Kassim Al-Khatib

Common waterhemp (Amaranthus rudis) resistance to protoporphyrinogen oxidase-inhibiting herbicides

Abstract Resistance to protoporphyrinogen oxidase (protox)-inhibiting herbicides was identified in a population of common waterhemp that had been treated with acifluorfen for several years. The protox-resistant biotype of common waterhemp was approximately 34, 82, 8, and 4 times more resistant than a susceptible common waterhemp biotype to acifluorfen, lactofen, fomesafen, and sulfentrazone, respectively. The resistant biotype also showed a high level of resistance to acetolactate synthase–inhibiting herbicides thifensulfuron and imazethapyr but not to glyphosate or paraquat. An organophosphate insecticide was applied with acifluorfen or lactofen to determine if metabolism could be the mechanism of resistance. No differences were observed between resistant plants treated with an organophosphate plus a protox-inhibiting herbicide and plants treated with a protox-inhibiting herbicide alone. Nomenclature: Acifluorfen-methyl; lactofen; fomesafen; sulfentrazone; thifensulfuron-methyl; imazethapyr; glyphosate; paraquat; malathion; diazinon; common waterhemp, Amaranthus rudis Sauer AMATA.

Temperature effects on germination and growth of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis)

Abstract Experiments were conducted to determine the effects of temperature on seed germination and growth of redroot pigweed, Palmer amaranth, and common waterhemp. At 15/10 C day and night temperature, respectively, no seed germination was observed in any species. Seed germination increased gradually as temperature increased. Germination peaked at 25/20 C in common waterhemp and at 35/30 C in redroot pigweed and Palmer amaranth. Seed germination of all three species declined when temperatures increased above 35/30 C. All three species produced less biomass at 15/10 C than at 25/20 C and 35/25 C. Redroot pigweed and common waterhemp biomass were similar at 15/10 C and higher than that of Palmer amaranth. However, Palmer amaranth produced more biomass than redroot pigweed and common waterhemp at 25/20 and 35/30 C. At 45/40 C, redroot pigweed, common waterhemp, and Palmer amaranth plants died 8, 9, and 25 d after initiation of heat treatment, respectively. The largest root volume among the three species was in Palmer amaranth grown at 35/30 C, whereas the smallest root volume was produced by Palmer amaranth grown at 15/10 C. Potential quantum efficiency (Fv/Fmax) of Palmer amaranth was higher than that of redroot pigweed and common waterhemp at higher temperature. The greater growth of Palmer amaranth at higher temperatures may be attributed in part to its extensive root growth and greater thermostability of its photosynthetic apparatus. Nomenclature: Common waterhemp, Amaranthus rudis Sauer AMATA; Palmer amaranth, A. palmeri S. Wats. AMAPA; redroot pigweed, A. retroflexus L. AMARE.

Soil microbial and nematode communities as affected by glyphosate and tillage practices in a glyphosate-resistant cropping system

Abstract Field experiments were conducted at Ashland Bottoms in northeastern Kansas and at Hays in western Kansas in 2001, 2002, and 2003 to determine the response of soil microbial and nematode communities to different herbicides and tillage practices under a glyphosate-resistant cropping system. Conventional herbicide treatments were a tank mixture of cloransulam plus S-metolachlor plus sulfentrazone for soybean and a commercially available mixture of acetochlor and atrazine for corn. Glyphosate was applied at 1.12 kg ai ha−1 when weeds were 10 or 20 cm tall in both corn and soybean. Soil samples were collected monthly at Ashland Bottoms during the growing period for soil microbial biomass (SMB) carbon determination. In addition, substrate-induced respiration (SIR) and BIOLOG substrate utilization were determined at the end of the growing season each year at Ashland Bottoms, and nematode populations were determined at the beginning and the end of the growing season at both sites. Direct effects of glyphosate rates on soil microbial and nematode communities were also studied in a controlled environment. Values for SMB carbon, SIR, and BIOLOG substrate utilization were not altered by glyphosate. Nematode community response to the glyphosate treatment was similar under both conventional tillage and no-till environments. Total nematode densities were similar with the glyphosate and conventional herbicide treatments. SMB carbon and BIOLOG substrate utilization did not differ between tillage treatments. Nematode densities were greater under conventional tillage than in the no-till system. This study showed that soil health when glyphosate was applied in a glyphosate-resistant cropping system was similar to that of cropping systems that used conventional herbicides. Nomenclature: Glyphosate; corn, Zea mays L. ‘Asgrow RX718RR’, ‘DeKalb 520RRYG’, ‘DeKalb 53-34’; soybean, Glycine max (L.) Merr. ‘Asgrow 3003RR’, ‘Asgrow 3302RR’.

