Controlling Whitetop & Perennial Pepperweed
& Perennial Pepperweed
are both members of the mustard family and as such they respond much the same way to cultural and chemical control methods. These are both very hardy perennial broad-leafed weeds that require plenty of chemical and correct timing to have any success at control. Bio control measures for these two grasses are out on the horizon, but not an effective tool to date. Whitetop can be found mentioned in some of Utah's earliest weed irradiation guides. One of the methods used in the early 1900's was lots and lots of salt. Fortunately, we have some very effective herbicides available today. Once again, it is extremely important that you READ AND FOLLOW THE LABEL with any herbicide you chose to use. The "time line" featured near the bottom of the page represents a generalized guide to the most effective timing of chemical weed control here in Northern Utah.
Both of these stubborn perennial weeds thrive in non-crop sites. Once the decision has been on bare ground or selective weed control, the rest is a matter of timing. If grasses are not to be taken out, the best selective herbicide is Telar® by DuPont. It is pricey, but very effective and label rates are at just one ounce of product per acre. GOOD agitation is required during application to keep the herbicide from settling out of the carrier water. 2,4-D amine at 4 pounds active ingredient per acre applied at bud to early bloom stage is also effective.
For bare ground, we like Arsenal® or Oust® tank mixed with diuron for most all bare ground jobs. Using a tank mix like this one will help ensure that resistant weeds such as kochia will not take advantage of the situation and sprout back with a vengeance. Timing gets to be a problem when trying to take utilize the dual action properties of Arsenal® or Oust®. The best time to kill perennial weeds through folar action is when they are mature and flowering. Very little rainfall is available at that time of year (middle June on) to incorporate the herbicide into the ground for root uptake. So, if all you are going to get is folar action anyway, perhaps Roundup® (see below) is the most cost effective choice. See labels for rates on your soils. CAUTION Watch sloping ground for potential runoff in the event of heavy rain or overhead irrigation!
Roundup® may be the best non-selective bet on whitetop and perennial pepperweed, particularly if the infestation is solid and a few years old. After the initial big hit with Roundup®, a bare ground tank mix early enough in the following season to assure sufficient rainfall ought to finish the job. A 3 quart rate is effective and a good surfactant is a must! Again, timing is everything! Don't waste your Roundup® on mature pepperweed in July ....... it is just too late. Mowing is not acceptable as a control measure because both weeds are perennial and will still be there when the snow flies. And as you might imagine, the very fine seeds are easily spread via the implement to other non-infested areas.
Rights of Way
Irrigation ditches and streams pose the usual concerns when trying to target whitetop and perennial pepperweed next to them. Arsenal® or Telar® are widely used along concrete irrigation ditches to control these damaging perennials but overspray into the irrigation stream must be avoided. Roundup® or Rodeo® are also very good in these situations and chemical allowed in the water is of little downstream consequence. You put a pencil to the rates and use the one that is cost effective for your budget.
Along roadsides, we find that the usual treatments of Campaign® or 2,4-D and Banvel® will usually keep whitetop in check. If a dense patch becomes a concern, a spot treatment with Telar® should eliminate the problem.
Most labels for herbicides used in crops do not specifically mention perennial pepperweed or whitetop specifically. Croplands in production will not generally be troubled with either one of these weeds if good farming practices are applied. If rowcrops or alfalfa are being considered for a piece that has been infested with these broadleaf weeds, might be a good idea to plant cereal grains the first year, make the young grain weed free with your favorite chemical, and follow up after harvest if any late weed sprouts appear with Roundup® or 2-4,D. Then the following year, the tillage and/or chemical treatments you would normally use on rowcrops or alfalfa should keep any remaining invaders in check.
Most appropriate months for treatment of whitetop or perennial pepperweed