General Information


Peak is a selective herbicide applied after emergence of both crop and weeds for the control of broadleaf weeds in field corn, grain sorghum, winter wheat, spring wheat, barley, rye, oats, triticale, proso millet, and postemergence to weeds following small grain harvest. In addition, preemergence applications can be used in some areas for broadleaf weed control in sorghum. Peak is a water-dispersible granule formulation which must be thoroughly mixed in water and applied as a spray.

Refer to Tables 1 and 5 for a listing of weeds controlled when Peak is applied postemergence.

The degree of weed control resulting from application of Peak is dependent upon weed species, weed size at application, rate of Peak applied, and growing conditions. Weed control is optimum when ample soil moisture exists and weeds are actively growing.

Peak provides control or partial control of many broadleaf weeds. When reference is made to weeds partially controlled, this means that Peak provides significant weed control activity, but not always at a level generally considered acceptable for commercial weed control. Peak does not control grass weeds; therefore, if grasses are expected, a grass herbicide (such as Dual II Magnum, or Bicep Lite II Magnum preemergence in sorghum) should be applied.

Throughout the label, where rate ranges are listed, use the lower rate of Peak when weeds are in the middle or shorter portion of the recommended size range and the infestation is light or moderate. Use a higher rate of Peak when weeds are in the taller portion of the recommended size range or the infestation is heavy, and when a longer duration of weed control is desired.

Growth of susceptible weeds is inhibited soon after application of Peak. The leaves of susceptible plants turn yellow, red, or brown after several days, followed by death of the growing point. Complete plant death occurs 1-3 weeks after application, depending upon weed species and growing conditions. Weeds not completely killed by Peak are often stunted and are less competitive to the crop. Following postemergence applications, Peak provides residual/soil activity for up to 4 weeks.

This herbicide controls weeds by inhibiting a biochemical process which produces certain essential amino acids necessary for plant growth. The inhibited enzyme system is acetolactate synthase (ALS). Occurrence of ALS-resistant weed biotypes can be prevented or delayed by using this product in tank mixtures or in sequence with other herbicides having a different mode of action, and by using some form of mechanical control or a herbicide with a different mode of action to control weed escapes before they set seed.

Peak applied in accordance with the label rarely causes crop injury. When injury occurs, it is generally of short duration and yield potential is not affected.

Restrictions: To avoid possible illegal residues: (1) Do not graze or feed forage from Peak-treated crops to livestock until 30 days after application. (2) Do not harvest silage until 40 days after application. (3) Do not harvest grain until 60 days after application. (4) Do not apply more than 1 oz./A of Peak in the cropping season. (5) Complete all Peak applications before sorghum exceeds 30 inches in height or before head emergence; or before small grain cereal crops have the second node detectable in stem elongation.

Do not use Peak in the San Luis Valley of CO. In WA, abide by all sulfonylurea aerial application rulings in effect by the Washington Department of Agriculture.

Weed Resistance to ALS-Inhibiting Herbicides

In some fields, there are naturally-occurring biotypes of kochia, Russian thistle, chickweed, prickly lettuce, and annual ryegrass that will not be controlled by ALS-inhibiting herbicides.

Control of these weeds may be excellent with the use of Peak in many fields; but, where there is the known occurrence of ALS-resistant biotypes, Peak must be tank mixed or applied sequentially with an appropriate registered broadleaf weed control herbicide having a different mode of action* to insure control of these ALS-resistant biotypes.

*Mode of action is the biochemical mechanism for interfering with plant growth.

The occurrence of ALS-resistant weed biotypes can be prevented or delayed by using Peak in tank mixtures and/or in sequential applications with a registered herbicide having a different mode of action, and by not allowing weed escapes to flower.

Postharvest tillage or application of a herbicide with a different mode of action must be made to control any weed escapes before they flower or set seed. If weeds will flower before harvest, make a sequential application of an appropriate herbicide with a different mode of action from Peak. A list of herbicides with the same mode of action as Peak can be obtained from your local Syngenta representative.

Do not use Peak alone in any field where ALS-resistant biotypes of any weed species have been identified.

An application of a herbicide with a different mode of action from Peak, or a tillage operation, must be made to control any weeds before they flower that may be present in post harvest fields treated with Peak.

Do not apply Peak or other herbicides with the same mode of action within a 12-month period after a Peak application, except for split applications as described below. If additional weed control is needed, use a herbicide with a different mode of action from Peak.


