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A { .‘_‘ Eula-r?- R rm ”I, b .‘.r;~.‘.,¢ I! .w' a Q ‘ .9’9‘” 45‘4—4. flhsyug- In“ ‘51 take U111Ve1 131w Av \.A’ / This is to certify that the thesis entitled THE INFLUENCE OF ENVIRONMENTAL AND GENETIC FACTORS ON CORN (Zea mays L.) TOLERANCE TO TRIFLURALIN presented by FRANK CLARENCE ROGGENBUCK has been accepted towards fulfillment of the requirements for MASTER'S degreem CROP AND SOIL SCIENCE W- 4,); Major professor Date 05$ if? /7§/.3 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU LIBRARIES “ RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. THE INFLUENCE OF ENVIRCNMENI‘AL AND GENETIC FACTORS (N CDRN (Zea maxs L.) TOLERANCE '10 TRIFLURALIN By Frank Clarence Roggenbuck A THESIS Sutmitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Crop and Soil Sciences 1983 ABSTRACT THE INFLUENCE OF ENVIRONMENTAL AND GENETIC FACTORS (N CORN (Zea mays L.) TOLERANCE TO TRIFLURALIN By Frank Clarence Roggenbuck Corn (gee gays L.) can be injured by carry-over of trifluralin (a,g,_a,-trif1uoro—2,6-dinitro-y_,§-dipropyl-p-toluidine) from one crop year to the next. Controlled environment, greenhouse, and field experiments were conducted to determine factors that could influence corn tolerance to trifluralin residues. One hundred eight (108) inbred lines and 5 hybrids were tested to determine genetic variability of corn tolerance to trifluralin. Several corn hybrids were found to be more sensitive to trifluralin at 15 C than at 25 C. Soil moisture had lesser but significant effects for certain hybrids. The addition of phosphorus and alachlor [2-chloro-2',6'-diethy1fi§7 (methoxymethyl)acetanilide] did not alter corn tolerance to trifluralin. Shallow trifluralin incorporation reduced stand, whereas deep incorporation reduced shoot height and increased stunting. A wide range of trifluralin tolerance was evident in the corn tested. The results suggest two mechanisms for trifluralin tolerance in corn. Copyright by FRANK CLARENCE ROGGENBUCK 1983 To my wife Laurie, for her patience, understanding, and help in completing this thesis. ii ACMLEIXEMEN'IS I am deeply indebted to Dr. Donald Penner for his encouragement, enthusiasm, and counsel during the research and in the preparation of this manuscript. I wish to thank Dr. Elmer Rossman and Dr. Dean Krauskopf for serving as members of my guidance comittee and for their valuable suggestions and assistance on my research. My appreciation is extended to Carla Billings and Susan Schoultz for their assistance in the laboratory and field. Finally, my special appreciation is extended to Laurie, whose hard work made this thesis possible. iii TABLE OF CONTENTS Page LIST OF TABLES . . . . . . . . . v INTRODUCTION . . . . . . . . . . 1 CHAPTER 1. EFFECT OF TRIFLURALIN CN CORN . . . . . 2 Introduction . . . 2 Herbicidal Effects of Trifluralin on Corn . . 3 Morphological and Physiological Components of Selectivity . . . . . 5 Factors Influencing Tblerance . . . . . 12 Conclusions . . . . . . . . 16 Literature Cited . . . . . . . 18 2. FACTORS INFLUENCING CORN TOLERANCE TO TRIFLURALIN . 27 Abstract . . . . . . . . . 27 Introduction . . . . . . . 27 Materials and Methods . . . . . . 32 Influence of environment . . . . 32 Influence of phosphorus and alachlor . 33 Genetic variability . . . . . . 34 Results . . . . . . . . . 34 Influence of environment . . . . 34 Influence of phosphorus and alachlor . . . 38 Genetic variability . . . . . . 40 Discussion . . . . . . . . 48 Literature Cited . . . . . . . 51 3. DIFFERENTIAL TOLERANCE RESPONSES CF CORN INBREDS AND HYBRIDS TO'TWO INCORPORATION DEPTHS OF TRIFLURALIN . . . . . . . . 55 Abstract . . . . . . . . . 55 Introduction . . . . . . . 56 Materials and Methods . . . . . . 58 Results . . . . . . . . . 60 Discussion . . . . . . . . 79 Literature Cited . . . . . . . 83 4. SUMMARY AND CONCLUSIONS . . . . . . 85 .APPENDIX . . . . . . . . . . 88 iv LIST OF TABLES TABLE CHAPTER 2 1. The interaction of trifluralin, soil moisture level, and temperature on two parameters of four Pioneer corn hybrids as a percent of control . . . 2. The main effects of trifluralin, soil moisture level, and temperature on four Pioneer corn hybrids . . 3. Visual injury ratings on plant shoots of two Pioneer corn hybrids treated with combinations of trifluralin, alachlor, and phosphorus . . . 4. The interaction of trifluralin, phosphorus, and alachlor on the shoots of two Pioneer corn hybrids . . . . . . . . 5. The interaction of trifluralin, phosphorus, and alachlor on the roots of two Pioneer corn hybrids . . . . . . . . . 6. The main effects of trifluralin and phosphorus fertilizer on thirteen corn hybrids . . CHAPTER 3 l. Inbred corn line numbers and codes from the 1982 IRMIE entry list that were used in the trifluralin residue field studies . . . . . . 2. Plant stand response of inbred corn lines to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . . 3. Plant stand response of Pioneer corn hybrids to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . 4. Plant shoot height response of inbred corn lines to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . . 5. Plant shoot height response of Pioneer corn hybrids to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . Page 35 39 41 43 45 47 61 62 63 65 66 TABLE Page 6. ‘Visual injury response of inbred corn lines to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . . 67 7. Visual injury response of Pioneer corn hybrids to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . . 68 8. Stunting response of inbred corn lines to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . . 71 9. Stunting response of Pioneer corn hybrids to trifluralin treatments in 1982 and 1983 field studies . . . . . . . . . 72 10. Ranking of tolerance index values of inbred corn lines that were treated with 0.56 kg/ha trifluralin at two incorporation depths in a 1982 field study . 73 ll. Ranking of tolerance index values of inbred corn lines that were treated with 0.56 kg/ha trifluralin at two incorporation depths in a 1983 field study . 76 12. Ranking of tolerance index values of Pioneer corn hybrids that were treated with 0.56 kg/ha trifluralin at two incorporation depths in 1982 and 1983 field studies . . . . . . 80 APPENDIX Al. The interaction of trifluralin, soil moisture level, and temperature on four Pioneer corn hybrids . . 88 A2. The interaction of trifluralin, soil moisture level, and temperature on three parameters of four Pioneer corn hybrids as a percent of control . . 90 A3. The interaction of trifluralin and phosphorus fertilizer on thirteen corn hybrids . . . 93 Vi INTRODUCTION Although conservation tillage may be a novelty in certain regions of the United States, the practice appears to be increasing in corn and soybean growing areas. Conservation tillage practices leave persistent pesticides near the soil surface, particularly if the pesticides are not subject to leaching. In northern areas and in other areas that experience cool, dry years, trifluralin has been reported to persist in high enough concentration to injure subsequent crops. When conservation tillage methods are used to plant corn following a trifluralin—treated soybean crop, there also appears to be an even greater chance for corn injury. The objectives of this study were to determine (1) the conditions under which trifluralin injury to corn was most likely to occur, and (2) the variability in the genetic tolerance of corn to trifluralin. CHAPTER 1 EFFECT OF TRIFLURALIN ON CORN INTRODUCTION In 1960, researchers from Eli Lilly and Company reported on the herbicidal properties of several substituted 2,6-dinitroanilines (5). Trifluralin1 was the first herbicide of this class developed for agronomic crops (84). It was most effective as a soil-incorporated, preemergence herbicide in broadleaf crops. Trifluralin selectively killed grass weeds and some broadleaf weeds with limited to no crop injury to soybean (Glycine nax (L.) Merr.), peanut (Arachis hypogaea L.), and cotton (Gossypium hirsutum L.). It was first registered for use on cotton in 1963 (77). The agronomic potential of the dinitroanilines was quickly identified and other companies developed herbicides in this class of compounds. Their greatest use has been in soybean and cotton, with other registered uses in agronomic, vegetable, and tree fruit crops (10). There have been several reviews published on the dinitroanilines (10, 44, 76, 90, 112). The scope of this review will be limited to one dinitroaniline, trifluralin, its herbicidal effects on corn, and factors that influence corn tolerance. 