Last week I wrote about using herbicides or weed control as a tool to reduce fuel cost for irrigation. The longer you can keep a field weed-free, the longer the flood can be delayed from a weed management standpoint.
There eventually comes a time when the field must be flooded for other reasons. However, effective preflood weed control can allow you to supplement rainfall with timely flushing to delay the flood until that point.
In my experience the key to both an effective and an extended preflood weed control period is the proper use of residual herbicides. This means not only using the proper residual herbicides but also keeping them activated properly.
There are two schools of thought on the early use of Command to begin the program. One is to make the pre-emergence application automatic and hope it rains for activation. The other is to wait and use the aerial label to try to time the application just in front of a rain or flush. I have seen both methods work well.
Last year it did not rain at planting and most rice farmers would not flush due to high fuel costs. In most years I feel you are better off to apply some Command at planting.
Regardless of when it is applied, you can only consider it as part of the program when it is activated. If the plan is to use residual herbicides to delay the flood, it may mean having to flush sometimes for activation when you would rather not.
To extend the length of control from the residual herbicides, some residual herbicide needs to be added to the program. It is too much to ask of a pre-emergence application to hold as well as you would like and as long as you would like.
If Command is used pre-emergence (my philosophy of rice weed control is to treat every acre with Command pre-emergence) some weeds will escape and will require postemergence treatment. That is a good spot to add some more residual herbicide in the mix. Command can be added up to a season total of 1.6 pints per acre. Facet fits into a lot of the postemergence scenarios as well.
Sorely needed are some three-way tank mixes on the Command aerial label. Command is too cheap not to be able to add some to about any postemergence treatment going out. However, if the postemergence situation requires Super Wham and Facet or Ricestar HT and Permit for example, Command can not be added even though it could be added to any one of those herbicides in a two-way mix. This is outdated thinking going back to the fear that we are going to “screw up” the Command aerial label when Command is about the safest herbicide we are using from an off-target standpoint.
The combinations of treatments or herbicides that can be used are nearly infinite. My point is if you wish to extend residual periods of weed control, you need to supplement the pre-emergence treatment and activate the supplemental treatments.
The health of the rice crop and the herbicide program must be considered in the water management program. It would be nice if timely rainfalls occurred and you could just slip all of the treatments right between the rains and everything would work perfect. It does not work that way. However, you can take advantage of rainfall forecasts or the need to flush the field from a plant health standpoint if rainfall does not occur.
Try to take advantage of the rainfall or every flush to time postemergence herbicides and to slip a little more residual herbicide into the program and get it activated. Delaying the flood could actually take an extra flushing or two to keep the herbicide program going if Mother Nature does not cooperate. Failure to do so can put you into a salvage situation and wind up costing far more in herbicides than you can hope to save on pumping costs.
Ford Baldwin, Practical Weed Consultants. e-mail: firstname.lastname@example.org.