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mustard seed weed killer

Sheron C., Albuquerque

Mustard weeds have annual lifecycles, although they can germinate and grow as both winter and summer annuals depending on temperatures. Additionally, mustards like flixweed and shepherd’s purse have the ability to survive as weak biennials depending on temperatures and moisture availability. Plants with annual and biennial lifecycles must germinate from seed during each growth season. Thus, the key to controlling these plants is to target them when they are newly germinated before they have the ability to produce copious amounts of viable seed and disperse them into the soil to germinate later (in some cases decades later). Mulching (2-4 inches thick) or laying plastic over areas of bare soil will help to block sunlight and prevent germination of mustard seeds. I often get questions asking if allowing plastic covering to be exposed to the sunlight will heat the soil surface to a temperature that will kill dormant weed seeds. While this practice, known as solarization, may help some (which is better than none), generally the soil will not get hot enough at enough of a depth to really make a dent in the seed population. Using a weed burner or a propane flame torch may be effective on germinating plants, but again the soil acts as a great buffer against heat and will not damage seeds unless they are right on the surface. In addition, great caution should always be taken with using flame to control weeds. If you are not opposed to herbicides, a preemergence barrier with the active ingredient pendimethalin will also help to control the weed as they germinate.

If you have mature mustard plants and it is late in the season (such as now) the plant may be too mature to respond completely to an herbicide application, synthetic or organic. In the southern portion of the state (Las Cruces, Deming, Hobbs, et.) temperatures have been so mild this winter that mustard plants are already beginning to produce seed heads with viable seed…at this point the most effective method of control is to cut the roots, rake, or hand-pull and remove the plants prior to dropping their seed. In some of the more northern cities (Albuquerque, Santa Fe, etc.) temperatures may still be cold enough to delay the production of seed heads in mustard plants. If this is the case, as the temperatures start to get a little warmer you can apply a postemergence herbicide, such as glyphosate, as the plant is actively growing and developing a seedhead.

If you are not opposed to herbicide applications for weeds that have germinated, you want to try and time these applications when the plant is young (the younger the better) and actively growing. Applications with products with active ingredients like 2, 4-D, dicamba, triclopyr, and glyphosate have been reported to control mustard weeds. If organic options like acids or oils are preferred, make sure that the product that you use is labeled as a herbicide, such as enhanced vinegars. Home-use distilled vinegar is not labeled for use as an herbicide. Since these products only burn and damage the surface of the plant, it is also essential to try and make this application when the plant is young and most susceptible.

Q.) I have mustard weeds all over the place defying temperatures in the teens. What can I do?

Wild mustard control can be a challenge because this is a tough weed that tends to grow and create dense patches that out-compete other plants. Wild mustard is a pain, but it is a bigger problem for farmers than for home gardeners. You can use both physical and chemical strategies to manage or eliminate wild mustard in your yard or garden.

Herbicides can also be effective in controlling wild mustard. There are several different types of herbicides that will work against wild mustard, but there are some that the weeds have grown resistant to and that will no longer work.

About Wild Mustard Weeds

Because it’s so tough, getting rid of wild mustard can be a real project. If you do not want to use chemicals in your garden, the only way to eliminate this weed is to pull it out. The best time to pull mustard weeds is when they are young. This is because they will be easier to pull out, roots and all, but also because removing them before they produce seeds will help limit future growth.

Unfortunately, there are no other cultural or biological control methods for wild mustard. Burning does not help, nor does allowing animals to forage. The seeds of wild mustard can actually be toxic to livestock.

If you have too many to pull, you can mow down wild mustard before seed production, during the bud to bloom stages. This will limit seed production.

Herbicides used for weed control in mustard can be discussed in two different groups: in-crop herbicides, and pre-harvest herbicides. Within in-crop herbicides there are soil active herbicides typically applied prior to the seeding of the crop and foliar herbicides applied after crop and weed emergence. Due to the limited selection of registered in-crop herbicides for mustard, it is important that good weed control is maintained throughout the crop rotation. Because of herbicide resistance concerns and for the best crop yield response, it is recommended that a combination of the herbicides listed below be used with an approach called “herbicide layering.”

It is important that the timing, rates and pre-harvest intervals stated on the herbicide label be followed. Deviation from the application instructions listed on the label will alter the efficacy of the product and may result in herbicide residues higher than established Maximum Residue Limits (MRLs) which could reduce the marketability of the harvested grain.