Paraquat provides options to control volunteers

Corn volunteers growing between the new crop rows.Volunteer plants – those that grow from seed shed by the previous crop – are weeds that bring the same problems as wild ones, or worse. Volunteers can form a ‘green bridge’ from one crop to the next carrying insect pests and fungal diseases. Volunteers reduce yields and quality, and hinder crop management. They can be difficult to control, especially if they are growing in a new crop of the same species. Options for controlling volunteers before planting the next crop can be particularly limited if they carry a herbicide tolerance trait to glyphosate, glufosinate or both. However, recently reported research has shown that paraquat boosted by the addition of a PSII inhibitor herbicide provides a good option to control volunteer corn (maize) before a new crop is planted1. More information about PSII inhibitors and herbicide modes of action can be found here.

Volunteer problems

Concerns that 2012 could be a bad year for volunteer corn were raised in the southeast US last year when lodged crops and late harvests from flooded fields pointed to significant grain loss2. This season there have, indeed, been reports of widespread problems in the US3,4. Volunteer corn competes for water and nutrients, and can attract corn rootworm (Diabrotica spp.). Corn following a soybean break crop normally suffers much less from corn rootworm than continuous corn. However, the presence of volunteer corn in a soybean crop can result in a build-up of the corn rootworm population. If corn volunteers are not controlled before flowering corn rootworm beetles are attracted and lay eggs that hatch the following spring5. Research at Iowa State University (USA), found that one volunteer plant per 10 feet in 30-inch rows (2.3 m2), could cause yield losses of 1.3% in corn. Research in South Dakota (USA) found that higher densities of volunteers (up to eight times more) could cause yield losses up to 13%3.

Control options

There are more options for controlling corn volunteers within soybean crops as selective grass weed


The leaves are "narrow" as opposed to the "broad" leaves of broadleaved weeds. Also called 'monocots' having one seed leaf opposed to 'dicots' having two seed leaves.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world. 
herbicides can be used. The more serious problem is volunteer corn in corn. One option is to plant a glufosinate tolerant hybrid to follow a glyphosate tolerant one (or vice versa), but often both traits are stacked and glufosinate can perform poorly under cool spring conditions1. Avoiding over-use of these herbicides to avoid weed resistance


The inherited ability of a plant/weed to survive a dose of a herbicide normally lethal to that species.

Authoritative On-line References and Resources The International Survey of Herbicide Resistant Weeds monitors the evolution of resistant species and assesses their impact. All confirmed instances of new cases are listed.
problems is also an important consideration.
Pre-planting, there are a few control options, but these depend on the presence of any herbicide tolerance traits in the volunteers and whether the residual properties of any potential herbicide could unacceptably delay the planting of the next crop. The case where a poorly established corn crop needs to be removed to allow an alternative crop of perhaps soybeans or cotton to be planted is a particular issue. Earlier in the 2012 season in Illinois there were reports of below freezing temperatures damaging young corn crops sufficiently to warrant replanting6. Clethodim herbicide is an option, but corn cannot be replanted for seven days after application6. In no-till


Also known as conservation tillage or zero tillage is a way of growing crops from year to year without disturbing the soil through tillage ie cultivating the soil usually with tractor-drawn implements.

Authoritative On-line References and Resources  A portal for on-line information about no-till farming.
fields, farmers will be reluctant to return to cultivations to destroy the failed crop.
However, paraquat provides a good option. Paraquat’s great advantages are that it is the fastest acting herbicide and it is deactivated immediately on contact with soil so a new crop can be planted straightaway. More information about paraquat’s unique soil properties can be found here. Adding a PSII inhibitor boosts activityFor best effects on corn, a PSII inhibitor herbicide such as atrazine, diuron or metribuzin should be added to paraquat. Like paraquat, these herbicides also have a mode of action involving photosynthesis, but a different and complementary one. Results from recently published research shown in the chart demonstrate this well. The paraquat-based mixtures not only have the fast-action advantage expected of paraquat, but the degree of control is more thorough over time. PSII inhibitor herbicides slow photosynthesis just enough to allow paraquat to move a little further into the plant than normal before the desiccation of conductive tissue prevents this. In weed species that are harder to control this allows a better and longer-lasting effect. Paraquat plus PSII inhibitors or the pre-mix of paraquat and diuron available in many countries provide good options to control corn volunteers and other tough weeds.


  1. Norsworthy, J K, Smith, K L and Griffith, G (2011). Evaluation of combinations of paraquat plus photosystem II-inhibiting herbicides for controlling failed stands of maize (Zea mays). Crop Protection, 30, 307-310.
  2. Lingenfelter. Dwight (2011). Watch out for volunteer corn in 2012. Southeast Farm Press.
  3. Hartzler, Bob (2012). How much can volunteer corn affect corn yields? Iowa State University, Integrated Crop management News.
  4. Stahl, Liz & Coulter, Jeff (2012). Volunteer corn – an issue in corn and soybean. University of Minnesota Extension Service Crop News.
  5. Pratt, Katie (2010). Control volunteer corn early. Southeast Farm Press.
  6. Jongeneel, S (2012). Herbicide injury can be a factor in replanting corn. Southeast Farm Press.


The brand name of the leading paraquat product is Gramoxone. The brand name of paraquat + diuron is Gramocil.