Dry summer sparks concern over planting options
Author: Sarah Jeffrey | Date: 09 Apr 2014
The unseasonably dry summer has sparked concern among some northern region advisors that fallow applications of the pre-emergent herbicide imazapic Flame®, and other similar products, will adversely impact upcoming winter crops.
Flame has become an increasingly popular tool in the battle against summer fallow weeds, particularly hard-to-kill weeds such as barnyard grass, liverseed grass, button grass and a range of other grass and broadleaf weeds, due to its long residual effectiveness in summer fallows.
However, a severe rainfall deficit over large areas of the northern cropping belt this summer has raised questions over the breakdown of the product and whether the carry-over soil residues will affect following crops.
The label states that wheat (except for varieties with Clearfield® technology), barley, lucerne and chickpea can be planted four months after application and faba beans three months after application.
However, there are important additional conditions that are particularly applicable for northern growers this year given the way the season has eventuated, according to ICAN senior consultant Mark Congreve.
“The label also requires that for following crops of wheat (other than Clearfield varieties), barley and lucerne, Flame should not be applied in fallow later than the end of December and shouldn’t be applied if rainfall from spraying to sowing of cereals is expected to be less than 200mm,” Mr Congreve said.
“No one expected just how little rainfall would occur in the first three months of this year and therefore there are likely to be some growers who have not had the required minimum of 200mm rainfall to assist herbicide breakdown to allow planting of conventional cereals.
“That means those growers will need to make alternative management decisions for the upcoming plant to avoid crop damage.”
Mr Congreve said growers looking to take advantage of the recent rain with an early wheat or barley plant could consider a number of alternative strategies if they believed their situation was marginal following imazapic application on summer fallow country.
“Firstly, look for new grass weed germinations following rainfall. If grass weeds have germinated and are growing healthily then this would suggest that the herbicide has probably broken down,” he said.
“Secondly, know the soil pH as the lower the soil pH the higher the risk of carryover residues.
“When it comes to selecting rotational crops, chickpea and faba beans are more tolerant than cereals so these may be a viable choice for some growers.”
He said growers who wished to plant cereals into imazapic-treated paddocks but did not meet the four-month and 200mm rainfall pre-requisite, should select varieties containing Clearfield technology which provides a safe level of tolerance to imidazolinone herbicides such as Flame.
“Likewise if Spinnaker® herbicide has been used in the preceding mungbean or soybean crop and summer rainfall has been limited, then growers should also consider a Clearfield variety,” Mr Congreve said.
“For the northern region, Elmore CL Plus is the primary wheat variety to consider as it has good tolerance to imazapic residues and has also consistently yielded above the trial mean average in National Variety Trials (NVT) so it is a well-adapted main season variety.
“If growers desire to grow barley then Scope CL is also a well-adapted variety for the northern region, again which performed well in the NVT trials.”
Mark Congreve, Senior Consultant ICAN
Sarah Jeffrey, Senior Consultant Cox Inall Communications
Region North, South, West