The widespread evolution of multiple herbicide resistance in annual weeds infesting Australian cropping fields has dramatically depleted the available herbicide options and forced investigation into the development of alternative weed control strategies. One approach that is now widely adopted in Australian cropping systems is referred to as harvest weed seed control (HWSC), which targets weed seed during grain harvest to minimize seed inputs to the seedbank.
June 28, 2016 By Michael Walsh Associate Professor and Director of Weed Research University of Sydney Australia
Harvest weed seed control came about because of an opportunity to target weed seeds during crop harvest. Farmers figured out quite quickly how to target weeds with HWSC. Their four main weed species were wild oats, wild radish, bromegrass and annual ryegrass. They all have very high seed retention at crop maturity.
Seed retention is the proportion of total seed production retained at a height that can be collected during the harvest operation (see Table 1).
Seed retention changes over time. The proportion of weed seed retention declines the longer harvest is delayed past crop maturity. Wild radish and annual ryegrass have about one per cent decrease in seed retention per day over a 28-day period. Bromegrass and wild oats have a loss of seed retention of about two per cent per day. As a result, crop and weed maturity have an impact on the success of HWSC.
What used to happen at harvest in Australia was the combine spread the weed seeds back across the field, reseeding the weeds for next year. Growers in western Australia recognized they needed to interrupt that process and started to import chaff carts from Canada. They soon developed a love/hate relationship with chaff carts, which dragged on for about 20 years. Although the carts were effective they were frustratingly difficult to use.
Chaff carts collect the weed-seed-bearing chaff material, which is then left in piles around the field. The chaff piles are grazed by livestock or moved to feedlots, but with fewer sheep raised in Australia, the piles are typically burned to kill the weed seeds.
Ten years ago, a farmer, Lance Turner, modified the chaff cart by putting an elevator system on it to efficiently transfer the chaff out of the combine into the cart. The big impact was that the piles of chaff now burned out in two to four hours instead of up to two days. As a result, the adoption has increased and, in western Australia, at least 200 of these new chaff cart systems have been introduced since 2013.
One of the first users of the chaff cart system imported from Canada was the Shields family in western Australia. They subsequently developed a completely different system, called residue baling. During harvest, all residue goes into an attached baler. Farmers in locations where excess straw is an issue, and where there are markets for this material, can profit from the sale of baled residue. At the same time, weed seeds are removed – up to 95 per cent of annual ryegrass seed can be removed in baled harvest residue.
Another innovation in western Australia is the chaff lining system, which came about because not all growers like to burn residue. Burning means a loss of nutrients. Chaff lining systems collect chaff and drop it in the wheel tracks of a tramline system where there are dedicated wheel tracks in the field. Those wheel tracks are usually left unseeded and the weed seeds are left to break down in a hostile environment.
Another chaff lining approach is to catch and concentrate the chaff into a narrow strip. This chaff is concentrated in a row placed between narrow 17-centimetre row spacings where there is a mulch effect on the weed seeds.
Preliminary research measured survival of seed placed under chaff at harvest just prior to seeding the next year. Some of the findings were unexpected. Weed seeds didn’t typically survive under canola and barley chaff, perhaps because of some allelophathic effect. Interestingly in wheat, there was quite high survival of annual ryegrass seed underneath the wheat chaff, which is unexplained. More research is required, but overall, chaff lining works to reduce seed survival and is being rapidly adopted across Australia. (See Fig. 1.)
The next HWSC technology was chaff processing, developed by Ray Harrington 20 years ago. The technology uses a rotating mill to kill weed seeds. In research conducted with the Australian Herbicide Resistance Initiative (AHRI), it was found the technology provided greater than 90 per cent control of annual ryegrass through the mill across a range of speeds, and no effect of chaff type on weed seed destruction.
The first Harrington Seed Destructor was developed in 2006 as a pull-type unit attached to the combine where it collects and pulverizes the chaff and weed seed. The combine spreads straw separately. AHRI research found it worked just as well as the prototype, with seed destruction in the chaff at 95 per cent for annual ryegrass, 92 per cent for wild radish, 99 per cent for wild oats and 98 per cent for bromegrass.
