Ronald E. Talbert

Differential activity of allelochemicals from Secale cereale in seedling bioassays

Abstract Differential activities of BOA, DIBOA, and crude water extract of Secale cereale ‘Elbon’ were studied in culture dish bioassays using several vegetable and weed species. On average, DIBOA was about seven times more inhibitory to root growth and four times more inhibitory to shoot growth than BOA. Allelochemicals from S. cereale inhibited shoot more than root elongation of cucurbits Cucumis melo, Cucumis sativus, and Cucurbita pepo. Small-seeded crops Lycopersicon esculentum and Lactuca sativa were sensitive to S. cereale. Large-seeded crops, including the cucurbits and Zea mays var. rogusa, were tolerant. Among the small-seeded weeds Amaranthus palmeri, Digitaria sanguinalis, Echinochloa crus-galli, and Eleusine indica, E. crus-galli was least susceptible. Inhibition of germination by BOA or DIBOA occurred only in small- to medium-seeded species, including A. palmeri, D. sanguinalis, E. indica, L. sativa, L. esculentum, and Sida spinosa. Large-seeded species C. melo, C. sativus, C. melopepo, Z. mays var. rogusa, Ipomoea hederacea var. integriuscula, Ipomoea lacunosa, and Senna obtusifolia were tolerant to allelochemicals from S. cereale. This bioassay indicated a promising potential for controlling small-seeded weeds in large-seeded crops. Nomenclature:BOA, (3H)-benzoxazolinone; DIBOA, 2,4-dihydroxy-1,4-(2H)benzoxazine-3-one; Echinochloa crus-galli L. Beauv. ECHCG, barnyardgrass; Ipomoea hederacea var. integriuscula L. IPOHE, entireleaf morningglory; Eleusine indica L. Gaertn. ELEIN, goosegrass; Digitaria sanguinalis L. Scop. DIGSA, large crabgrass; Amaranthus palmeri S. Wats. AMAPA, Palmer amaranth; Ipomoea lacunosa L. IPOLA, pitted morningglory; Sida spinosa L. SIDSP, prickly sida; Senna obtusifolia L. CASOB, sicklepod; Cucumis melo L., cantaloupe; Cucumis sativus L., cucumber; Lactuca sativa L., lettuce; Secale cereale L., rye; Cucurbita pepo var. melopepo L. cv. Alef., summer squash; Zea mays var. rogusa Bonaf, sweet corn; Lycopersicon esculentum Mill., tomato.

Growth inhibition and root ultrastructure of cucumber seedlings exposed to allelochemicals from rye (Secale cereale)

Inhibition of “Calypso” cucumber seedling growth by rye allelochemicals, 2(3H)-benzoxazolinone BOA and 2,4-dihydroxy-1,4(2H)-benzo- xazin-3-one DIBOA, was studied by analyzing the growth of seedling tissues and organs. Light and electron microscopy of seedling root cells were also carried out to investigate the mechanism(s) of root growth inhibition and mode of action of these compounds. BOA inhibited root elongation and reduced the number of cucumber lateral roots by 77 and 100% at 0.1 and 0.43 mg BOA/mlDeionized (DI) water, respectively. DIBOA also inhibited root growth, but did not affect the number of lateral roots. BOA increased size of cucumber cortical root cells fivefold, but DIBOA had no effect. Both compounds reduced the regeneration of root cap cells and increased the width of cortical cells resulting in increased root diameter. BOA and DIBOA caused increased cytoplasmic vacuolation, reduced ribosomeDensity and dictyosomes, reduced number of mitochondria, and reduced lipid catabolism. Starch granules in amyloplasts of seedling roots treated with BOA and DIBOA were also greatly reduced compared to the control. Changes in cellular ultrastructure indicated that BOA and DIBOA reduced root growth by disrupting lipid metabolism, reducing protein synthesis, and reducing transport or secretory capabilities.