1 2,3,3-trifluoro-2,6-dinitro-N_,_N—dipropyl-p-toluidine (TREFLAN) HERBICIDAL EFFECTS OF TRIFLURALIN (N CORN Corn often follows soybean in a cropping rotation. In 1980, trifluralin was used on approximately 30 million acres, or one-third, of the soybeans in the major soybean producing states (115). There have been numerous casual observations that following cool, dry years there is sufficient trifluralin residue present in the second crop year to cause injury to corn. Trifluralin carry-over injury to corn has been reported in the literature (29). The factors involved in the injury of corn by carryhover amounts of trifluralin have not been fully determined. ‘With few exceptions, trifluralin is more toxic to :monocots than dicots (12). Corn is a monocot that is injured or killed when grown in soil treated with trifluralin (38, 55, 56, 100); however, corn seed germination was not inhibited when treated with trifluralin in the laboratory (100). Trifluralin is absorbed by both emerging shoots and roots of plants from treated soil (78). Prendeville et al. (88) found corn shoots to be the major site of trifluralin uptake. ‘When corn seedlings are treated so that only the shoot or only the root is exposed to trifluralin, the greater sensitivity of the shoot becomes apparent (71). The herbicidal effect must take place between the time of radicle and shoot emergence from the seed and subsequent emergence of the seedling from.the soil (76). Trifluralin injury in corn is characterized by a swelling of the root tip (16, 38, 55, 100, 102). Corn root elongation is inhibited by trifluralin and the root tip swells within 6 hours after treatment (56). Lateral roots are inhibited by trifluralin (38, 55, 56, 102). Hacskaylo and Amato (38) found "root pruning" in cotton, but a total failure of radicle and seminal roots in corn from the same concentration of trifluralin. Corn shoots emerging from the trifluralin treated soil are prostrate and twisted, stunted, and exhibit an increased purple coloration, similar to phosphorous deficiency (38, 76). Bayer et al. (17) sumnarized anatomical and morphological effects of trifluralin in cotton roots. Time course studies of root tip cell development in the presence of herbicidal levels of trifluralin demonstrated that elongation ceased within 24 hours of treatment. Enhanced radial expansion compensated for inhibited elongation, resulting in approximately the same volume change for treated and untreated tissues. This radial expansion produced the commonly observed bulbous root tips. As the time of exposure increased, the proportion of apical meristem cells to differentiated cells decreased. Meristematic cells ultimately vacuolated with a general loss of organization in the tissue. Cytological studies with corn roots treated with trifluralin indicate that mitosis is inhibited, resulting in multinucleate cells (16, 38). Bartels and Hilton (16) observed that trifluralin arrested cell division at metaphase in corn root tips. The absence of cell plate and cell wall formation was noted in trifluralin treated roots of corn (38). Trifluralin caused the loss of both cortical and spindle microtubules from corn root cells (16). Hess and Bayer (45, 46) concluded that at obtainable water-soluble concentrations, trifluralin specifically inhibits microtubule-mediated processes in plants . MORPHOLGBICAL AND PHYSIOLOGICAL CGTPCNENTS OF SELECTIVITY The factors that contribute to the selectivity of trifluralin between dicots and monocots are not clear. There would appear to be two components to selectivity; a morphological and a physiological component. The morphological component involves the root systems of dicots and:monocots. In dicots, the primary root tends to grow vertically downward forming a tap root system (7). Lateral roots occur initially as branches of the primary root. The primary root system remains throughout the life of the plant. This system would be typical for soybeans. In many monocots, particularly in the grasses, the primary root system stops growing, and may even die, while the plants are young (7). This system.is replaced by a fibrous root system that has numerous adventitious roots originating close to the base of the stem. The adventitious roots tend to grow laterally at first, and then turn downward in the soil. The roots of corn plants first grow nearly parallel to the soil surface, remaining in the upper 7.5 to 15 cm of soil. ‘When the plants have their seventh or eighth leaf, and the roots have extended 0.6 to l m from the base of the stalk, the roots turn downward rather abruptly (7). In the dicot cotton, when the tap root grows through the layer of soil treated with trifluralin, lateral root production in that zone is restricted (8, l7). Trifluralin is strongly bound to the soil, does not leach downward, and is active throughout the depth to which it is incorporated (9). The inhibition of lateral roots by itrifluralin was affected more by depth of incorporation than by dosage (8, 73, 107). Lateral or secondary roots below the treated zone may be nearly normal and shoots are usually uninjured. The growth of the tap root is unaffected by trifluralin at doses which completely inhibit lateral root formation (8, 17, 57). It has been hypothesized that cells of the pericycle and endodermis are more sensitive to trifluralin than cells in the tap root tip (17, 57). The early lateral growth of corn roots maximizes their contact with trifluralin treated soil. Corn roots tend to stay in the top layer of soil, prolonging injury, while dicot roots tend to grow rapidly downward and escape injury. Daring the seedling stage, root growth is critical in the establishment of one species and failure of another (113). The most rapidly established species will have a competitive advantage and will seriously delay growth of other species. The physiological component of selectivity is more complex than the morphological component. The differences between dicots and monocots are not as obvious. The physiological component can be divided into three categories: 1. absorption and translocation; 2. lipid content; and 3. metabolism. The amount of trifluralin absorbed and translocated by plant tissue, by whatever node of presentation or site of contact, is relatively small (112). Evidence for and against absorption and translocation is present in the literature. Parka and Soper (76) suumarized the topic by stating that trifluralin is either absorbed or adsorbed by the roots because of their proximity to the herbicide, while translocation from the root to the shoot is minimal. Corn 7 shoots are more sensitive to trifluralin than the roots (71). Once the corn shoot has emerged from the soil, little translocation of trifluralin from the roots is evident. However, absorption by the shoot of trifluralin which volatilized from the treated soil can cause shoot injury (71, 111). The critical processes controlling selectivity may occur within the cell walls and the cytoplasm. Strang and Rogers (110) used microradioautography to study the absorption and translocation of 14C—trifluralin by cotton and soybean. Radioactivity was found primarily on the surface of the roots due to a tenacious adsorption or binding to the epidermis or cuticle. The epidermis was the major barrier to entrance of trifluralin. Movement through the cortex appeared to be prhmarily via the cell walls, with binding occurring in the cortical cell walls. Little movement out of the soybean root was observed, but some radioactivity was found in cotton leaves. Entrance of radioactivity into the roots of these species was greatly facilitated by breaks in the epidermis, as might occur from seedling diseases, mechanical damage, or lateral root emergence. Lateral roots develop from.a cell layer deep in the root called the pericycle. As lateral roots form, they break through the endodermis, creating an opening in the suberized layer called the Casparian strip. In corn, cortical cells in the path of the emerging root primordia collapse completely as they are contacted, allowing its unimpeded passage (7). As Strang and Rogers (110) suggest, a pathway for absorption of trifluralin to the interior of the root is opened as lateral roots form. This pathway may help explain the increased sensitivity of lateral roots compared to tap roots. When the primary barrier of the root, the epidermis, is crossed, binding to cell walls occurs as trifluralin moves into the root. A gradient develops from the relatively high concentration outside the root to very low concentrations at the dividing root tip cells that are most sensitive to trifluralin. Sawamura and Jackson (98) worked with cell cultures of Tradescantia paludosa and found disrupted phases of mitosis at 0.2 ppb trifluralin. The pathway consists of crossing the epidermis, movement via cell walls to the plasmalemma, crossing the plasmalemma to enter the cytoplasm, and reaching the sensitive microtubules. The ability of this pathway to bind or detoxify trifluralin may be a key step in selectivity. Lipid content is the second physiological component of selectivity. Lipids may play a role in reducing the amount of trifluralin that reaches the interior of the root. Trifluralin is highly lipid soluble and has been shown to influence several processes that involve lipids structurally or functionally. Mann and Pu (58) found no effect of trifluralin on lipogenesis as evidenced by incorporation of malonic-2-14C acid into lipids in hemp sesbania (Sesbania exaltata (Raf.) Cory). Penner and Meggitt (81) observed that treatment with trifluralin did not alter the percent oil content of soybean seeds. However, at 1.12 kg/ha, trifluralin significantly reduced the stearic acid and increased the linoleic acid content of seeds compared to the controls. The saHErresearchers reported that chemical weed control practices did not alter percent oil or oil quality in corn grain (82). In contrast, Ashton et al. (11) reported that lipid synthesis was the most sensitive metabolic site of inhibition by trifluralin in red kidney bean (Phaseolus vulgaris L.) 9 single cells. Trifluralin inhibited lipid synthesis by 27% at 10"5 M. Crop seeds differ extensively in lipid and fatty acid composition (27, 48, 53, 119). The