Agronomist Paul McIntosh discusses the impact of weeds in broadleaf crops
Protecting broadleaf crops
.THERE are many of us still waiting for significant rain to plant a summer crop and others who have good crops after the heavy mid-December rain.
Whatever your situation, weeds may still be playing a detrimental part in your farming system.
My thoughts for this week are controlling weeds in crop, specifically in the hardest situation is controlling broadleaf weeds in broadleaf crops.
The photo attached is of a mungbean crop in the extreme hot and dry times of March 2017. All crops around this area were under a lot of pressure and even thinking about spraying weeds was a low necessity. As you can see the medium width rows of mungs had very few weeds growing however not all crops are so lucky .
A lot of our herbicide labels advise to apply to young actively growing weeds and that is what we all try to do, however we have this environment factor, where very little rainfall in crop occurs and the air temperatures in summer can reach the official 40 degrees, but can be much higher on bare soils.
We know in our mungbean, soybeans and other registered broadleaf summer crops that the herbicide active ingredient Aciflurofen (originally Blazer when first released in 1980) needs excellent coverage on small susceptible actively growing broadleaf plants.
Nothing has changed much in these specific needs apart from the mungbean rate with Hasten crop oil, being reduced to 1L/ha. Of course, not only do the weeds need to be actively growing, but so does the crop for crop safety angles. Temperatures above 30 degrees C and low humidity at application time, can also play havoc on soft broadleaf crops with an oil based adjuvant.
Even with the increased efficacy of this hasten oil being added, the end result on large bladder ketmia (wild cotton), noogoora burr, bell vine and the gooseberry family are going to be less then good. Suppression only maybe your best result for many of the broadleaf weed spectrum. So be aware of this less than perfect result.
The total in crop post emergent broadleaf herbicide list for mungs is a fairly short list of two only, with only some Imazamox products like Raptor and Claw, also allowed to be applied under the permit 82490. All these post emergent Imi products need to be applied to any actively growing crop plants, even lucerne crops, to prevent any crop damage. This safety angle is brought about by the crop plant being able to metabolise or grow out, the applied herbicide into a form that does not impact the crop plant. Anything that puts the crop under stress such as dry and hot conditions, waterlogging or frost can reduce the crops ability to effectively metabolise the selective herbicide applied.
Along with these crop safety principles, you also have your WHP or withholding period to adhere too. These days are not like the 1980s and 1990s, where WHP were treated with little concern with our insecticide and herbicide products. You really need to be mindful of your WHP, especially with our fop and dim grass herbicides in your pulse crops. Stat decs, that you fill out at delivery time, are there to protect you and our entire export industry. Please obey the rules and if a mistake has been made. Do not just cross your fingers and hope for the best, you are best advising your preferred marketer to make the best decision with you and for you.
NOT-SO-COOL BEANS: March 2017, in a very dry/hot time, a crop of mungbeans in southern Queensland. Paul McIntosh says mungs are tougher than they look.