RAIN last month made this season's grain harvest even more hectic than usual for Nandaly grower Greg Martin.

As the wheat and barley came off, the summer weeds began to rear their ugly heads and suck valuable moisture from the soil.

So, while other family members drove the header during the day, Greg would jump into his new self-propelled sprayer in the middle of the night and head across the newly bare paddocks.

"We're about halfway through spraying now," he said.

Greg, who managed the family farm with his brother Chris, and their wives Jacinta and Lucy, said they had converted to a no-till operation five years ago and had no intention of cultivating the soil again for any reason.

"I'll never go back," he said. "It's not cheaper (for controlling weeds).

"We had a lot of wind erosion problems in this country.

"There's also the benefit of cropping 100 per cent of the farm 100 per cent of the time, which is a bonus . . . and there's been no reduction in yield."

Greg said his three-week-old Case 4420 Patriot sprayer, with its 36.5m boom and a top working speed of 30km/h, was capable of covering more than 400ha a night.

"You can't do that with cultivation," he said.

"The cost of Roundup has been a problem, but it's coming back down."

Greg said the main problem weeds on their 5665ha at Nandaly and Pier Millan were afghan and paddy melons, heliotrope and self-sown cereals.

The crop rotation focuses on cereals, with 15 per cent pulses sown in paddocks known to have ryegrass or brome-grass problems. "The seasons have been pretty ordinary but we've still had an OK year," he said.

"I'd like to get one year when it rains properly, so we can see what the (no-till) system can do.

"It all comes down to gross margins at the end."

Department of Primary Industries senior agronomist Rob Sonogan said summer weed control was vital and "fair-dinkum" direct-drillers were spraying weeds even though it was twice the cost of cultivating.

"By the time you include chemicals to kill weeds like heliotrope, skeleton weed and caltrope, it costs about $22/ha to spray, compared with less than $10/ha for a single cultivation," he said.

"Cultivation is more likely to be used on heavier soils with less erosion risk."

Mr Sonogan said data from the Birchip Cropping Group and Mallee Sustainable Farming showed weeds used all available soil moisture and robbed cereals of even more.

"Some paddocks are left in deficit because of the ability of the weed roots to extract more moisture than cereal roots can," he said.

"For this reason, there can be 20mm or more (of moisture) required in the soil before anything becomes available to grain crops.

"Weeds are also using up valuable nitrogen, phosphorus and other nutrients."

Mr Sonogan said research had shown good weed control could conserve 30mm to 80mm of moisture, which could translate into as much as two tonnes/ha of extra crop.