lipid content of nearly all trifluralin—tolerant weed seeds was found to be within the range of conmercial oil seeds such as soybeans and corn (47, 99, 109). Susceptibility of plants to trifluralin decreased as the percentage of total lipid in dry seeds increased (68). There was also a significant negative correlation between root lipid content and sensitivity to trifluralin (68). Corn cultivars with a wide range of seed lipid content (4.45 to 17.0% of dry weight) were grown in trifluralin-treated soil. Seedlings grown from seeds with high lipid levels were observed to accumulate higher precentages of lipids in their roots and were less susceptible to trifluralin than roots with lower lipid levels (67). Externally applied lipids (such as D—a-tocopherol, oleic acid, corn oil, and others) protect plants from trifluralin injury, both in the laboratory and in the field (24, 25, 47). Much of the lipid found in cells occurs in membranes. The cell uembrane consists of a protein-lipid micellar structure that may also trap small amounts of lipid soluble compounds that move into it (118). The plasmalenma may contain higher levels of lipid in lipid-rich roots, allowing it to trap more trifluralin. Hilton and Christiansen (47) hypothesized that selective phytotoxicity of trifluralin to young seedlings was determined in part by the amount of endogenous lipid available to trap trifluralin and keep it from its site of phytotoxic action. Ndon and Harvey (69) state that differential rates of de novo synthesis of membrane lipids in roots 10 nay account for the differences of lipids in roots and, hence, the differential responses of roots to trifluralin. In addition, total oil content of corn has been positively correlated with early spring vigor (37). High lipid content may protect corn from trifluralin as well as increase vigor early in the growing season. Several reviews have been published on plant membrane lipid composition and permeability (18, 104, 114, 117). Metabolism is the third physiological component contributing to selectivity. Hatzios and Penner (42) reviewed the role of herbicide netabolism in plants and in selectivity. Limited absorption and translocation have restricted the amount of trifluralin within the roots of some species, contributing to selectivity. Lipid content also affects selectivity. When trifluralin enters the symplast of the plant, it is subject to the final protective mechanism the piant has to prevent phytotoxicity, metabolism. After crossing the plasmalemma, trifluralin is subject to metabolism or alteration which may limit phytotoxicity. If it is bound in the lipid portion of the plasmalemma, it can also be subject to metabolism. Morre (64) reviewed membrane turnover and two models of membrane degradation. Various times are reported for membrane turnover, ranging from several hours to several days. In one model, membrane constituents associate and dissociate from the nembranes, and only in the dissociated state are they subject to intracellular degradative processes. In the other model, organelles or fragments of membranes are internalized by autophagic vacuoles. Lysosomal enzynes are added and membrane breakdown is completed within the confines of the resulting digestive vacuole. The products are then 11 available for redirected synthesis of lipid membranes. If trifluralin were present in the membrane, it could be altered by lysosomal enzymes as well. If trifluralin were released as in the first model, or simply crossed the plasmalemma and entered the cytoplasm, metabolism could also occur. Probst et al. (91) grew soybeans and cotton plants in soil containing 14C— trifluralin. The resulting radioactivity in the plants was distributed in lipids, glucosides, hydrolysis products, proteins, and cellular fractions. They concluded that the universal distribution of the radioactivity without definite identification of trifluralin or recognizable metabolites suggests nondescript incorporation or total metabolism of trifluralin. Carrots (Daucus carota L.) were grown in greenhouse soil into which 14C—trifluralin was incorporated (33). After 110 days, two-thirds of the radioactivity in the root was in the surface layer. In general, the amount of trifluralin progressively decreased from the surface to the center of the root; however, a somewhat higher amount was found in the layer containing the xylemrphloem junction. The major compound found was unaltered trifluralin. Biswas and Hamilton (19) exposed peanuts and sweet potato (ngmga. batatas Lam.) roots to solutions containing 14C-trifluoromethyl— labeled trifluralin. After 72 hours, less than 1% of the radioactivity was unaltered trifluralin in peanut, whereas this value was 17% in sweet potato. Penner and Early (80) treated corn roots with 14C-trifluralin and examined it after 12 hours. Less than 9% of the 14C co-comatographed with trifluralin. Sixty percent of the 14C was present in the 80% methanol-insoluble residue. The remaining 12 .radioactivity was in water-soluble and hexane-soluble fractions and was not trifluralin. These results indicated that corn roots rapidly metabolized trifluralin. A.related dinitroaniline, fluchloralin [Nf(2-chloroethyl)-2,6- dinitroegfpropyl-4-(trifluoromethyl)aniline] differs from trifluralin only by the substitution of one chlorine for one hydrogen atom. Marquis et a1. (59) discovered that fluchloralin was metabolized by soybean roots at a rate sufficient to prevent irreversible injury while corn roots metabolized it.more slowly and were severely injured. Fluchloralin selectivity between corn and soybeans appeared due to both the rate of netabolism and the ability of soybean roots to escape the herbicide zone more rapidly than corn. Currently, trifluralin selectivity in corn can only be achieved by utilizing a post-plant layby application made to the soil and shallowly incorporated with a rolling cultivator (1, 3, 15, 35, 63). The corn needs to be at least 20 cm tall and the brace roots covered with soil by cultivation prior to the layby herbicide treatment. The age of the corn, the shallow incorporation, and the strong soil adsorption likely limited the injury to the corn shoots and roots (51, 87, 97). FACTORS INFLUENCING TOLERANCE The limited tolerance of corn to trifluralin takes on new meaning when the current patterns of tillage practices are examined and future projections are considered. A recent survey of research and extension workers in 25 leading corn states indicated that no-till 13 corn will increase from 5 to 10% of the crop in 1980 to 26% by 1990 (122, 123). Reduced tillage corn will increase from 28% of the crop in 1980 to 48% in 1990. These results are fairly well in agreement with predictions made in a U.S.D.A. technology assessment report on minimum tillage in 1975 (116). Phillips et al. (83) predicted that 65% of the corn and soybeans in the southern corn belt would be grown by no-till methods by the year 2000. Currently, the nost corrnon reduced tillage method involves fall chisel plowing and one-pass spring seedbed preparation (108). Trifluralin was estimated as being applied to approximately a third of the soybean acreage in 1980 in the major soybean producing states (115). Corn planted with conservation tillage, which can be any combination of no-till or reduced tillage practices less than moldboard plowing, is a common crop following soybeans. Burnside (22) maintains that trifluralin persistence is extremely important in the western part of the corn belt due to the widespread use of this herbicide on soybeans and because much of the treated land is rotated to grass crops. When these facts are combined with the finding that conservation tillage can increase the chance of carry—over trifluralin injury on corn (29), a problem of increasing concern is evident. To be a problem, trifluralin must persist from the application year to subsequent cropping year. The evidence for and against this persistence is extensive (2, 14, 20, 21, 23, 30, 34, 39, 40, 41, 43, 50, 52, 60, 61, 62, 73, 77, 89, 91, 92, 93, 95, 96, 97, 101, 106, 121, 125). Helling (44) concluded that for normal use rates, trifluralin persistence in soils ranges from 5 to 6 months. 