Interspecific hybridization and gene flow of ALS resistance in Amaranthus species

Abstract Several inbred lines of acetolactate synthase (ALS)-inhibiting herbicide-resistant (ALS-R) Palmer amaranth and ALS-susceptible (ALS-S) common waterhemp were developed in the greenhouse. Interspecific hybrids were obtained by allowing several ALS-S common waterhemp females to be pollinated only by ALS-R Palmer amaranth in a growth chamber. Putative hybrid progeny were treated with an ALS-inhibiting herbicide, and the hybrid nature verified using a polymorphism found in the parental ALS gene. Polymerase chain reaction (PCR) was used to amplify a region of the ALS gene in both parental plants and putative hybrids. Restriction enzyme digestion of the ALS-R Palmer amaranth PCR fragment resulted in two smaller fragments, whereas the PCR fragment in the ALS-S common waterhemp was not cut. Restriction digestion of the putative hybrid PCR fragment showed a combination of ALS-R Palmer amaranth double fragments and an ALS-S common waterhemp single fragment. Approximately 4 million flowers were present on 11 common waterhemp females and produced about 44,000 seeds that appeared viable. From the approximately 3,500 putative hybrid seedlings that were screened, 35 were confirmed as hybrids using herbicide resistance as a phenotypic and molecular marker. The data collected here verify that interspecific hybridization does occur between these two species, and even at a low rate, it could contribute to the rapid spread of ALS resistance in these species. Nomenclature: Imazethapyr; common waterhemp, Amaranthus rudis Sauer AMATA; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA.

Efficacy of glyphosate, glufosinate, and imazethapyr on selected weed species

Abstract Experiments were conducted to determine the efficacy, absorption, and translocation of glyphosate, glufosinate, and imazethapyr with selected weed species. In the greenhouse glyphosate, glufosinate, and imazethapyr were applied at 0.25, 0.5, and 1 times their label rates of 1,121, 410, and 70 g ha−1, respectively, on 10- to 15-cm black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, ivyleaf morningglory, prairie cupgrass, velvetleaf, and yellow nutsedge. Glyphosate applied at the 1-time rate caused injury greater than or similar to injury from the 1-time rate of glufosinate or imazethapyr on black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, prairie cupgrass, and velvetleaf. The 1-time rate of glufosinate injured ivyleaf morningglory and yellow nutsedge more than did the 1-time rate of glyphosate or imazethapyr. Under field conditions glyphosate caused the greatest injury to common waterhemp, prairie cupgrass, and velvetleaf across plant growth stages. Giant ragweed and ivyleaf morningglory injury was more dependent on growth stage, with the 15- and 30-cm growth stages more susceptible to glyphosate than to glufosinate or imazethapyr. Differential response of these weed species may be caused by differences in herbicide translocation. Glyphosate was translocated more in both giant ragweed and ivyleaf morningglory, and these species were injured more by glyphosate than by glufosinate or imazethapyr at the larger growth stages. Nomenclature: Glufosinate; glyphosate; imazethapyr; black nightshade, Solanum nigrum L. SOLNI; common waterhemp, Amaranthus rudis Sauer AMATA; eastern black nightshade, Solanum ptycanthum Dun. SOLPT; field bindweed, Convolvulus arvensis L. CONAR; giant ragweed, Ambrosia trifida L. AMBTR; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; prairie cupgrass, Eriochloa contracta Hitchc. ERICO; velvetleaf, Abutilon theophrasti Medicus ABUTH; yellow nutsedge, Cyperus esculentus L. CYPES.

