Kevin D. Brewer

Purple Nutsedge Control and Potato (Solanum tuberosum) Tolerance to Sulfentrazone and Halosulfuron1

Five field studies on sandy soils with ≤ 1% organic matter in south Texas showed that halosulfuron at 0.066 kg/ha preemergence (PRE) controlled ≥ 92% purple nutsedge and at 0.066 kg/ha postemergence (POST) controlled purple nutsedge 77 to 95%. Sulfentrazone at 0.11 to 0.28 kg/ha PRE or POST controlled purple nutsedge < 65% at one location but > 75% at two other locations. Poor control at the one location may have been due to a lack of early-season rainfall or irrigation. Potatoes were stunted 5 to 26% with halosulfuron PRE, whereas POST treatments caused 7 to 40% stunting. Sulfentrazone at 0.11 to 0.28 kg/ha applied PRE or POST caused 2 to 38% stunting. ‘Atlantic’ potato stunting with sulfentrazone POST at 0.14 to 0.28 kg/ha was ≥ 20%, whereas ‘Snowden’ and ‘1625’ potatoes were stunted ≤ 20%. Potato yields were reduced 65 and 39% with sulfentrazone and halosulfuron POST, respectively, at the high rates, but yield reductions occurred with all POST treatments on Atlantic potatoes 10- to 20-cm tall. Halosulfuron PRE at 0.033 kg/ha and sulfentrazone PRE at 0.14 kg/ha did not reduce yields; however, all other treatments of halosulfuron and sulfentrazone reduced potato yields. Nomenclature: Halosulfuron; sulfentrazone; purple nutsedge, Cyperus rotundus L. #3 CYPRO; potato, Solanum tubersum L., ‘Atlantic’, ‘Snowden’, ‘1625’. Additional index words: Preemergence, postemergence. Abbreviations: OM, organic matter; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting.

S-Metolachlor Compared with Metolachlor on Yellow Nutsedge (Cyperus esculentus) and Peanut (Arachis hypogaea) 1

Abstract: S-metolachlor was compared with metolachlor at four field locations in Texas during the 1996 and 1997 growing seasons in terms of yellow nutsedge control, peanut injury, and peanut yield. S-metolachlor caused peanut injury comparable to metolachlor when either herbicide was applied preplant incorporated or preemergence. Yellow nutsedge control was similar and peanut yields were comparable with the two herbicides. At one location where yellow nutsedge failed to develop, the untreated check produced one of the highest yields. Nomenclature: Metolachlor; S-metolachlor; yellow nutsedge, Cyperus esculentus L. #3 CYPES; peanut, Arachis hypogaea L. ‘Florunner’, ‘AT-120’, ‘GK-7’. Additional index words: Groundnut, herbicide efficacy, peanut stunting. Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Citronmelon (Citrullus lanatus var. citroides) Control in Texas Peanut (Arachis hypogaea) Using Postemergence Herbicides1

Abstract: Field studies were conducted from 1995 through 1998 to evaluate citronmelon control with postemergence (POST) herbicides. Imazapic at any application timing and late postemergence (LPOST) applications of 2,4-DB were the only herbicides that provided >80% control of citronmelon late season. Other herbicides such as acifluorfen, imazethapyr, lactofen, and pyridate provided acceptable (>75%) early-season control of citronmelon, but control was inadequate at harvest. Nomenclature: Acifluorfen; imazapic; imazethapyr; lactofen; pyridate; 2,4-DB; citronmelon, Citrullus lanatus var. citroidas #3 CITCL; peanut, Arachis hypogaea L. ‘GK-7’. Additional index word: Groundnut. Abbreviations: DAP, days after planting; EPOST, early postemergence; LPOST, late postemergence; POST, postemergence.

Weed Control and Grain Sorghum (Sorghum bicolor) Response to Postemergence Applications of Atrazine, Pendimethalin, and Trifluralin'

Field studies were conducted from 2000 through 2002 to evaluate the effects of atrazine, pendimethalin, and trifluralin applied alone or in combination followed by cultivation when weeds and grain sorghum were less than 7 cm tall (early postemergence [EPOST]) or when weeds and grain sorghum were 10 to 15 cm tall (late postemergence [LPOST]). Atrazine plus pendimethalin applied EPOST caused 9 to 14% sorghum stunting all 3 yr while atrazine plus trifluralin applied EPOST caused 1 to 4% grain sorghum stunting. When applied LPOST, atrazine plus pendimethalin or trifluralin resulted in no greater than 3% stunting. Tumble pigweed was controlled at least 99% with atrazine plus pendimethalin or trifluralin applied EPOST or LPOST, whereas Texas panicum was controlled at least 97% with atrazine plus pendimethalin or trifluralin applied EPOST, and 76 to 100% with LPOST application. Sorghum yields were reduced with atrazine plus pendimethalin applied EPOST when compared with all herbicide combinations in one of 3 yr. Nomenclature: Atrazine; pendimethalin; trifluralin; tumble pigweed, Amaranthus albus L. #3 AMAAL; Texas panicum, Panicum texanum Buckl. # PANTE; grain sorghum, Sorghum bicolor (L.) Moench. ‘DKS 54-00’, ‘Pioneer 8313’. Additional index words: Cultivation, crop tolerance, stunting, yield reduction. Abbreviations: EPOST, early postemergence; LPOST, late postemergence; WAP, weeks after planting.

Weed Management and Net Returns Using Soil-Applied and Postemergence Herbicide Programs in Peanut (Arachis hypogaea L.)

