Stoneville, MS

Glyphosate has revolutionized weed control in cotton (Gossypium hirsutum) in just the past 10 years. The repetitive use of glyphosate and in most cases the sole reliance on this one herbicide has led to development of glyphosate-resistant weeds in many southern cotton producing states. Glyphosate-resistant horseweed (Conyza canadensis), Palmer amaranth (Amaranthus palmeri), and Italian ryegrass (Lolium multiflorium) have been documented in cotton in states across the southern US cotton region. The advent of glyphosate resistance and shifts to weed species that proliferate in a total glyphosate weed control program, such as late-season annual grasses, necessitate inclusion of residual herbicides in a glyphosate-based weed control program. KIH-485 is a new chemistry under investigation for its potential to supplement glyphosate-based weed control programs in the southern US cotton.     

Experiments were conducted on or near the Delta Research and Extension Center, Stoneville, MS. Soil type was a Dundee silt loam. Experiments were conducted to evaluate KIH-485 in burndown, preemergence (PRE), or postemergence (POST) programs. Treatments were applied in early March (Burndown), early May (PRE), or to 1-leaf (EPOST), 4-leaf (MPOST), or 6-leaf (LPOST) cotton in the POST trial. KIH-485 was applied at rates ranging from 0.044 to 0.186 lb ai/A. KIH-485 was applied with glyphosate (0.77 lb ae/A) plus dicamba (0.25 lb ae/A) in all burndown treatments. KIH-485 was applied alone in PRE treatments and with glyphosate (0.77 lb ae/A) in all POST treatments. Roundup Ready Flex cotton was planted in late April (burndown trial) to early May (PRE and POST trials). A nonionic surfactant at 0.25% v/v was added to all POST treatments. Treatments were applied with a CO₂-propelled backpack sprayer equipped with 11003 flat fan nozzles at a delivery rate of 15 gallons per acre.  Weed control and cotton injury was documented throughout the growing season. Weeds evaluated included browntop millet (Brachiaria ramosa) in the burndown trial, Palmer amaranth (PRE and POST trials), and barnyardgrass (Echinochloa crus-galli) in the burndown, PRE, and POST trials. Data were subjected to the SAS PROC MIXED procedure.  Least square means were calculated and mean separation for treatments were produced at P≤0.05. 

Burndown and PRE applications of KIH-485 resulted in no cotton injury. Cotton injury from POST applications of KIH-485 was transient as injury ranged from 13 to 18% by two weeks after treatment when applied to 4-leaf cotton as compared to 0% injury by four weeks after treatment. KIH-485 applied to 1-leaf or 6-leaf cotton resulted in no cotton injury. Browntop millet and barnyardgrass control was as high as 99% by 12 weeks after treatment with burndown and PRE applications of KIH-485. Palmer amaranth and barnyardgrass were controlled 90 to 100% by 4 weeks after treatment with PRE or POST applications of KIH-485. Residual control of small seeded broadleaves and grasses can be excellent with KIH-485. This new chemistry, once registered, can be an excellent residual tool for managing weeds in a glyphosate-based weed control programs and potentially prevent the advent of glyphosate-resistant weeds.