April 29 (Reuters) - Coffee farmers in Vietnam, the world's largest producer of robusta coffee, have sharply increased use of irrigation in the main producing regions of the country amid excessive dryness, but they are now running low on water, a report said on Monday.

So far this season, many farmers have used irrigation as much as seven times already, compared with five times usually in a normal season, and they are seeing the need to irrigate coffee trees for an eighth time if they have water, said J.Ganes Consulting LLC in notes from a crop tour in Vietnam.

"The severe water deficiency and extreme temperatures have caused nutrient imbalances for the trees," said soft commodities analyst Judith Ganes, president of J.Ganes Consulting, adding that wells used by the farmers to get water for irrigation are running low.

The report says that the hot and dry environment has favored the spread of pests such as cochinilla in some farms. That insect can hurt flowers and small fruits in the trees, leading to lower agricultural yields.

An

intense heatwave

is sweeping through Southeast Asia, and maximum temperatures measured in several parts of northern and central Vietnam ranged from 40.2 to 44.0 degrees Celsius (104-111°F), the country's national weather agency said on Sunday, adding that temperatures will not subside until Wednesday.

Vietnam's weather was the latest factor behind record high prices for robusta coffee. The market was already hot due to below-average production for Vietnam and Indonesia in the last crop, and now the climate conditions have not been favorable for the development of the new crop.

"The incidence of cochinilla in Gia Lai is extensive and not yet under control. The speed at which cochinilla can spread is very fast and so this situation is very concerning," said the report regarding one of the main coffee producing regions in Vietnam.

Ganes said there is forecast for rains coming in May, which could relieve the dryness.

(Reporting by Marcelo Teixeira in New York Editing by Marguerita Choy)