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Harvest weed management Peter Newman, Alex Douglas and Sally Peltzer Weeds Research Officers, Geraldton, Katanning and Albany Copyright © Western Australian Agriculture Authority, 2010 Welcome to the first state wide edition of Weed Management. These Weed Management sections of the Ag Memo will appear three to four times per year across the state over the next three years. The information presented will be relevant to the time of year and will focus on Integrated Weed Management (IWM) of herbicide resistant weeds in cropping situations. This initiative is a part of a GRDC funded project with Peter Newman as the principle researcher based in the Geraldton DAFWA office. The information presented will focus on lessons learnt from the Northern Agricultural Region, including case studies, as well as more general information about herbicide resistance and its occurrence throughout the state. Clearly this information will reach a range of growers throughout the state from those who are living with full blown herbicide resistance through to those who are relatively new to cropping and are living in the honeymoon period where the herbicides are still working. These growers do, however, have one thing in common. If they choose to use only herbicides to manage weeds, the weeds will win. Growers that are taking an integrated approach are proving that it works and many of their case studies will feature in future articles. Peter Newman, Geraldton ph. 9956 8563 Weed seeds at harvest – spread, catch, divert, burn or destroy? A wise man once said to me; “It seems ironic that we spend all year spraying weeds with thousands of dollars worth of herbicides only to turn around and spread all of the surviving weed seeds evenly all over the paddock”. Targeting weed seed has been identified as a key strategy in controlling resistant annual weed populations. The control of these populations is a numbers game and weed seed removal is an excellent strategy that can be used to keep the numbers low. A number of techniques can be used to destroy / remove at least 50% of weed seeds of annual ryegrass and wild radish populations at harvest. But is this enough to make an impact on the weed seed bank and the development of herbicide resistance? Computer modelling suggests that 50% seed removal at harvest will not fix a weed control system that is not working. It will, however, have a significant impact where a weed seed bank is being maintained or increasing slowly. The figure below shows the results of computer simulation with the RIM (Ryegrass Integrated Management) program developed by WAHRI at UWA. This demonstrates that for a continuous cropping system where only 90% ryegrass control is achieved each year the seed bank of the ryegrass increases slowly over a 10 year period. By adding a chaff cart or baler at harvest that removes 50% and 75% of the ryegrass seeds in the paddock each year respectively, the ryegrass seed bank is eroded over time. Our aim for managing resistant weeds should simply be to continually reduce weed seed banks. Removing weed seeds at harvest is probably the most important non-herbicide weed management tool to achieve this. 2000 nil chaff cart 50% baler 75% 2 1500 /m Ryegrass seeds in soil RIM computer simulation of ryegrass seedbank lupin: wheat rotation Trifluralin every year 90% control 1000 500 0 0 1 2 3 4 5 6 7 8 9 10 Year Figure 1 Computer simulation using RIM program showing the predicted ryegrass seed bank (seeds /m2) in a lupin wheat rotation where 90% weed control is achieved each year for three harvest options; Nil (conventional harvest), Chaff cart removing 50% of weed seeds in each crop, or a baler towed behind the header removing 75% of the weed seeds in each crop. Which tool? Table 1 Summary of some of the main harvest weed seed management tools. Tool Set up cost Pros Cons $100 to Windrow Cheap to get into. No Involves burning. Wind $500 burning loss of harvest efficiency. erosion risk. Difficult in Very effective. cereals. Time consuming in autumn. Nutrient banding. Chaff Cart $30K to Minimises area of Reduces harvest $50K paddock burnt. Can efficiency. Cost. Burning provide feed source for heaps in autumn is very livestock. time consuming. $400 to Chaff Cheap. No burning. No Must have fully matched diversion onto $5000 loss of harvest efficiency. tramline system. tramlines Reduces dust during Unproven. High weed summer spraying. density on tramlines About Harrington No burning. Nothing to Cost. Extra piece of Destructor $100K do after harvest. Very machinery. (possible robust machine – can release 2012 handle house bricks! / 2013) About Baling No Burning. Additional Cost. Extra nutritional everything – $150K to income from bales. Most drain on soil. Need a $200K Glenvar effective tool on the market for bales. Handling system market. of lots of bales. Chaff carts / Harrington Destructor / Diversion onto tramlines should be able to remove 70 to 80% of the ryegrass / wild radish that enters the harvester. However, due to ryegrass shedding / lodging this represents approximately 50% of the total weed seeds in the paddock. The baler and windrow burning should be able to