Ground Spray Equipment: Spray nozzles should be uniformly spaced and of the same size, and should provide accurate and uniform application. Use spray nozzles which provide medium droplets.

To help assure accuracy, calibrate sprayer at the beginning of the season before use and recalibrate frequently. For ground application, use a minimum of 5 gals. of water per acre. Higher volumes (i.e., at least 20 gals./A) should be used for severe weed infestations to ensure adequate spray coverage. Always include crop oil concentrate or nonionic surfactant in the spray mixture (see the Mixing Procedures section which follows).

Use a pump with capacity to: (1) maintain 35-40 psi pressure at nozzles and (2) provide sufficient agitation within the tank to keep product in suspension. Lower pressures may be used with extended range or drift reduction flat fan nozzles. A centrifugal pump which provides shear action for dispersing and mixing the product is recommended.

The pump should provide a minimum of 20 gals./minute/100 gals. tank size circulated through a correctly positioned sparger tube or jet agitators. If jet agitators are used, at least 2 agitators should be aligned on the bottom of the tank pointing toward each end. Agitation during both mixing and application is essential. Screens or strainers placed on the suction side of the pump should be 16-mesh or coarser. Do not place a screen in the recirculation line unless a roller or piston pump is used for spraying the solution. Use 50-mesh or coarser screens between the pump and boom, and when required, at the nozzles. Check nozzle manufacturer’s recommendations.

Good weed coverage with the spray mixture is essential for optimum weed control results. Observe sprayer nozzles frequently during the spraying operation to ensure that the spray pattern is uniform. Avoid large spray overlaps which result in excessive rates in the overlap areas. Also, avoid application under conditions when uniform coverage cannot be obtained or when excessive spray drift may occur. To reduce spray drift, do not apply under windy conditions. Allow adequate distance between target area and desirable vegetation to prevent drift to nontarget areas. For application to sorghum, avoid placing nozzles directly over the row and concentrating spray into the sorghum whorls. Boom height for broadcast over-the-top application should be based upon the free-standing height of the crop, not height above the soil surface; and should be at least 15 inches above the crop.

Peak can be applied to the crop postemergence over-the-top or directed. In row crops, if the crop canopy would prevent adequate weed coverage, apply Peak with drop nozzles directed onto the weeds.

Avoid all direct or indirect contact (such as spray drift) of Peak with crops other than those recommended for treatment on the label, since injury may occur.

Aerial Application: Apply Peak in water using a minimum spray volume of 2 gals./A. Include crop oil concentrate or nonionic surfactant in the spray mixture (see following Mixing Procedures. Avoid application under conditions where uniform coverage cannot be obtained or where excessive spray drift may occur. Make applications at a maximum height of 10 ft. above the crop with low-drift nozzles at a maximum pressure of 40 psi and wind speed not exceeding 10 mph to help assure accurate application within the target area.

Avoid application to humans or animals. Flagmen and loaders should avoid inhalation of spray mist and prolonged contact with skin.

Do not apply Peak by aerial application in New York state.

Crop Failure

If a crop treated with Peak is lost due to a natural catastrophe such as hail or frost; an IR or IMR field corn hybrid or a small grain cereal crop (wheat, barley, rye, oats, or triticale) may be replanted immediately. Normal field corn or grain sorghum may be replanted, but not until one month or more after application. For control of weeds in a replanted crop, Peak may be applied a second time only if the total Peak applied during the cropping season does not exceed 1 oz./A.

Refer in the label regarding tank mix information.

Limitations, Restrictions, and Exceptions


Sorghum Tank Mix Rate (0.5 oz/A)

Enhanced Rate (1.0 oz/A)

Peak controls many broadleaf weeds, including triazine-resistant biotypes, in grain sorghum.

Postemergence Application (In All Sorghum Growing Areas)

Postemergence application should be made to sorghum at the rates and timings recommended in Table 2. Refer to the Rotational Crops Following Applications of Peak section regarding limitations for planting certain rotational crops at the higher application rates. If weeds are larger than the optimum size range recommended, only partial control may be obtained. For optimum control, if cultivation is to be used, cultivation is recommended 7-14 days after application of Peak.

Peak may be applied postemergence (over-the-top or directed) to actively growing sorghum between 5 and 30 inches in height and prior to head emergence. Within that broad window of application, it is more important to time applications to the optimum weed heights listed in Table 2, rather than crop height. Applications made to sorghum which is less than 5 inches tall increase the likelihood of crop injury. To insure good spray coverage of weeds, applications made after the sorghum is 20 inches tall should generally be directed or semi-directed using drop nozzles. In drier climates, crop oil concentrate (COC) is the preferred additive, instead of nonionic surfactant, when applying Peak alone.