14 ,Persistence increases with decreasing soil temperature and moisture content; seasonal carrybover sometimes occurs. Areas likely to have carryhover problems would be northern areas with shorter growing seasons, areas with low amounts of rainfall, or any area that has a cool and/or dry growing season. Conservation tillage would likely increase the problem in these areas as well. Since trifluralin is strongly adsorbed to soil organic matter (49) and does not leach (9) it stays in the zone of incorporation. Conservation tillage limits the dilution of this layer with deeper soil areas. If carrybover trifluralin is present, corn planted in this layer of treated soil will show injury. Moldboard plowing of soil containing phytotoxic concentrations dilutes the trifluralin concentration and places it below the zone of maximum phytotoxicity (22). Plowing provides a practical means of eliminating phytotoxic amounts of trifluralin when a soil residue problem exists (23, 52). Conservation tillage leaves more crop residue on the soil surface than conventional moldboard plowing. This residue tends to keep the soil shaded and cooler in the early spring, reducing soil temperatures (122). Corn absorbs more trifluralin at low soil temperatures than at higher soil temperatures (79). Plant growth is slower at lower soil temperatures. The longer that sorghum (Sorghum bicolor (L.) Moench) shoots were exposed to trifluralin, the greater the injury (13). Conservation tillage is an integral part of double cropping systems. Double cropping involving minimum tillage planting has become popular in parts of this country (70). It reduces the tine available for trifluralin degradation, as a second crop is planted 15 later the same season. The effect of tillage is evident on trifluralin carryover in this type of cropping system. Plowing eliminated injury to sweet corn following trifluralin treated canning peas, while on minimum tillage plots, the sweet corn was stunted, had reduced stands and reduced yield (69). In another study of double cropped grain sorghum, corn, and soybeans following trifluralin treated canning peas, the soybeans had no injury, the corn was slightly injured, and the sorghum was severely injured (70). The sorghum stand was reduced by 44%. The carry-over and lack of degradation of trifluralin through the cold winter period can be exploited in conservation tillage systems. A system has been described that recommends application of trifluralin directly to crop residue in the fall (75). The herbicide is incorporated with the fall primary conservation tillage operation. Subsequent secondary tillage in the spring incorporates trifluralin adequately for effective weed control during the growing season. While conservation tillage tends to reduce the tolerance of corn to trifluralin, there is some evidence that genetic tolerance may exist that could be exploited. Davis et a1. (26) tested 18 parental lines and 34 single crosses for tolerance to 0.56 kg/ha of trifluralin. The lines ranged from 0 to 70% injury in their response to trifluralin. Genetic resistance to trifluralin has been developed in butternut squash (Cucurbita moschata Poir) by a selective breeding program (4). Genetic control of enzyme systems responsible for herbicide metabolism in corn with herbicides other than trifluralin has been reported (28, 36, 103). Differential responses of inbred as well as hybrid corn have been shown for several other herbicides (6, 16 31, 32, 66, 72, 85, 94, 124). Development and incorporation of genetic tolerance of corn to trifluralin would solve the problem of carrybover. CONCLUSIONS In this discussion, three broad areas of effects of trifluralin on corn have been examined: 1. herbicidal action; 2. the morphological and physiological components of selectivity; and 3. factors that can influence tolerance. This examination of the literature reveals that several important questions concerning the effect of trifluralin on corn are still unanswered. 1. What specific environmental, chemical, and cultural factors interact with trifluralin residue carry-over to cause trifluralin injury in corn? 2. What corn hybrids are particularly sensitive or tolerant to trifluralin carryover residues? Several seed producers have advised buyers of their seed in regard to the sensitivity of a particular hybrid to certain herbicides (105). If this question can be answered, farmers can be advised what varieties to grow or not grow if they suspect a trifluralin carry-over problem. 3. Can one select for morphological and physiological components in corn that influence its response to trifluralin? The literature suggests that it may be possible. Nagel (65) has been able to genetically select for plants with a strong, spreading type root system with an abundance of secondary and fine roots. Any corn line that could rapidly penetrate downward through a trifluralin layer would sustain less injury than one that followed the normal early 17 shallow rooting pattern. Genetic modifications of oil content and fatty acid composition in corn kernels is feasible (54, 86, 119, 120). Field tolerance of flax (Linum usitatissimum L.) lines to trifluralin was thought to be a function of more than one mechanism (74). Advances made in any area could lead to a more tolerant corn line. 4. What is the sensitivity of corn inbred lines to trifluralin carrybover residues? When identified, very sensitive inbred lines could be avoided for use in producing hybrids. Tolerant inbred lines could be used to produce crosses with hybrid tolerance. Answers to these questions could help in eliminating the current problem of corn injury from trifluralin carrybover, a problem Chat will likely increase in magnitude as conservation tillage increases in the future. If genetic bases for tolerance in corn can be defined, advances in breeding are possible. If corn tolerance could be advanced to a level at which trifluralin could be used as a weed control agent without crop injury, it would be a comparatively cheap herbicide to use in corn. The combination of trifluralin to control grasses and a low rate of a triazine herbicide to control broadleaf weeds could provide economical weed control in corn. 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M. 1966. Some structural and dynamic aspects of lipids in biological membranes. Ann. N.Y. Acad. Sci. 137:717-730. Van Overbeek, J. and R. Blondeau. 1954. Mode of action of phytotoxic oils. Weeds 3:55-65. Weber, E. J. 1978. Corn lipids. Cereal Chem. 55:572-584. Widstran, N. W. and M. D. Jellum. 1975. Inheritance of kernel fatty acid composition anong six maize inbreds. Crop Sci. 15:44-46. Wiese, A. F., E. W. Chenault, and E. B. Hudspeth, Jr. 1969. Incorporation of preplant herbicides for cotton. Weed Sci. 17:481-483. Worsham, A. D. 1980. No-till corn - its outlook for the 80's. Proc. Am. Corn Sorghum Res. Conf. 35:146-163. Worsham, A. D. 1982. Weed managenent for reduced tillage corn production. Abstr., Weed Sci. Soc. Am. pp. 136-137. Wright, T. H., C. E. Rieck, and C. G. Poneleit. 1974. Effect of R-25788 on EPIC injury to corn genotypes. Abstr., Weed Sci. Soc. Am. p. 1. Zimdahl, R. L. and S. M. Gwynn. 1977. Soil degradation of three dinitroanilines. Weed Sci. 25:247-251. CHAPTERZ FACIOIE INFLUENCIMS CORN TOLERANCE TO TRIFLURALIN Abstract. Corn (Loam L.) can be injured by carry-over of tr iflural in (_a_,_a,_a_-tr ifluoro-2, 6-dinitro—N,N—dipropyl-p—toluidine) from one crop year to the next. Factors that influence corn tolerance to carry-over concentrations of trifluralin were studied in controlled environment chambers and greenhouse experiments. For several hybrids, greater injury occurred at low than high temperatures. This injury was especially evident for Pioneer 3320 and Pioneer 3572 if the soil moisture was at 100% field capacity. Addition of phosphorus fertilizer did not interact with trifluralin to increase injury, but did interact with alachlor [2-chloro-2',6'-diethyl-§-(methoxymethyl)acetanilide]. Alachlor plus trifluralin injured corn in an apparently additive manner. Significant differences were found in genetic tolerance of corn to trifluralin within a group of hybrids. Tblerance of specific hybrids to trifluralin was altered by environmental conditions. INTPDDUCTICN Effective herbicides should provide weed control for a cropping season, then degrade to innocuous products (24). Persistence beyond the period necessary for control leads to carry-over problems in succeeding crops. Trifluralin is used extensively for season-long 27 28 weed control in soybeans (Glycine max L. (Merr.)). Corn often follows soybeans in a cropping rotation and can be severely injured by trifluralin carry-over. Fink (16) reported injury to corn following soybeans treated with trifluralin in west Central Illinois. This injury was thought to be due to a relatively dry soybean season combined with a lack of .moldboard plowing. Moldboard plowing dilutes the trifluralin concentration and places it below the zone of maximum phytotoxicity (9, 10, 16, 24). This practice provides a practical means of eliminating trifluralin carry-over problems. The persistence of trifluralin reflects the total of all processes (physical, chemical, and biological) nodifying the herbicide in the soil (10). The eventual fate of trifluralin presumably is decomposition, but the variable rates of breakdown reactions lead to the occurrence of some soil residues (10). Helling (21) reviewed and summarized the soil persistence of dinitroaniline herbicides. He concluded that trifluralin persistence for normal use rates was 5 to 6 months and increased with decreasing soil temperature and moisture content. Seasonal carry-over occurred with cool, dry conditions. Temperature, soil moisture, soil phosphorous levels, other herbicides, and genetic differences may all influence the tolerance of corn to trifluralin, but these factors have not been thoroughly researched. Hammerton (l9) reviewed the effects of temperature before, during, and after herbicide application. He proposed that plants grown at different temperatures may vary both morphologically and metabolically. An increase in phytotoxicity at 10 C has been 29 reported for atrazine [2-chloro—4-(ethylamino)-6-(isopropylamino)-§- triazine] on corn (46). This increase was attributed to reduced detoxication as well as greater foliar penetration under wet conditions. Penner (36) reported that trifluralin-treated corn showed a greater reduction in dry weight at 30 C than at 20 C in comparison to the control. However, corn accumulated a higher concentration of 14C-trifluralin in both roots and shoots when grown at 20 C compared to 30 C (36). Temperatures between 20 and 30 C did not effect the phytotoxicity of trifluralin to soybeans or navy beans (Phaseolus vulgaris L.) (36, 37). Temperatures within the range of 10 to 24 C did not effect trifluralin toxicity to barley (Hordeum vulgare L. 