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Should I Crop-top in a Dry Finish?

It is that time of year again

for desiccating and crop-topping pulse crops. Despite both crop-topping and desiccation being the application of a desiccant herbicide near pulse maturity, they have different objectives. Crop-topping aims to stop weed seed set without affecting grain yield and quality, while desiccation is about preparing the pulse crop for harvest by drying down late maturing areas. Moisture levels at the end of a season can dictate which product is best to use.

Dry conditions so far this Spring means that depending on what happens from here; it’s likely many crops will simply run out of moisture. Under this scenario using the cheapest option available (paraquat) will be the best strategy for a few reasons. Paraquat (Smart Paraquat 250) is better on grasses than diquat but is less effective on broadleaf plants, including pulse crops. When pulse crops and broadleaf weeds ripen with moisture, they are harder to kill and can require diquat or even glyphosate. Under limited moisture conditions, paraquat will be sufficient for both desiccation and crop-topping.

The maximum rate to use

when crop-topping pulses with paraquat is 800mL/ha. This is the label rate and should be adhered to. There are several ways to achieve a higher efficacy out of the product. Firstly, the addition of 0.2% Spray Volume (2L/1,000L water) of Smart Wet 1000 will help improve the spread and uptake of the product. Paraquat can move through living cells in plants however it mostly gets trapped where it lands as it kills the plant tissue making it unable to move. Increasing spray coverage will help overcome this problem by using higher water rates (80-100L) and smaller droplets. Applying in the early morning or evening can also improve the efficacy.

If no more rain arrives this season, some pulse crops could easily ripen by themselves. If grass weeds have viable seeds present using a premium wetting surfactant adjuvant like 0.25% (2.5L/1,000L water) Wetter TX/Apparent GlyAssist 1040 will allow paraquat to penetrate grass weed seed heads with a finer droplet allowing spreading and penetration efficiency to reduce seeding viability.

In summary

unless you have zero weeds in your crop or your crop is already dead or fully ripened, there is always a return on investment from crop topping or desiccating in a dry finish.

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