Sprayin' Weeds

            We have good soil on the West Boulder – it grows good grass and good hay, as well as good weeds.  Spraying those weeds is always major task in early summer.

            High priority on our ranch are four invasive species: Leafy Spurge, Russian Knapweed, Hoary Cress, and Woodlands Sage.  Left alone, any of these four will move in and take over, displacing the crops and grasses.  Constant vigilance is necessary to keep these aggressive weeds in check.

Also high on the list are three noxious species: Thistle, Hounds Tongue, and Burdock.  These are unsightly and stickery nuisances for which control is required by state law.

Tall Larkspur is a poison weed that has infested the summer range on our ranch in years past.  Many cattle in Montana have been killed by larkspur, and we spent several weeks each year for three successive years spraying out this plant.

The best time to spray is early in the summer before the grass gets too tall, and before the weeds bloom.  The smaller the plant the less spray is required.  Once the weeds have gone to seed it is too late to accomplish anything more for this year.

For large rangeland infestations we use a tractor-mounted sprayer that jets out 30 feet to each side.  In places where the tractor won’t go we can use the 4-wheeler with a spray boom that covers 7 feet.  But most of the spraying is done afoot with a back-pack and a spray wand.

The first step in weed control is to select an herbicide.  We mostly use a combination of two selective broad-leaf herbicides that don’t affect the grasses.  Then one must calibrate the sprayers to determine how much water we are laying down per acre.  That requires measuring the output per minute and calculating width and ground speed.  With both the tractor and the ATV we are laying down about 15 gallons of water per acre at 5 MPH.  Hand spraying puts down about 40 gallons per acre.

When spraying with jets one must gauge the distance from the tracks left by the last pass to minimize any gaps or overlap.  When spraying by hand we add a dye to the formulation to see where we have been.

It usually takes several years to eradicate weeds in a particular patch.  While the larger weeds are not hard to spot, young seedlings are easily missed among the grass.  Even if a person were to see and kill every plant that is growing this year, seeds from prior years can germinate for several years into the future.

Some of these plants can also reproduce from root runners, so one must search all around a mature plant, looking for additional sprouts.

With the mature plants that are missed, this year’s young sprouts, and seeds that are dormant in the soil, it takes a full three years to manage an infestation.   And it seems that just when you have one patch under control you find another patch that you hadn’t seen before. 

Fresh new seeds are contnually being carried in by the wind, by wildlife, and by vehicles – assuring job security for the herbicide applicator.