or baled for fodder or for feeding grain.
Weed seed collection at harvest
Harvesting provides an excellent opportunity to remove weed seeds from the system and prevent them from being spread across the paddock or farm.
Headers collect a large proportion of the weed seed, which generally ends up either in the grain tank with the harvested grain or spread on the paddock with the straw and chaff.
Used in conjunction with other procedures, weed seed collection at harvest has the potential of collecting almost all weed seeds.
If other procedures have failed through the season and weeds remain with viable seed at harvest, weed seed collection is a salvage tactic to prevent additional weed seeds from entering the seed-bank.
A number of systems have been developed to avoid returning viable seeds to the seed-bank. Although weed seed collection at harvest is costly (in time more so than money), the cost of herbicide resistant seed being added to the seed-bank may be greater in the long term.
Weed seed collection at harvest will not increase grain yield as the weeds have already caused damage to the crop. The aim is to prevent increases to the seed-bank, although it may give a subsequent yield advantage to the next season’s crop through reduced weed numbers in that season.
Weed seed collection at harvest is the last time in the cropping season that seeds can be prevented from being added to the weed seed-bank. This can be a time consuming and costly exercise, but it will be beneficial in the long term.
Weed seed collection at harvest needs to be planned in advance. The weed species has a major influence on the proportion of weed seed removed from the paddock when collected at harvest.
Successful collection and control is dependent on the weed:
- Maturing at the same time, or later than, the crop being harvested
- Having seeds at a similar or greater height compared to the crop being harvested – this may be overcome by setting the header at a height such that weed seeds are captured
- Having seeds that do not shed or shatter prior to or during harvest
- Having seeds that are able to be threshed and are of a size that end up in the chaff component of the harvested crop.
For example, annual ryegrass is much more susceptible to collection than wild oats, which tend to shed seed before harvest. The similarity in size and shape between wheat grain and wild radish pods means that a large portion of wild radish seed entering the header can be collected.
Timing of harvest will affect the amount of seed removed from the paddock when residue is collected. If harvest is delayed, a greater proportion of the weeds will shatter or lodge, reducing the total proportion of seed able to be collected.
Seed collection procedures depend on weed type. Weeds that mature at or close to the same time as the crop, and which are similar in size are most suitable for control by seed collection. However, this method should be used in conjunction with other control procedures to avoid placing too much selection pressure on a particular target weed. Diversity is the key to managing weeds.
The additional product from seed collection at harvest will be chaff dumps and straw. These two products will contain the collected seed and therefore need to be managed appropriately.
Chaff dumps are usually burned or fed to livestock, and both options require careful management. Dumps can burn for a long time, creating fire and pollution hazards. Livestock fed on chaff dumps can spread weed seeds if not well managed. Grazed chaff dumps that have been spread out and lowered in height burn more quickly than ungrazed heaps.
Take care to manage livestock after grazing fodder contaminated with weed seed. A percentage of weed seeds ingested by livestock will remain viable and take as long as 10 days to pass through. The number of seeds that remain viable will depend on the weed species and the grazing animal so it is important to develop a feed-out strategy to contain the problem in all scenarios.
Cereal chaff dumps have insufficient feed value to maintain the bodyweight of adult sheep. The feed value of chaff dumps from crops such as lupins and field peas will be higher than from cereals.
When grazing harvest residues containing weed seeds remember the following:
- Livestock can spread weed seeds.
- In areas where weed toxicity is a problem, veterinary advice should be sought before grazing harvest residues.
Narrow header trail
Facilitating narrow header trails (also known as trash windrows) is the cheapest, simplest form of collecting residue. It is done by disconnecting the straw spreaders on the header and allowing the straw, chaff and weed seeds to fall in a narrow trail behind the header.
Adding a simple chute forces the residue into an even narrower, more discrete row. The trail can then be burned during autumn. This has become common practice in many districts when harvesting canola. The high fuel load in the row results in a hot burn and a good weed seed kill. However, any unburned seeds will produce seedlings that will need to be controlled using an alternative method.
In a controlled traffic cropping system straw can be spread while chaff and weed seed are deflected onto the wheel track where they are less likely to grow.
Weed seed numbers can be reduced by using the narrow header trail technique and burning the trails.
Windrowing improves the benefit of using narrow header trails. The efficacy of using the narrow header trail technique improved substantially when used in conjunction with windrowing at crop.
Grazing stock tend to spread and bury seed, which will reduce the efficacy of burning the weed seeds in windrows. As with any residue burning, grazing will reduce the benefit by:
- Spreading the header rows and reducing the fuel load, thus lowering the temperature of the fire
- Burying the seed, therefore protecting it from the hot fire.
Chaff cart
In this system the chaff and weed seeds are collected and thrown into a trailing cart. When the cart is full the gate is tripped and the cart self-empties to create a chaff dump. The header operator can control the emptying of the cart to place the dumps in a particular area of the paddock. This eases management of the dumps postharvest although location of chaff dumps in a specific area will significantly reduce header efficiency.