'Larker') (30). An increase in phytotoxicity with an increase in temperature have been reported for several herbicides (ll, 25, 29, 31, 36, 37, 38, 42, 48, 50). Soil water content may influence herbicide phytotoxicity (26, 27, 44, 49). Herbicide phytotoxicity generally increases as soil water content increases. However, Stickler et a1. (44) found a decreasing response of giant foxtail (Setaria faberii Hernm.) to trifluralin with increasing moisture. Mass flow and diffusion were probably the major factors involved in providing dinitroaniline herbicide activity in the soil (23). Bode et al. (6) found trifluralin diffusion to be low in air-dry soil at all temperatures studied. Diffusion increased to a maximum between 8 and 15% w/w soil moisture content and then decreased steadily as moisture content increased. Standifer and Thomas (43), however, have noted that trifluralin is generally effective under dry soil conditions. There was not a marked difference in trifluralin phytotoxicity to cats (Avena sativa L. 30 'Dal') between 55 and 100% soil field moisture capacity (23). Monocot plants emerge from trifluralin-treated soil with an increased red-purple coloration, similar to phosphorus deficiency (35). Inhibition of root growth is also a characteristic of phosphorus deficiency and trifluralin injury. Cathey and Sabbe (12) reported the phosphorus uptake by soybean and cotton (Gosgypium hirsutum.L.)‘was decreased when the phosphorus and trifluralin were located in the same soil zone. Trifluralin has also been shown to inhibit phosphorus uptake by tomato (Lycopersicon esculentum Mill.) (52), soybean, and cat (8). Trifluralin caused a greater reduction of tomato root growth at low phosphorus rates than at high rates (52). Phosphorus was less effective in pronoting root growth as the trifluralin rate increased. The phosphorus level in the soil may also influence herbicide phytotoxicity (1, 14, 41, 45, 47). Rahman et al. (39) discovered that the addition of low rates of phosphorus (up to 300 ppmw) had either no effect or slightly enhanced the phytotoxicity of trifluralin to German millet (Setaria italica (L.) Beauv.). At high rates, phosphorus significantly reduced the toxicity of the herbicide. combinations of herbicides applied together can result in synergistic, antagonistic, or additive effects (20). An interaction is possible between trifluralin residues and the herbicide applied for weed control in corn. The effect of the combination of linuron [3-(3,4-dichlorophenyl)-l-methoxy-1emethyl urea] and trifluralin on three grass species was found to be additive (28). Diuron [3-(3,4-dichlorophenyl)-l,1-dimethylurea] or dichlobenil 31 (2,6-dichlorobenzonitrile) were combined with trifluralin to treat black mustard (Brassica nigra L. 'Alsace') or sorghum (Sorghum vulgare Pers. 'Hybrid 610') (22). The effect was found to be additive for both species with both herbicide combinations. Data on alachlor, a commonly used corn herbicide, and trifluralin combinations were not available in the literature. It was suggested in 1960 that greater emphasis be given to the role of genetics in the use of agricultural chemicals to attain the goal of protecting the economic crop from both chemical and pest damage (51). variations in tolerance of corn hybrids and inbred lines have been reported for atrazine, simazine [2-chloro-4,6-bis (ethylamino)-§-triazine], diclofop [2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid], butylate (S-ethyl diisobutylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), alachlor, and propachlor (2-chloro-N-isopropylacetanilide) (2, 3, 4, 5, 17, 18, 32, 33, 40). Davis et al. (13) tested 18 inbred lines and 34 single crosses of corn for tolerance to 0.56 kg/ha of trifluralin and found a range from 0 to 70% injury. Francis and Hamill (l7) conducted a greenhouse study of corn seedling tolerance to alachlor and concluded that reliable prediction of hybrid tolerance from knowledge of inbred response is not possible. The objective of this study was to determine the conditions in which trifluralin injury to corn was most likely to occur by evaluating the influence of trifluralin levels, temperature, soil uoisture, soil phosphorus levels, an alachlor application, and a range of hybrids on trifluralin injury to corn. 32 MATERIALS AND METHODS Influence of W. Controlled environment chambers were used to test the effect of temperature, soil moisture, and trifluralin levels on four corn hybrids, Pioneer 37471, Pioneer 3320, Pioneer 3572, and Pioneer 3541. The Chambers were kept at a constant temperature of either 15 t 2 or 25 1 2 C, with a 14 hr daylength at an irridation of 400/uE~mf2~s‘1. A Marlette sandy clay loam (Glossoboric Hapludalf fine-loamy, mixed, mesic) was mixed (1:1,v/v) with sand to fermulate a soil nix with 2.0% organic matter, a pH of 7.7, and a phosphorus content of 43 kg/ha. This soil mix was used for all experiments in the study. The field moisture capacity (FC) was determined according to Fedorovskii (15) . The two soil water contents used in the experiments were 11.6% w/w (48% soil FC) and 24.2% w/w (100% soil FC). Treatments of 0, 0.22, or 0.45 kg/ha trifluralin were applied in water at 281 L/ha to air-dry soil mix in 946 ml plastic pots. The treated soil in each individual pot was inmediately mixed in a plastic bag to insure uniform incorporation and returned to the pot. Two corn seeds were planted 2.5 cm deep in each pot and the pots then adjusted to 48% or 100% soil FC. The pots were checked daily and watered to maintain the appropriate soil moisture level. Of the four hybrids tested for tolerance, personnel from.Eli Lilly and Company identified Pioneer 3747 and Pioneer 3320 as being susceptible and Pioneer 3572 and Pioneer 3541 as being tolerant to trifluralin 1 As used throughout this chapter, this format indicates brand- variety, e.g., Pioneer brand, variety 3747. 33 residues in the field. The plants were harvested 21 days after planting. Shoot and root fresh and dry weight and shoot length data were recorded at harvest. The experimental design was a completely randomized four factor factorial. There were two replications of each treatnent with two plants per replication. The entire experiment was repeated and the data presented in the tables are the means of the two experiments. Influence of m and W. The influence of phosphorus and alachlor on corn tolerance to trifluralin was tested in a greenhouse study. The phosphorus was obtained as a 0-40-0 analysis granular commercial fertilizer and ground to a fine powder using a mortar and pestle. Phosphorus application rates were 0 or 112 kg/ha, incorporated as described earlier for trifluralin. Trifluralin was applied at 0 or 0.22 kg/ha in water at 281 L/ha and incorporated as previously described. The alachlor was applied preemergence at 0 or 3.36 kg/ha in water at 281 L/ha. Two hybrids were used, Pioneer 3747 and Pioneer 3572. The corn seeds were planted as previously described. Temperatures were maintained at 15 t 3 C at night and 15 to 21 C during the day. Natural illumination was supplemented by cool-white fluorescent lighting to maintain a daylength of 14 hr. The pots were watered daily as needed. Visual injury ratings were taken 20 and 33 days after planting. The plants were harvested 35 days after planting. Shoot and root length, fresh weight, and dry weight data were recorded at harvest. The experimental design was a completely randomized four factor factorial. The data presented are the means of two experiments with four replications each with two plants per replication. 34 Genetic variability. A range of corn hybrids were tested for tolerance to trifluralin in a greenhouse experiment. Twelve Pioneer hybrids and one Migro hybrid were treated with 0 or 0.45 kg/ha trifluralin and 0 or 112 kg/ha phosphorus applied and incorporated as described previously. A list of the hybrids included in this experiment is given in the tables. The temperatures, lighting, soil, planting, and watering were as described for the chemical factor experiment. The plants were harvested 35 days after planting. Shoot and root length, fresh weight, and dry weight data were recorded at harvest. The experimental design was a completely randomized three factor factorial. The data presented are the means of two experiments with three replications each with two plants per replication. Data for all experiments were subjected to analysis of variance and the means separated by the Duncan's multiple range test. RESULTS Influenza of W. Among the parameters measured, shoot length and root fresh weight were the most sensitive and precise measures of trifluralin injury. The data for these two parameters are presented as the percent of untreated control for clearer interpretation (Table l) . The means of the data and the percent of control values for the remaining three parameters can be found in the appendix (Tables Al and A2). Increasing rates of trifluralin caused a significant reduction in shoot length and root fresh weight averaged over all hybrids (Tables 35 nan m.mm nno e.ee me e e.o~ he m.~o me can on o.m~ we e.eo me one o.em fl H.em me we meme nno «.me one o.ee me an: e.