Low soil temperatures could see maize crop growth stunted by grass weeds.
Many Northland crops have more grass weeds germinating than previous years, said Ravensdown Agrochemical technical manager Ryan Glover.
"The difference in maize crops with poor and good weed control practices is massive."
"Grass weeds compete for nutrients, space and light," he said.
"If not controlled they reduce maize yields through further light competition with the lower maize leaves. Weed pressure will also cause maize to hold upper leaves more upright reducing the light intercepted, reducing overall yield.