The Harrington Seed Destructor (HSD) introduced a new way to control weeds in Australia. The cost of the pull-type machine is approximately $200,000 Cdn.
In 2010 and 2011, research was conducted comparing narrow windrow burning, chaff carts and the Harrington Seed Destructor at 25 replicated sites across Australia. It compared the three systems at the same sites at the same time with effects of these at harvest treatments assessed by measuring the impact on weed emergence. The overall result was that each technology reduced annual ryegrass emergence in the autumn prior to seeding by an average of 57 per cent. There was no difference between treatments at any of the sites. This makes sense because they are all targeting the chaff fraction, and if they are working properly, they should have the same result.
Recently, an integrated Harrington Seed Destructor (iHSD) has been developed that is incorporated into the combine harvester. It was launched into commercial production in March. This is a twin mill system. The previous pull-type HSD had counter rotating rotors. The iHSD has a fixed top plate and a spinning base plate. It is hydraulically driven and is powered by the combine harvester. De Bruin Engineering of Mount Gambier, South Australia, is manufacturing the iHSD (ihsd.com).
The iHSD works very well. Compared to previous research, it worked just as well or even better, with almost 100 per cent weed seed kill on the four weed species. This is a very exciting, new, non-chemical weed control system. The company is currently taking orders and is looking at building a small number in 2016, around 10 units. In the following year, they hope to go into full-scale production.
The most important HWSC message is the long-term impact on weed populations. Research by colleague Peter Newman, starting in 2001, looked at problem fields where annual ryegrass was out of control with plant populations of more than 100 plants per square metre. Twenty-five fields were monitored with 13 of the fields using herbicides alone; another 12 fields used herbicides plus a HWSC system.
After 12 years in the herbicide-only fields, annual ryegrass populations were reduced to about five plants per square metre and were stabilized at that level after six or seven years. Where herbicides plus HWSC were used there was even better control, with populations reduced to less than one plant per square metre.
When growers reduce annual ryegrass populations down to around one plant per square metre, managing weed populations to improve crop management/cropping is so much easier because the weeds don’t dictate how you manage the cropping system. Rotations can be changed. Herbicide applications can be dropped to take pressure off of herbicide selection. HWSC adds some insurance to your weed control program at harvest time.
Across the same 25 field sites, annual ryegrass seed set was estimated. The fields with five to 10 plants per square metre have about 1000 seeds going into the seedbank per square metre. The field with less than one plant per square metre has only a few seeds going into the seedbank. HWSC dramatically changes the whole weed control program.
A survey of 600 growers across Australia looked at HWSC adoption in 2013. Narrow windrow burning was adopted by 40 per cent of Australian crop producers. This practice is most widely adopted in western Australia, but is now becoming more common across all wheat growing areas.
One of the factors that has driven the adoption of narrow windrow burning and chaff lining is their low cost. It just requires a chute to concentrate the chaff and straw material; subsequent burning or mulching will potentially provide 95 per cent control of weed seeds. One of the lessons from the development of HWSC is the need for inexpensive but relatively effective alternatives that growers can use to evaluate the efficacy of these systems for themselves.
Low weed densities are the best insurance against herbicide resistance. The biggest driver against herbicide resistance is to have fewer weed seeds in your fields.