Efficacy and metabolism of MON 37500 in Triticum aestivum and weedy grass species as affected by temperature and soil moisture

Abstract Spray application of 24 and 46 g ha−1 MON 37500 was used in efficacy studies, and vacuum infiltration or droplet application of radiolabeled MON 37500 was used in metabolism studies to evaluate temperature and soil moisture on MON 37500 efficacy and metabolism. Day/night temperatures before vs. after application of MON 37500 of 25/23 vs. 25/23, 25/23 vs. 5/3, 5/3 vs. 25/23, and 5/3 vs. 5/3 C were evaluated for the efficacy study, whereas day/night temperatures of 5/3 and 25/23 C were used for the metabolism study. Soil moisture of one-third and full pot capacities was evaluated for both studies. No Triticum aestivum injury was observed at the different temperatures or soil moistures because of rapid metabolism of MON 37500 by T. aestivum. Weed control was greater when the temperature after application was 25/23 C or soil moisture was at full pot capacity than when the temperature was at 5/3 C after application or soil moisture was at one-third pot capacity. Susceptibility to MON 37500 was greatest for Bromus tectorum, moderate for Avena fatua, and least for Aegilops cylindrica. This pattern of susceptibility for the weed species was related to their ability to metabolize MON 37500. Aegilops cylindrica metabolized more MON 37500 in the first 24 h than did A. fatua, whereas B. tectorum metabolized the least MON 37500. Cool air temperatures decreased MON 37500 metabolism in all species, whereas soil moisture had no effect. Nomenclature: MON 37500, 1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea; Triticum aestivum L., spring wheat ‘Len’; Aegilops cylindrica Host. AEGCY, jointed goatgrass; Avena fatua L. AVEFA, wild oat; Bromus tectorum L. BROTE, downy brome.

Gene flow from imidazolinone-resistant domesticated sunflower to wild relatives

Abstract Gene flow from imidazolinone (IMI)-resistant domestic sunflower to IMI-susceptible common sunflower and prairie sunflower was studied. Under greenhouse conditions, pollen from IMI-resistant domesticated sunflower was applied to flower heads of IMI-susceptible common and prairie sunflower. In addition, field studies were conducted in 2000 and 2001 near Manhattan, KS, to evaluate IMI-resistant gene flow from IMI-resistant domesticated sunflower to common and prairie sunflower under natural conditions. Common and prairie sunflower were planted in concentric circles at distances of 2.5, 5, 15, and 30 m around a densely planted IMI-resistant domesticated sunflower species. For both greenhouse and field studies, IMI-resistant gene flow was determined by treating the progeny of both wild species with 40 g ai ha−1 of imazamox. Greenhouse crosses made by hand showed that 94% of common sunflower and 79% of prairie sunflower were resistant or moderately resistant. The resistant plants were allowed to grow in the greenhouse and were backcrossed with the corresponding susceptible wild parents. Progeny of the backcross showed a 1:1 ratio of resistant to susceptible plants. In the field, gene flow was detected up to 30 m from the pollen source for both species, and it decreased as distance from the pollen source increased. In 2000, 11 to 22% of the progeny were resistant at 2.5 m from the pollen source and 0.3 to 5% were resistant at 30 m. In 2001, the number of resistant progeny did not exceed 7 and 2% at 2.5 and 30 m from the pollen source, respectively. The results of this study showed that IMI-resistant domesticated sunflower outcrosses with common and prairie sunflower over distances typically encountered near production fields. Also, backcrosses of resistant hybrids with wild parents are successful, further increasing the potential for the spread of IMI-resistant feral sunflowers. Nomenclature: Common sunflower, Helianthus annuus; prairie sunflower, Helianthus petiolaris.

