MSU Extension

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

As the end of May quickly approaches dry beans will soon be planted throughout most of the state. One pest that can lead to major yield reductions, quality problems and issues with harvest are weeds. To help stay ahead of these pests, below is a summary of what weed control options are available in dry edible beans with approximate herbicide costs. Estimations of herbicide costs are calculated from an average of three 2005 in-season herbicide price lists. For additional information on weed control in dry beans please consult the 2006 MSU Weed Control Guide for Field Crops (E-434).

Review of soil-applied herbicide options

Preplant incorporated only

Trifluralin (Treflan), pendimethalin (Prowl H 2O, Prowl, Pendimax), and Sonalan: Annual grass control is excellent with all three herbicides. Trifluralin and Sonalan provide better pigweed control than pendimethalin. Pendimethalin and Sonalan provide better common lambsquarters control than trifluralin. None of these herbicides will control eastern black nightshade or common ragweed. Eptam should be tank-mixed with each of these herbicides for additional annual grass and broadleaf weed control. The application rate of Trifluralin 4L is 1 pt/A (~$2.50/A); Prowl H 2O is 1.6 pt/A (~$5.85/A); Sonalan is 2 pt/A (~$6.80/A).

Eptam: Eptam provides excellent control of several annual grasses and good control of common lambsquarters. Eptam also will suppress common ragweed, wild mustard and nightshade species. Thus tank-mixing Eptam with trifluralin, pendimethalin (Prowl), or Sonalan will improve control of these weeds. Eptam is applied at 1.25 qt/A (~$10.30/A). It is important to weigh these costs against the weed control benefits. A Section 18 has been granted for Reflex for the 2006 season, so Reflex could be applied postemergence for control of common ragweed and nightshade.

Pursuit Plus: Pursuit Plus provides fair control of common cocklebur, jimsonweed and smartweed and good to excellent control of several broadleaf and annual grass weeds. Common ragweed is not controlled. Pursuit Plus is typically applied at 20 fl oz/A (~$7.60/A). On heavy soils with more than 2% O.M. this rate can be increased to 30 fl oz/A. Crop injury can occur from applications of Pursuit Plus. Precautions that need to be taken to avoid crop injury include: do not apply on sands or loamy sand soils, do not apply if cold or cold, wet conditions are predicted one week after planting and remember that dry bean varieties can vary in their sensitivity to Pursuit, so keep this in mind when trying a new dry bean variety. Rotation restrictions are also critical with Pursuit Plus. These restrictions include 40 months and a bioassay for sugar beets, cucumbers and tomatoes; 18 months for oats; and 26 months for potatoes.

Alachlor (IntRRo, Micro-Tech): Alachlor provides excellent control of several annual grasses and good control of pigweed and eastern black nightshade. Alachlor should be incorporated in the top 2 inches of soil to minimize dry bean injury. Do not use alachlor on sands or sandy loam soils or injury can occur. Alachlor can be tank-mixed with Eptam, pendimethalin (Prowl), Sonalan or trifluralin for common lambsquarters control. Postemergence applications of a broadleaf herbicide may be needed for additional broadleaf weed control. IntRRo is typically applied at 2 qt/A (~$9.90/A).

Preemergence or preplant incorporated

Dual Magnum and Outlook: A preplant incorporated application of either Dual Magnum or Outlook minimizes crop injury compared with preemergence applications. Navy and black beans are more sensitive to Outlook than Dual Magnum. Dual Magnum and Outlook both provide good control of pigweed and excellent control of annual grass weeds. However, Outlook provides better pigweed and eastern black nightshade control compared with Dual Magnum. Dual Magnum and Outlook can be tank-mixed with Eptam, pendimethalin (Prowl), Sonalan, or trifluralin for common lambsquarters control. Postemergence applications of a broadleaf herbicide may be needed for additional broadleaf weed control. The typical use rate for Dual Magnum is 1.33 pt/A (~$16.80/A) and Outlook is 14 fl oz/A (~$15.50/A).

Pursuit: Pursuit may be applied preemergence or preplant incorporated. Pursuit 70DG at 0.72 oz/A (~$8.75/A) can be tank-mixed with other soil-applied herbicides for additional broadleaf weed control and to control annual grasses. Remember Pursuit will not control common ragweed. Similar to Pursuit Plus, crop injury can occur and precautions need to be taken to avoid injury. These precautions include: do not apply on sands or loamy sand soils, do not apply if cold or cold-wet conditions are predicted one week after planting, and dry bean varieties vary in their sensitivity to Pursuit applications. Rotation restrictions are critical with Pursuit. These restrictions include 40 months and a bioassay for sugar beets, cucumbers, and tomatoes; 18 months for oats; and 26 months for potatoes.

