Henry P. Wilson

A New Mutation in Plant Als Confers Resistance to Five Classes of Als-inhibiting Herbicides

Abstract Experiments were conducted to evaluate a biotype of smooth pigweed that had survived applications of sulfonylurea (SU) and imidazolinone (IMI) herbicides in a single season. The source field had a history of repeated acetolactate synthase (ALS)-inhibiting herbicide use over several years. Whole-plant response experiments evaluated the resistant (R11) biotype and an ALS-inhibitor susceptible (S) smooth pigweed biotype to herbicides from the SU, IMI, pyrimidinylthiobenzoate (PTB), and triazolopyrimidine sulfonanilide (TP) chemical families. The R11 biotype exhibited 60- to 3,200-fold resistance to all four ALS-inhibiting herbicide chemistries compared with the S biotype. Nucleotide sequence comparison of Als genes from R11 and S biotypes revealed a single nucleotide difference that resulted in R11 having an amino acid substitution of aspartate to glutamate at position 376, as numbered relative to the protein sequence of mouseearcress. This is the first report of an amino acid substitution at this position of an Als gene isolated from a field-selected weed biotype. To verify the role of this mutation in herbicide resistance, the Als gene was cloned and expressed in Arabidopsis. Transgenic Arabidopsis expressing this Als gene exhibited resistance to SU, IMI, PTB, TP, and sulfonylaminocarbonyltriazolinone ALS-inhibiting herbicide classes. Nomenclature: Chlorimuron cloransulam imazethapyr propoxycarbazone pyrithiobac thifensulfuron smooth pigweed, Amaranthus hybridus L. AMACH mouseearcress, Arabidopsis thaliana (L.) Heynh. ARBTH.

Mesotrione combinations in no-till corn (Zea mays)

Field studies were conducted in 1999, 2000, and 2001 to determine the effectiveness of mesotrione applied preemergence (PRE) or postemergence (POST) in no-till corn. Also, a proposed prepackage mix of mesotrione plus acetochlor (1:11 ratio of mesotrione–acetochlor) in combinations with the trimethylsulfonium salt of glyphosate (glyphosate-TMS), paraquat, and 2,4-D was investigated. Mesotrione PRE at 235 g ai/ha or greater controlled common lambsquarters, smooth pigweed, and common ragweed at least 80%. POST mesotrione at 35 g/ha and higher controlled common lambsquarters 91% or greater. Mesotrione applied POST at 140 g/ha controlled smooth pigweed greater than 97%. Common ragweed control from POST mesotrione was inconsistent, ranging from 56 to 97%. PRE and POST applications of mesotrione did not adequately control goosegrass, giant foxtail, fall panicum, johnsongrass, or cutleaf eveningprimrose. The mesotrione plus acetochlor prepackage mix plus glyphosate-TMS or paraquat controlled field pansy and ivyleaf morningglory similar to or better than did the prepackage mixture of the isopropylamine salt of glyphosate (glyphosate-IPA) plus atrazine plus acetochlor. But common ragweed control by mesotrione plus acetochlor plus glyphosate-TMS or paraquat was occasionally lower than control by the prepackage mixture of glyphosate-IPA plus atrazine plus acetochlor. Corn injury was generally less than 10% with PRE and POST mesotrione applications. Nomenclature: Acetochlor; atrazine; 2,4-D; glyphosate-Ipa (isopropylamine salt of glyphosate); glyphosate-TMS (trimethylsulfonium salt of glyphosate); mesotrione; paraquat; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L.# AMBEL; cutleaf eveningprimrose, Oenothera laciniata Hill # OEOLA; fall panicum, Panicum dichotomiflorum Michx. # PANDI; field pansy, Viola arvensis Murr. # VIOAR; giant foxtail, Setaria faberi Herrm. # SETFA; goosegrass, Eleusine indica (L.) Gaertn # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L. Additional index words: Bleaching herbicides, burndown, nonselective herbicides, triketone herbicides. Abbreviations: COC, crop-oil concentrate; DAT, days after treatment; fb, followed by; PRE, preemergence; POST, postemergence; UAN, urea ammonium nitrate; WAT, weeks after treatment.

