By Chris Hogg
BBC News, Bangkok
Farmers in the delta normally provide two-thirds of Burma's rice harvest
Farmers in the areas most affected by Cyclone Nargis need rice seed by the end of June, or Burma's rice harvest will fail, the United Nations says.
The UN has warned that the harvest could fail this year and next, making the country - currently a net rice exporter - a net importer of rice.
It says that to prevent this, farmers in the worst affected areas must be given all the help they need.
The cyclone devastated the fragile ecosystem in five coastal areas.
The UN says that, in places, the damage caused by the huge wave that hit the Irrawaddy Delta two weeks ago was worse than that wreaked by the tsunami in 2004.
Deforestation meant the wave swept further inland. Food stocks and rice seed were lost - livestock, tools and equipment, too.
Farming is the most important means of livelihood for more than 70% of Burma's population.
Usually, farmers in the Irrawaddy Delta provide two-thirds of the country's rice harvest.
The high cost of imported fertilisers and low crop prices were already making life hard for them, even before the cyclone, and for many families life was already very harsh and insecure.
Now it has got much worse.
Time running out
Diderik de Vleeschauwer from the UN's Food and Agriculture Organisation (FAO) says while the emergency relief operation continues for those in the worst affected areas, efforts need to be made now to get the region's farmers back on their feet.
"Time is running out," he says. "We are running against the clock. If rice seeds are not received within the next 40 to 50 days, planting will not happen in time, and people will not be able to harvest rice by the end of this year."
Although many paddy fields have been flooded, most can be repaired
The UN is trying to source strains of rice seed that will grow better in salty soil.
In most places the paddy fields can be repaired, but the damage caused by the seawater is harder to reverse.
The heavy rains that have fallen in the area over the last few days have helped by diluting the brackish water a little, but it is still a problem.
"In situations like this, the World Food Programme can provide rations for people so that they won't be tempted to eat any rice they've been given for seed," says the World Food Programme's Marcus Prior.
But if a new crop of rice cannot be planted in time, it will not just be the families in the delta that suffer. People across Burma will go hungry.
The UN's experts believe the paddy fields in the Irrawaddy Delta are not that badly damaged.
They could be repaired with quite basic technology, but new equipment will be needed to replace what was lost, including tractors and land tills, and livestock for ploughing - like buffaloes - will be needed.
Agencies were already providing food aid before the cyclone struck
The greatest challenge, of course, will be getting the rice seed and fertiliser to the farmers. Many of the roads in the delta are in a bad state.
The largest trucks cannot use them. Bridges have been damaged. Few vehicles are available.
The fishing industry will also need support. It is estimated that around 100,000 households who relied on fishing for their livelihood have been affected.
The destructive wave of saltwater will have washed away or smashed a lot of boats in the coastal areas, which bore the brunt of the wall of water, but those inland could have been sunk too.
Much fishing equipment will have been lost.
The UN says the distribution of simple fishing gear with the early deliveries of emergency food aid could help people to start helping themselves early on.
It may not be possible to replant crops in flooded areas straight away, but they can be fished.
Dr Simon Funge-Smith, Aquaculture Officer with the FAO in Bangkok, says that where you have people who fish as part of their livelihood, "it's a coping strategy in times of crisis. People will fall back on their natural resources."
Humanitarian organisations like the World Food Programme were operating in Burma before the cyclone struck, providing food aid to half a million people across the country.
After the destruction of rice mills, new equipment is urgently needed
UN figures showed that one in three children was chronically malnourished.
The fear now is that as a result of this damage to the area known as the country's "rice bowl", a bad situation will get a lot worse.
The bill for providing rice seeds, fertiliser and equipment is estimated by the UN to be around $243m (£122m).
To rebuild the fishing industry, "very substantial" further sums are needed.
The officials are warning, though, that if they cannot raise the money and - just as challenging - get access to the areas in need to deliver aid in time, the costs in terms of lives lost, an increase in poverty and overall economic damage to the Burmese economy will be far greater.