Permit/Sandea: Permit provides excellent control of pigweeds and wild mustard and good control of common ragweed and velvetleaf. Permit is an ALS-inhibiting herbicide, so it will not control ALS-resistant weeds such as ALS-resistant common ragweed. Permit can be tank-mixed with Dual Magnum or Outlook for grass control. Application rates of Permit range from 0.5 oz/A (~$10.90/A) to 0.67 oz/A. The lower use rate should be used on sandier soils. Dry bean varieties appear to vary in their sensitivity to Permit, so precautions should be taken. The rotation restriction for Permit to sugar beets is 21 months.

Review of postemergence options for broadleaf weed control

Keeping in mind that Assure II, Targa, Select, Arrow and Poast are all registered for postemergence annual grass control in dry beans. Recommendations for herbicides used for postemergence broadleaf weed control tend to be a little more complicated. Options for postemergence broadleaf weed control in dry beans are limited to three registered herbicides: Basagran, Raptor, and Pursuit and Reflex, which has a Section 18 label for 2006.

When looking at these different options there are a few things to consider when using these herbicides alone or in combination. One of the first things to consider is, “What are the weeds that need to be controlled?” These weeds will typically be ones that escape control from soil-applied herbicides and may include common ragweed, common lambsquarters and eastern black nightshade. Selection of an herbicide or combination of one or more of these herbicides will be dependent on the weed complex in the field (Table 1). When making these weed control decisions it is important to consider certain guidelines such as rotation restrictions, herbicide use rates, adjuvant selection, application timings and tank-mixtures with other herbicides.

Rotational restrictions: All postemergence broadleaf herbicides, with the exception of Basagran, have rotational crop restrictions. Some of these restrictions may influence your herbicide selection, depending on your cropping system. For example, the rotation restriction for Reflex is 10 months for corn and 18 months for alfalfa, sugar beets, potatoes, cucumbers, canola and tomatoes. The rotation restriction for Raptor is 18 months for sugar beets (extended to 26 months if pH is less than 6.2) and canola. Pursuit’s rotation restriction is 40 months and a bioassay for sugar beets, canola, cucumbers and tomatoes.

Use rates: The use rate for Reflex is 1 pt/A (~$12.70/A). Reflex can only be used once in a two-year period. Common ragweed less than 4-leaf will be controlled ½ pt/A of Reflex.The use rate for Raptor is 4 fl oz/A (~$15.70/A) in edible legumes. Pursuit 70DG is generally used at 0.72 oz/A (~$8.75/A) and Basagran rates range from 8 fl oz to 2 pt/A (1.25 pt/A ~$13.60/A) depending on weed species, size and herbicide tank-mixture.

Grass control: Foxtail control is good when Raptor is tank-mixed with Basagran at 8 fl oz/A + COC + 28%N (or AMS – ammonium sulfate). Barnyardgrass and crabgrass control are only fair. Assure II, Targa, Select, Arrow and Poast can be tank-mixed with Basagran, Reflex or Basagran + Reflex for grass control. However, do not tank-mix Assure II, Targa, Select, Arrow or Poast with Raptor or Pursuit, because grass control will be compromised.

Adjuvant selection: Basagran alone should be applied with 1 qt/A of a crop oil concentrate (COC). Reflex should be applied with a non-ionic surfactant (NIS) at 0.25 to 0.5% v/v or a COC at 0.5 to 1.0% v/v. Include COC when tank-mixing Basagran + Reflex. Raptor or Pursuit alone should be applied with 0.25% v/v of NIS. These herbicides alone will only provide limited control of selected weed species. To increase control, 12-15 lb/100 gal of spray solution of AMS can be added to Raptor + Basagran + COC or Pursuit + Basagran + NIS applications. The addition of at least 8 fl oz of Basagran to Raptor or Pursuit will “safen” these applications. To control common cocklebur, jimsonweed or provide good control of common lambsquarters, increase the rate of Basagran to 16 fl oz when tank-mixed with Raptor and use COC + AMS. Do not add AMS when tank-mixing Raptor and Reflex.

Application timing: Raptor, Reflex, Basagran or Pursuit should only be applied after dry beans have one fully expanded trifoliate. Do not apply these herbicides once dry beans start to bloom.

Rain-free periods: The rain-free period is 1 hour for Assure II, Targa, Select, Poast, Pursuit, Raptor, and Reflex and 8 hours for Basagran.

Table 1. Weed response to postemergence broadleaf herbicides in dry edible beans.

Click here to view larger PDF version of Table 1.

Dr. Sprague's work is funded in part by MSU's AgBioResearch.