ROSTHERN, Sask. – Adopting a direct seeding program that builds soil organic matter can help reduce the threat of residual herbicide damage to crops.
Eric Johnson of Agriculture Canada’ research farm in Scott, Sask., told producers at the annual Seager Wheeler direct seeding field day in Rosthern, Sask., that consecutive dry years in the western Prairies have created a situation where herbicides haven’t broken down as they normally would.
The key to herbicide breakdown is moisture and microbial and chemical activity.
Farmers might think that if they received rain in September and October they are safe from herbicide residue, but that might not be the case, he said.
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“Really a lot of the rain came too late. The soil temperature started to drop and we missed that real optimum month of July, so I don’t think we’ll have seen as much break down as many people hope.”
In dry conditions, herbicides become bound in the soil and immune from breakdown, but when rain returns they revert to their solution form and crops can be injured.
Johnson said building soil organic matter through direct seeding is one way to protect against herbicide residue problems.
He does a lot of work on the Group 2 “imi” type herbicides Odyssey, Pursuit and Assert, which are more affected by moisture than other herbicides.
“Generally on high organic matter soils you tend to have less problem with herbicide carryover.”
The high organic soil tends to have more moisture and there is more microbial activity, he said. Also, high organic soil tends to bind the chemical more tightly and reduces the bioavailability of the residue to the plant.
Soil’s pH level is also a factor in persistence. Acidic soil with a pH below seven tends to cause problems with “imi” product residue. Because pH can vary across a field, farmers can see patches of herbicide residue damage.
Spring wheat is more tolerant of imi residue than barley, and durum falls between the two.
Imi damage is identified in cereals in early two to three leaf development by the striping on the base of the newest leaf. In barley, purple colour on the older leaves might be visible. Other evidence of herbicide residue damage on cereals includes shortened internodes, thin leaves, reduced tillering and delayed maturity.
In canola, the crop will emerge OK, but then stop. Imi damage is apparent when the middle growing point turns red.
“Growth will cease,” Johnson said.
“It will just stay at that stage for a long time.”
Farmers who suspect herbicide residue damage should contact the manufacturer, he said.
And some herbicide damage isn’t necessarily the end of the world.
“If you get some herbicide injury, it doesn’t always result in yield or quality loss,” particularly if the crop gets average to above average moisture, Johnson said.
