Weed infestations popping up

While moisture is needed to alleviate drought conditions, the recent snow storm came at the right time to help the already sprouting weeds.

Two early weed infestations that are most noticeable across the valley are Flixweed/Tansy Mustard and Hoary cress.

Flixweed and Tansy mustard are very similar weeds. These native annual plants are typically seen in the early spring. Appearing almost fern-like as young plants, these weeds have finely divided leaves and a single stalk. The stalk is long with yellow flower clusters at the top. As the weed matures, the stalk elogates and seed pods, with rows of orange seeds, are formed. These weeds tend to dry out in May/June and unless removed, become tall, wispy, dry stalks after dispersing their seeds.

Flixweed/Tansy mustard may produce hundreds of seeds per plant. Therefore, removing the plant before it goes to seed is highly recommended. Mechanical removal of this weed by pulling or mowing when they are young plants is an easy remedy for yard weed control. Cutting or pulling prior to seed production helps minimize next season’s regrowth. As a single stalked weed, they are relatively easy to pull. Because they are soft as young plants, mowing is a viable removal option before it goes to seed. Broadleaf weed killer can be used to treat Flixweed/Tansy mustard. However, applications need to be done when the plants are very young or in their rosette stage. Typically, early spring is not the best time for post-emergent herbicide applications as the cooler temperatures are not peak conditions for herbicide use and effectiveness. Certain pre-emergent herbicides can be used to treat this weed and fall applications of broadleaf weed killer will provide control of rosettes as we go into late Fall and early winter.

Flixweed and tansy mustard are somewhat toxic to livestock due to sulfur compounds and occasionally high nitrate levels. However, large quantities of this plant must be consumed to have this adverse effect.

Hoary cress is a second weed that is actively growing during this time. As a weed, it thrives in disturbed and alkaline soil. If you had soil brought into your yard or if you have an alkaline soil base to your yard or along your roadside, do not be surprised if you see Hoary cress plants. Hoary cress is also a member of the Mustard family. Unlike Flixweed/Tansy mustard, Hoary cress is listed on the Nevada State (Category C) Noxious list (NRS 55.010). Though Hoary cress is generally established and widespread, being listed as a noxious weed means that it is the property owner or occupant’s responsibility to control, as it is a detriment to crop yields and property values. Hoary cress is commonly referred to as “Short Whitetop”, whereas Perennial pepperweed is referred to as “Tall Whitetop.”

Hoary cress tends to grow as a monoculture infestation as it outcompetes other plant species. This plant can successfully invade disturbed lands as it reproduces by seeds and a spreading root system. Hoary cress has a vertical tap root with the potential for may lateral roots that send up shoots. These lateral roots eventually turn downward and become vertical roots, as well. Depending on the depth of the water table, it is not uncommon for established infestations to reach into the water table. Each flowering stem of the plant can produce hundreds of seeds.

Hoary cress can be treated with various herbicides, but the selection of herbicide treatment is dependent on the stage of the plant when treated. Applications of a broadleaf weed killer (both spring and fall) prior to the bud stage are effective. Other herbicides: chlorsufuron, metsufuron and imazapic can be used in later growth stages of this weed. Cultivation of this weed can actually spread this plan and is not recommended. Mowing of this plant before it goes to seed may reduce future plant density but can be somewhat labor intensive depending on the acreage. Significantly more diligence is required in the effort to control Hoary cress, and it may require multiple seasons to treat infestations effectively than the previously mentioned weeds. Actively identifying and controlling smaller infestations is highly recommended.

If you are interested in treating weeds on your property, contact the Noxious Weed District at 775-423-2828. Staff will assess the weeds on your property and offer options as to what works best for your situation. The District focuses specifically on noxious weeds along roadsides and easements but can assist local property owners with identifying weeds, callibrating spray equipment and giving advice on herbicide and surfactant mix ratios per gallon of water used as a carrier used for best results for weed control.