Ohio State University researchers are testing whether chaff lining can play an assist to herbicide programmes by lining weeds up in tidy rows ahead of the sprayer. Chaff lining is an inexpensive, do-it-yourself form of harvest weed seed control: a chute on the back of the combine funnels chaff and weed seeds into narrow rows across the field, where they are easier to manage and face harsher growing conditions.

'We know other states have done chaff lining and had success with it, but can we make it fit with our specific cropping systems?' asked Amber Emmons, a graduate student and water-quality extension associate, who with Dr Eugene Law, assistant professor of weed ecology, has picked giant ragweed and waterhemp as candidates. The Ohio Soybean Council-funded work, now in its second year, confirms that a rigorous pre- and post-emergence herbicide programme is still needed; chaff lining then traps what escapes at harvest and may suppress germination if enough chaff is present.

Past research shows the practice can concentrate 95% of weed seeds such as waterhemp into 5% of a field, and it could be paired with targeted sprayers to treat only the chaff rows. Chutes can be built from materials on hand or bought for $500–1,000 — Ohio State's cost under $200 — yet Law reports farmers show more interest in seed impact mills, which pulverise seed as it leaves the combine but start at $70,000, can affect combine performance and, unlike chaff lines, promise an immediate seedbank reduction.

The first harvest surprised the team: chaff was only slightly more concentrated behind the chute than without it, though they suspect weed seed was concentrated more, since a combine without a chute blows light seed farther than heavy chaff. Studies of seed survival at different chaff densities suggest a little chaff can insulate and protect seeds while a lot can reduce germination in species such as waterhemp: a 90% cut in waterhemp emergence needed chaff equivalent to a 100-bushel soybean crop, though typical 50-bushel chaff likely still reduces germination over time.

'Chaff lining is a small tweak that provides an accelerating impact on your weed seedbank,' Law said. Corn plots have been added to gather data on foxtails, marestail and barnyardgrass, and the researchers think the tactic could help against Italian ryegrass — resistant to as many as seven herbicide modes of action — in wheat, where harvest comes before the ryegrass drops its seed.

Source: CropLife