remove 95% of ryegrass and wild radish that enters the front of the harvester. This represents approximately 70% of weed seeds in the paddock. Walsh and Parker (2002). Case study – Rod Birch, Coorow Rod Birch from Coorow is demonstrating that it is possible to maintain continuous crop while managing resistant ryegrass by targeting weed seeds. Rod is a big believer in the use of windrow burning as a tool and he is one of the pioneers in the area. 350 Ryegrass / m 2 300 250 200 150 100 50 0 2001 2002 2003 2004 2005 Figure 2 Birch #5 - Ryegrass plants (in August) / m 2006 2007 2008 2009 2 Table 2 Control used on crops over specific years. Year 2001 2002 2003 2004 2005 2006 2007 2008 2009 Crop Lupin Wheat Canola Wheat Lupin Wheat Canola Wheat Lupin Ryegrass Herbicide Simazine & Fusion Trifluralin + SU Atrazine & Select Trifluralin + SU Simazine & Motsa Trifluralin + SU Atrazine – Sacrificed with glyphosate Trifluralin + SU Simazine & Select Non herbicide Burn narrow windrows Burn narrow windrows Burn narrow windrows Burn narrow windrows Burn narrow windrows Dry year - no windrow burn Burn narrow windrows Will make narrow windrows Rod’s comments This paddock was out of control with ryegrass in the 1990’s so we decided to take an aggressive approach to herbicide resistance and use as many tools as possible. We have burnt header windrows for a number of years. I think of the header as a big seed collector. The trick to burning wheat windrows without burning the whole paddock is to harvest very low and to not graze the paddock at all. Livestock will disturb the windrows too much. We ensure that the header never ever leaves its track so we end up with one big un-disturbed spiral of windrow. We use a chute mounted to the back of the header to make narrow (600mm wide) windrow. Burning windrows has caused some issues with potassium levels in some paddocks. We observed strips of high nutrition in cereal crops. We subsequently worked with Bill Bowden (DAFWA) to identify that Potassium was the issue and have adjusted our fertiliser program to address this problem. We are also finding that trifluralin works best when it has maximum contact with the soil. Burning windrows reduces trash which aids this soil contact. The lupin / wheat / canola / wheat rotation is a good one for ryegrass management because it enables some different weed management each year. For example, we swath the canola and often crop top in the lupin phase. In the wheat phase we aim to grow a competitive crop and use trifluralin. Making narrow windrows this harvest For growers who want to make a start at weed seed management this harvest, windrow burning is probably the most achievable option given that harvest will soon be upon us. A good place to start will be in canola and / or lupin crops as it is easier to contain the burn to the windrow. It is necessary to mount some sort of chute to the rear of the header to concentrate all of the trash and straw into a narrow windrow. The opening at the bottom of the chute should be 500 to 600mm wide depending on how thick the crop is. Your model of header will determine what sort of chute is appropriate. If you would like more information in this area please email me at [email protected] and I will send you some photos of chute designs for a range of header types. If you do mount a chute to your header, remember to reverse immediately when you stop to avoid the header blocking up. See Rod Birch’s comments above relating to successful windrow burning. We will follow up with more information in Autumn relating to conditions to achieve a successful burn. Peter Newman, Research Officer, Geraldton ph. 9956 8563 What is herbicide resistance? Herbicide resistance is the inherited ability of an individual plant to survive a herbicide application that would kill a normal population of the same species. Within any weed population there may be some plants that already contain a rare gene that enables them to survive the application of a particular herbicide that would normally kill this species. Genetic variation may alter physiological traits that enable herbicide uptake, translocation and activation at the site of action (target-site resistance). Alternatively, changes may influence the plant’s ability to detoxify herbicides, or enable transport to a site within the plant where the herbicide is not lethal (Non-target-site resistance). Each time the herbicide is applied, susceptible plants die and those with resistance survive. Factors affecting the development of resistance include: Selection Pressure – Every time herbicide is used, susceptible individuals are killed and resistant individuals survive. The greater the number of susceptible individuals killed by the herbicide, the higher the selection pressure. Initial frequency of the resistance gene within a population – The more resistant genes in a population the quicker resistance develops. For example the resistance frequency can be as high as 1 plant in 10 000 (Group B) and as rare as 1 plant in 100,000,000 (Group M, eg glyphosate) Weed density – the higher the number of weeds, the greater likelihood that a particular resistance gene is present. Sally Peltzer, DAFWA, Albany [email protected]