Seed destruction of weeds in southern US crops using heat and narrow-windrow burning

Jason K Norsworthy,Tom Barber,Michael J Walsh,Jeremy K Green,Trent L Roberts

doi:10.1017/wet.2020.36

Abstract

AbstractNarrow-windrow burning has been a successful form of harvest weed seed control in Australian cropping systems, but little is known about the efficacy of narrow-windrow burning on weed seeds infesting U.S. cropping systems. An experiment was conducted using a high-fire kiln that exposed various grass and broadleaf weed seeds to temperatures of 200, 300, 400, 500, and 600 C for 20, 40, 60, and 80 s to determine the temperature and time needed to kill weed seeds. Weeds evaluated included Italian ryegrass, barnyardgrass, johnsongrass, sicklepod, Palmer amaranth, prickly sida, velvetleaf, pitted morningglory, and hemp sesbania. Two field experiments were also conducted over consecutive growing seasons, with the first experiment aimed at determining the amount of heat produced during burning of narrow windrows of soybean harvest residues (chaff and straw) and the effect of this heat on weed seed mortality. The second field experiment aimed to determine the effect of wind speed on the duration and intensity of burning narrow windrows of soybean harvest residues. Following exposure to the highest temperature and longest duration in the kiln, only sicklepod showed any survival (<1% average); however, in most cases, the seeds were completely destroyed (ash). A heat index of only 22,600 was needed to kill all seeds of Palmer amaranth, barnyardgrass, and Italian ryegrass. In the field, all seeds of the evaluated weed species were completely destroyed by narrow-windrow burning of 1.08 to 1.95 kg m−2 of soybean residues. The burn duration of the soybean harvest residues declined as wind speed increased. Findings from the kiln and field experiments show that complete kill is likely for weed seeds concentrated into narrow windrows of burned soybean residues. Given the low cost of implementation of narrow-windrow burning and the seed kill efficacy on various weed species, this strategy may be an attractive option for destroying weed seed.

Highlights

Chemical weed control options have been steadily decreasing over the last two decades because of increasing herbicide resistance in dominant weed species
There is a need to shift weed control programs toward strategies that involve the use of nonchemical approaches in conjunction with current herbicide programs if herbicides are to continue as a sustainable and effective option for growers
Slowing selection for herbicide resistance involves implementing several different techniques, some of which may include tillage, rotating and mixing herbicide sites of action, cover crops, and implementing a weed control technique known as harvest weed seed control (HWSC) (Norsworthy et al 2012)

Summary

Introduction

Chemical weed control options have been steadily decreasing over the last two decades because of increasing herbicide resistance in dominant weed species. Harvest weed seed control strategies are currently being investigated to determine their potential fit for weed management programs in U.S crop production systems. Narrow-windrow burning, is a widely adopted practice for destroying rigid ryegrass (Lolium rigidum Gaudin) seed and decreasing the soil seedbank when growing wheat (Triticum aestivum L.), canola (Brassica napus L.), and lupin (Lupinus angustifolius L.) in Australia (Walsh et al 2013). In southern U.S soybean production systems, there is an opportunity to use narrow-windrow burning of chaff and straw residues in an effort to destroy weed seed that escaped a weed management program and are harvested with the crop (Norsworthy et al 2016)

Objectives

Methods

Results