Mageuzi ya upinzani wa dawa nyingi za kuua magugu katika magugu ya kila mwaka yanayopiga mashamba ya Australia yamepunguza sana chaguzi za dawa za kuua magugu zinazopatikana na kulazimisha uchunguzi katika maendeleo ya mikakati mbadala ya kudhibiti magugu. Njia moja ambayo sasa imechukuliwa sana katika mifumo ya kilimo ya Australia inajulikana kama udhibiti wa mbegu za magugu ya mavuno (HWSC), ambayo inalenga mbegu za magugu wakati wa mavuno ya nafaka ili kupunguza pembejeo za mbegu kwa benki ya mbegu. "Mwanzoni mwa mwaka wa 2016, Michael Walsh, profesa na mkurugenzi wa utafiti wa magugu katika Chuo Kikuu cha Sydney, Australia, alisema: ""Mafunzo ya magugu ya mavuno yalitokea kwa sababu ya fursa ya kulenga mbegu za magugu wakati wa mavuno." Wakulima walipata haraka jinsi ya kulenga magugu na HWSC. Aina zao nne kuu za magugu zilikuwa oats ya mwituni, radish ya mwituni, bromegrass na ryegrass ya kila mwaka. Zote zina uwezo mkubwa sana wa kuhifadhi mbegu wakati wa kukomaa kwa mazao. Kuhifadhi mbegu ni sehemu ya jumla ya uzalishaji wa mbegu uliohifadhiwa kwa urefu ambao unaweza kukusanywa wakati wa shughuli ya mavuno (tazama Jedwali 1). Uhifadhi wa mbegu hubadilika kadiri wakati unavyopita. Uwiano wa kuhifadhi mbegu za magugu hupungua wakati mavuno yanacheleweshwa zaidi baada ya kukomaa kwa mazao. Rabies ya mwituni na ryegrass ya kila mwaka hupunguza kiasi cha mbegu kwa siku kwa siku moja kwa siku 28. Bromegrass na oats ya mwituni wana hasara ya kuhifadhi mbegu ya karibu asilimia mbili kwa siku. Kwa hivyo, kukomaa kwa mazao na magugu kuna athari kwa mafanikio ya HWCS. Wakati wa mavuno, mkusanyaji wa majani ya magugu alisambaza mbegu za magugu kwenye shamba na kuzalisha tena kwa mwaka ujao. Wakulima katika Australia magharibi walitambua kwamba walihitaji kuvuruga mchakato huo na wakaanza kuagiza magari ya chaff kutoka Kanada. Baada ya muda mfupi, uhusiano wao wa upendo na chuki ulianza, na ulidumu kwa miaka 20. Ingawa magari hayo yalikuwa yenye matokeo yalikuwa magumu sana kuyatumia. Magari ya kuokota magugu hukusanya magugu hayo, ambayo huwekwa kwenye rundo kuzunguka shamba. Miti ya magugu huchinjwa na mifugo au kuhamishwa kwenye mashamba ya kulisha, lakini kwa kuwa kuna kondoo wachache sana nchini Australia, kwa kawaida milima hiyo huchomwa ili kuua mbegu za magugu. Mkulima Lance Turner alibadilisha gari la kuokota magogo kwa kuweka mfumo wa kuinua ili kuhamisha magogo kutoka kwenye mashine ya kuokota magogo hadi kwenye gari. Matokeo yalikuwa kwamba makundi ya majani ya mwaloni yaliungua kwa muda wa saa mbili hadi nne badala ya siku mbili. Kwa sababu hiyo, matumizi ya mifumo hiyo yameongezeka na, katika Australia Magharibi, angalau mifumo 200 ya magari hayo mapya ya kuendesha magari ya kuendesha magari ya kuendesha magari ya kuendesha magari ya kuendesha magari ya kuendesha magari ya kuendesha magari ya kuendesha magari ya kuendesha magari ya kuendesha magari. Mmoja wa watumiaji wa kwanza wa mfumo wa gari la magamba ulioletwa kutoka Kanada alikuwa familia ya Shields katika Australia magharibi. Baadaye walibuni mfumo tofauti kabisa, unaoitwa kuunganisha mabaki. Wakati wa kuvuna, mabaki yote huingia katika chombo cha kufungia mizigo kilichounganishwa. Wakulima katika maeneo ambapo nyasi kupita kiasi ni suala, na ambapo kuna masoko