Rice and red rice interference. II. Rice response to population densities of three red rice (Oryza sativa) ecotypes

Abstract Red rice, which grows taller and produces more tillers than domestic rice and shatters most of its seeds early, is a major weed in many rice-growing areas of the world. Field experiments were conducted at Stuttgart, AR in 1997 and 1998 to evaluate the growth response of the Kaybonnet (KBNT) rice cultivar to various population densities of three red rice ecotypes. The ecotypes tested were Louisiana3 (LA3), Stuttgart strawhull (Stgstraw), and Katy red rice (KatyRR). Compared with KBNT alone, LA3, the tallest of the three red rice ecotypes, reduced tiller density of KBNT 51%, aboveground biomass at 91 d after emergence (DAE) 35%, and yield 80%. Stgstraw, a medium-height red rice, reduced KBNT tiller density 49%, aboveground biomass 26%, and yield 61%. KatyRR, the shortest red rice, reduced KBNT tiller density 30%, aboveground biomass 16%, and yield 21%. Tiller density of rice was reduced by 20 to 48% when red rice density increased from 25 to 51 plants m−2. Rice biomass at 91 DAE was reduced by 9 and 44% when red rice densities were 16 and 51 plants m−2. Rice yield was reduced by 60 and 70% at red rice densities of 25 and 51 plants m−2, respectively. These results demonstrate that low populations of red rice can greatly reduce rice growth and yield and that short-statured red rice types may affect rice growth less than taller ecotypes. Nomenclature: Red rice, Oryza sativa L. ORYSA, ‘KatyRR’, ‘LA3’, ‘Stgstraw’; rice, Oryza sativa L., ‘Kaybonnet’.

Growth Response of Rice (Oryza sativa) and Red Rice (O. sativa) in a Replacement Series Study1

A replacement series study was conducted in a greenhouse in 1998 and 1999 to evaluate the interference interactions among two rice cultivars and two red rice ecotypes. Plants were established in proportions of 3:0, 2:1, 1:2, and 0:3 (rice–red rice) plants/pot. Relative yield of Kaybonnet based on the shoot dry weight was lower than that of KatyRR or LA3, whereas PI 312777 was comparable to that of KatyRR and LA3. These results indicate that Kaybonnet was less competitive than PI 312777 when contrasted with KatyRR and LA3 red rice ecotypes. Kaybonnet (commercial rice cultivar) was dominated by both KatyRR (suspected rice × red rice cross) and LA3 (tall red rice ecotype) in tiller production, whereas PI 312777 (weed-suppressive cultivar) was comparable to either KatyRR or LA3. Both KatyRR and LA3 considerably reduced the leaf area of Kaybonnet. In contrast, PI 312777 reduced the growth of KatyRR, and its leaf area was comparable to that of LA3. The data suggest that high tillering capacity, as demonstrated by PI 312777, should be considered when breeding for rice cultivars that are competitive against weeds. This agronomic characteristic of rice may improve the success of reduced herbicide rate application programs. Nomenclature: Red rice, Oryza sativa L. #3 ORYSA ‘KatyRR’, ‘LA3’; rice, Oryza sativa L. ‘Kaybonnet’, ‘PI 312777’. Additional index words: Leaf area, red rice growth, relative yield, rice growth, strawhull. Abbreviations: DAE, days after emergence; RY, relative yield; RYT, relative yield total.

History and Management of Herbicide-Resistant Barnyardgrass (Echinochloa crus-galli) in Arkansas Rice

Arkansas has been the leading state in rice production in the United States for many years. Barnyardgrass is the dominant weed in Arkansas rice. Propanil was the first highly effective herbicide for weed control in rice and has been used in Arkansas since 1959 as the primary herbicide for rice weed control. By 1989, its continual use led to the development of propanil-resistant barnyardgrass, which had spread to 16 of the 38 rice-producing counties in Arkansas by 1992. Arkansas rice growers are dependent on herbicides for the control of weeds in this drill-seeded crop. The residual herbicides thiobencarb, molinate, and pendimethalin mixed with propanil applied early postemergence improved control of propanil-resistant barnyardgrass. But it was quinclorac, introduced in 1992, that became the real replacement treatment for propanil-resistant barnyardgrass. Then in 1999, a barnyardgrass biotype with resistance to both quinclorac and propanil was confirmed in Craighead County, Arkansas. Additionally, problems with quinclorac drift to other crops, especially tomato, led to restrictions on application of quinclorac in Arkansas by 1994. Fortunately, alternative herbicides for barnyardgrass control were developed, and clomazone was introduced in 2000. Clomazone is currently the standard herbicide for annual grasses in rice, including barnyardgrass. Herbicides recently developed for rice allow a broad range of options for a resistance management program, based on rotational and sequential herbicide applications. These include fenoxaprop and cyhalofop (both acetyl-CoA carboxylase [ACCase] inhibitors), bispyribac and penoxsulam (acetolactate synthase [ALS] inhibitors), and imazethapyr and imazamox (also ALS inhibitors for imidazolinone-resistant rice). From a global standpoint, there is considerable evidence that barnyardgrass has the propensity to develop resistance to most of these herbicide groups. Therefore, efforts to manage and monitor for herbicide resistance in this species need to be diligently continued. Research on nonchemical options is in progress utilizing weed-suppressive rice breeding lines to control barnyardgrass. Nomenclature: 2,6-bis[(4,6-dimethoxy-2-pyrimidinyl)oxy]benzoic acid, proposed common name bispyribac-sodium; clomazone; cyhalofop; fenoxaprop; imazamox; imazethapyr; molinate; pendimethalin; 2-(2,2-difluoroethoxy)-6-(trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl))benzenesulfonamide, proposed common name penoxsulam; propanil; quinclorac; thiobencarb; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; rice, Oryza sativa L; tomato, Solanum lycopersicum L.

