Weed Control Options

Sweet corn growers have more weed management tools at their disposal in 2009 compared to even five or 10 years ago. Although more products are available, weed control in sweet corn can still be a challenge.

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Because sweet corn is usually planted at lower plant populations than field corn, it is slower growing, shorter, and produces a less-dense canopy than field corn. The result is more light penetration to the soil surface and lower canopy, favoring weed growth. Those factors make sweet corn less competitive with weeds than field corn and more susceptible to losses due to weeds. Weeds may also interfere with the operation of mechanical pickers.

Chemical Controls

As mentioned, several products have been added to the grower’s tool-box. Newer herbicides include the acetochlor products: Breakfree from Dupont Crop Protection, Degree and Harness from Monsanto, and Dow AgroSciences’ Keystone, Surpass, and TopNotch. Others include Bayer CropScience’s Laudis (tembotrione) and Option (foramsulfuron).

These are on top of the recent registrations of Stinger (clopyralid, Dow AgroSciences), Callisto (mesotrione, Syngenta Crop Protection), Impact (topramezone, Amvac Chemical Corp.), and Syngenta Crop Protection’s products with the active ingredient metolachlor: Lumax, Lexar, and Camix.

To be most effective and economical, herbicides should be used in combination with cultural and mechanical methods in an integrated approach, as this is the basis of integrated pest management. Product labels must be read and followed, and pro-per sprayer calibration is essential for success.

Also consider any recrop restrictions associated with herbicide use. Certain products, such as atrazine and some ALS (acetolactate synthase), and HPPD (4-hydroxyphenylpyruvate dioxygenase) herbicides, can limit what rotational or cover crops can be planted after application. Vegetables are
generally more sensitive than many agronomic crops.

The ALS herbicides of concern are Accent (nicosulfuron, DuPont), Sandea/Permit (halosulfur-on-methyl, Gowan), and the herbicides containing HPPD-inhibitors: Callisto, Lumax, Lexar, Camix, Impact, and Laudis.

Growers should put down soil-applied herbicides before the weeds emerge and are normally activated by rainfall. These herbicides typically control small-seeded annual grasses and broadleaf weeds and generally have no activity on established perennial weeds.

In the postemergence area, those types of herbicides should only be used in sequence after a soil-applied herbicide. Total post-weed control is not recommended because sweet corn seedlings are very non-competitive with weeds, and weather conditions that prevent postemergence herbicide application may delay weed control until it is too late to prevent loss.

Using a soil-applied herbicide improves overall weed control, provides additional herbicide modes of action for resistance management, and provides some insurance in case postemergence herbicides cannot be sprayed on time.

In Penn State research, a two-pass system provided more effective weed control overall compared to single application timing. If growers are spraying a post treatment, for best results, they should apply when the weeds are small, typically less than 3 inches tall.

Cultural Controls

In the cultural control area of integrated weed management, growers should minimize the impact of weeds by including soil testing for proper fertility and lime requirements to ensure healthy, competitive sweet corn plants. They also need to plant varieties at the proper time and populations and scout fields to identify problems when they are small and easier to control.

For weeds that have no adequate control, such as shattercane, quackgrass, and thistle, growers should consider not growing sweet corn in those fields and use another crop that will allow the weed to be managed.

Mechanical Controls

Tillage can also help manage weeds, including destroying any emerging seedlings, but it may also bring deeply buried seeds to the surface where they germinate. In addition, tillage sometimes can increase weed problems, especially of perennials, such as Canada thistle, by spreading root and stem pieces around the field.

Cultivation can help destroy emerged plants, but it is usually not effective in the crop row. Other mechanical controls include mowing weed patches and hand removal. One side note: with more herbicide options available, no-till sweet corn production is becoming less challenging.

A War That Can Be Won

In summary, weed control in sweet corn can be difficult, due to the less competitive nature of sweet corn plants and the limited number of products that can be used. With the new and effective products have been registered for sweet corn recently, this greatly enhances the grower’s toolbox. Controlling weeds is a challenge, and successful and profitable management requires an integrated approach that includes prevention, cultural controls, and proper use of registered herbicide products.