~m “an m.oo on can one o.mm nnn m.me me man m.mm one o.eo me me comm one ~.~e one e.ee me nne m.ee one e.He me can one ~.ee one m.ee me one a.ee one o.me me me eeem me.o one e.~e one m.oa mm ooo o.me one m.eo ma eon one e.eo one e.ee no eoo m.em one e.em me me some one e.mo ano m.oe mm oon e.~o one H.~m me one nno H.ee one m.mm me “no e.em nno m.ee me we meme e e.ee one e.me me one m.em e o.mon me eon one H.ne one m.~m mm nne m.oe nan e.oo me we oemm on e.mo one o.oe me one e.mo ne m.ooH me eon ne o.ee one ~.om me one e.oo one ~.me me we seem -.o eoanoeoeoeH nnnnnneooneoo no evnnnn loo laneoeneo oeeoo e1 Aen\one n5 swoon fimcoa Booms ooumgeoo mo cu boom ooonm oneneoooeea ooonenoe anon neocoem cafleooflonna eoooooo oécuucoo mo ucooumm o no moans? 58 $983 How mo 332:..qu 03» so 333%... one .chH announce Sow 533333 mo scouoououca one .H manna. 36 n ~.em n e.oe me.o neeeoeeonoo e e.Ho e e.eo -.e on nooooo one: e o.om ne ~.ee me n e.oe on o.oo me Home n o.ee oo e.ee me n e.oe o o.He me meme e e.em e o.oe me n e.~e oo e.oe me eemm ooooeooneon e ~.mm e e.oo en en onenen e m.om ne e.oe me eeem on connoenonee on e.om on o.oe cod no H.~m e m.oe me Home o H.ee o m.ee eon o m.em o «.me me Nemm ne m.mm e e.ee one o woe o m.e.e. we ommm 8330.: no c.4m e H.oo cos Hone en onenen e o.em ne H.ee me even on eonnoeoonee nno o.me one m.eo me eno e.em eno o.mo me eoe eno e.ee nnn H.4e on gum m.oo one e.om me we vam mo.o oceuoououcH nnnneeooneoo mo eennnn lo. leoeoeneo.oeoeo we leneoxv o3,neooo nomeoe onenen oooeoeoo on on poem uoocm ousuouogewa monumeos How 3283 5135339 mucouum A 83358 .H canon. 37 Jam» 0053 3333. 95055 on... 3 aged wm on» on occuouueo heucmoemecmew uoc one. amused .5580 o 5H3 9.96 muomumo on 5:33 9:38 o 5:33 memo: o e m.em e o.om mm oonuenomeon n e.oe n e.ee me no nooooo one: e e.ee e e.ee ooe onenemoenemoe e e.ee e e.ee we no nooooo see: no e.em e o.ee Home o e.me n e.ee meme n e.om e o.ee omee onenen e e.em e o.oe eeee no nooooo one: nnnneeoonnoo mo eennnn not Aeoeoeoeo oeomo on Aen\oxv ”5 good 593 peso»: oouooEco on on once uoonm oneneoonaoe ooooemoe emom nooeoeo neeeeeeoeoe eoooooo eooeeeneoov .e oenee 38 l and 2). However, for individual hybrids this response was not equal under all environmental conditions (Table 1). Pioneer 3572 was the most sensitive to trifluralin injury. Plant response to the two levels of soil moisture was not significantly different when averaged over all other factors in the study on a percent of control basis (Table 1). However, individual hybrids did show significantly differing responses to the two soil moisture levels (Table 1). Shoot length of Pioneer 3320 was significantly less, shoot length of Pioneer 3747 and Pioneer 3572 the same, and shoot length of Pioneer 3541 greater at 48% soil FC than at 100% soil FC. Root fresh weight of Pioneer 3320 and Pioneer 3572 were significantly less, while Pioneer 3747 and Pioneer 3541 were the same at 48% soil FC compared to 100% soil FC. Significant interaction of hybrids with temperatures was also evident. Plant response to the two temperatures was significantly different when averaged over all other factors in the study both on a percent of control basis (Table l) and on a weight or length basis (Table 2). The 15 C treatment caused a greater reduction in the parameters measured than the 25 C treatment overall, although individual hybrids showed differing responses (Table 1). Pioneer 3320 was much more sensitive to trifluralin at 15 C than 25 C. Individual hybrid responses show significant interactions between trifluralin tolerance and soil moisture and temperature levels (Table 1). Thus Pioneer 3541 was also more sensitive to trifluralin at 15 C than 25 C, but only when the soil moisture was at 100% EC. Influence of W m alachlor. Visual corn injury from the 0.22 kg/ha trifluralin treatment was insignificant 20 days after 39 .umcu emcee. magi... mimosa on... an egg mm on» on ucouomueo mangoeuecmem no: one umuuoa c9560 o fies aboum uomuuo ceme— o 5:33 5530 o 553 mono: m e mo.o e oe.e e med e emm e ode mm onenenoaeon n me.o n mo; n :5 n oe.o n n: S on nooooo fie: n :5 e com e ems e me; e e.ge OS ooeueeoe :8 e eed n 8m n on... n 84 n fem we no nooooo 5e: n 3.5 n oe.m e me e em; e m.em Home n wee o Hem n 25 o mm; n oém meme e GS e eoe e me n me; n .......m omee bonnet. n 86 n Hem e emd e mo; e o.em eeee on nooooo fie: n ems o me; n me.o o eee o e4: mod emeeoneoeh ne med n He; no 35 n 35 n Tee mm... «o nooooo e eeo e Sm e 2.0 e em; e «.3 e 5e: Amueoaoo 5 SC :3 :3 2.3 6v oeotd e enact: owe—nose .5 ho t. neoh e. ho t. noon neocoe oneness. omonen on 3 none noonm oneneoooefl Sow oooooE :23:de oooooom eeomonen 500 50:03 How so 833%» can 49,2” 39.5er How 5:35.32» mo muoowmo see... 05. .N canon. 40 planting (Table 3). However, after 33 days, significant visual injury was evident (Table 3). Trifluralin injury on the corn shoot (Table 4) and root lengths and weights (Table 5) are more clearly demonstrated. Shoot and root lengths, fresh and dry weights of the controls are significantly greater than the 0.22 kg/ha trifluralin-treated plants (Tables 4 and 5). The addition of 112 kg/ha of phosphorus resulted in an increase in corn injury in the main effects data averaged across hybrids and alachlor treatments (Table 3). This phosphorus addition also caused heavier shoots, but lighter roots in the main effects data in Tables 4 and 5. Differences due to the addition of phosphorus appeared to be caused more by a phosphorus-alachlor interaction, rather than a phosphorus-trifluralin interaction based on the injury ratings shown in Table 3. The main effects data in Table 3 show that the 3.36 kg/ha rate of alachlor caused slight but significant visual injury to the corn and also significantly reduced the lengths and weights of corn shoots and roots (Tables 4 and 5). Pioneer 3747 was more tolerant than Pioneer 3572 to both trifluralin and alachlor (Tables 4 and 5). Chaotic variability. The 13 corn hybrids displayed a range of responses to trifluralin depending on the plant part or parameter examined (Table 6). The main effects data for this experiment are shown in Table 6 and the interaction data are found in the appendix (Table A3). Trifluralin at 0.45 kg/ha significantly reduced all growth parameters compared to the controls. The addition of phosphorus at 112 kg/ha resulted in significantly longer and heavier shoots and heavier roots than the controls. 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Effects to be compared effect of trifluralin Main MM 00 Ol‘ 00 .DM nnno \Ol‘ 29.9 a 29.7 a .0!!! H0 mm 00 .0“! 00 FIN .06 HI‘ N 112 Main effect of phosphorus Main effect of 47 noggoflfiflofifiofi Q‘NNQNn—lwn—llfimm M l‘l‘OWI‘l‘wl‘mOO \D a a a o a a a a a a a a a 0000000000000 BBoBBfifineBnoB 000mFMMNNKDNv—ll‘ O l I O O O O I I I I I O hmmmmhhhmmhmm 11.1%111111. 1 HNMFGSONONNI‘MH MNNNN comm MNNMM eiiieiieeoiie OMQFNO‘LfiNv-ULDCDO‘I‘ omwmmvmmmwewv o a a a a o o o o o a a a 0000000000000 138.11...Bsse OOSCDONQHQ‘OI‘I‘l‘O NHHNNHNNNHHHH o nnonn8nen88oo mNoHn-nn-noooommwmm HQ‘WQ‘N N0 NNN NNNNN NN hybrid the 5% level by the Duncan's multiple range test. b‘With the exception of SPX 49, a Migro hybrid, all are Pioneer hybrids. a Means within a column within a main effect group with a common letter are not significantly different at 48 phosphorus-trifluralin interaction in this experiment. There were significant growth differences among the hybrids in the absence of trifluralin (Table A3). The 0.45 kg/ha trifluralin treatment appeared to limit plant growth so that the differences among lines disappeared (Table 6). This could be interpreted as trifluralin causing the greatest growth inhibition to the hybrids showing the greatest growth . DISCUSSICN The degree of trifluralin tolerance displayed by a particular corn hybrid is dependent upon the environmental conditions under which the test was conducted. The first study showed that temperature was a more definitive modifier of trifluralin injury than soil moisture levels, but that both could be important depending on the response of a particular hybrid to specific conditions. This study tested only two levels of each factor, however, a much more complex situation exists in the field. MJCh of the trifluralin research reported in the literature deals with tests on only one variety or one plant species under one set of environmental conditions, or with field conditions that change from year to year. This may explain some of the confusing differences found in the literature concerning trifluralin effects on plants. By changing one factor, such as temperature from 15 C to 25 C, one could conclude that a hybrid was tolerant rather than susceptible to trifluralin. A change in the variety or hybrid used for the research could also result in a different conclusion. 