6 Weeds to Battle in Soybean Fields

Palmer Amaranth

Palmer amaranth is an aggressive and fast-growing weed. It has become a serious problem for vegetable and row crops growers across the country. This weed has adapted to heat, drought and herbicides. If Palmer amaranth emerges before or with the crop, it can cause significant yield loss in all agronomic row crops.

Experts suggest scouting every two or three days after crop planting to check for Palmer amaranth emergence. If pigweed has emerged, it is best controlled by applying a high-performance post-emergence herbicide, like INTERLINE^® or INTERMOC™, prior to growing to 3" tall, or removing by hand.

PREVIEW 2.1 herbicide controls the weed before emergence. A major component of this herbicide is metribuzin, one of the most effective active ingredients in managing resistant weeds. PREVIEW 2.1 herbicide combines metribuzin and sulfentrazone to combat Palmer amaranth.

Waterhemp

One of the most common weeds producers face is waterhemp. Although it is a part of the Amaranth family, it presents some unique challenges. Waterhemp emerges throughout the growing season, but the majority of the plants emerge later in the season than most of the other summer annual weeds.

Growers can help control waterhemp through scouting, timing herbicide application and using herbicides with multiple modes of action. Other practices, such as row spacing and planting rate, can help increase the effectiveness of the herbicide.

Redroot Pigweed

Another member of the amaranth family is redroot pigweed. It is not uncommon to find all three varieties of amaranth growing in the same field. Redroot pigweed can also serve as hosts for common pests that can damage crops. These weeds are especially numerous in no-till fields.

Like the rest of the family, redroot pigweed has developed herbicide resistance. The weeds are not visibly distinguishable from the susceptible weeds.

Pigweeds are susceptible to most soil-applied and post-emergent herbicides recommended for general control of broadleaf weeds. Residual control is most desirable because multiple rounds of germination can occur. Pigweed seedlings can be controlled by cultivation or hoeing, although proceed carefully with this tactic: older plants can recover from partial damage if the root has not been completely cut.

Kochia

Kochia is an annual broadleaf weed. It is problematic because of its early spring emergence, rapid growth and ability to tolerate heat, drought and saline soil conditions. Emerging kochia has small, fine, white hairs on the leaves during its button stage. Herbicide application is discouraged during the button stage because the leaf hairs can reduce foliar absorption by suspending droplets of the herbicide above the leaf cuticles.

It is best to control kochia during the germination stage or as seedlings. Kochia does not survive long in the soil, so pre-emergent herbicides are effective. It has developed a resistance to group 2, 4, 5 and 9 herbicides, which has resulted in the use of pre-emergent herbicides, such as PREVIEW 2.1 herbicide, as the base for control programs.

Lambsquarter

Lambsquarter is another member of the amaranth family. It grows rapidly and competes aggressively with surrounding crops. Lambsquarter populations start patchy but quickly become dense. On average, each lambsquarter plant produces 72,000 seeds. These seeds have a long dormancy and it can take up to 12 years to exterminate 50 percent of the seeds from the seedbed.

Tilling at night has proven to reduce the emergence of lambsquarter by 30 to 70 percent. Another method of control is tilling in the spring and planting later (mid-May) because the weed will have emerged and be controlled by the tilling. Lambsquarter is very hard to control with post-emergence herbicides. Also, lambsquarter is one of the first weeds to become difficult to control under dry conditions. It is best to control this weed in the early stages of its growth.

Morning Glory

Morning glory, also known as field bindweed, is a persistent weed with deep-running roots and strangling vines. Morning glory vines grow low to the ground until they find a structure they can climb. Once established, they are hard to eradicate because each plant can produce up to 500 seeds that are capable of 60 years of dormancy in the soil. Another problem is that pulling these weeds by hand can break the weed’s extensive root system and cause more growth.

Morning glory weeds are hard to control because of their large seed size and the impenetrable seed coat, which can make pre-emergence herbicides less effective. These weeds also can germinate late in the season after the crop has been established. A method that can help control is through cultural practices such as narrow row spacing.

If emergence occurs before planting, a pre-plant burndown herbicide treatment should be used. Soil-applied pre-emergence herbicides combined with timely post-emergence herbicides have been proven effective in controlling weeds. Finally, it is important to scout the field 10 to 14 days after all herbicide application is completed to ensure the effectiveness of the control measures.