Managing Burcucumber in Agronomic Crops

Burcucumber

• Burcucumber is an aggressive, viny, summer annual broadleaf weed that can germinate throughout the summer, significantly reducing crop yield and causing harvest problems.
• Burcucumber management is possible with the use of an integrated control approach that includes preventive, cultural, mechanical, and chemical control tactics.

Prevention

• Prevent burcucumber seed spread by thoroughly cleaning tillage and harvesting equipment before leaving infested fields.

Cultural Control

• Encourage aggressive crop growth through good cultural practices such as maintaining adequate soil fertility, choosing appropriate high-yielding crop varieties, and regularly scouting for and managing pests.
• Include crops in the rotation that provide early competition, such as alfalfa or small grains.
• Plant shorter-season hybrids and harvest burcucumber-infested fields for silage to prevent viable seed production.

Mechanical Control

• Hand-pull, mow, till, cultivate, or harvest early for silage to manage burcucumber plants and prevent seed production.
• Include no-till in fields that are infested with burcucumber. Research suggests that no-till allows burcucumber seed to remain near the soil surface, thus allowing germination to occur over a shorter time period and reducing the number of germination flushes. This also improves herbicide effectiveness and performance.

Chemical Control

• Herbicides are essential in a burcucumber management program, but use them in combination with other control methods.
• Several herbicides provide good control of burcucumber. Include herbicides that have residual activity to control new burcucumber flushes.
• Postemergence (foliar-applied) herbicides provide the best burcucumber control. For residual control, include atrazine and Peak (prosulfuron) in the corn herbicide program and chlorimuron (Classic) in soybean programs, if possible.

Burcucumber (Sicyos angulatus) is a summer annual broadleaf weed that can be a serious problem in agronomic crops. Because of its prolonged seedling emergence and aggressive growth habit, burcucumber is not easily controlled using conventional weed management strategies. Like most weeds, burcucumber cannot be eradicated; however, an integrated control approach can reduce the size of burcucumber infestations and slow or stop further spread of the weed.

Burcucumber can be identified by its pentagon-shaped leaves, long vines, and spiny seed clusters. The individual seeds are flattened, have a hard seed coat about the size of a watermelon seed, and are enclosed in a prickly, fleshy shell or pericarp. The hard seed coat contributes to burcucumber’s prolonged seed dormancy, which means fields currently infested with burcucumber will have a lasting seed reservoir in the soil and a potential burcucumber problem for many years.

In Pennsylvania, burcucumber emerges from early May through mid-August, although plants emerging after mid-July often do not produce viable seed. Vines of some mature plants can be over 20 feet long and span more than six corn rows. Because of this aggressive growth habit, burcucumber can significantly reduce crop yield and make harvesting of both grain and forage nearly impossible. Burcucumber begins to flower in August and continues to produce flowers until it is killed by frost. Seed clusters composed of 2 to 30 seeds form shortly after flowering and remain green and fleshy through mid-September. After drying, the seed clusters shatter, depositing the seeds on the ground.

Burcucumber, also known as wild pickle, star cucumber, and nimble kate, can be confused with the less commonly encountered wild cucumber (Echinocystis lobata). Wild cucumber has clearly defined star-shaped leaves and large, prickly, egg-shaped fruits containing numerous seeds, and it is usually found along woodlands, streambanks, roadsides, and waste places.

The goal of an integrated weed management program is to provide reliable, effective, economic weed control while minimizing environmental risks. An integrated program for burcucumber combines multiple methods of control to reduce burcucumber interference with the crop. The methods of control may be preventive, cultural, mechanical, or chemical.

