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Eastern Black Nightshade: Re-emergence Of an Old Nightmare For Soybean Growers

Dean Riechers Dean Riechers
Assistant Professor
Department of Crop Sciences
(217) 333-9655; riechers@illinois.edu
Bill Simmons
 

Bill Simmons
Associate Professor
Department of Natural Resources and Environmental Sciences
(217) 333-9649; fsimmons@illinois.edu

 

Eastern black nightshade (EBN; Solanum ptycanthum) is a dynamic species that becomes more or less important with changes in weed management practices. Early on, when soil-applied herbicides such as Treflan, Prowl, Sonalan, and Sencor were commonly used, EBN was a serious problem in soybeans. When Scepter and Pursuit were commonly used, EBN became less of a problem. In the mid 1990s, the addition of Raptor also helped keep EBN in check. However, widespread use of glyphosate-tolerant soybeans (beginning in the late 1990s) may be contributing to an increase in this species in soybean fields. Also, we recently found an EBN biotype in Illinois resistant to the herbicides Pursuit and Raptor.

EBN plants can produce hundreds of thousands of seeds in a single growing season. Seeds can germinate late into the season, and seedlings can exist under the soybean canopy after postemergence herbicide applications. When soybean leaf drop begins in the fall, EBN plants continue to grow and reproduce because they are able to intercept light and are not affected by light frosts. These actively growing plants cause harvesting problems and delays, and the fleshy pulp from ruptured berries causes soil and debris from the field to cling to combine parts, resulting in plugged machines. More serious than harvesting problems, however, is the reduction in grain quality, since the purple berries can stain the soybeans as they go through the combine.

Young seedling of eastern black nightshade

Figure 1. Young seedling of eastern black
nightshade

Mature, branching EBN plant with dark purple berries. Each berry may contain hundreds of seeds.

Figure 2. Mature, branching EBN plant with
dark purple berries. Each berry may
contain hundreds of seeds.

Since EBN is a late-emerging weed and is shade tolerant, it has the potential to escape glyphosate applications in soybeans. The biology of EBN, coupled with the newfound resistance to ALS inhibitors that was recently discovered in Illinois, suggests that EBN may become more problematic for soybean growers in future years.

Many herbicides used in corn are effective for controlling EBN, so managing this weed might be easier in corn than
in soybeans. However, soil-applied herbicides in soybean that are effective for EBN control are Authority, Canopy XL, Dual II Magnum, Frontier, Scepter, and Pursuit. Postemergence herbicides that are effective in soybeans are Pursuit (which also provides soil residual), Raptor, glyphosate, and the diphenyl ethers (Blazer, Cobra, and Flexstar). ALS inhibitors such as Raptor and Pursuit might not be effective if the EBN population is resistant, or if other ALS-resistant weeds are present in the field.

EBN has presented a cyclical problem for growers due to the potential for weed spectrum shifts in response to changing management practices. For example, these shifts could be caused in part by conservation tillage or through use of glyphosate-tolerant soybeans. Glyphosate has no soil residual activity, and weeds either protected by the soybean canopy or germinating after glyphosate application, such as EBN, may not be controlled. Herbicides such as Pursuit and Raptor can provide the soil residual activity necessary to control ALS-susceptible EBN. However, the occurrence of ALS-resistant EBN may limit the effectiveness of this important weed management strategy and could have serious consequences for Illinois soybean growers.

Currently, we are conducting studies to help document the severity of the problem in Illinois and better understand the genetics and mechanisms of ALS resistance in EBN.

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