Management of Eastern Black Nightshade in Agronomic Crops

By Dwight D. Lingenfelter and  William S. Curran

Eastern black nightshade (Solanum ptycanthum Dun.), an annual broadleaf plant, is a problem weed in northeastern field crop production. It is native to the Americas and commonly found throughout the United States east of the Rocky Mountains. Nightshade begins germinating in May and can continue throughout the growing season. Although it can cause reductions in crop yield, more important, it can interfere with the harvest and lower crop quality.

At soybean harvest time, nightshade foliage is green and the berries are still intact. During harvest, the berry juice causes soil, nightshade seeds, and other foreign materials to adhere to the grain, producing a pasty mixture that can clog and gum the sieves, cylinders, and augers of combines. If allowed to dry, this mixture can harden, resulting in downtime or even costly repairs. The berry juice can stain seed, potentially resulting in dockage at the mill; in addition, the moisture in the berries can cause poor bulk flow of soybeans and promote mold formation during storage.

Eastern black nightshade is a member of the nightshade (Solanaceae) family. Although weeds belonging to this family have many similarities, individual species should be identified carefully because they react differently to many herbicides. The cotyledons of eastern black nightshade are small and green on both surfaces with short hairs on the margins. The true leaves are simple, alternate, petioled, ovate, or ovate-lanceolate. The seedling leaves have a red-purple coloration on the lower surface and margins that vary from entire to slightly serrated. Leaf pubescence (hair) depends on the environment and varies from nearly hairless to moderately hairy. The stem of the eastern black nightshade plant is erect, becomes widely branched, and reaches 1 to 2 feet in height. As the plant matures, white flowers form in umbel-like clusters of four to five star-shaped flowers each. The fruit is a 3/8-inch, round, green berry that turns purplish black at maturity. Each nightshade plant is capable of producing up to 1,000 berries. Contained in each berry are 50 to 100 round, flattened, tan-colored seeds, each 1/16 inch in diameter (approximately the size of a pinhead).

Other annual members of the black nightshade complex that are sometimes confused with eastern black nightshade include American black nightshade (Solanum americanum Mill.), black nightshade (Solanum nigrum L.), and hairy nightshade (Solanum sarrachoides Sendtner). Of these three, only hairy nightshade is found in the northeastern United States. It can be distinguished from eastern black nightshade by the lack of red-purple coloration on the lower surface of the leaves, and upon close inspection of the fruit, the calyx (sepals) may cover as much as half the berry. Eastern black nightshade is the predominant annual nightshade species in Pennsylvania.

In addition to the annuals, the perennial smooth groundcherry (Physalis subglabrata) and horsenettle (Solanum carolinense) seedlings look like the eastern black nightshade seedling. However, both of these typically emerge from rootstock, distinguishing them from annuals.

Eastern black nightshade is toxic, as are most plants in the nightshade family. All parts of the plant are considered poisonous, but the green leaves, stems, and seeds are especially toxic. The green fruit may be quite poisonous, while the ripe fruit may be relatively nontoxic. The concentrations of the toxins are higher following dry conditions and often lower following damp, rainy periods. The toxic properties are relatively heat stable and not removed by drying. Portions of the plant stored with forage will remain poisonous, so producers must be cautious when feeding livestock nightshade-contaminated hay.

The toxicity of the green plant material varies from 0.1 to 1 percent of an animal’s body weight. The toxic principles include tophane and steroidal alkaloids, which commonly induce symptoms in farm animals similar to those of an atropine overdose, which includes colic, diarrhea, salivation, and vomiting. Very high doses may induce intestinal dysfunction and constipation, loss of coordination, weakness, tremors, depression, posterior weakness, paralysis, and low heart rate and blood pressure. Clinical signs develop rapidly. Most animals succumb or recover within 24 to 48 hours. Limited therapies are available for treatment.

As with most weeds, an integrated control program combining preventive, cultural, mechanical, and chemical methods is most effective.

Illustration by Rae Chambers

Prevention

Once eastern black nightshade has become established, prevent it from spreading into new areas. Clean seeds and berries from tillage implements and harvest equipment before using them in uninfested areas. Hay, straw, and crop seed may contain evidence of eastern black nightshade, so purchase it from a reliable source. Avoid spreading contaminated manure onto uninfested fields.

To reduce spreading, spot treat isolated patches of eastern black nightshade with an effective herbicide before the plants reach maturity. Birds have been known to eat ripe eastern black nightshade berries and transport them to uninfested fields. Spot treating with an herbicide or mowing any isolated patches in noncropland or fallow fields can reduce the occurrence of this type of spreading.

General Cultural Control

The germination of eastern black nightshade is sporadic throughout the growing season, making it difficult to control in many crops; however, crop competition can aid in minimizing spread. Good cultural practices promote healthy crop stands, and the resulting canopy shading helps control weeds. The following guidelines will help you maximize cultural control opportunities:

• Follow soil test recommendations for lime and fertilizer.
• Plant high-yielding varieties adapted to climate, soil, and field conditions.
• If soil temperatures and conditions are optimal, plant early using narrow row spacing and high plant populations, when possible.
• Follow practical integrated pest management programs that monitor disease, insects, and weeds, and use appropriate control tactics when necessary.
• Avoid certain herbicide programs that increase the potential for eastern black nightshade problems, such as Classic/chlorimuron plus Harmony/thifensulfuron in soybeans.

