Title: Weed Seed Collection at Harvest
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. Harvesting provides an excellent opportunity to remove weed seeds from the system and prevent them from being spread across the paddock or farm. Used in conjunction with other procedures, weed seed collection at harvest has the potential of collecting almost all new weed seeds, reducing the overall weed seed-bank.
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.
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 new weed seeds being added to the seed-bank may be greater 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
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. Delaying harvest greatly reduces the proportion of weed seeds 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.
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.
Narrow header trail
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.
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.
Article: CulturalWeedControl70 (
permalink)
Date: 8 January 2013; 2:25:01 PM AEDT
Author Name: Zheljana Peric
Author ID: zper12