kwa ajili ya nyenzo hii, wanaweza kupata faida kutoka kwa uuzaji wa mabaki ya baled. Kwa mfano, mbegu za magugu huondolewa, na hadi asilimia 95 ya mbegu za nyasi za mwaka zinaweza kuondolewa katika mabaki ya mavuno. Mfano mwingine wa Australia ni mfumo wa kuunganisha mchanga na mchanga, ambao umebuniwa kwa sababu wakulima wengi hawapendi kuchoma mabaki ya mchanga. Kuungua humaanisha kupoteza virutubisho. Mifumo ya kufunika chaff hukusanya chaff na kuipiga katika reli za gurudumu la mfumo wa tramline ambapo kuna reli za gurudumu zilizowekwa katika uwanja. Kwa kawaida, nyayo hizo za magurudumu hazipandwi mbegu na mbegu za magugu huachwa ziharibike katika mazingira yenye uhasama. Njia nyingine ya kufunika majani ni kukamata na kukusanya majani hayo katika ukanda mwembamba. Mimea hii huwekwa katika safu iliyowekwa kati ya safu nyembamba za sentimita 17 ambapo kuna athari ya mulch kwenye mbegu za magugu. Utafiti wa awali ulipima uhifadhi wa mbegu zilizowekwa chini ya magugu wakati wa mavuno kabla tu ya kupanda mwaka uliofuata. Baadhi ya matokeo hayo hayakutarajiwa. Mbegu za magugu kwa kawaida hazikuishi chini ya canola na shayiri ya shayiri, labda kwa sababu ya athari fulani ya allelophathic. Kwa kushangaza, katika ngano, kulikuwa na uhifadhi wa juu sana wa mbegu za ryegrass ya kila mwaka chini ya chaff ya ngano, ambayo haijaelezwa. Utafiti zaidi unahitajika, lakini kwa ujumla, laini ya chaff inafanya kazi kupunguza kuishi kwa mbegu na inakubalika haraka kote Australia. (Tazama Mchoro. 1.) Teknolojia ya HWSS ya kwanza ilitengenezwa na Ray Harrington. Teknolojia hiyo hutumia mashine inayozunguka ili kuua mbegu za magugu. Katika utafiti uliofanywa na Australia Herbicide Resistance Initiative (AHRI), iligunduliwa kuwa teknolojia hiyo ilitoa udhibiti wa zaidi ya 90% wa ryegrass ya kila mwaka kupitia kinu katika safu ya kasi, na hakuna athari ya aina ya chaff juu ya uharibifu wa mbegu za magugu. Harington Seed Destructor ni mashine ya kuharibu mbegu ya mwani ambayo ni ya aina ya pull-type, ambayo inashikilia na kuunganisha mbegu za magugu na magugu. Mashine hiyo hutandaza nyasi kando-kando. Utafiti wa AHRI uligundua kwamba ilifanya kazi sawa na mfano wa awali, na uharibifu wa mbegu katika chaff kwa asilimia 95 kwa ryegrass ya kila mwaka, asilimia 92 kwa radish ya mwituni, asilimia 99 kwa oats ya mwituni na asilimia 98 kwa bromegrass. Harington Seed Destructor (HSD) ni mbinu ya kuharibu magugu. Gharama ya mashine ya aina ya kuvuta ni karibu $ 200,000 Cdn. Katika mwaka wa 2010, utafiti ulifanywa kulinganisha kuchoma kwa upepo mwembamba, magari ya chaff na Harrington Seed Destructor katika maeneo 25 ya Australia. Mifumo mitatu ililinganishwa katika maeneo sawa wakati huo huo na athari za matibabu ya mavuno yaliyokadiriwa kwa kupima athari juu ya kuibuka kwa magugu. Kwa ujumla, kila mbinu ilifanya kuonekana kwa nyasi ya kijani-kibichi kupungua kwa wastani wa asilimia 57 kila mwaka kabla ya kupandwa. Hakukuwa na tofauti kati ya matibabu katika maeneo yoyote. Hii ina maana kwa sababu wote ni lengo la sehemu ya chaff, na kama wao ni kazi vizuri, wanapaswa kuwa na matokeo sawa. Harvesters pia hutumia vifaa vya kuharibu mbegu za Harrington (iHSD) na kuharibu mbegu za mbegu za mbegu za mbegu. Ilizinduliwa katika uzalishaji wa kibiashara mwezi