Mesotrione plus atrazine mixtures for control of Canada thistle ( Cirsium arvense )

Abstract Studies were conducted to determine if mesotrione alone or in mixtures with low rates of atrazine would control Canada thistle. In the field, mesotrione applied alone did not adequately control Canada thistle, although smaller plants in the rosette stage of growth were more susceptible than plants in the bolting stage. A mixture of mesotrione at 105 g ai ha−1 and atrazine at 280 g ai ha−1 improved control of Canada thistle over that with mesotrione alone. In the greenhouse, mixtures of mesotrione plus atrazine at 560 g ha−1 reduced Canada thistle regrowth more than mesotrione alone or mesotrione plus 280 g ha−1 atrazine. Mesotrione plus atrazine mixtures increased the rate of tissue necrosis compared with the slower development of bleaching symptoms normally associated with mesotrione alone. Uptake, translocation, and metabolism of 14C-mesotrione in Canada thistle were generally slow, and results did not explain the increased control associated with mesotrione plus atrazine mixtures. However, higher levels of absorption and translocation and reduced root metabolism of mesotrione in rosette stage plants compared with bolting plants may explain the greater susceptibility to mesotrione in the rosette stage. The changes in symptomology and increased control with mixtures of mesotrione and atrazine were likely due to the interrelationship between the modes of action of these herbicides. Nomenclature: Atrazine; mesotrione; Canada thistle, Cirsium arvense (L.) Scop. CIRAR.

Glyphosate Interactions with Manganese

Abstract: Field experiments were conducted on the Eastern Shore of Virginia from 1999 to 2001 to evaluate the effects of tank mixture applications of isopropylamine or trimethylsulfonium salts of glyphosate with two liquid formulations of manganese (Mn lignin or Mn chelate) on spray solution pH and weed control in glyphosate-resistant soybean. Additions of manganese to herbicide solutions resulted in a reduction in the acidifying effects of the herbicides as well as in the control of common lambsquarters, large crabgrass, morningglory spp., and smooth pigweed. Reduced control caused by manganese could be overcome with higher rates of the herbicides on some species, but reduced control of common lambsquarters was seen when manganese was included with any herbicide application rate. For most species, Mn chelate caused a greater reduction in control than did Mn lignin. Although manganese caused significant decreases in weed control, soybean yield was not influenced by glyphosate salt, application rate, or manganese. Reduced weed control caused by the addition of manganese to herbicide solutions may be due to the complexing of the herbicide formulations, which could result in the formation of insoluble salt complexes that are not readily absorbed through the plant cuticle, resulting in decreased glyphosate phytotoxicity. Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #3 CHEAL; large crabgrass, Digitaria sanguinalis L. # DIGSA; morningglory spp., Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; soybean, Glycine max (L.) Merr. ‘Asgrow 5401 RR’. Additional index words: pH, reduced weed control, tank mixture. Abbreviations: Ipa, isopropylamine; POST, postemergence; Tms, trimethylsulfonium; WAP, weeks after planting; WAT, weeks after treatment.

Mesotrione, Acetochlor, and Atrazine for Weed Management in Corn (Zea mays)1

Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and crop safety with preemergence (PRE) and postemergence (POST) applications of mesotrione alone and in tank mixtures with acetochlor and atrazine. Corn injury was less than 4% with all mesotrione treatments in 1999 and 2001, but it was 8 to 20% in 2000, when rainfall was 3.1 cm 7 d after PRE applications. Mesotrione PRE at 0.16 and 0.24 kg ai/ha did not adequately control most broadleaf weeds or giant foxtail. Tank mixtures of mesotrione plus acetochlor controlled smooth pigweed and giant foxtail but did not adequately control common ragweed, common lambsquarters, or morningglory species. Control by tank mixtures of mesotrione plus atrazine at 0.56 kg ai/ha was frequently low and varied with rainfall after PRE applications. All weed species were controlled 80% or more by mesotrione plus acetochlor PRE or atrazine plus acetochlor PRE followed by mesotrione POST at 0.11 kg/ha. Nomenclature: Acetochlor; atrazine; mesotrione; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L. Additional index words: HPPD-inhibiting herbicides, triketone herbicides. Abbreviations: COC, crop oil concentrate; DAT, days after treatment; fb, followed by; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate; WAT, weeks after treatment.

