Don’t get bitten hard in weed control

CONTINUING with these double-cropping thoughts in our chickpea crops' residual herbicides, I will now divert my thoughts to those states which have the Imi product of Spinnaker registered.

This product has been around Australia for more than 20 years now and has been used in many legume crops across Australia.

Most times in chickpea crops with a Balance or Spinnaker the first choice of product, you may also add a triazine product like Simazine to enhance the weed control spectrum.

So to calculate a Spinnaker plant-back or re-cropping interval is a complex matrix of rotation crop options and rainfall quantity, plus summer or winter use, to say nothing about rate per hectare.

So if you choose to plant a grain sorghum crop, then the one part of the label suggests it could well be 34 months after post-plant pre-emergent of this Group B product.

Add this to the rainfall required of over 300mm or 12 inches and it would be safe to say many of our southern cousins would get fairly scared of using this handy product of Imazethapyr.

Another part suggests 10 months' time-lapse plus 32 inches of rain.

So all in all, the label can be confusing. However, make no mistake, this highly effective residual product can bite you hard if you get blase about assessing its residual nature and these comments cover more than just chickpea crops in southern Australia.

So, practically speaking, our more southern cousins would be inspecting their paddocks for very sensitive weed germinations and growth, to determine if the Spinnaker residual had dissipated enough to plant a sorghum or millet crop.

Sensitive weeds, by my estimation, would be mint, red pigweed, New Zealand spinach and some of the common amaranthus plants.

A much better option in this situation would be to plant a legume crop like mung beans or soybeans in December, with a cautious approach on the companion triazine product and rate used earlier in the year.

This low rate of Imazethapyr used in chickpeas and faba beans in other states may well make a comeback to the label in Queensland, particularly now we seem to get a lot of practice with the deep planting of our chickpea seed.

The one solid option that could be planted this summer is IT maize into former chickpea ground, with a caution on the triazine product and rate used.

You certainly do not need me to point out that moisture levels are diabolically low at the present moment.

However, we have all seen it turn around, especially for the central Queensland area with its fairly traditional wet season.

Even we in the southern Queensland cropping area were given a huge boost last summer over the Australia Day long weekend with steady rain of four inches or more received.

Our summer crops were doing it tough until that time and our sorghum and cotton crops responded magnificently.

Another old product that made a bit of comeback in chickpea weed control last year was Prometryne.

This original cotton product from the '60s and '70s is also a triazine, and has a six-month plant-back to sensitive crops and, once again, suggests you perform paddock inspections for actively growing, triazine-sensitive plants, like black and red pigweed or mint, before making any summer crop seed commitment to the soil.

Both these triazine products are similar to Atrazine and are root- absorbed, so positioning of any future planting seed below the level of possible herbicide surface infiltration will provide that bit of extra crop safety.

All in all, it is possible to double crop your 2013 chickpea ground. However, as I was taught to be cautious, so should you adopt this principle. Scout your ground carefully for actively growing signs of broadleaf, herbicide-sensitive plants.

Topics:  herbicides paul mcintosh weeds

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