Field studies were conducted during the 1997 and 1998 growing seasons to compare Palmer amaranth and Texas panicum control and peanut pod yield and net returns by dimethenamid, ethalfluralin, or S-metolachlor applied alone or with sequential postemergence (POST) applications of acifluorfen, acifluorfen plus bentazon, bentazon, imazapic, imazethapyr, or pyridate. The addition of a POST herbicide to ethalfluralin did not improve Texas panicum control over ethalfluralin alone. Dimethenamid followed by imazapic POST or S-metolachlor followed by imazapic or imazethapyr POST improved Texas panicum control over those two soil-applied herbicides used alone. Palmer amaranth control was acceptable with imazapic or imazethapyr alone (82 to 93%). Only imazapic applied POST following ethalfluralin improved Palmer amaranth control over ethalfluralin alone. The addition of any POST herbicide to dimethenamid improved Palmer amaranth control over dimethenamid alone while only the addition of bentazon or pyridate to S-metolachlor did not improve Palmer amaranth control over S-metolachlor alone. Peanut yield increased as herbicide inputs increased. Herbicide systems which include imazapic applied POST following ethalfluralin, dimethenamid, or S-metolachlor soil-applied provided the highest peanut yield and net return.

Flufenacet and Metribuzin Combinations for Weed Control and Corn (Zea mays) Tolerance1

Field studies were conducted in 1999 and 2000 at seven locations in south Texas to evaluate flufenacet plus metribuzin for weed control and corn tolerance. Texas panicum control with flufenacet plus metribuzin was variable with less than 70% control in 1999 and greater than 75% control in 2000. Palmer amaranth and pitted morningglory control ranged from 41 to 100%. Corn stunting (4 to 13%) was noted in soils with greater than 75% sand. Corn yields with flufenacet and metribuzin combinations were increased up to 19% over the untreated check where stunting was not observed. Nomenclature: Flufenacet; metribuzin; Palmer amaranth, Amaranthus palmeri S. Wats. #3 AMAPA; pitted morningglory, Ipomoea lacunosa (L.) # IPOLA; Texas panicum, Panicum texanum Buckl. # PANTE; corn, Zea mays L. ‘AS986’, ‘Pioneer 3223’, ‘Pioneer 32K61’, ‘DK-668’. Additional index words: Corn tolerance, ivyleaf morningglory, weed management. Abbreviations: POST, postemergence; PRE, preemergence.

Interaction of Pyrithiobac and Graminicides for Weed Control in Cotton (Gossypium hirsutum)1

Field studies were conducted from 1996 through 1998 to evaluate control of broadleaf signalgrass and slender amaranth by clethodim, fluazifop-P-butyl, and fluazifop-P-butyl plus fenoxaprop-P-ethyl applied alone, in combination with pyrithiobac, or sequentially with pyrithiobac. Broadleaf signalgrass control with graminicides alone was 75 to 100%. Although broadleaf signalgrass control with clethodim was not reduced by pyrithiobac, control with fluazifop-P-butyl and fluazifop-P-butyl plus fenoxaprop-P-ethyl was reduced by pyrithiobac. Pyrithiobac controlled slender amaranth 85 to 100% when applied alone. However, slender amaranth control by pyrithiobac was inconsistent when pyrithiobac was applied in mixture or sequentially with graminicides. A reduction in slender amaranth control may have resulted from a combination of reduced graminicide efficacy and interference caused by broadleaf signalgrass with slender amaranth (pyrithiobac alone). Cotton yields were highest when pyrithiobac was applied 24 h after graminicides. Nomenclature: Clethodim; fenoxaprop-P-ethyl; fluazifop-P-butyl; pyrithiobac; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #3 BRAPP; slender amaranth, Amaranthus gracilis Desf. # AMAVI; cotton, Gossypium hirsutum L. ‘Deltapine 50’, ‘Paymaster H-1215’, ‘DP5690RR’. Additional index words: Amaranthus gracilis, AMAVI, antagonism, Brachiaria platyphylla, BRAPP, herbicide interaction. Abbreviations: POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Sesame (Sesamum indicum L.) tolerance with various postemergence herbicides

Abstract Field studies were conducted in weed free areas of south Texas from 1994 to 1997 to evaluate various postemergence (POST) herbicides for sesame tolerance and effects on yield. Sethoxydim or fluazifop-P caused no injury to sesame and produced yields comparable with the untreated check. Acifluorfen, imazapic, imazethapyr, and 2,4-DB reduced sesame yield when compared with the untreated check at two of five locations. Bromoxynil and bentazon reduced sesame plant height at two locations but has no effect on yield.

Citronmelon (Citrullus lanatus var. citroides) Control in Texas Peanut (Arachis hypogaea) Using Soil-Applied Herbicides1

Field studies were conducted from 1995 through 1998 to evaluate citronmelon control in peanut with various preplant and preemergence combinations of dimethenamid, flumioxazin, imazethapyr, lactofen, metolachlor, oxyfluorfen, and pendimethalin. Pendimethalin alone or in combination with imazethapyr, metolachlor, or dimethenamid did not control citronmelon. Flumioxazin alone, pendimethalin plus flumioxazin, or pendimethalin followed by (fb) lactofen controlled citronmelon at least 85% early season. Pendimethalin fb lactofen controlled citronmelon at least 75% late season, whereas all other herbicide treatments controlled less than 70%. Nomenclature: Dimethenamid; flumioxazin; imazethapyr; lactofen; metolachlor; oxyfluorfen; pendimethalin; citronmelon, Citrullus lanatus var. citroides (Bailey) Mansf. #3 CITLC; peanut, Arachis hypogaea L. ‘GK-7’. Additional index words: Groundnut, piemelon, preemergence, preplant incorporated. Abbreviations: DAP, days after planting; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE; preemergence; WAP, weeks after planting.