Pokeweed

This video discusses Pokeweed biology and management in field crops.
Pokeweed - Videos

Instructors

William S. Curran, Ph.D.

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- [Presenter] Welcome to the Learn Now video about pokeweed biology and management in field crops.

Common pokeweed is an herbaceous perennial broadleaf weed that typically infests wooded areas, pond edges, roadsides, fenced rows, farm fields, and other disturbed areas.

Pokeberry and inkberry are two other names for this plant.

Pokeweed is a simple perennial, which means it relies on seeds for propagation.

It is native to the United States and Canada.

It has a large, persistent taproot.

Also, the whole plant is toxic.

The roots are the most toxic while the berries are the least toxic.

Pokeweed is capable of abundant seed production.

On average each berry contains nine seeds.

These seeds are dispersed by birds and other animals, machinery, and seeds dropping from the mother plant.

Like all weeds, pokeweed competes for nutrients, water, and sunlight.

So why is pokeweed management important?

There has been an increase of questions regarding pokeweed control over the last several years.

There could be an increase of abundance for several reasons.

First, there's been a higher rate of adaption of no-till.

Perennial weeds like pokeweed thrive in no-till situations.

There has also been a reduced use or lower rates used of atrazine in corn.

Residual herbicides like atrazine are important for controlling later-emerging seedlings.

More acres have been planted in soybean and the use of residual herbicides have been on the decline in soybean as well.

The increase of urbanization could also be a potential cause with more places for birds to roost and spread the seeds.

Also, the Pennsylvania Soybean Board thought that this was an important issue and provided funding for research that was done at Penn State and we thank them for their support.

Let's take a look at the pokeweed seedling emergence patterns and how that plays a role in managing pokeweed.

In 2012 and 2013 pokeweed seedlings were counted every two weeks out in the field in order to determine the emergence period.

This graph shows the cumulative percentage of total seedlings emerged over growing degree days or GDD.

GDDs are an accumulation of heat units and calculated based on the minimum and maximum daily temperatures and a base temperature, in this case 50 degrees Fahrenheit.

The corresponding calendar months are listed below the GDDs.

50% of the seedlings emerged by 360 GDDs.

This is approximately mid to late May in State College, which is located in the central part of the state.

90% of the seedlings emerged by 580 GDDs, which is approximately late May into June for State College.

These are pictures of what the seedlings looked like by October.

The time that which they emerged is shown in each picture.

The earliest emerging plants produced berries and seeds.

The first two emerged produced over 200 berries, that's over 1,800 seeds.

Note that there were some seedlings that emerged in July and August.

While they did not produce berries they still had the potential to regrow the next year.

Using a residual herbicide or rotating to a small grain or perennial heat crop will help to manage these later emerging seedlings.

In the next few sections we'll take a look at some management tips starting with corn.

Here is a list of corn herbicides that were tested on pokeweed.

This table includes the herbicide name, active ingredient, mode or site of action, and the Weed Science Society of America or WSSA Group number.

This group number is based on the mode of action.

The herbicides with the same mode of action have the same color.

These herbicides were applied in mid May either by themselves and/or in combination at the legal rate and with appropriate adjuvants.

This graph shows the percent control of each treatment 12 weeks after application.

The herbicides are listed at the bottom with the rate in parentheses.

All herbicides provided at least 80% control except for the Liberty plus atrazine treatment.

Liberty is a contact herbicide.

It only kills the part of the plant which it touches.

Systemic herbicides are translocated throughout the plant and are the best choice for perennial weeds since the root is the part of the plant that needs to be killed.

Here are some pictures of the herbicide injury to pokeweed.

Liberty plus atrazine, which just burned the pokeweed but it regrew, Roundup plus Status, Callisto plus atrazine with the bleaching of the Callisto, and the twisting from Clarity.

Some herbicide treatments, especially those which did not include a residual herbicide, had new seedlings emerging by August.

This reinforces the importance for residual herbicides or a crop rotation to control the leader emerging seedlings.

The following spring the only thing that was left of some of the pokeweed plants that were sprayed was a hole in the ground.

Although, this was not specific to one herbicide it indicated that the herbicide that was sprayed completely killed the roots.

Management in soybean.

Here is a list of soybean herbicides that were tested on pokeweed.

This table includes the herbicide name, active ingredient, mode or site of action, and the WSSA Group number.

These herbicides were applied in mid June either by themselves and/or in combination at the legal rate and with appropriate adjuvants.

This graph shows the percent control of each treatment 12 weeks after application.

The herbicides are listed at the bottom with the rate at the end.

The herbicide treatments, which included glyphosate, the active ingredient in Roundup, provided at least 80% control.

The ALS inhibitor herbicides when applied alone provided 60% control or less.

This indicates that Roundup Ready soybeans are important for effective pokeweed management in soybean.

The picture on the left shows pokeweed after being sprayed with FirstRate, an ALS inhibitor herbicide.

The picture on the right shows pokeweed after being sprayed with glyphosate.

Let's now focus on glyphosate and how application timing affects pokeweed control.

This graph shows the percent control of each glyphosate application at various times throughout the year.

Applications before mid June provided less than 70% control.

Applications at or after mid June provided at least 93% control.

Around the mid June time frame pokeweed is beginning to flower.

At flowering, perennials like pokeweed begin to translocate nutrients and resources down to the roots for winter storage.

If a herbicide is applied at this time, the plants will take the herbicide down to the roots, injuring or killing the roots and disabling it from regrowing the following spring.

Corn and soybean herbicides are typically applied from mid May to mid June which is in this window of reduced control.

Since soybeans are a shorter crop waiting until later in the season to spray for pokeweed could be an option.

Another option would be to rotate the field into a small grain, let the pokeweed regrow, and then spray during August.

In summary, the later a seedling emerges the smaller the plant is and the few berries and seeds it produces.

However, those seedlings are important to manage because they eventually become the perennial plant which can regrow each year and produce more seeds.

Control is possible in both corn and soybeans.

Herbicides in each crop can generally provide at least 80% control of pokeweed.

Roundup Ready soybeans are an important tool for effectively managing pokeweed in soybeans.

And with glyphosate, a later application timing is better for better control.

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