot of damage to crops.