Many more crops were devastated in the northwest, where residents were still trying to recover from intense battles between the Taliban and the army last year.
At least 4 million people will need food assistance across Pakistan for the next three months at a cost of nearly $100 million.
Farmers have returned to find their fields and crops destroyed.
"I had 200 kilos of corn at my home which the flood took away with it," said Dil Aram Khan, a farmer from Pirpai in Nowshera District.
"All of our wealth is destroyed along with our wheat."
An official in Pakistan's northwestern province of Khyber Pakhtunkhwa said maize, rice, sugarcane and vegetable crops were the most affected.
Another farmer said he used to hand any excess produce to the poor.
"Now the situation is this that we ourselves are waiting for charity," Iltaf Hussain Kakar said.
The desperate situation, however, was not deterring Pakistanis from undertaking the Muslim fast in the holy month of Ramadan.
"We will fast but we don't know how will we break the fast, whether we will find any food or not. Only Allah knows," Nusrat Shah, a displaced Pakistani in Sukkur, told the Reuters news agency.
Fakhar Zaman, a businessman in Swat Valley, said: "You know the people of Swat, they would never skip fasting."
Call to reject aid
Pakistan's Taliban, meanwhile, have denounced all foreign aid for flood victims and said they can match the latest US pledge of $20 million.
"We condemn American and other foreign aid and believe that it will lead to subjugation. Our jihad against America will continue," a spokesman for the group, Azam Tariq, told the AFP news agency.
"The government should not accept American aid and if it happens, we can give $20 million to them as aid for the flood victims," he said.
||Four million left homeless
||13.8 million displaced or affected
||558,000 hectares of farmland under water
"We will ourselves distribute relief under leadership of our chief Hakimullah Mehsud among the people, if the government assures us that none of our members will be arrested."
The US announced on Tuesday it would increase its flood aid by another $20 million to $55 million.
Daniel Feldman, a senior US State Department official working on Afghanistan and Pakistan, dismissed reports of extremist groups providing aid to needy Pakistanis as "quite overblown".
Referring to US efforts to win public support in a country where anti-American feeling runs high, Ward said the US government tries to "brand as much as possible" of its aid.
"In this crisis, in the face of this disaster, we very much want the Pakistani people to know that the people of the United States are behind them, are helping," Ward said.