Rice yield and quality as affected by cultivar and red rice (Oryza sativa) density

Abstract Previous research has examined the extent to which red rice affects both yield and grain quality of cultivated rice. However, this research was conducted over 15 yr ago. Modern long-grain rice cultivars have the potential to produce yields above 10,000 kg ha−1; however, it is unknown whether modern rice cultivars sacrifice competitiveness to achieve higher yields, or if, in fact, they are more competitive. Field studies were conducted in 2002 and 2003 at the Southeast Research and Extension Center near Rohwer, AR, and at the University of Arkansas Pine Bluff Research Farm near Lonoke, AR, to investigate the effect of red rice density on interference between red rice and five rice cultivars (‘CL161’, ‘Cocodrie’, ‘LaGrue’, ‘Lemont’, and ‘XL8’). White rice yield reductions were between 100 and 755 kg ha−1 for every red rice plant m−2. The hybrid rice, XL8, had higher yields than the conventional cultivars. Red rice contamination in milling samples increased linearly as a function of red rice density at Lonoke and Rohwer in 2003. Dockage for each cultivar was calculated on the basis of the relationship between red rice density and red rice contamination. Semidwarf Lemont was the most contaminated and hybrid XL8 the least contaminated by the various densities of red rice. Nomenclature: Red rice, Oryza sativa L. ORYSA; rice, Oryza sativa L. ‘CL161’, ‘Cocodrie’, ‘LaGrue’, ‘Lemont’, ‘XL8’.

A proposal to standardize soil/solution herbicide distribution coefficients

Abstract Herbicide soil/solution distribution coefficients (Kd) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter (OM), however clay minerals (CM) and metallic hydrous oxides are more retentive for cationic, phosphoric, and arsenic acid compounds. Weakly basic herbicides bind to both organic and inorganic soil colloids. The soil organic carbon (OC) affinity coefficient (Koc) has become a common parameter for comparing herbicide binding in soil; however, because OM and OC determinations vary greatly between methods and laboratories, Koc values may vary greatly. This proposal discusses this issue and offers suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement. Nomenclature: Readers are referred to the WSSA Herbicide Handbook and Supplement for the chemical names of the herbicides.

