Determination of impact energy to devitalise annual ryegrass (Lolium rigidum) seed from one impact using double and single sided impacts

Herbicide resistance is one of the most significant challenges for cropping systems that rely on herbicides for weed control. To address this challenge, mechanical weed control methods are being investigated that apply impact energy to weed seeds in the chaff after they exit the sieve of a combine harvester. A pendulum impact tester applying a double-sided impact and a rotational impact tester applying a single-sided impact were used to apply a single impact to annual ryegrass (Lolium rigidum) seeds. The impacted seeds were evaluated for physical damage and germination potential under controlled conditions using paper and soil. A logistic regression was used to model energy dose response for visibly damaged seeds and seed devitalisation based on: normal germinated seeds on paper; total germinated seeds on paper (normal + abnormal) and emerged seedlings in soil bins. The median effective dose (ED50) of impact energy for visibly damaging seeds was lower for the double-sided impact of the pendulum impact tester (6.5 mJ) compared to the single-sided impact of the rotational impact tester (8.7 mJ). However, the rotational impact tester was more efficient at devitalising seeds having a median effective dose of 7.1 mJ and 3.0 mJ for devitalisation based on both normal germination and total germination, respectively; compared to 15.7 mJ and 6.8 mJ, respectively for the pendulum impact tester. These energy values required to devitalise seeds is data that can be used in the design of machinery for mechanical weed seed control.