PGRO technical director Anthony Biddle warned: "Pre-emergence herbicides perform poorly on dry soil."
Applications were best made when the soil surface was moist or when rain was forecast, said Biddle, whose organisation promotes research in beans and peas.
Biddle said soil conditions in many areas had improved following spells of dry weather, and many spring beans were now drilled.
"But on the heavier land, under-surface drying has been slow and may need to be lifted before drilling can take place. This may mean drilling of beans is delayed.
"But try and plant spring beans before Easter, mid-April. Temperatures are now increasing and, once planted, the beans should establish quickly."
Anthony Biddle said growers needed to watch sowing rates. High-density beans competed for light and nutrients, resulting in low yields and high disease risk.
Optimum density for spring beans was 40 plants per sq m. For white and blue peas it was 75 plants per sq m, and marrowfat varieties 65 plants per sq m.