49 The response of corn to the addition of both phosphorus and trifluralin showed no consistent pattern of interaction, which is in agreement with the report of Rahman et a1. (39). A more definitive case can be made for a phosphorus-alachlor interaction, a serendipitous discovery that needs to be more thoroughly researched. Bucholtz and Lavy (7) reported that both alachlor and trifluralin protected cats from photosynthesis inhibiting herbicides by inhibiting root growth, thereby reducing absorption of these herbicides. In the present study, alachlor reduced corn root and shoot growth and this effect was additive with trifluralin effects on corn. This conclusion is in agreement with the results of other researchers who tested for interactions of linuron, diuron, or dichlobenil with trifluralin (22, 28). Significant differences were found in the tolerance of a range of corn hybrids to trifluralin. Pioneer 3572 was sensitive to trifluralin while Pioneer 3747 was tolerant. This genetic variability is in agreement with the findings of Davis et al. (13), who found from 0 to 70% injury to a range of corn hybrids and inbred lines to 0.56 kg/ha trifluralin in a field study. In the present study, the trifluralin was incorporated throughout the total soil volume of the pot, thus the corn roots were not able to escape the herbicide. In the field, herbicide residues would likely be in the top two or three inches of soil only, thus corn roots could penetrate this layer and escape injury. Differences in tolerance of hybrids to trifluralin.were found in experiments with corn grown in pots when compared to field reports from Eli Lilly and Company. This difference would suggest two different mechanisms for tolerance - 50 physiological tolerance when the roots are confined to trifluralin-treated soil and morphological tolerance, or the ability to escape the herbicide by growing through and away from it, as in the field. Corn could have varying degrees of both types of tolerance. A study of the tolerance of 113 flax (giggly usitatissimum L.) lines to trifluralin revealed similar results (34). Field results and greenhouse results were significant. However, no consistent relationship was noted between field and greenhouse results. Different rates of trifluralin resulted in differential responses of the lines. Since differences were detected in all tests, the author suggested that field tolerance was a function of more than one mechanism. When the variability in tolerance of corn is combined with the specific responses of hybrids to trifluralin in different environmental conditions, a very complicated problem.of predicting field responses becomes apparent. At the same time, the potential for improvement is also apparent. If corn hybrids and inbred lines can be identified that have several mechanisms of trifluralin tolerance, perhaps a fully tolerant corn hybrid can be produced by crossing that will solve the problem of injury due to trifluralin car ry-over . 10. 11. 12. l3. 14. 51 LITERATURE CITED Adams, R. 8., Jr. 1965. Phosphorus fertilization and phytotoxicity of simazine. Weeds. 13:113-116. Andersen, R. N. 1964. Differential response of corn inbreds to simazine and atrazine. Weeds 12:60-61. Andersen, R. N. 1976. Control of volunteer corn and giant foxtail in soybeans. Weed Sci. 24: 253-256. Andersen, R. N. and J. L. Geadelmann. 1979. Varietal influence on control of volunteer corn with diclofop. Agric. Res. Results, Sci. Educ. Admin. U. S. Dep. Agric. ARR-NC-l. 8 pp. Andersen, R. N. and J. L. Geadelmann. 1982. The effect of parentage on the control of volunteer corn (Zea mays) in soybeans (Glycine max). Weed Sci. 30:127-131. Bode, L. E., C. L. Day, M. R. Gebhardt, and C. E. Goering. 1973. Prediction of trifluralin diffusion coefficients. Weed Sci. 21:485-489. Bucholtz, D. L. and T. L. Lavy. 1978. Pesticide interactions in cats (Avena sativa L. 'Neal'). J. Agric. Food Chem. 26:520-523. Bucholtz, D. L. and T. L. Lavy. 1979. Alachlor and trifluralin effects on nutrient uptake in cats and soybeans. Agron. J. 71: 24-26. Burnside, O. C. 1972. Tblerance of soybean cultivars to weed coupetition and herbicides. Weed Sci. 20:294-297. Burnside, O. C. 1974. Trifluralin dissipation in soil following repeated annual applications. Weed Sci. 22:374-377. Carlson, W. C. and L. M. Wax. 1970. Factors influencing the phytotoxicty of chloroxuron. Weed Sci. 18:98—101. Cathey, G. W. and W. E. Sabbe. 1972. Effects of trifluralin on fertilizer phosphorus uptake patterns by cotton and soybean seedlings. Agron. J. 64:254-255. Davis, J. L., J. R. Abernathy, and A. F. Wiese. 1978. Tolerance of 52 corn lines to trifluralin. Proc. South. Weed Sci. Soc. 31:123. Doll, J. D., D. Penner, and W. F. Meggitt. 1970. Herbicide and phosphorus influence on root absorption of amiben and atrazine. Weed Sci. 18:357-359. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 52 Fedorovskii, D. V. 1965. Methods for determination of some physical and moisture properties of soil used in field and pot—culture experiments. Pages 453-521 in Agrochemical Methods in Study of Soils. Academy of Sciences of USSR, V. V. Doluchaev Institute of Soil Science. Fink, R. J. 1972. Effects of tillage method and incorporation on trifluralin carryover injury. Agron. J. 64:75—77. Francis, T. R. and A. S. Hamill. 1980. Inheritance of maize seedling tolerance to alachlor. Can. J. Plant Sci. 60:1045-1047. Geadelmann, J. L. and R. N. Andersen. 1977. Inheritance of tolerance to Hoe 23408 in corn. Crop Sci. 17:601-603. Hammerton, J. L. 1967. Environmental factors and susceptibility to herbicides. weeds 15:330-336. Hardcastle,‘W. S. and R. E. Wilkinson. 1970. Bioassay of herbicide combinations with rice. weed Sci. 18:336-337. Helling, C. S. 1976. Dinitroaniline herbicides in soils. J. Environ. Qual. 5:1—15. Horowitz, M. and G. Herzlinger. 1973. Interactions between residual herbicides at low concentrations. weed Res. 13:367-372. Jacques, G. L. and R. G. Harvey. 1979. Dinitroaniline herbicide phytotoxicity as influenced by soil moisture and herbicide vaporization. WEed Sci. 27:536-539. Jacques, G. L. and R. G. Harvey. 1979. Persistence of dinitroaniline herbicides in soil. Weed Sci. 27:660-665. Kelly, S. 1949. The effect of temperature on the susceptibility of plants to 2,4-D. Plant Physiol. 24:534-536. Knake, E. L., A. P. Appleby, and‘W. R. Furtick. 1967. Soil incorporation and site of uptake of preemergence herbicides. weed Sci. 15:228-232. Lambert, S. M. 1966. The influence of soilemoisture content on herbicidal response. Weeds 14:273-275. Marriage, P. B. 1974. Lack of interaction of herbicides in annual grasses. Can. J. Plant Sci. 54:591-593. Marth, P. C. and F. F. Davis. 1945. Relation of temperature to the selective herbicidal effects of 2,4-dichlorophenoxyacetic acid. Bot. Gaz. 106:463-472. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 53 Mulder, C. E. G. and J. D. Nalewaja. 1978. Temperature effect of phytotoxicity of soil-applied herbicides. weed Sci. 26:566-570. mzik, T. J. and W. G. Mauldin. 1964. Influence of environment on the response of plants to herbicides. weeds 12:142-145. Narsaiah, D. B. and R. G. Harvey. 1977. Differential responses of corn inbreds and hybrids to alachlor. Crop Sci. 17:657-659. Niccum, C. E. 1970. variations in inbred and varietal tolerance to butylate, alachlor and propachlor. Proc. NOrth Cent. weed Control Conf. 25:33-35. Palafox de la Barreda, A. 1981. Selection of flax (Linum usitatissimum L.) lines for tolerance to EPTC and trifluralin as a source of breeding stock. Dissert. Abstr. B. 41:3974. Parka, S. J. and O. F. Soper. 1977. The physiology and mode of action of the dinitroaniline herbicides. weed Sci. 25:79-87. Penner, D. 1971. Effect of temperature on phytotoxicity and root uptake of several herbicides. weed Sci. 19:571-576. Penner, D. and D. Graves. 1972. Temperature influence on herbicide injury to navy beans. Agron. J. 64:30. Prasad, R. and G. E. Blackman. 1965. Studies in the physiological action of 2,2-dichloropropionic acid. I. The effects of light and temperature on the factors responsible for the inhibition of growth. J. Exp. Bot. 16:86-106. Rahman, A., B. E. Manson, B. Burney, and L. J. Matthews. 1975. Effects of phosphorus on the phytotoxicity and residual activity of trifluralin. Proc. 5th Asian-Pacific weed Sci. Soc. Conf., Tbkyo, Japan. pp. 162-166. Sagaral, E. G. and C. L. Foy. 1982. Responses of several corn (Zea ma 8) cultivars and weed species to EPTC with and without the antidote R-25788. weed Sci. 30:64-69. Selman, F. L. and R. P. Upchurch. 1970. Regulation of amitrole and diuron toxicity by phosphorus. ‘Weed Sci. 18:619-623. Sheets, T. J. 1961. Uptake and distribution of simazine by cat and cotton seedlings. weeds 9:1-13. Standifer, L. C. and C. H. Thomas. 1965. Response of johnsongrass to soil incorporated trifluralin. weed Sci. 13:302-308. 44. 45. 47. 48. 49. 50. 51. 52. 54 Stickler, R. L., E. L. Knake, and T. O. Hinesly. 1969. Soil .moisture and effectiveness of pre-emergence herbicides. weed Sci. 17:257-259. Stolp, C. F. and D. Penner. 1973. Enhanced phytotoxicity of atrazine-phosphate combinations. weed Sci. 21:37-40. Thompson, L., Jr., F. w. Slife, and H. S. Butler. 1970. Environmental influence on the tolerance of corn to atrazine. weed Sci. 18:509—514. Upchurch, R. P., G. R. Lebbetter, and F. L. Selman. 1963. The interaction of phosphorus with the phytotoxicity of soil applied herbicides. Weeds. 11:36-41. Vbstral, J. H., K. P. Buchholtz, and C. A. Kust. 1970. Effect of root temperature on absorption and translocation of atrazine in soybeans. weed Sci. 18:115-117. Walker, A. 1971. Effects of soil moisture content on the availability of soil applied herbicides to plants. Pestic. Sci. 2:56-59. wax, L. M. and R. Behrens. 1965. Absorption and translocation of atrazine in quackgrass. weeds 13:107-109. Wiebe, G. A. and J. D. Hayes. 1960. The role of genetics in the use of agricultural chemicals. Agron. J. 52:685-686. Wilson, H. P. and F. B. Stewart. 