Pre-harvest glyphosate: best practice in oilseed rape
The indeterminate growth of oilseed rape can make the crop a challenge to harvest. Such growth results in uneven ripening between the early- and late-formed branches. As a result, pre-harvest glyphosate applications are more common in oilseed rape crops, compared to cereals.
Glyphosate application timing is critical
Glyphosate should only be applied when the seeds have less than 30%. This can be determined using the following visual test:
Select an area of the crop that is representative of the field as a whole. Then choose an area of canopy that is typical of the maturity of most of the crop. Depending on the canopy, this may be pods in the middle of the main raceme or on the side branches. At random, pick 20 pods from several plants.
Open each pod and observe how many seeds have changed from green to brown. If this change is observed in at least two-thirds* of the seeds per pod in at least 15 of the pods picked, then the earliest correct stage** for spraying has been reached. Typically, the crop should be sprayed within four days. If the weather is very cool, however, this can be extended to seven days.
Check the assessment is representative of the entire field (repeat steps one and two, as required)
* If approximately half of the seeds are turning brown, then the earliest correct stage for spraying is likely to be in three days, but it is important that the procedure is repeated to check that the correct stage has been reached.
**Spraying too early will result in poor desiccation.
All estimates should be confirmed using a moisture meter.
The statutory harvest interval is 14 days. Up to 21 days, however, may be necessary before combine harvesting.
The target weeds should be green, healthy and actively growing. Weeds that have senesced or died back or are suffering from drought may not be as susceptible. Ensure the dose is matched to the weed species present (check the product label).
- Do not use glyphosate in crops grown for seed production
- Do not use glyphosate-treated straw as a horticultural growth medium or mulch
- Poor results can be expected from treatment of heavily laid crops with major secondary growth or significant areas of uneven ripening (eg caused by pigeon damage or poor drainage)
- Poor results can also be expected from laid crops where stems have been broken, although kinked stems are acceptable