There were a large number of fall armyworm infestations in July and August in hayfields and pastures throughout parts of eastern Kansas. In most fields harvested in mid-to-late July, cool-season smooth brome and tall fescue are starting to regrow slowly due to hotter temperatures. Some of these fields were sprayed with insecticide already, but there is potential for a second generation of fall armyworms to cause additional damage while the grasses use their reserves for regrowth. As a result, some damaged fields may need to be replanted. Fields with localized patches of damaged forage are likely to have weed encroachment, likely from late summer and winter annuals (Figure 1).
Figure 1. Broadleaf weed horsenettle encroaching into a fall armyworm-damaged smooth brome hayfield in Jackson County. Photo by Tina Sullivan, K-State Research and Extension.
For the dead fields, growers could reseed or overseed in the fall or spring, but weeds should be controlled to limit competition and additional weed seed in the seed bank. Controlling emerged weeds will be critical for successfully establishing a new stand. Light tillage or a non-selective herbicide can be used to control any emerged winter annual weeds prior to seeding. Herbicide options are limited during establishment (Table 1). Mowing is a non-chemical option that could be considered to reduce weed competition and prevent weed seed production during grass establishment. If a herbicide application is needed prior to seeding, be sure to observe plant-back intervals that may interfere with establishment.
On the other hand, in some of the damaged fields, growers can wait to see if the desired grass will come back. In this case, more herbicide options are available; however, several will suppress forage growth (Table 1).
Table 1. Herbicides labeled for post-emergence weed control in cool-season forage grasses (SB=smooth brome; TF=tall fescue). Consult the label for the appropriate rate and adjuvant selection.
|
Herbicide |
Active ingredient |
Desired grass species |
Weeds controlled |
Used in establishment |
Plant-back interval |
Smooth brome suppression |
|
2,4-D |
2,4-D |
SB, TF |
Broadleaf |
After 6 leaf stage |
30 days |
Unlikely |
|
Amber |
Triasulfuron |
SB |
Broadleaf |
60 days after emergence |
4 months |
Unlikey |
|
Chaparral |
Metsulfuron + aminopyralid |
SB, TF |
Broadleaf |
No |
1 year |
Likely |
|
Cimarron Plus |
Metsulfuron + chlorsulfuron |
SB, TF |
Broadleaf |
6 months – SB 24 months - TF |
2 months |
Likely |
|
Clarity, others |
Dicamba |
SB, TF |
Broadleaf |
No |
45 days per 16 fl oz/A |
May be injured with > 16 fl oz/A |
|
Crossbow |
2,4-D + triclopyr |
SB, TF |
Broadleaf |
No |
3 weeks |
Possible |
|
DuraCor |
Aminopyralid + florpyrauxifen |
SB, TF |
Broadleaf |
No -SB 3 leaves - TF |
45 days – SB 15 days - TF |
Likely |
|
Escort, others |
Metsulfuron |
SB, TF |
Broadleaf |
6 months – SB 24 months - TF |
2 to 4 months – SB 18 months - TF |
Likely |
|
Facet, others |
Quinclorac |
SB, TF |
Grass/broadleaf |
No |
10 months |
Unlikely |
|
Grazon P+D |
Picloram + 2,4-D |
SB, TF |
Broadleaf |
No |
60 days – SB 21 days - TF |
Likely |
|
GrazonNext HL |
Aminopyralid + 2,4-D |
SB, TF |
Broadleaf |
No |
Grasses may be reseeded in the fall following an application in spring or early summer |
Likely |
|
Huskie FX |
Pyrasulfotole, bromoxynil, fluroxypyr |
TF |
Broadleaf |
> 2 leaves |
1 month |
Not labeled for use in SB |
|
Milestone |
aminopyralid |
SB |
Broadleaf |
No |
1 year |
Likely |
|
PastureGard HL |
Triclopyr + fluroxypyr |
SB, TF |
Broadleaf |
After tillering |
3 weeks |
Possible |
|
Plateau, others |
Imazapic |
SB |
Grass/broadleaf |
No |
26-36 months |
Likely |
|
Range Star |
2,4-D + dicamba |
SB, TF |
Broadleaf |
> 6 leaves |
3 weeks per quart |
Possible |
|
Rave |
Triasulfuron + dicamba |
SB |
Broadleaf |
60 days after emergence |
4 months |
Possible |
|
Remedy Ultra, others |
Triclopyr |
SB, TF |
Broadleaf |
No |
3 weeks |
Possible |
|
Tordon 22K |
Picloram |
SB, TF |
Broadleaf |
After tillering |
Grasses may be reseeded in the fall following an application in spring or early summer |
Likely at rates > 1 qt/A |
|
Yukon |
Dicamba + halosulfuron |
SB, TF |
Broadleaf |
No |
2 months |
Possible |
The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.
Sarah Lancaster, Weed Management Specialist
slancaster@ksu.edu
Tina Sullivan, Northeast Area Agronomist
tsullivan@ksu.edu