Collecting crop residue with a chaff cart can significantly reduce the numbers of weed seeds returning to the seed-bank.
Windrowing improves the benefit of using a chaff cart.
Reduces crop volunteers in the following season, particularly relevant where malting barley will follow a wheat crop.
A crop must be harvested as soon as it is ripe to collect the greatest number of weed seeds. Excellent control has been recorded in wild radish where efficacy is strongly linked to the relative maturity of the crop and weeds.
Delaying harvest greatly reduces the proportion of weed seeds collected.
Other options for weed seed collection at harvest
Baling systems: Baling crop residue, directly from the header at harvest, minimises weed seed additions to the seed-bank.
Baling the chaff is an alternative to grazing. Because the material is already chopped, chaff bales are more attractive to dairy farmers than the conventional straw bales. As proximity to market and price can be limiting factors, this option appeals to those farmers who have access to a stock-feed market such as a dairy, beef feedlot or stock-feed mill.
Three baling systems are practised. The most efficient involves trailing a baler behind the header and directing all the chaff and straw into the baler.
Alternative systems involve baling the header trails and the chaff dumps from a chaff cart system. Picking up header trails with a baler once the material has been on the ground is problematic because much of the seed is missed. This applies even where a system devised to put straw underneath the chaff is employed, referred to as a ‘Chafftop’.
The Chafftop uses a device fitted to the header to collect the chaff and straw. It concentrates the chaff on top of the straw windrow for later baling, which is the reverse of the usual harvesting technique of scattering the chaff behind the header
Baling systems offer a distinct advantage by processing the material into a transportable and therefore saleable state. Markets for straw and chaff include:
• Roughage in cattle feedlot rations and dairies
• Briquettes
• Mulch
Grazing crop residues
Grazing weed contaminated crop residue can be a cost-effective way of controlling weed growth. Animal digestion of weed seeds prevents a large proportion from entering the seed-bank.
It should be noted that the feed value of the crop residue will be variable, and grazing has the potential to spread undigested weed seeds.
Grazing reduces the number of weed seeds added to the soil seed-bank. Depending on the weed species, grazing can greatly reduce the number of viable seeds in the soil seed-bank. Animals eat the seed heads and vegetative growth of the weed, thus decreasing the number of seeds entering the seed-bank.
Grazing can be used to dispose of, and gain value from, weed seed contaminated fodder. Weed seed contaminated fodder includes not only hay, silage and feed grain but also harvest residues that may be weed infested. Harvest residues can be collected using chaff carts to remove residue and weed seeds from the header, leaving chaff dumps in the paddock which can be used as a low-value livestock feed source.
Whole-farm benefits: There are additional benefits to be obtained when using grazing of crop residue as a weed management method:
- Weed seeds can provide a significant proportion of the nutritional value when stock graze crop residue.
- Post-harvest grazing may reduce crop establishment problems through reduction in stubble burdens.
- Seed burial through trampling may enhance weed germination pre-sowing.
- Seed of desirable plants (pasture species) may be distributed in faeces.
Contaminated fodder needs to be checked for its feed value and the presence of toxins. It should be fed in a sacrifice area (such as a feedlot) to minimise the spread of seeds.
The impact of grazing on weed numbers in the seed-bank is dependent on the biological features of the weed. Grazing is successful in reducing weed seed numbers in weeds that are palatable and where the seeds can be easily eaten and digested. However, seed palatability varies from weed to weed. The presence of awns, thorns or biochemical traits makes some weeds less attractive to grazing animals, than others.
Seed location: Stock must be able to access seed to ingest it. Seed still in the head, or in chaff dumps or feed troughs, is easier to access than seed lying on the soil surface.
Seed size: Once shed from the seed head, small seeds are more difficult for animals to graze. Small seeds are also more likely to survive ingestion and digestion.
Hard seeds: A high proportion of hard seeds will remain viable after digestion. The digestive process can also break seed dormancy, encouraging the germination of seeds shed in faecal matter.
Livestock trampling tends to bury weed seed, which can decrease the efficiency of burning as a means of killing seeds. Depending on the weed species, burial may also increase germination rates. In the process of grazing, stock will knock seed to the ground and bury weed seeds with their hooves. Shallow burial during grazing may result in increased germination, similar an autumn tickle, due to the placement of the seed in a better environment for germination.
Grazing may also cause:
• An increased risk of soil, water and wind erosion
• Increased soil compaction
• Potential toxicity issues
Silage
Sillage is less risky because cutting is carried out when the weed seeds are less mature. More importantly, the silage process kills most weed seeds although some do survive the ensiling process.
Article: CulturalWeedControl62 (
permalink)
Date: 8 January 2013; 1:49:47 pm Australian Eastern Daylight Time
Author Name: Zheljana Peric
Author ID: zper12