Machi. Hii ni mfumo wa kinu cha mapacha. HSD ya awali ya aina ya kuvuta ilikuwa na rotors za kuzunguka kinyume. IHSD ina sahani ya juu ya kudumu na sahani ya msingi ya kuzunguka. Ni hydraulically inaendeshwa na inaendeshwa na combine harvester. De Bruin Engineering ya Mount Gambier, Australia Kusini, ni utengenezaji wa iHSD (ihsd.com). IHSD inafanya kazi vizuri sana. Kwa kulinganisha na utafiti wa awali, ilifanya kazi vizuri au hata bora, na karibu asilimia 100 ya mbegu za magugu kuua spishi nne za magugu. Hii ni ya kusisimua sana, mpya, yasiyo ya kemikali mfumo wa udhibiti wa magugu. Kampuni hiyo sasa inazingatia kuunda idadi ndogo ya magari katika mwaka 2016. Katika mwaka uliofuata, wanatumaini kuanza uzalishaji wa kiwango kamili. Ujumbe muhimu zaidi wa HWCS ni athari ya muda mrefu kwenye idadi ya magugu. Utafiti uliofanywa na Peter Newman, mwanzilishi wa The New York Times, ulichunguza mashamba yenye matatizo ambapo nyasi ya kila mwaka ilikuwa nje ya udhibiti na idadi ya mimea ya zaidi ya mimea 100 kwa mita ya mraba. Mashamba 25 yalionekana na 13 ya mashamba kutumia dawa za kuua magugu tu; mashamba mengine 12 kutumika dawa za kuua magugu pamoja na mfumo wa HWSC. Baada ya miaka 12 katika mashamba ya dawa ya kuua magugu tu, idadi ya mwaka wa ryegrass ilipunguzwa hadi mimea mitano kwa mita ya mraba na iliimarika katika kiwango hicho baada ya miaka sita au saba. Wakati dawa za kuua magugu na HWSSC zilitumiwa, kulikuwa na udhibiti bora zaidi, na idadi ilipunguzwa hadi chini ya mmea mmoja kwa mita ya mraba. Wakati wakulima kupunguza idadi ya kila mwaka ryegrass chini ya karibu mmea mmoja kwa mita mraba, kusimamia idadi ya magugu ili kuboresha usimamizi wa mazao ni rahisi sana kwa sababu magugu si kuamuru jinsi ya kusimamia mfumo wa mazao. Mzunguko waweza kubadilishwa. Maombi ya dawa za kuua magugu yanaweza kuondolewa ili kuondoa shinikizo la uteuzi wa dawa za kuua magugu. HWVSA inatoa huduma ya uhifadhi wa dawa za kulevya kwa ajili ya ufugaji wa magugu wakati wa mavuno. Katika maeneo hayo 25 ya shamba, seti ya mbegu ya kila mwaka ya ryegrass ilikadiriwa. Katika mashamba yenye mimea 5 hadi 10 kwa mita ya mraba, mbegu 1,000 za mbegu huingia kwenye benki ya mbegu kwa mita ya mraba. Shamba lenye mimea chini ya moja kwa mita ya mraba lina mbegu chache tu zinazoingia katika benki ya mbegu. HWDC inabadilisha kabisa mfumo wa udhibiti wa magugu. Uchunguzi uliofanywa kwa wakulima 600 kote Australia ulichunguza kupitishwa kwa HWCS mnamo 2013. Kuungua kwa upepo wa karibu ni njia ya kuchochea mwendo wa karibu na wakulima wa Australia. Zoea hilo limetumiwa sana magharibi mwa Australia, lakini sasa linaenea zaidi katika maeneo yote ya kulima ngano. Moja ya sababu za kuanzishwa kwa mashine za kupasha moto kwa upepo ni gharama ya chini. Kwa hivyo, kwa sababu ya kuunganisha mchanga na nyasi, kuchoma au kufunika kwa mchanga kunaweza kutoa udhibiti wa asilimia 95 ya mbegu za magugu. Moja ya masomo kutoka kwa maendeleo ya HWCS ni haja ya mbadala za bei nafuu lakini zenye ufanisi ambao wakulima wanaweza kutumia kutathmini ufanisi wa mifumo hii wenyewe. Uwiano mdogo wa magugu ndio bima bora dhidi ya upinzani wa dawa za kuua magugu. Kumbuka kwamba moja ya sababu kuu ya upinzani wa dawa za kuua magugu ni kuwa na mbegu chache za magugu katika mashamba yako.