Maize is the staple crop in the southern African nation, where the government has set a target of 2 million tonnes this year after a devastating drought in 2016.

Godfrey Chikwenhere, the chief entomologist in the Ministry of Agriculture, said that the armyworm was affecting crops in eight out of Zimbabwe's ten provinces. The government has not yet estimated the amount of maize affected, he said.

The worms become moths and their name derives from the fact that they "march" across the landscape in large groups while in the caterpillar stage, feasting on young maize plants and wiping out entire fields.

"The armyworm is the biggest challenge to farmers at the moment and the government has distributed a contact pesticide to eradicate the worms," Chikwenhere said.

He added that the armyworm could become resistant to chemicals if farmers did not correctly apply the pesticide.

Zambia, Zimbabwe's northern neighbour and major maize producer, has started a campaign aimed at stemming the armyworm, which has affected 124,000 hectares of maize in that country.

Source: Reporting by MacDonald Dzirutwe; editing by Ed Stoddard – used with permission by the Thomson Reuters Trust (www.news.trust.org)