Evaluation of rice by-products for weed control

Abstract Rice by-products were evaluated in the greenhouse for herbicidal activity on various weeds and crops. Rice by-products and corn gluten meal (CG) were applied at 0, 125, 250, 500, and 750 g m−2 preemergence (PRE) and preplant incorporated (PPI). The efficacy of rice by-products and CG in reducing weed emergence and shoot weight of broadleaf species was in the order of medium-grain fatty rice bran (MF) > long-grain fatty rice bran (LF) > CG > defatted rice bran (DF) > long-grain hull (LH) > medium-grain hull (MH). For reducing grass emergence, MF = CG > LF > DF > LH > MH, and for shoot weight reduction, CG > MF > LF > LH > DF = MH. Palmer amaranth and ivyleaf morningglory were the most susceptible weeds (91 and 82%) followed by sicklepod, hemp sesbania, and prickly sida (65 to 70%). Velvetleaf was the most tolerant broadleaf weed. Grasses were not as susceptible to rice bran as broadleaf weeds. In general, MF was the best material for reducing weed emergence and its efficacy was not affected by application method. Cotton and corn were the most tolerant direct-seeded crops to MF (6% reduction in plant stand), and soybean, Italian ryegrass, tomato, and rice had intermediate tolerances (30 to 86% stand reduction). Mustard, cucumber, and lettuce were the most susceptible crops (71 to 98% reduction in plant survival). The minimum effective rate was 250 g m−2 MF PPI or PRE. Nomenclature: Corn, Zea mays L.; cotton, Gossypium hirsutum L.; cucumber, Cucumis sativus L.; hemp sesbania, Sesbania exaltata Raf. SEBEX; Italian ryegrass, Lolium multiflorum L. LOLMU; ivyleaf morningglory, Ipomoea hederacea (L.) Jaq. IPOHE; lettuce, Lactuca sativa L.; mustard, Brassica arvensis L.; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; prickly sida, Sida spinosa L. SIDSP; rice, Oryza sativa L.; sicklepod, Cassia obtusifolia L. CASOB; soybean, Glycine max L.; tomato, Lycopersicon esculentum Mill.; velvetleaf, Abutilon theophrasti Medic. ABUTH.

Resistance mechanism of propanil-resistant barnyardgrass : II. In-vivo metabolism of the propanil molecule

Propanil-resistant barnyardgrass populations, previously verified in Arkansas rice fields and in greenhouse tests, were examined in the laboratory to ascertain if the resistance mechanism in this weed biotype was herbicide metabolism. Propanil-resistant barnyardgrass was controlled >95% in the greenhouse when carbaryl (an aryl acylamidase inhibitor) was applied two days prior to propanil. Laboratory studies with 14 C-radiolabelled propanil indicated that the herbicide was hydrolysed in propanil-resistant barnyardgrass and rice to form 3,4-dichloroaniline, but no detectable hydrolysis occurred in susceptible barnyardgrass. Two additional polar metabolites were detected in propanil-resistant barnyardgrass and rice and tentatively identified by thin layer chromatography. Overall, metabolites in the resistant barnyardgrass had R f values similar to those in rice, indicating similar metabolism for both species. These data, coupled with data from a previous report on the resistant biotype showing no differential absorption/translocation or molecular modification of the herbicide binding site in the resistant biotype, indicate that the resistance mechanism is metabolic degradation of propanil.

Cross- and multiple resistance of diclofop-resistant Lolium spp

Abstract Eighteen Lolium spp. (ryegrass) accessions collected in 1998 from several locations in Arkansas were tested for resistance (R) to diclofop in both seed and whole-plant response bioassays. Eleven accessions were L. temulentum and eight were L. perenne. Fourteen of eighteen accessions were confirmed resistant to diclofop in whole-plant assay. Three of the susceptible (S) accessions were L. temulentum. The GR50 (diclofop concentration that reduced shoot or root length by 50%) R/S ratios based on whole-plant response were greater than those of the seed bioassay in all test populations, indicating that the whole-plant bioassay was more sensitive than the seed bioassay for determining diclofop resistance in Lolium spp. The most resistant (#18) and most susceptible (#3) accessions of L. temulentum were used for multiple resistance and enzyme assay experiments. Based on whole-plant bioassay, accession #18 was 411 times more resistant to diclofop than the susceptible accession #3. Accession #18 exhibited cross-resistance to fenoxaprop and multiple resistance to chlorsulfuron applied preemergence or postemergence. Resistance to other herbicide families was not observed. Resistance to chlorsulfuron was not detected in the seed bioassay. Acetyl-CoA carboxylase (ACCase) from accession #18 was 833 times more resistant to diclofop and 10 times more resistant to sethoxydim than ACCase from accession #3. Cross-resistance to sethoxydim was not observed at the whole-plant level. Resistance to diclofop among Lolium spp. from Arkansas may be due to an alteration in the target enzyme, ACCase. Nomenclature: Chlorsulfuron; diclofop; fenoxaprop; Lolium multiflorum Lam. LOLMU, Italian ryegrass; Lolium perenne L. LOLPE, perennial ryegrass; Lolium temulentum L. LOLTE, poison ryegrass.