RIM - Resistance and Integrated Management

A decision tool for integrated weed management

Assumptions of RIM

This page is based on Chapter 3 of the RIM User's Manual.

Crop and pasture options included

Within the model there are seven enterprise options: wheat, barley, canola, lupins, clover pasture, cadiz pasture and volunteer pasture. Any sequence of these enterprises can be specified in the Select strategy sheet. The sequence of crops and pastures affects their yields because:

• Non-legume crops (wheat, barley or canola) grown after a legume (lupins, clover or cadiz) will give a higher yield than after a non-legume.
• If you grow canola or lupins after a break of only one year, they will give a lower yield than normal because of disease. The level of yield penalty in this case is specified in the Crops & weeds sheet.
• The set of available weed control options is different in the different crops and pastures, so their sequence will affect the levels of weed competition.

There is one important limitation on the sequence of crops: you cannot select two consecutive years of canola or two consecutive years of lupins due to the very high yield losses that would occur from disease.

The model has been designed to represent a farming system based on soil types suited to lupins. The price, yield, rotational impacts and competitiveness of lupins could be adjusted to approximate another legume crop if desired (e.g. field peas, chick peas, faba beans). The treatment options available to the other legume using this proxy approach would be those available for lupins. It would not be possible to represent both lupins and another legume crop in a single model run.

The options available for use in canola are based on it being a triazine-tolerant (TT) variety. If, however, you wished to analyse a non TT variety, it would possible to do so by self regulating the use of triazines (simazine and atrazine) – that is, not using them – and making any necessary adjustments to canola yields.

Similarly barley has been built in to the model with values that relate to Unicorn barley, but with sufficient flexibility for you to adapt the variety to suit your needs, provided again that you self regulate in your selection of treatments.

Cadiz exists in the model as a representative of a new class of phase pasture species that are re-sown regularly rather than regenerating naturally after a crop phase.

It is assumed that the clover included in the model is self-regenerating. A cost for establishment is included however, if the interval between clover phases in the rotation is three years or greater.

Timing of treatments and weed germinations

Treatments occur at different times through the year and weed germinations occur at different times following the break of season, continuing well into the growing season. RIM keeps track these timings, which are important because a treatment can only kill those weeds that have germinated by that time. Germination time also affects the competitiveness of weeds; late-germinating weeds are less competitive and so produce fewer seeds per plant.

Other assumptions

• The main outputs (results) for each year in the Select strategy sheet are ryegrass seed numbers in the soil in April (per square metre), ryegrass plants setting seed in Spring (per square metre) and profit (gross margin) ($/ha). In addition, many other biological and economic results are provided in the Biological results and Economic results sheets (see Chapter 7).
• The user can specify the number of shots available for each herbicide group, prior to the onset of resistance (in either the Start here sheet or the Select strategy sheet). If ryegrass is fully resistant to a herbicide group, the limit for that group should be set to zero.
• RIM does not represent year to year variation in weather, potential yield or herbicide performance. Yields in the model do vary from year to year due to the sequence of crops and pastures selected, and the level of weed competition. Climatic conditions do not rule out any of the treatment options. Users can self-impose constraints on the use of different treatments.
• RIM will not tell you which strategy is "best". You evaluate strategies using experimentation and trial and error.
• Weeds other than ryegrass are assumed to be adequately controlled.
• If special machinery is required for a treatment (e.g. seed catching), we assume that it is purchased new and repaid over a specified period – by default, 8 years. If you are able to purchase machinery second hand, you can adjust the purchase cost in the Prices & rates sheet.
• Because control methods are conducted at different times, their combined impacts are assumed to be multiplicative rather than additive. For example, if you combine two methods each with 40 percent survival, the combined effect is 16 percent survival.
• The assumed tillage system is minimum tillage.

• It is assumed that a minimum tillage crop establishment system (one pass operation) is used. An autumn tickle is included as a control option that you can select.
• RIM contains assumptions regarding the control effectiveness (kill percentage) of the different weed control options. These values can be found in the Control % sheet. They have been selected through the review of trial results conducted in Western Australia and elsewhere and have been checked against farmer experience. It is possible to alter these values to reflect the level of control that you think occurs on your farm.

RIM home page

Order form
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

Copyright © David J. Pannell, 1999
Last revised: August 14, 2008.