Figure 1. Burcucumber. Illustration by Rae Chambers

Prevention

Once established in a field, burcucumber is virtually impossible to eradicate; therefore, preventing the spread of burcucumber into new fields is an important step in managing this problem weed. Burcucumber seed is spread by many means, but of primary importance to the farmer is the spread of seed by harvesting equipment. The following strategies can help minimize the spread of burcucumber:

• Thoroughly clean all tillage and harvesting equipment before removing it from an infested field. Simply letting the harvest equipment run to clean itself out will not remove all burcucumber seeds; therefore, use a pressure washer or compressed air for thorough cleanup. Burcucumber vines with seed can wrap around disks, shanks, and harvest reels, especially on tillage equipment and forage harvesters.
• Avoid harvesting heavily infested areas for grain. Burcucumber seed may pass through a combine and end up back out into the field or into the grain bin. Because of its size and density, burcucumber seed is difficult to separate from contaminated corn or soybean seed.
• Plant only certified weed-free crop seed. If planting noncertified seed, be familiar with the source of the seed and be certain the field did not have a burcucumber problem.
• Lastly, scout fields to locate burcucumber and isolate and control small infestations before they become large problems. Most infestations of burcucumber start as small patches near the edge of a field. Without management, the entire field can become polluted with burcucumber within a four- or five-year period.

Cultural Control

Encouraging aggressive crop growth through good cultural practices can help manage all weeds. The following cultural practices encourage crop growth and vigor:

• Follow soil test recommendations for fertilizer and lime.
• Plant high-yielding varieties adapted to your climate, soil, and field conditions.
• Scout fields regularly for weeds, diseases, and insects, and control them when necessary.
• Include in the rotation crops that provide early competition, such as alfalfa or small grains.
• Consider planting shorter-season hybrids and harvest burcucumber-infested fields for silage to prevent viable seed production.

Mechanical Control

Mechanical control methods include hand-pulling, hoeing, mowing, plowing, disking, cultivating, and early harvesting. Hoeing and hand-pulling work well for controlling individual plants or isolated burcucumber patches, but they are impractical for larger infestations. Mowing will destroy emerged vines and prevent burcucumber seed production in hayfields, pastures, and noncropland areas. Small grain crops can be harvested before burcucumber is competitive or produces mature seed. Mowing or tillage after this harvest will prevent burcucumber seed production that season.

Preplant tillage can bury weed seeds deeply enough to prevent their germination; however, because burcucumber can germinate and emerge from depths of up to 6 inches, tillage tends to encourage multiple flushes of burcucumber throughout the growing season. Penn State research suggests that burcucumber may be better controlled in no-till fields as opposed to conventional or minimum-tilled fields. In no-till situations, burcucumber seeds are left near the soil surface, where they may or may not germinate; if they do germinate, it will occur over a shorter emergence cycle. The apparent advantage of no-till may be due to both a shorter emergence cycle and better postemergence herbicide performance. In conventional or reduced-tillage systems, cultivating, especially in conjunction with an herbicide program, may also provide control of burcucumber, but the impact of cultivation on subsequent burcucumber flushes is not known.

Because burcucumber seeds mature relatively late in the season, harvesting or destroying the crop early can prevent viable burcucumber seed production. Penn State research shows that ensiling green or immature burcucumber seed (green or cream-tan colored) is an effective technique for killing viable seed, but ensiling does not affect mature seed (dark brown seed coats; Table 1). This suggests that early harvesting of a crop as silage may prevent viable seed production in burcucumber-infested fields. Silage harvest also prevents mature seed from reentering the field through the combine.

Table 1. Effect of an eight-week ensiling period on burcucumber seed viability at different seed maturities.

*as compared to nonensiled seeds
Source: Messersmith, D. T., Master's Thesis, The Pennsylvania State University, 1997.

Chemical Control

Herbicides, when combined with preventive, cultural, and mechanical control methods, are an essential component of a burcucumber control program in corn and soybeans. To ensure effective, safe, and economical herbicide use, always:

• Select the appropriate herbicide for your weed problem and crop. Stage of weed and crop growth, temperature, soil moisture, and soil pH can affect herbicide performance. For additional information, refer to the current edition of the Penn State Agronomy Guide or consult the extension educator in your county.
• Read the herbicide label carefully and follow directions. The label provides important information on safe use, application, disposal, and storage.
• Apply herbicides at the proper time.
• Apply the recommended amount to avoid crop injury, soil residues, or poor control.
• Calibrate application equipment several times during the season to ensure the correct amount of herbicide is applied.
• Wear protective clothing.
• 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.

