Australian Pulse Bulletin

Desiccation and croptopping in pulses

Desiccation and croptopping are well established techniques to improve the rotational fit, benefits and profitability of the pulse crop. While they are essentially the same physical operation of applying a desiccant herbicide close to final maturity of the pulse, they do achieve different objectives and must be applied with care. Windrowing may be considered as an alternative to desiccation. The timing of windrowing is similar to desiccation.

Quick reference guide for pulses and canola

  • Desiccation and croptopping achieve different objectives

  • Croptopping is rarely possible in chickpea

  • Faba bean is suited to desiccation, and to some extent croptopping

  • Lentil crops can benefit greatly from desiccation and croptopping

  • Do not desiccate or croptop field pea destined for the sprouting market

  • Yield reductions of about 5–10% can occur if the lupins are not fully mature

Purpose

Desiccation and croptopping are used to achieve different objectives.

Desiccation prepares the pulse crop for harvesting by removing moisture from plants and late maturing areas of the paddock.

Desiccation is an aid to a timely harvest, particularly where uneven ripening occurs across a paddock, and is now a common practice in lentil and chickpea. Desiccation enables a timely harvest to avoid weather damage. Application timing is based on the crop when the grain is 75% to 90% mature, to avoid reducing the quality of the harvested grain. Windrowing can be considered similar to desiccation in timing and benefits to harvest.

Croptopping aims to stop the seed set in surviving weeds without substantially affecting crop yield and grain quality. Croptopping is timed for the weed growth stage to control weed seed set from survivors of normal in-crop weed control. Croptopping cannot be used in all pulses.

It is effective in early maturing species like field pea and common vetch and early maturing varieties of narrow leafed lupins, e.g. Mandelup. It is also effective in drying off late maturing weeds to reduce high moisture or contamination of harvested grain.

Timing is aimed at the soft dough stage of the target grass weed species, typically annual ryegrass, to stop seed set. If radish is the target, the herbicide should be applied at the pre-embryo stage. In most crops, targeting radish exposes the crop to a heightened risk of crop damage.

When used correctly in the appropriate pulse species, the crop will be almost or fully mature and grain quality will be unaffected. Croptopping is part of an Integrated Weed Management strategy and should not be used as a sole strategy.

Timing

With correct timing, desiccation and croptopping can improve profitability in pulses.

The major differences between desiccation and croptopping are:

  • Application timing is different and initiated by different criteria.
  • Herbicides for croptopping and desiccation are not always the same.
  • Herbicide rates for desiccation are higher than that required for croptopping.
  • Croptopping will advance the harvest timing in some pulse crops.
  • Neither desiccation nor croptopping can be used effectively in all pulses.
  • Both will cause reduced grain quality and yield if applied at the wrong maturity stage of the crop.

Seed crops

Don’t risk a pulse crop for seed!

Desiccation and croptopping can affect seed viability if applied incorrectly. To avoid damaging seed viability, it is advisable not to desiccate or croptop a pulse seed crop. Field peas destined for the sprouting market, should not be desiccated or croptopped.

Treating crops

Which crops can you desiccate or croptop, and what should you use?

Pulse species differ in their time to maturity, making some unsuitable for croptopping. Croptopping is conducted before the target weed species mature, later maturing pulse species will be adversely affected.

Early maturing species such as field pea, lupin and vetch are well suited to croptopping. They will be close to maturity at the time of herbicide application, minimising the risk to yield and grain quality.

Chickpea and broad bean are late maturing species. Croptopping these will usually lead to unacceptable yield and quality problems as the grain will be too immature at the correct weed maturity stage.

With care, yield and quality losses can be minimised with croptopping, while desiccating at the correct maturity stage of the pulse will minimise any risk.


Desiccation Croptopping
Desi chickpea Yes, at 80-85% yellow-brown pods No
Kabuli chickpea Yes No
Narrow leaf lupin Yes (rarely warranted) Yes
Albus lupin Yes No
Lentil Yes Yes
Field pea Yes (rarely warranted) Yes
Faba bean Yes Yes
Broad bean Yes No
Vetch No Yes
Mungbean Yes No

Registered products

The following table details the registered herbicides for use when croptopping or desiccating pulses.

NOTE:- It is imperative that only registered products are used at label rates.

Exceeding maximum label rates will lead to the detection of chemical residues in excess of the allowable Maximum Residue Level (MRL) jeopardising market access and the future of the Australian grains industry.

Herbicide
Example trade names
Operation
Crop
Rate
Withholding period
Diquat 200g/L Reglone® Desiccation Chickpea, faba bean, dry pea, lentil, lupin, mungbean 2 to 3 L/ha Grazing/stockfeed (GSF): 1 day
Harvest: 0 days (lupin, dry pea)
2 days (chickpea, lentil, faba bean)
Paraquat 250g/L Gramoxone® Croptopping Chickpea, faba bean, field pea, lentil, lupin, vetch 400 to 800 mL/ha GSF: 1 day (7 days for horses) Stock must be removed from treated areas 3 days before slaughter
Harvest: 7 days
Glyphosate 480g/L Ripper 480® Croptopping Faba bean, field pea 360 to 765 mL/ha GSF: 7 days
Harvest: 7 days
Desiccation Chickpea, faba bean, field pea, lentil, mungbean 765 mL to 2.025 L/ha GSF: 7 days
Harvest: 7 days
Glyphosate 500g/L Touchdown Hi Tech® Croptopping Faba bean, field pea 300 to 700 mL/ha GSF: 7 days
Harvest: 7 days
Glyphosate 540g/L Roundup PowerMAX® Croptopping Faba bean, field pea 320 to 680 mL/ha GSF: 7 days
Harvest: 7 days
Desiccation Chickpea, faba bean, field pea, lentil, mungbean 680 mL/ha to 1.8 L/ha GSF:7 days
Harvest: 7 days
Metsulfuron + Glyphosate 540 g/L Ally® + Roundup PowerMAX® Desiccation + knockdown weed control Chickpea 5 g + 500 mL to 1.1 L/ha GSF: 7 days
Harvest: 7 days
Saflufenacil
Sharpen
Desiccation Field pea, faba/broad bean,
chickpea, lentil, lupin
34 g/ha plus recommended label rate of glyphosate or paraquat herbicide plus
1 % Hasten or high quality MSO
GSF: 7 days
Harvest: 7 days

GSF - Withholding period for grazing or cutting for stock food

Note: Observe the Harvest Withholding Period and GSF for each crop.

Glyphosate is not registered for seed crops and should not be used in pulses intended for seed production or sprouting.

Controlling annual ryegrass

Getting the best result from croptopping for the control of ryegrass is a race between the maturity of the crop to avoid yield and quality losses, and the latest possible time before the ryegrass seeds mature to ensure that all have emerged. A typical result is about 80% control of ryegrass seed-set with little damage to the pulse. Consi