Planting options for herbicide treated paddocks
If you suspect that there will be an issue with herbicide carryover from the previous year, it may be prudent to plant a crop that is more tolerant to the residual herbicide. Planting options for the common carryover problems are listed in Table 1.
| Previous crop | Herbicide residue | Crops at risk | Crop options | Comments | |
|---|---|---|---|---|---|
| 1a | TT canola or Lupins | Simazine/atrazine | Cereals | Lupins | Following canola, lupins are the most tolerant crop, but lupins after canola are often poor. Volunteers are a big problem. Delay sowing until volunteer canola germinates then control with glyphosate. Remaining volunteers will compete until Eclipse® can be used. |
| 1b | TT Canola | Following lupins, if the soil is suitable and disease not an issue, this is the best option by far. | |||
| 1c | Peas/Chickpeas | As for lupins. Delay sowing as above. Delayed sowing is a better prospect in peas than in lupins. Use Broadstrike® to control canola volunteers. | |||
| 1d | Barley | Risky option. Barley is the most triazine tolerant of the cereals. Sow as late as possible to allow some breakdown. Atrazine will be more damaging than simazine. 4 L/ha in the previous season is unlikely to be tolerated unless sowing is delayed by 6 weeks. Sow with knife points, putting the seed below the herbicide as much as possible. Sow after a rain event. A drying topsoil will help as the plants will tend to produce deep roots and so minimise residue absorption. Sow the shortest season variety possible. Not an option if the break is delayed. | |||
| 1e | Wheat | The riskiest option. Machete is very sensitive, and should NOT be grown. Newer varieties have not been tested. Sowing rules as for barley, 1c. | |||
| 1f | Pasture | Grasses and clover may struggle, but there will be plenty of canola. Some lupin seed could also be top dressed to fix N2. Take the opportunity to prevent grass seed set and the paddock will be set up for wheat the following season. | |||
| 2a | Clearfield ® canola Imidazolinone tolerant | Imazapyr + Imazapic (OnDuty®) | Cereals | Field Peas | Safe option. Canola volunteers are a problem. Chickpeas are not an option, as Broadstrike® will not control volunteers. Faba beans may be an option. |
| 2b | IT wheat | Safe option. For sound resistance management do not apply a Group B herbicide in this season. Use phenoxy and/or diflufenican/pyrasulfotole (e.g. Tigrex®, Jaguar®, Velocity®) based products and mixes for control of canola volunteers. | |||
| 2c | Clearfield® canola (Imidazolinone tolerant) | Imazapyr + Imazapic (e.g. Sentry®) | Non-Imi tolerant crops | IT wheat, IT barley and IT oats | Safe option. For sound resistance management do not apply a Group B herbicide in this season. Use phenoxy and/or diflufenican (e.g. Tigrex®, Jaguar®) based products and mixes for control of canola volunteers. |
| 2d | Clearfield® canola (Imidazolinone tolerant) | Imazamox + Imazapyr (e.g. Intervix®, Intercept®) | Non-Imi tolerant crops | IT wheat and IT barley | For sound resistance management do not apply a Group B herbicdie in this season. Use phenoxy and/or diflufenican/pyrasulfotole (e.g. Tigrex®, Jaguar®, Velocity®) based products and mixes for control of canola volunteers. No registered herbicide options for control of volunteer canola in IT faba beans and IT lentils. |
| 3a | Pulses | Imazethapyr (e.g. Spinnaker®) | Cereals | IT wheat | As for 2b above. |
| 3b | IT canola | If the soil is suitable and disease not an issue, this is a good option. Use Lontrel® if volunteers are a problem. | |||
| 4a | Cereal | Sulfonyl ureas – Chlorsulfuron, triasulfuron, metsulfuron | Legumes | Cereal | The easy and safe option with wheat being the safest choice. |
| 4b | Non IT canola | IT canola | If canola was the planned rotation crop, IT (Clearfield®) varieties will be safe. The ability to tolerate soil residues of sulfonyl ureas does not imply that these herbicides can be used in-crop. TT and conventional varieties are not as sensitive to low SU residues as legumes, and may be safe. Do a pot test to check. | ||
| 5 | Cereals and canola | Clopyralid (e.g. Lontrel®) | Legumes | Cereals | Use registered herbicides with the appropriate crop species for weed control. |
Further information on safe plant back periods is available on all herbicide labels. Note: the plant back period refers to the period of time, usually in months, that is deemed safe to plant sensitive crops following the application of a residual herbicide.