Control in Corn

Herbicides are essential in a burcucumber management program, but use them in combination with other control methods. Because burcucumber can emerge throughout the growing season, it is difficult to manage with herbicides that lack residual activity. Furthermore, one-pass preemergence (PRE) herbicide programs will not be adequate either. Seedling burcucumber can be killed with several effective postemergence (POST) herbicides; however, season-long control of burcucumber is rarely achieved with any herbicide. Effective management must include both PRE and POST (foliar-applied) herbicides (Table 2). POST herbicides provide the best burcucumber control. POST programs that include effective foliar and residual herbicides will enhance season-long control by killing later emerging burcucumber flushes. Several corn herbicides provide good control of burcucumber, and they are most effective on young seedlings rather than larger plants. Prosulfuron (Peak) has provided the best season-long control of burcucumber in Penn State field research, but be cautious of its long recrop restrictions. Some two-pass programs that have proved effective include products such as Lexar, Acuron, Corvus + atrazine, or Balance Flexx + atrazine preemergence followed by various combinations of the following POST products: Peak/Spirit, dicamba/ Status, Callisto/Halex GT, atrazine, glyphosate, and Liberty 280. Make foliar applications to corn within recommended crop growth stages and when burcucumber is less than 12 inches long and has not yet vined. Generally, foliar-applied herbicides require additives to be mixed with the spray solution. When appropriate, apply the POST herbicides as late as possible (e.g., on 24- to 36-inch-tall corn) to extend the residual control later into the season. In cases where corn is too tall, the use of drop nozzles may be necessary. These types of later applications are only possible using herbicides labeled for this purpose.

Table 2. Corn Herbicides for burcucumber control.

Weed control rating: 10 = 95–100%; 9 = 85–95%; 8 = 75–85%; 7 = 65–75%; 6 = 55–65%; + = upper end of rating scale; — = not available.

Control in Soybeans

Burcucumber control in soybeans may be easier and less costly than in corn. Because burcucumber can be better monitored, rescue herbicide treatments and later access are more feasible in soybeans than in corn. Planting soybeans in 30-inch rows can allow for cultivation and later postemergence herbicide applications; however, the quick canopy closure that occurs in narrower rows can also help reduce later emerging weeds, including burcucumber. Split herbicide applications (e.g., PRE and POST) might be necessary for best control of later emerging burcucumber seedlings (Table 3). Soil-applied treatments in soybeans will not provide adequate control of burcucumber. Although several preemergence herbicides can suppress burcucumber growth by 60 to 70 percent, an additional foliar-applied herbicide will be necessary for season-long control. In general, products that contain chlorimuron and/or metribuzin provide the best initial early season suppression of burcucumber. These soil-applied products include Authority MTZ 45DF (sulfentrazone + metribuzin), Authority XL 70WG (sulfentrazone + chlorimuron), Canopy 75DF (chlorimuron + metribuzin), Envive 41.3WG (chlorimuron + flumioxazin + thifensulfuron), Fierce XLT 62.41WG (pyroxasulfone + flumioxazin + chlorimuron), Panther Pro 4.23SC (metribuzin + flumioxazin + imazethapyr), Pursuit 2AS (imazethapyr), Trivence 61.3WG (chlorimuron + metribuzin + flumioxazin), and Valor XLT 40.3WG (flumioxazin + chlorimuron). Make postemergence (foliar) applications to soybeans within recommended crop growth stages and when burcucumber is less than 12 inches long and has not yet vined. Herbicides containing chlorimuron (Classic, Synchrony) have provided the most consistent control of burcucumber in Penn State field studies. Chlorimuron provides both foliar and residual activity on burcucumber. In Xtend soybean systems, dicamba-containing products can be used to control existing burcucumber. It is best to tank-mix glyphosate or glufosinate (Liberty) in the POST application to improve control, but make sure the soybean variety has tolerance to the herbicides that will be applied. In general, foliar-applied herbicides require additives to be mixed with the spray solution. Refer to current product labels or the Penn State Agronomy Guide for application information and other important restrictions.

