RIM - Resistance and Integrated Management
A decision tool for integrated weed management
Treatment Options Included in RIM
This page is based on Chapter 6 of the RIM User's Manual.
There are a total of 35 different weed treatment options included in RIM. They can be broken into four separate groups: selective herbicides (11), non-selective herbicides (5), non-chemical treatments (16) and user-defined treatments (3). Each of the treatment options is explained in this chapter, followed by tables indicating their effectiveness and their costs. Within RIM these options are listed in chronological order, with the first applied treatment options listed first (using April as the starting point of each year). However, they are described here within the four groups indicated above.
Selective herbicides
Trifluralin (pre-emergence)
Trifluralin is a dinitroaniline herbicide (group D). Under conventional crop establishment systems, it is incorporated into the soil one to two weeks prior to sowing. In RIM we assume that trifluralin is sprayed out and incorporated by seeding. The herbicide is taken up by the plant through the roots and the coleoptile. It acts by stopping cell division in the growing points of the roots and coleoptile (Piper, 1993).
Trifluralin kills around 70 percent of germinated ryegrass plants, with a range of 50 to 90 percent (Gill, Holmes and Kelly, 1994).
Simazine (pre-emergence or post-emergence)
Simazine is a triazine (Group C). It will control broadleaf and grass weeds in lupins or canola (provided it is triazine-tolerant canola, which we assume it is). Simazine can be used either as a pre-emergence or a post-emergence herbicide, and both of these options are included in RIM. It is absorbed by the plant through the roots and interferes with photosynthesis. As the plant is no longer able to produce carbohydrates it eventually starves to death (Piper, 1993).
Simazine kills around 75 percent of germinated ryegrass plants, with a range of 40 to 90 percent (Gill, Holmes and Kelly, 1994).
Atrazine (pre-emergence or post-emergence)
Atrazine will control broadleaf and grass weeds in canola. It is another triazine (group C) and, like simazine, it can be used either pre-emergence or post-emergence.
Atrazine kills around 75 percent of germinated ryegrass plants.
Glean® (pre-emergence or post-emergence)
RIM includes both pre-emergence and post-emergence Glean® options. Glean® is used to control ryegrass and a range of broadleaf weeds in wheat and barley. Only the post-emergence option is permitted in barley.
The active ingredient in Glean® is chlorsulfuron, a sulfonylurea (Group B). It is taken up by the leaves and roots of a plant and inhibits the activity of the enzyme acetolactate synthase. This enzyme is involved in producing branched chain amino acids essential for growth. It stops root and shoot development (Piper, 1993).
The standard ryegrass kill rates for Glean® included in RIM are 75 percent pre-emergence and 50 percent post emergence.
Hoegrass® and Fusilade® (post-emergence)
Hoegrass® (diclofop methyl) can be used in all four crop options, while Fusilade® is offered for canola and lupins only. They are aryloxy phenoxy propionate herbicides or "fops" (Group A). The herbicide is taken up by the leaves of the plant and is translocated to the growing point where it inhibits the activity of acetyl co-enzyme A carboxylase. This enzyme is involved in the production of fatty acids and turpenes and in the plant’s use of carbohydrate for energy. The herbicide quickly stops root and shoot development (Madin, Bowran and Zaicou, 1993). Broadleaf plants and some grasses are not affected by these herbicides.
The assumed control percentage for ryegrass is 95 percent for both herbicides. Kill rates from 50 to 98 percent are observed in practice (Gill, Holmes and Kelly, 1994).
"Dim" herbicides (post-emergence)
Two Dim herbicide options (Group A) are included for use on lupins or canola: Select® (clethodim) and "Other Dim". The "Other Dim" option may be set up to represent any of a number of possible Dim herbicides. The default settings in RIM are based on Sertin® (sethoxydim).
The assumed control percentages for ryegrass are 90 to 95 percent.
Non - selective herbicides
Non-selective herbicides cannot be applied to growing crops at normal rates because the crops would be killed. The are either applied prior to crop emergence or used to prevent seed production by weeds growing within a pasture (or sometime a lupin crop). There were no known cases of herbicide resistance to these herbicides until recently (Powles, 1997), but the recently discovered cases are expected to be the first of many in years to come.
Glyphosate or Spray.Seed® at sowing
Glyphosate is phosphonomethyl glycine, a foliar translocated herbicide (Group M). It inhibits the enzyme EPSP synthase which is involved in making aromatic amino acids (Piper, 1993).
Spray.Seed® is a mixture of two bipyridyl (Group L) herbicides, paraquat and diquat, and is a contact herbicide. It uses some of the plants photosynthetic energy to produce highly reactive forms of oxygen such as hydrogen peroxide. These chemicals then kill the plant (Piper, 1993). Spraying prior to seeding will achieve a high level of control of those weeds that have germinated (Gill, Holmes and Kelly, 1994).
Gramoxone® top lupins or pasture
Gramoxone® or paraquat (Group L) can be sprayed in-crop in lupins or applied to pasture just before weed seed set for prevention of weed seed production. If sprayed too early it can severely damage the crop or pasture but if used properly it can result in a worthwhile level of control.
The standard kill rates in RIM are 80 percent in lupins and 85 percent in pasture, based on an observed range of 50 to 90 percent (Gill, Holmes and Kelly, 1994).
Pasture top with glyphosate
Glyphosate can also be used on a pasture to control weed seed production. It needs to be applied when the seed heads of ryegrass are flowering, but the pasture legumes have already set seed.
