Cold weather forced the state to postpone spraying for mosquitoes early today around the Inner Harbor in Baltimore.
The Department of Agriculture decided to delay the spraying late yesterday after receiving forecasts of downtown temperatures in the 40s overnight.
Spraying is considered impractical when temperatures fall below 55 degrees, because the mosquitoes don't fly.
"We're day-by-day at this point," said department spokesman Don Vandrey. The forecast calls for lows tonight in the low to mid-50s.
The spraying program was planned in response to the discovery of a dying crow in Federal Hill that later was found to be infected with the West Nile virus.
Two other crows infected with the virus have been found in Maryland this year, prompting ground spraying last weekend in the Relay section of Baltimore County and in Columbia.
No infected mosquitoes have been found in the state, and no human cases of the illness have been reported.
West Nile fever can produce flu-like symptoms in healthy adults, but it is rarely fatal. Thousands of New Yorkers were infected last year, with seven elderly people dying from the disease.