Table 3. Soybean Herbicides for burcucumber control.

Control in Alfalfa and Small Grains

Burcucumber is less of a problem in alfalfa and small grains, and an herbicide application often is not necessary. An exception may apply to new spring-seeded forages or cereals such as spring oats. Because of its seed longevity, burcucumber may become problematic again when a field is rotated back to corn or soybeans.

Because of frequent cutting, burcucumber is usually not able to compete in established forage stands. In new spring seedings, Maestro 2E (bromoxynil) will control small burcucumber plants in newly seeded alfalfa. Apply 1 to 1.5 pints of Maestro 2E to spring-seeded alfalfa with at least four trifoliate leaves. Unacceptable crop injury may occur if Maestro is applied when temperatures are expected to exceed 70°F at or during the three days following application.

Small grain crops are able to compete well with burcucumber because of their vigorous growth and dense canopy in the spring. Also, small grains are harvested before burcucumber has a chance to reach a significant size and interfere with the crop. However, burcucumber may compete with spring oats, especially if the oats are seeded late in the spring. For small infestations, hand-pulling the burcucumber is recommended. If burcucumber begins to thrive, harvest the oat crop as a forage or apply 0.5 ounce of Peak 57WG per acre or Harmony Extra SG 50WG at 0.45 to 0.9 ounce per acre. Include an appropriate spray additive in the spray mixture. Maestro 2E at 1 to 2 pints per acre could also be applied to reduce burcucumber competition. Refer to the specific product label for information on application and crop rotations.

Spot Treatments, Harvest Aid Applications, and Nonselective Control

Glyphosate can be used to control emerged burcucumber prior to planting or in noncropland areas. Glyphosate can also be used to spot-treat heavy infestations in a crop to prevent burcucumber seed production. Apply 1 to 1.5 quarts of glyphosate per acre in 10 to 20 gallons of water per acre. For smaller areas, mix glyphosate at a 1 percent solution rate (1.3 fluid ounces per gallon of water).

If burcucumber cannot be removed with corn silage harvest (as previously suggested), harvest aid herbicides are generally not effective on burcucumber and will not necessarily control the weed before grain harvest. In most cases, if the corn is harvested for grain, the mature seeds will simply end up back in the field (or in the grain), making the problem worse for future years. But if necessary, paraquat (Gramoxone, others) is usually the most effective preharvest herbicide in this situation. However, other late season corn herbicide options may provide some suppression and desiccation (Table 2). Keep in mind that this type of application in corn requires high-clearance equipment or aerial application. Herbicide applications made during this late timeframe are used primarily to help desiccate green weed tissue to improve the harvesting process. Herbicides such as glyphosate, paraquat, Aim, and Clarity can be used as harvest aids prior to soybean harvest. In most cases, contact herbicides are usually better as harvest aids; however, efficacy can vary by weed species and usually requires at least a week to desiccate weeds. Some of these herbicides are not that effective on large weeds or certain species. Harvest aids are not intended to (and usually do not) help speed up crop maturity. If applied too early, they can interfere with the natural crop maturation process. Illegal herbicide residues can result if specific application timing and other label guidelines are not followed. See specific product label to determine correct rate, timing, weed species controlled, and other restrictions with this type of application.

Prepared by Dwight D. Lingenfelter, extension weed scientist; David Messersmith, agricultural extension educator and administrator; and William S. Curran, professor emeritus of weed science.