Mechanical Control

Mowing, plowing, disking, and cultivating are some of the more commonly used mechanical methods for field crop weed control. Existing nightshade infestations in hay crops or pastures can be controlled by timely mowing or swathing to prevent seed production. Repeated mowing may be necessary due to the sporadic germination of the plant.

Fall or spring tillage can bury weed seed deep enough to reduce emergence. This strategy is especially effective for small-seeded weeds such as eastern black nightshade. Such tillage requires the use of a moldboard plow or another tool that will invert the soil and bury the seed. However, if soil erosion is a problem, intensive tillage may not be possible or practical. Less intensive types of tillage such as chisel plowing, disking, or field cultivating prior to planting can destroy weeds that have already emerged, but they may also stimulate additional weed emergence.

Cultivating row crops removes or buries small weeds and makes them less competitive. In corn or soybeans, one or two cultivations during the first six weeks after planting helps control weeds missed by a preemergence herbicide treatment and provides a good alternative to a postemergence herbicide application. Cultivation will not control weeds within the crop rows, nor is it effective on late germinating weeds. Studies have shown that harvesting soybeans can be difficult with as little as one nightshade plant per 10 feet of row; therefore, for soybeans, cultivation alone may not be worth the time and extra effort required.

Chemical Control

To ensure effective, safe, and economical herbicide use:

• Select the appropriate herbicide for your weed problem and crop. The stage of weed and crop growth, temperature, and soil moisture and pH can affect herbicide performance. For additional information, refer to the Penn State Agronomy Guide or consult with the extension educator in your county or another agricultural professional.
• Read the herbicide label carefully and follow the directions. The label provides important information on safe use, application, disposal, and storage.
• Apply herbicides at the proper time.
• Apply the recommended rate to avoid injury, soil residue, and poor control.
• Calibrate application equipment several times during the season to ensure the correct amount of herbicide is applied.
• Wear proper protective equipment (PPE) when working with pesticides.
• Learn to predict weed problems. Scout fields regularly and record the types and locations of weeds present. Use field records to plan an integrated control program.

Eastern black nightshade is typically not a major problem in corn—it is not very competitive and can be easily controlled with many common corn herbicide programs that contain atrazine. However, several other herbicides can also be used to control nightshade (Table 1).

Control in soybeans can be achieved with effective herbicides applied Pre (preemergence) and/or Post (postemergence or foliar). The chloroacetamide herbicides (e.g., Dual/metolachlor and Harness/acetochlor) will provide some control of eastern black nightshade. For more severe infestations, a Pre program that includes flumioxazin (Valor) or sulfentrazone (Authority/Spartan) or Post control with a diphenyl ether (e.g., Cobra, Reflex, or Ultra Blazer) or Pursuit may be necessary (Table 2).

An effective herbicide program combined with early canopy closure can increase eastern black nightshade control in soybeans. Early canopy closure can be achieved through planting in narrow rows or with drilled beans.

At times, nightshade can present a problem for seedling forages such as alfalfa. To reduce the chance of competition from eastern black nightshade in alfalfa, plant the forage crop as early in the spring as possible, well in advance of nightshade germination. If nightshade becomes a problem in alfalfa, use Pursuit herbicide early postemergence or Maestro before daytime temperatures become too warm (see product labels for rates and additional information).

 Table 1. Corn herbicides for eastern black nightshade control.

Weed control rating: 10 = 95–100%; 9 = 85–95%; 8 = 75–85%; 7 = 65–75%; 6 = 55–65%; + = upper end of rating scale.

Table 2. Soybean herbicides for eastern black nightshade control.

Weed control rating: 10 = 95–100%; 9 = 85–95%; 8 = 75–85%; 7 = 65–75%; 6 = 55–65%; + = upper end of rating scale.

Harvest Aids

If herbicides fail, harvest aids can be used in soybeans. Although several harvest aid herbicides are labeled for use in soybean, paraquat-containing products (e.g., Gramoxone) provide the most consistent desiccation and quickened berry drop of eastern black nightshade prior to soybean harvest. If the nightshade plants are still green and have not yet been frosted, apply 10.7 fluid ounce of Gramoxone SL 3.0 plus surfactant as a harvest aid. (Note: Gramoxone/paraquat is a restricted-use pesticide and special training must be completed before using this herbicide.) Apply in 20 gallons per acre spray volume at least 15 days before harvest. For indeterminate varieties, apply when at least 65 percent of the seed pods have reached a mature brown color or seed moisture is 30 percent or less; and for determinate varieties, apply when plants are mature (i.e., beans are fully developed, half of leaves have dropped, and remaining leaves are yellowing). In the absence of a harvest aid herbicide, delay the soybean harvest for as long as possible to allow for additional berry drop. Nightshade berries will drop slowly following maturity or after a hard frost.