Evaluation of the mechanism of action of the bleaching herbicide SC-0051 by HPLC analysis

Abstract The accumulation of leaf pigments in soybean [ Glycine max (L.) Merr. cv. Essex] plants treated with the bleaching herbicides norflurazon (20 ppm, w w ) and SC-0051 (2.5 ppm, w w ) was investigated by means of high-performance liquid chromatography analysis. SC-0051 is a new experimental herbicide whose chemistry has not been released. Both SC-0051 and norflurazon reduced the relative concentrations of xanthophylls, chlorophylls, and colored carotenoids and induced the accumulation of the colorless carotene, phytoene, in the leaves of treated soybeans. These results confirm that the mechanism of the bleaching action of the herbicide SC-0051 is similar to that of norflurazon and includes the inhibition of the desaturation reactions of carotenoid biosynthesis. In addition to their phytoene-accumulating activity, both SC-0051 and norflurazon induced the accumulation of an additional pigment which was not present in leaf extracts obtained from untreated soybeans. Although the exact identity of this pigment is unknown, it appears to be a derivative of phytoene.

ALS resistance in several smooth pigweed (Amaranthus hybridus) biotypes

Abstract Experiments were conducted to identify acetolactate synthase (ALS, EC 2.2.1.6 [formerly EC 4.1.3.18]) mutation sites in eight biotypes of smooth pigweed and correlate these mutations with patterns of herbicide cross-resistance. Four herbicide-resistant smooth pigweed biotypes (R5, R6, R7, R8) collected from fields in Virginia, Delaware, and Maryland, showed a similar response to postemergence applications of the ALS-inhibitors imazethapyr, pyrithiobac, chlorimuron, thifensulfuron, and cloransulam. These R biotypes ranged from 261- to 537-fold resistant to imazethapyr and 29- to 88-fold resistant to pyrithiobac. The biotypes also had reduced sensitivity to chlorimuron and thifensulfuron of 2- to 14-fold and 10- to 25-fold, respectively, relative to a susceptible smooth pigweed biotype (S). Biotypes R6, R7, and R8 had reduced sensitivity of 3- to 10-fold to cloransulam relative to the S biotype, whereas R5 had increased sensitivity. All of these biotypes were found to have a serine to asparagine substitution at amino acid position 653, as numbered relative to the protein sequence of Arabidopsis thaliana. This stands in contrast to four other imidazolinone (IMI)-resistant smooth pigweed biotypes (R1, R2, R3, R4) that were collected from fields in Somerset County, Maryland. These biotypes were found to have an alanine to threonine substitution at position 122 of the ALS enzyme and were previously characterized at the whole-plant level with high-level resistance to IMI herbicides, increased sensitivity to pyrimidinylthiobenzoate and triazolopyrimidine sulfonanilide herbicides, and low to no cross-resistance to sulfonylurea herbicides. Nomenclature: Chlorimuron; cloransulam; imazethapyr; pyrithiobac; thifensulfuron; smooth pigweed, Amaranthus hybridus L. AMACH.

Absorption, translocation, and metabolism of CGA 362622 in cotton and two weeds

Abstract Absorption, translocation, and metabolism of the herbicide CGA 362622 were studied in cotton, spurred anoda, and smooth pigweed. 14C-labeled CGA 362622 was foliarly applied to cotton at the cotyledon to the one-leaf growth stage or at the two- to three-leaf growth stage and to spurred anoda and smooth pigweed at the four- to six-leaf growth stage. Differential absorption, translocation, and metabolism contributed to the differential tolerance of cotton, spurred anoda, and smooth pigweed to CGA 362622. Rapid translocation and a slow rate of metabolism appear to explain the susceptibility of smooth pigweed. Reduced absorption and translocation as well as rapid metabolism contribute to the CGA 362622 tolerance of cotton at the two growth stages. Limited translocation may explain the intermediate tolerance of spurred anoda to CGA 362622. Nomenclature: CGA 362622, N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; cotton, Gossypium hirsutum L. GOSHI; smooth pigweed, Amaranthus hybridus L., AMACH; spurred anoda, Anoda cristata (L.) Schlecht., ANVCR.

