Common pokeweed an emerging issue in Michigan crops

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Over the last week common pokeweed plants have become more apparent in several Michigan fields. While common pokeweed is generally not a problem that most Michigan farmers think about, this weed has become increasingly prevalent throughout most of the state. In fact, in some cases common pokeweed infestations have reached populations that could interfere with crop yields. While there are no silver bullets to eradicate this weed from many fields, understanding the biology and conditions in which common pokeweed flourishes will ultimately help with management of common pokeweed.

Common pokeweed biology

Common pokeweed is a deep-rooted perennial that reproduces from root buds and seeds. Aboveground shoots of this plant arise from the taproot and consist of diffusely branched, fleshy stems (resembling a small tree) that can reach heights of 6 to 8 feet under fertile conditions (view photo1). In older plants, the taproot can be up to 6 inches in diameter and can grow to depths of more than 12 inches (view photo 2). Common pokeweed fruit is produced in late summer as clusters of green berries that turn purple to black at maturity and contain a profuse amount of red juice (view photo 3). The green leaves, fleshy stem, and purple berries of common pokeweed can inhibit the harvesting process and lead to discounts at the elevator for high seed moisture and staining. Areas with heavy infestations of common pokeweed can compete and reduce yield in both corn and soybeans. Numerous bird species are known to feed on the berries and are capable of randomly dispersing pokeweed seeds over sizeable areas. In fact, many times new common pokeweed plants are found at the base of trees or along electrical and telephone wires. Seedlings can emerge from mid-spring through early summer. Within five to nine weeks after emergence, seedlings of common pokeweed develop a taproot that is capable of regrowth (becomes perennial). New plants from dispersed seeds are capable of becoming entrenched as their taproots develop.

Many plants that form taproots generally do not tolerate intensive tillage practices. Common pokeweed is generally not a problem in crop fields that are exposed to tillage. In fact, one of the most effective methods to control this weed is use of mechanical controls, such as moldboard plowing and disking. However, since reduced tillage has become a desirable practice for corn and soybean producers to help reduce soil erosion, decrease energy and crop production costs, and to save time during the planting season, alternative or chemical control methods are more desirable.

Cultural control

  • Common pokeweed establishment often begins in fence rows or under power lines (dispersal by birds); Monitor and control pokeweed in these areas to prevent spread.

Mechanical control

  • Common pokeweed does not become a problem in fields with intensive tillage.
  • Tillage will control true seedlings within five to six weeks after emergence.
  • After pokeweed establishment, reduced tillage will only suppress common pokeweed.

Chemical control

Several herbicides with residual activity are effective at controlling seedling common pokeweed. However, common pokeweed is more difficult to control once it has developed its taproot and becomes perennial. Because of the variable size of common pokeweed populations in a field, application timing is critical. For in-crop applications, time herbicide applications when common pokeweed is at least 8 inches tall and preferably less than 12 inches tall. Effectiveness ratings for several herbicides for common pokeweed control are available in the accompanying tables. Refer to the herbicide labels for maximum crop height and stage application restrictions for individual herbicides.

Soybeans

Herbicide a,b

Rate

Effectiveness

Raptor + NIS + N

5 fl oz

Fair

Classic + NIS

0.67 oz

Poor-Fair

FirstRate + NIS or COC + N

0.3 oz

Poor

STS SOYBEAN ONLY

 

 

Synchrony XP + COC + N

0.75 oz

Fair


Corn

Herbicide a,b

Rate

Effectiveness

Callisto + COC + N

3 fl oz

Good

Distinct + NIS + N

4 fl oz

Fair-Good

Clarity

0.5 pt

Fair-Good

Northstar + NIS + N

5 oz

Fair-Good

Beacon + COC or NIS + N

0.76 oz

Fair

2,4-D amine     

1 pt

Poor


Roundup Ready Crops

Herbicide a,b

Rate

Effectiveness

glyphosate + AMS

0.75 lb a.e.

Good

 fb.

 

 

glyphosate + AMS

0.75 lb a.e.

 

 (if needed)

 

 


Noncrop/Fallow (Fall) c


Herbicide a,b

Rate

Effectiveness

 

 

 

Glyphosate + AMS

1.5 lb a.e.

Good-Excellent

a Refer to herbicide label for maximum application heights and stages.
b NIS = non-ionic surfactant; COC = crop oil concentrate; N = 28% UAN or AMS (ammonium sulfate).
c Apply in late-September or early-October when common pokeweed is 8 to 24 inches tall, but before a frost.

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