Glufosinate efficacy, absorption, and translocation in amaranth as affected by relative humidity and temperature

Abstract Growth chamber experiments were conducted to evaluate the effects of relative humidity and temperature on the efficacy, absorption, and translocation of glufosinate at 205, 410, and 820 g ha−1 in Palmer amaranth, redroot pigweed, and common waterhemp. Low relative humidity decreased control of all three species by glufosinate. However, control increased as application rate increased at low relative humidity. Amaranth species grown under 21/16, 26/21, and 31/26 C day/night temperature regimes responded differently to glufosinate. At 26/21 C, glufosinate at 820 g ha−1 controlled redroot pigweed less effectively than it controlled Palmer amaranth and common waterhemp, whereas at 410 g ha−1, glufosinate controlled common waterhemp more effectively than it controlled the other two species. Neither temperature nor relative humidity altered the absorption of 14C-glufosinate in any of the three species. Most of the absorbed glufosinate remained in the treated leaves at all three temperature regimes and two relative humidity levels. However, glufosinate translocation was greater in plants grown at 90% than in those grown at 35% relative humidity, and this phenomenon coincided with greater control of the amaranth species at the high humidity level. The study showed that relative humidity had a greater effect than temperature on glufosinate toxicity to Palmer amaranth, redroot pigweed, and common waterhemp. Nomenclature: Glufosinate; common waterhemp, Amaranthus rudis Sauer AMATA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; redroot pigweed, Amaranthus retroflexus L. AMARE.

Glufosinate Efficacy on Amaranthus Species in Glufosinate-Resistant Soybean (Glycine max)1

Field studies were conducted in 1998 and 1999 to evaluate the efficacy of glufosinate on Palmer amaranth, redroot pigweed, and common waterhemp at different growth stages in soybean planted at early, normal, and late dates. At 2, 4, and 8 wk after treatment, common waterhemp control was greater than Palmer amaranth and redroot pigweed control with single glufosinate applications of 410 g ai/ha at 2- to 5-, 7- to 10-, or 15- to 18-cm Amaranthus height or with two sequential applications of 293 g/ha at 2- to 5-cm height and 2 wk later. Only the sequential applications of 410 and 293 g/ha resulted in more than 80% control of Palmer amaranth and redroot pigweed, but all five treatments controlled common waterhemp more than 80%. All glufosinate treatments reduced the dry weight of all Amaranthus species by more than 65%. However, the sequential applications resulted in the greatest dry weight reductions. Nomenclature: Glufosinate; common waterhemp, Amaranthus rudis Sauer #3 AMATA; Palmer amaranth, Amaranthus palmeri S.Wats. # AMAPA; redroot pigweed, Amaranthus retroflexus L. # AMARE; soybean, Glycine max (L.) Merr. Additional index words: Environmental conditions, herbicide-tolerant soybean, postemergence herbicide. Abbreviations: ALS, Acetolactate synthase (EC 4.1.3.18); OM, organic matter; RH, relative humidity; WAT, weeks after treatment.

Gene flow, growth, and competitiveness of imazethapyr-resistant common sunflower

Abstract This study was conducted to ascertain movement potential of imazethapyr resistance and to measure the relative growth and productivity of imazethapyr-resistant (IR) and imazethapyr-susceptible (IS) biotypes of common sunflower under noncompetitive and competitive conditions. Susceptible biotypes of common sunflower were planted in the field in concentric circles at distances of 5.5, 8.0, 15.0, and 30.0 m around a center of densely planted IR biotypes in four locations in northeast Kansas in 1998 and 1999. Pollen movement was analyzed by sampling the IS progeny for the presence of imazethapyr resistance. The distance in which resistance is first detected from the IR pollen source, first unnatural resistant distance (FURD), ranged from 12.1 to 15.5 m. Wind direction was highly correlated with FURD; the north sections had larger FURD. Greenhouse studies were conducted to study growth of IR and IS biotypes under noncompetitive and competitive conditions. Under noncompetitive conditions, leaf area and dry weight were slightly greater for the IR than the IS biotype at early growth stages, but photosynthesis and height were similar. Under competitive conditions, photosynthesis, leaf area, height, and dry weight of IR and IS biotypes were similar. As a result, IR–IR and IS–IS intracompetition equaled IR–IS intercompetition. Gene flow from IR to IS biotypes occurred with movement up to 15.5 m. The lack of differences between growth of the IR and IS biotype at late growth stages in noncompetitive conditions and similar growth of IR and IS biotypes under competitive conditions indicated no competitive advantage from imazethapyr resistance. Nomenclature: Imazethapyr; common sunflower, Helianthus annuus L. HELAN.