Mesotrione Alone and in Mixtures with Glyphosate in Glyphosate-Resistant Corn (Zea mays)1

Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and glyphosate-resistant corn tolerance to postemergence applications of mesotrione at 70, 105, and 140 g ai/ha applied with and without glyphosate at 560 g ai/ha. Mesotrione alone and mixed with glyphosate controlled smooth pigweed greater than 97% and common lambsquarters 93 to 99%. Control of common ragweed and morningglory species was variable. Common ragweed control was generally best when mesotrione was applied at 105 or 140 g/ha, and control increased only in 2000 with the addition of glyphosate. Giant foxtail control was below 25% with all rates of mesotrione, but mixtures of mesotrione plus glyphosate controlled giant foxtail 65 to 75%. Mesotrione injured glyphosate-resistant corn 4 to 24% when averaged over glyphosate rates, and injury was usually increased by higher mesotrione rates, with rainfall after herbicide applications, and in mixtures with glyphosate. Injury was transient and did not reduce corn yields. Mesotrione injury on glyphosate-resistant corn was confirmed in the greenhouse, where all mesotrione treatments reduced glyphosate-resistant corn biomass 9 to 23% compared with the nontreated check. Nomenclature: Glyphosate; mesotrione; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L. ‘Dekalb 626RR’, ‘Dekalb 5863RR’. Additional index words: IPOHE, IPOLA, Ipomoea hederacea (L.) Jacq., Ipomoea lacunosa L., Ipomoea purpurea L. Roth, IPOPU, total postemergence, transgenic crops, triketone herbicide. Abbreviations: DAT, days after treatment; POST, postemergence; WAT, weeks after treatment.

Preemergence Herbicides Followed By Trifloxysulfuron Postemergence In Cotton

Field studies were conducted in 1999, 2000, and 2001 to evaluate weed control and cotton response from PRE herbicides followed by (fb) trifloxysulfuron POST. In the first study, trifloxysulfuron at 3.8, 7.5, or 15 g ai/ha was applied POST with or without pendimethalin at 690 g ai/ha applied PRE in a factorial treatment arrangement. Visible crop injury occurred after all trifloxysulfuron applications, but injury was not affected by application of pendimethalin PRE. Cotton injury was 19 to 22% 7 d after POST treatment (DAT) from trifloxysulfuron at 3.8 to 15 g/ha but was 5 to 12% 28 DAT. Trifloxysulfuron controlled smooth pigweed, common ragweed, and common cocklebur, but spurred anoda, large crabgrass, goosegrass, and stinkgrass were not controlled by trifloxysulfuron. Morningglory species (tall morningglory, ivyleaf morningglory, and pitted morningglory) control with trifloxysulfuron at 7.5 and 15 g/ha was at least 79%, whereas velvetleaf was controlled 66% over all years. In a second study, clomazone, pendimethalin, pendimethalin plus fluometuron, pyrithiobac, or flumioxazin were applied PRE fb 7.5 g/ha trifloxysulfuron POST. Cotton injury from PRE herbicides fb trifloxysulfuron was 13 to 39% 7 DAT. Spurred anoda control exceeded 54% only with treatments that included flumioxazin or pyrithiobac PRE. Common lambsquarters, common cocklebur, and morningglory species were controlled at least 75% with all treatments that included trifloxysulfuron POST, whereas pendimethalin and clomazone usually controlled annual grasses. In both studies, the application of pendimethalin PRE controlled annual grass species and improved control of smooth pigweed and common lambsquarters over that controlled by trifloxysulfuron POST without a PRE herbicide. Nomenclature:Clomazone, flumioxazin, fluometuron, pendimethalin, pyrithiobac, trifloxysulfuron, common cocklebur, Xanthium strumarium L. XANST, common lambsquarters, Chenopodium album L. CHEAL, common ragweed, Ambrosia artemisiifolia L AMBEL, goosegrass, Eleusine indica (L.) Gaertn. ELEIN, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE, large crabgrass Digitaria sanguinalis (L.) Scop DIGSA, pitted morningglory, Ipomoea lacunosa L. IPOLA, smooth pigweed, Amaranthus hybridus L. AMACH, spurred anoda, Anoda cristata (L.) Schlecht. ANVCR, stinkgrass, Eragrostis megastachya (Koel.) Link, tall morningglory, Ipomoea purpurea (L.) Roth IPOPU, velvetleaf, Abutilon theophrasti Medicus ABUTH, cotton, Gossypium hirsutum L. ‘SG 125’