Bindweed, Field; Chickweed, Common; Henbit; Mallow, Common; Morningglory, Ivyleaf; Morningglory, Pitted; Morningglory, Tall; Sida, Prickly; Thistle, Canada; Waterhemp, Tall: Partially controlled or suppressed.

Amaranth, Palmer; Chickweed, Common; Kochia; Lettuce, Prickly; Pigweed, Redroot; Pigweed, Smooth; Thistle, Russian; Waterhemp, Common; Waterhemp, Tall: Certain biotypes of this weed species are known to be resistant to this and other ALS herbicides. Where these ALS-resistant biotypes are known to exist, an appropriate registered herbicide, active against that weed and with another mode of action, should be used alone or in tank mixture with Peak to control those biotypes.

Buckwheat, Wild: Spray after true leaves have emerged; earlier applications may result in unacceptable control.

Velvetleaf: For optimum control, include nitrogen in the spray mixture; refer to Mixing Procedures.

Notes: (1) One CustomPak bottle of Peak contains 15 oz. Each bottle treats 15 acres at the Enhanced Sorghum Rate, 20 acres at the Standard Sorghum Rate, and 30-60 acres at the Cereal or Tank Mix Rates. (2) Volumetric measuring cylinders should be used only as a guide or as a container for weighing, as the degree of accuracy varies. For more precise measurement, scales which weigh in ounces and calibrated to at least 0.1 oz. are recommended. (3) For band applications, use proportionately less product.

Refer to Table 3 for recommended tank mixture partners, rates, weeds controlled, weed sizes, additives, and crop stages. The tank mixtures in Table 3 will control the weeds listed in that table when treated at the growth stage recommended, plus the weeds and weed sizes listed in the Standard Rate section of Table 2.

For all tank mixtures of Peak with other herbicides, refer to both labels for weeds controlled and application information; and follow all restrictions and precautions on both labels. For example, if applying Peak in tank mixture with AAtrex or other brands of atrazine, all the restrictions and rate limitations on the AAtrex (atrazine) label must be followed if more restrictive/protective than those on the label.

Precautions – For All Applications of Peak to Sorghum

Follow these precautions to reduce chances of crop injury and/or to avoid reduced weed control:

1. Peak should not be applied to sorghum which is under severe stress due to drought, cold weather, hail, wind damage, sand abrasion, flooding, water-logged soil, compacted soil, disease, insect damage, nutrient deficiency (especially low nitrogen or iron levels), or other causes. Also, Peak should not be applied if weeds are under severe stress due to drought or if weeds are taller than the optimum heights listed in Table 2.

2. Do not apply Peak preemergence to early planted sorghum if cool, wet environmental conditions that stress sorghum are expected within 2 weeks after application. Cool, wet weather following Peak applications to sorghum may result in injury to the sorghum; this injury is normally temporary and yields are not affected.

3. If an organophosphate insecticide is applied to sorghum at planting time, do not use Peak preemergence. Do not make a foliar or soil application of any organophosphate insecticide within 15 days before or 10 days after an application of Peak.

4. Application of Peak, either preemergence or postemergence, to sorghum growing under stress caused by minor element nutrient deficiency (e.g., iron) or on highly calcareous soil (above pH 8.2), may result in crop injury. Applications of Peak to fields where iron chlorosis can occur in sorghum may result in enhanced iron chlorosis symptoms. Such enhanced iron chlorosis symptoms are generally of short duration and yields are not impacted; however, if such symptoms persist, they can be corrected by application of foliar iron fertilizer.

5. Peak can be applied to all grain sorghum hybrids, except those susceptible to iron chlorosis, which are being grown in areas where insufficient iron is available in the soil. Most inbred lines of sorghum have not been tested for sensitivity to Peak. Therefore, inbred lines must be thoroughly tested for sensitivity to Peak before treating large acreages.

6. Do not sprinkler irrigate within 4 hours after postemergence application of Peak. Rainfall or sprinkler irrigation occurring less than 4 hours after postemergence application may reduce weed control.

7. Do not apply Peak to sorghum that exhibits injury symptoms from a previous herbicide application or other causes.

8. Do not use Peak on sweet sorghum.

9. Observe all precautions and limitations on the label of each product used in tank mixtures with Peak.

Restricted Entry Interval

12 hours