No. 2 Article 4/April 4, 2008

Identification and Control of Burcucumber

Burcucumber (Sicyos angulatus) is a summer annual weed species typically found near creeks and rivers, but it has extended its range to include uplands and farm fields. This weed is troublesome in both corn and soybeans for three reasons: it has a discontinuous emergence pattern, with plants emerging late into the growing season when there are few effective herbicide options; it is very competitive (for example, it can reduce soybean yield by 43%); and its vining growth habit interferes with harvest.

Burcucumber, native to the U.S., belongs to the same family as the cultivated cucumbers we grow in gardens. Most burcucumber emerges in May and June, but emergence continues throughout the growing season through early fall, with subsequent flushes being associated with rainfall. After emergence, this weed can be identified by its large ovate cotyledons.

Burcucumber seedling.

Leaves are typically thin, with 3 to 5 lobes, a span up to 10 inches in diameter, and a sandpaper-like texture.

Burcucumber leaf.

Tendrils form at the base of the petioles and attach themselves to whatever is available. The stem is very pubescent, almost spiny. Burcucumber vines may reach lengths of 15 to 25 feet and can easily span across corn and soybean rows and cause lodging.

Burcucumber vine.

In the late summer and fall, green and white flowers develop on the burcucumber and produce small fruits, with one seed within each fruit. The fruits are typically found in clusters of up to 20.

Burcucumber fruit.

Burcucumber seed is similar in size to that of watermelon. The seed is covered in a thick seed coat, which aids in its persistence in the soil and is the reason burcucumber remains a problem long after establishment. The fruit encasing the seed is oblong, typically 2 to 5 cm long, and covered in long spines that aid in dispersal.

Burcucumber management requires an integrated approach of preventive, mechanical, and chemical programs. The preventive tactic focuses on seed movement, while the mechanical and chemical programs stress reducing the establishment of burcucumber. What programs you choose to use depend on your level of infestation, but the main goals are to prevent burcucumber introduction into areas where it is not already established and to prevent seed production in areas where burcucumber already exists.

Preventative tactics. Late-season scouting to locate suspected areas where populations are just becoming established is a must. This task may be very labor- and time-intensive, but it is less costly than controlling an already established population. If possible, avoid running a combine or tillage equipment through areas that are infested with burcucumber.

Burcucumber in corn.

It is also of great benefit to combine areas with established burcucumber populations last. Burcucumber seed is similar in size to several crops, so the seeds easily become hung up in the combine or other equipment and are then transported to new areas. Just running the separator and spreader of the combine is typically not enough to get these seeds out. Use of an air compressor, a water hose, and a broom to sweep out the combine is a very good idea and a more thorough method to rid the combine of these seeds.

Mechanical tactics. Mowing pastures, ditches, and roadsides where burcucumber is found can significantly reduce the plants. Tillage, however, has produced mixed results. Tillage can bury the seed, but seeds can germinate at depths of 6 inches. Germination was also found to be higher following tillage. Cultivation in areas with low infestation was effective at controlling burcucumber. Alternatively, no-till leaves the seeds on the soil surface where they may not germinate or germinate over a shorter period. Overall, the persistence of burcucumber seed makes it difficult to control regardless of the tillage practice used.

Other not-so-popular options are early harvest of corn as silage and destroying the infested area of the field. We advise these tactics only for severe infestations and if done before seed production.

Chemical tactics. Options for chemical control are available, but they generally are not as effective when used as stand-alone tactics. Because of burcucumber's extended emergence pattern, any herbicide program must follow a preemergence product with a postemergence product--one-pass programs do not stand a chance with burcucumber. Including a residual product is also very beneficial. There is no promise that even a pre-followed-by-post program will be sufficiently effective against this weed. Late flushes may require split shots or follow-up applications. Post-directed applications are also a viable option for severe infestations.

Glyphosate is effective at controlling emerged burcucumber, but it lacks soil residual activity. One benefit of glyphosate is that it can be applied quite late into the growing season on Roundup Ready crops. This may not provide 100% control of burcucumber, but these late-season applications may reduce seed production. Applications of glyphosate can be made on Roundup Ready Corn 2 up to 30 inches tall without drop nozzles and up to 48 inches with drop nozzles. In soybean, glyphosate can be applied through flowering (R2 soybean growth stage). Preharvest applications of glyphosate may be necessary to aid in harvest. Applications in corn can be made after black layer and in soybeans after seed set and when the pods have lost their green color; in either crop applications need to be made 7 days prior to harvest. Be sure to consider all weeds present in your field when selecting which herbicide program to use and to adhere to the label.

Tactics specific to corn. Historically, atrazine at the full use rate has been the primary recommendation for burcucumber control in corn. Any of the atrazine premixes, including Lumax, Lexar, Harness Xtra, Bicep II Magnum, Cinch ATZ, Fultime, Guardsman Max, and Keystone, along with products such as BalancePro, Epic, and Callisto at full labeled rates provide a good foundation for control. Postemergence herbicide options include atrazine, Beacon, Northstar, Marksman, Exceed/Spirit, Callisto, glyphosate, and Liberty.

Tactics specific to soybean. Burcumber management in soybean has to be intense: a soil-applied herbicide, postemergence application, cultivation, and a dense soybean canopy will help. Effective preemergence herbicides for burcucumber in soybean are quite few--Canopy, Scepter, and Pursuit, again at full labeled rates. Options for postemergence applications include Extreme, Sequence, Classic, Synchrony XP, Flexstar, Cobra, Ultra Blazer and glyphosate.--Dawn Refsell

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