Burcucumber: Don't Let it Get Out of Control

Burcucumber has started to germinate and grow and in some parts of the state it is already a few inches tall. Now is the time to take action to get it under control. Otherwise, as it starts to get viny and climb into the crop canopy it is more difficult to manage. Herbicides are essential in a burcucumber management program but use them in combination with other control methods. For best control, it will require at least a two-pass herbicide program, but more applications may be required. Because burcucumber can emerge throughout the growing season, it is difficult to manage with herbicides that lack residual activity. Furthermore, one-pass preemergence herbicide programs will not be adequate either. Seedling burcucumber can be killed with several effective postemergence herbicides; however, season-long control of burcucumber rarely is achieved with any herbicide. Effective management must include both pre and post (foliar-applied) herbicides. 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. Below are some suggestions for optimal control during the growing season.

Control in Corn

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 proven effective include the use of products such as Lexar, Acuron, or Corvus/TriVolt + atrazine preemergence followed by various combinations of these post products – Peak (0.5 oz/acre), dicamba/Status, Callisto/Halex GT/Acuron GT, atrazine, glyphosate, and Liberty 280. A useful post program for good burcucumber control and better crop rotation options includes Halex GT (3.6 pt/acre) + Peak (0.25 oz/acre). According to the Peak label if the use rate is 0.25 oz and is applied before July 10, then soybeans can be planted next season. 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., 24- to 36-inch-tall corn) to extend the residual control later into the season. In some cases, the use of drop nozzles may be necessary if corn is too tall. These types of later applications are only possible if using herbicides that are labeled for this purpose.

Control in Soybeans

Burcucumber control in soybeans may be easier and less costly than it is 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 for later postemergence herbicide applications; however, the quick canopy closure that occurs in narrower rows also can help to reduce later emerging weeds, including burcucumber. Split-applications (i.e., pre and post) of herbicides might be necessary for best control of later emerging burcucumber seedlings. Soil-applied treatments in soybeans will not provide adequate control of burcucumber. Although several preemergence herbicides can suppress (60-70%) burcucumber growth, 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), Valor XLT 40.3WG (flumioxazin + chlorimuron). Of all these, Canopy tends to provide the best initial control. 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, however Enlist One in E3 soybeans is typically not that effective on burcucumber. In whatever system, it is best to tank-mix glyphosate or glufosinate (Liberty) in the post application to improve control. Make sure the soybean variety has tolerance to the herbicides that will be applied. Generally, foliar-applied herbicides require additives to be mixed with the spray solution. Refer to the current product labels or to the Penn State Agronomy Guide for application information and other important restrictions.