Pasture topping can give 70 to 99 percent control of ryegrass (Gill, Holmes and Kelly, 1994). In the model the default is 85 percent.
Non - chemical control
These control methods are based on physical or ecological approaches (although some also include an application of glyphosate to enhance their effectiveness).
Cultivation and delayed sowing
Cultivation is used to stimulate germination and then uproot and kill plants. A shallow cultivation or "early tickle" is often used and is the cultivation method assumed in RIM. It buries weed seeds to a depth of one to two centimetres enhancing weed germination by increasing contact with soil moisture. A delay between the tickle and seeding is necessary to give an opportunity for the weeds to germinate and then be killed using a knockdown herbicide. The longer the delay in sowing, the more weeds germinate and the higher the kill. However a yield penalty is experienced when sowing is delayed. In RIM, sowing can be delayed by 10 or 20 days. Different yield penalties are specified for different crops (see the Crops & weeds sheet).
Year round grazing
When any of the three pasture types is selected, the model automatically chooses to graze the pasture. The stocking rates of sheep and the levels of control of ryegrass are specified in the Pasture sheet and can be adjusted by the user.
Sheep help to control ryegrass by eating ryegrass seed over the summer months and eating the ryegrass plants in the pasture. The different pasture types result in different levels of ryegrass control. The sub-clover pasture gives the best control as the sheep are easily able to select for ryegrass. The cadiz pasture gives a lower level of control as the cadiz grows taller than clover and can hide the ryegrass. The volunteer pasture is assumed to give the same level of control as does cadiz. It is less effective than clover because it is expected to be less competitive with the ryegrass.
High intensity grazing over winter/spring.
RIM includes the option of high intensity grazing over the winter/spring period. This is done by placing a high stocking rate on the pasture. The sheep should be stocked at a sufficient intensity as to stop seed set. Again the stocking rates and levels of ryegrass control are specified on the Pasture sheet.
Grazing with hay
If cutting hay or cutting silage is selected, the pasture is grazed before it is cut. The level at which it is grazed is specified on the Pasture sheet.
Green manure
Green manuring involves the ploughing of a growing crop or pasture into the soil prior to the weeds setting seed. This is a very effective method of weed control, assumed to prevent 98 percent of ryegrass seed production. However, if a crop is not harvested, it involves a substantial sacrifice in revenue.
Cut for hay or silage
Like green manuring and mowing, cutting hay or silage relies on acting before the weeds set seed. Both options are specified in RIM with a follow-up glyphosate application. The assumed ryegrass kill rate is 95 to 98 percent.
Swathing
Swathing involves cutting the crop while still green and laying it on the ground. Once it dries, it is harvested. Swathing can serve several purposed. One is to reduce losses of grain during harvest. (Dry canola crops are brittle, and seed can fall out of the seedpods before being gathered by the harvester). Another is to manage the moisture content of barley grain. Additionally, however, it provides a modest degree of reduction in ryegrass seed production by cutting off ryegrass plant heads before they have set seed. RIM includes seed reductions of 25 percent for swathing of barley, and 20 percent for canola or lupins. This benefit in barley would depend on it being the Unicorn variety of barley, which matures early enough for the swathing to cut off ryegrass heads before they have all set seed. If you assume that the barley variety was other than Unicorn, the control percentage would be lower - perhaps 10 to 15 percent.
Mowing
A mower is used to cut the tops off the weeds prior to them setting seed. This form of mechanical topping is particularly useful in pastures. This treatment plus a follow-up application of glyphosate is assumed to give 95 percent control.
Seed catch
Harvesting is an important opportunity to reduce the number of ryegrass seeds making it into the ryegrass seed bank. It is estimated that 75 percent or more of the ryegrass present at harvest passes through the harvester. Currently on most farms this processed ryegrass seed comes out of the back of harvesters to be returned to the soil. However some farmers are experimenting with seed catching.
Seed catching collects all the seed and chaff from the harvester’s top seive into a cart towed behind the header. When the cart is full, the trash is dumped in piles, which can then be burnt or removed. In RIM the control rate of seed catching has been set at 60 percent if only dumps are burnt or 68 percent if a total burn is conducted. The observed kill range is 40 to 80 percent.
Windrow/header trails
It is possible to concentrate harvest residues into header trails or windrows. This is done by removing the straw spreaders from the back of the header. Instead of the residues being distributed the width of the header path, they fall in a concentrated band behind the header . There are two options for disposal included in the model. The first, "Windrow – burn windrow", has a control rate of 50 percent and reflects that the burn is restricted to only burning the windrow. The other option is "Windrow – total burn" which gives a kill rate of 63 percent and involves burning all the cropped area..
Burn crop stubble or pasture residues
This strategy involves burning the residues remaining after harvest or grazing. The effectiveness of the burn depends on the type of fuel and density of the fuel across the paddock. In RIM the kill rate for ryegrass seed from a burn is 30 percent following crops or 20 percent following pastures.
User defined options
Three user-defined treatment options are included: one unspecified selective herbicide ("Other selective herbicide"), one treatment that is applied in spring ("User defined option A"), and one applied at or after harvest ("User defined option B"). To define these options, you must enter their costs into the Prices & rates sheet, and their kill rates into the Control % sheet. By default they are each given kill rates of zero and costs of $20 per hectare.
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Background information
Required
hardware and software
Assumptions
of RIM: An overview
How
to use RIM: An overview
The
treatment options included in RIM, both chemical and
non-chemical