Soil-Residual Herbicide Options For “Slow-To-Canopy” Soybeans

Soybean field pre-canopy
Figure 1. Soybean field at North Platte, weeks away from reaching full canopy. Photo taken 7/4/2017.

Soil-Residual Herbicide Options For “Slow-To-Canopy” Soybeans July 7, 2017

Soybeans have been slow to canopy in multiple fields across Nebraska and growers have expressed concern regarding weed management (Figure 1). At sites where soybeans have a ways to go until they reach full canopy, producers are encouraged to include soil-residual herbicides with their post-emergence program; otherwise, additional post-emergence applications may be necessary.

Below you will find a list of herbicides with soil residual activity that can be sprayed in established soybeans to control weeds that are yet to emerge (Table 1). These herbicide options are effective on late-emerging, small-seeded broadleaf weeds such as common lambsquarters, common waterhemp and Palmer amaranth, and small-seeded grass species such as foxtails and barnyardgrass. Given current soybean growth stages ranging from 4th trifoliate to blooming, First Rate, Outlook, Pursuit, Warrant and Warrant Ultra may be the options available to producers.

Late-season Palmer amaranth seedling
Figure 2. Late-emerging Palmer amaranth seedling. Photo taken on July 07, 2017.

The effectiveness of soil-residual herbicides applied post-emergence will depend on:

  • herbicide selected,
  • weed species present and actively germinating,
  • weed emergence window,
  • crop and weed density,
  • application rate and soil characteristics, and
  • rainfall following application. (A minimum of 0.5 inches is typically required to activate soil residual herbicides.)

Check herbicide labels for application rates, restrictions and tank mixture options. Application rates are dependent on herbicide program applied thus far in the season, geography, and soil texture, organic matter and pH. Some products may cause temporary stunting and leaf burn; however, yield reductions are not expected.

For additional information on pre- and post-emergence herbicide options for weed control in soybeans, please check the Guide for Weed, Disease and Insect Management in Nebraska.

Table 1. Pre-emergence herbicides that can be applied after soybean emergence*
HerbicideActive Ingredient
(Site of Action)
Maximum Crop StageMaximum Weed StageApplication RateCrop Harvest Interval
Anthem Maxx pyroxasulfone (15) +
fluthiacet-methyl (14)
3rd trifoliate 2” 2 – 5.7 fl oz/ac 60 days
Dual II Magnum s-metolachlor (15) 3rd trifoliate Unemerged 1.0 – 1.33 pts/ac 90 days
First Rate cloransulam-methyl (2) R2 (full flower) See label 0.3 – 0.6 oz/ac 70 days
Outlook dimethenamid-P (15) 5th trifoliate 2” 8 – 21 fl oz/ac NA
Prefix s-metolachlor (15) + fomesafen (14) 3rd trifoliate See label 2 - 2.33 pt/ac 90 days
Pursuit imazethapyr (2) R1 3” 4 fl oz/ac 85 days
Warrant acetochlor (15) R2 Unemerged 1.25 – 2 qts/ac NA
Warrant Ultra acetochlor (15) + fomesafen (14) R2 See label 48 – 70 fl oz/ac 45 days
Zidua pyroxasulfone (15) 3rd trifoliate Unemerged 1.0 – 3.5 oz/ac No required interval
*Table adapted from the 2017 Guide for Weed, Disease, and Insect Management in Nebraska.