1973. Relationship between trifluralin and phosphorus on transplanted tomatoes. weed Sci. 21:150-153. CHAPTER3 DIFFERENTIAL TOLERANCE RESPONSESOFQDRNINBREDSANDHYBRIDS'IO 'Im INCORPORATICN DEPTHS OF TRIFLURALIN Abstract. Publically available corn (Egg EEX§.L-) inbred lines (108) and hybrids (5) were evaluated for variability in tolerance to trifluralin (a,_a,a,-trif1uoro—2,6-dinitro-_N_,N_-dipropyl-p-toluidine) in field studies in 1982 and 1983. Furthermore, the influence of depth of trifluralin incorporation into the soil on corn tolerance was examined. The treatments were 0 kg/ha trifluralin double disked to a 15 cm depth, 0.56 kg/ha trifluralin incorporated to a 7.5 cm depth with a Kongskilde danish tine seed bed conditioner, and 0.56 kg/ha trifluralin incorporated to a 15 cm depth by double disking. All plots received preemergence applications of 2.24 kg/ha of both simazine [2-chloro-4,6-bis(ethylamino)-§-triazine] and alachlor [2-chloro-2',6'-diethylfi§-(methoxymethyl)acetanilide]. Trifluralin visual injury to corn, plant stand, shoot height and percent stunting were evaluated. The inbred lines showed from 10 to 90 percent visual injury while the hybrids ranged from 5 to 30 percent visual injury in response to the trifluralin treatments. Incorporation of trifluralin to 7.5 cm resulted in stand reduction, while 15 an trifluralin incorporation resulted in reduction of shoot height and increased stunting. Early maturing inbreds showed greater injury than later maturing lines. Responses of the corn inbred lines and hybrids to 55 56 the two incorporation depths suggest at least two mechanisms for corn tolerance to trifluralin. INTRODUCTION Incorporation of trifluralin into the soil is recoumended to position the herbicide in proximity to germinating weed seeds and to prevent loss of herbicidal activity by photodeccmposition and volatilization (20). Depth of incorporation is one of the more impOrtant factors determining the degree of trifluralin root injury to plants (16). Cotton (Gossypium hirsutum L.) and soybean (Glycine E (L.) Merr.) lateral roots were inhibited to the depth of trifluralin incorporation (16). Below the trifluralin incorporation depth, cotton roots rapidly increased in number, suggesting a compensation effect (16). Corn root elongation is inhibited by trifluralin (9,13). Since corn roots remain in the upper 7.5 to 15 cm of soil until the plant has its seventh or eighth leaf (2), they are particularly sensitive to varying trifluralin incorporation depths and carry-over trifluralin residues. Trifluralin is relatively nonpersistent in soil, with dissipation of most of the biological activity occurring within six months in warm, humid climates (16, 17, 19). However, trifluralin persistence increases with decreasing soil temperature and moisture content and carry-over to subsequent crops can occur (10). Increasing depth of trifluralin incorporation increases persistence (16, 20). Trifluralin carry-over injury to corn grown after soybeans has been 57 reported (6) and the problem is likely to increase as conservation tillage becomes more widely used. Moldboard plowing places the trifluralin concentration below the zone of maximum.phytotoxicity which does not occur with conservation tillage (3, 4, 6, 12). Davis et a1. (5) tested 18 parental lines and 34 single crosses of corn for tolerance to 0.56 kg/ha trifluralin. The corn showed from 0 to 70 percent injury in response to the trifluralin. Differential responses of inbred and hybrid corn have been reported for several herbicides other than trifluralin (l, 7, 8, 15, 18). These findings support the conclusion reached in Chapter 2 of this thesis that significant differences in genetic tolerance to trifluralin exist in 13 corn hybrids. To test the hypothesis developed in Chapter 2 that there are at least two mechanisms involved in trifluralin tolerance, physiological tolerance and morphological tolerance, a field study with a wider range of genetic material was most appropriate. Shallow incorporation would allow corn inbred lines and hybrids with rapid downward root growth to escape injury quickly, while deep incorporation would select for inbred lines and hybrids with physiological tolerance. The objective of this study was to evaluate the tolerance of 108 corn inbred lines and 5 hybrids to trifluralin incorporated at two depths and determine if two mechanisms of trifluralin tolerance exist. 58 MATERIAISANDMEI‘HODS Field experiments were conducted in 1982 and 1983 at East Lansing, Michigan on a Capac loam (Aeric Ochraqualf fine-loamy, mixed, mesic) with a pH of 7.0 and 2.1% organic matter content. The 1983 location was in the same field, but a different area than 1982, to avoid potential trifluralin carry-over injury. The same corn inbred lines (108) and hybrids (5) were evaluated each year. Inbred seed was obtained in 1982 from the Inter-Regional Maize Inbred Evaluation (IRMIE) trial. The inbred lines were hand-pollinated at another location in 1982 to produce seed for 1983 experiments. A list of the inbred lines included in this study is given in Table l. A list of the hybrids can be found in Table 3. Treatments of 0 or 0.56 kg/ha trifluralin were applied to the soil surface with a tractor-mounted sprayer at 215 L/ha and incorporated 7.5 cm deep with one pass of a Kongskilde danish tine seed bed conditioner or 15 cm deep with two passes of a tandem disk. The control plots were disked twice to produce the same level of soil compaction. A topdressing of 168 kg/ha of triple super-phosphate was made each year prior to herbicide application. Carbofuran1 (2,3-dihydro-2,2-dimethy1-7-benzofuranyl methylcarbamate) was applied at 11.2 kg/ha over the row with a corn planter as the rows were marked prior to hand-planting for corn rootworm control. At the same time, a 10-20-20 analysis fertilizer was banded next to the row at 224 kg/ha in 1982 and 202 kg/ha in 1983. 1 mm (106) 59 The rows were 4.6 m long and 91 cm apart with 30 seeds per row. The rows were hand-planted on May 14, 1982 and May 12, 1983. weed control each year consisted of 2.24 kg/ha simazine plus 2.24 kg/ha alachlor applied preemergence. Anhydrous ammonia was applied during the growing season at 134 kg/ha in 1983. The study was irrigated by overhead sprinklers as needed both years. Plant stand, shoot height, injury, and stunting were evaluated at appropriate intervals each year. These measurements were used to calculate a trifluralin tolerance index for the inbred lines and hybrids. The equation used to calculate the index value was: Trifluralin Tblerance Index value 8 [100 X A.X (l-B) X C X (l-D) X E] where for 7.5 cm trifluralin incorporation depth: A = early season plant stand mean as a percent of control a stunting percent mean minus the control stunting percent mean B C early season shoot height mean as a percent of control D early season injury mean minus the control injury mean E = late season control plant stand percent mean or for 15 cm trifluralin incorporation depth: A = late season plant stand mean as a percent of control B = stunting percent mean minus the control stunting percent mean C = late season shoot height mean as a percent control D II late season injury mean minus the control injury mean E a late season control plant stand percent mean. 60 This index is an attempt to quantify injury for each inbred line or hybrid for comparison purposes. The experimental design was a split-plot with four replications. Data were subjected to analysis of variance and the means separated either by the Duncan's multiple range test or the LSD test. Complete data on the 108 inbred lines are too voluminous to be included, and are available from.the author. The inbred data are presented as the main effects, while the hybrid data presented are means and main effects. RESULTS Trifluralin at 0.56 kg/ha incorporated to a depth of 7.5 cm caused a significant reduction in inbred corn stand in both years (Table 2). Inbred stand reduction was greater in 1983 than 1982, likely due to hot and dry conditions. There was a tendency for the early maturing inbreds to show a greater reduction in stand fromtthe trifluralin treatment (Table 2). Trifluralin at 0.56 kg/ha incorporated to a depth of 7.5 cm also caused a significant reduction in hybrid corn stand in 1982 when averaged over all hybrids (Table 3). In 1983, the 15 cm deep incorporation of trifluralin caused a significant stand reduction compared to the control when averaged over all the hybrids, but was not different from the 7.5 cm incorporated treatment. Pioneer 3320 showed the greatest stand reduction in 1982 when averaged over all trifluralin treatments, while Pioneer 3747 had the least (Table 3). Trifluralin incorporated to 7.5 cm caused greater stand reduction of Table l. 61 Inbred corn line numbers and codes from the 1982 IRMIE entry list that were used in the trifluralin residue field studies. Relative Maturity, Early - Groupl3a Middle - Groqpy46 Late - Grogp 78 Line Line Line Number Code NUmber Code NUmber Code 1 cums-b 37 A6l9+ 77 373+ 2 C0109+ 38 A632+ 78 M017+ 3 A661 39 885 79 N28HT+ 4 A665 40 A634 80 B68 5 A666 41 A635 81 B75 6 A671 42 ‘A659 82 B76 7 NDlOO 43 A670 83 B77 8 ND240 44 M042 84 B79 9 ND24l 45 A¥499 85 BB4 10 ND245 46 AY562 86 M014W ll ND246 47 NY378 87 M020w 12 ND300 48 NY821 LERF 88 M040 l3 ND301 49 NYD410 89 M042 l4 ND376 50 NYRW3 90 N132 15 ND408 51 NYRWZO 91 N139 l6 ND474 52 NYRW23 92 N152 l7 PA326 53 RA405 93 OHSO9A 18 RA329 54 FR19 94 08514 19 RA373 55 CH9 95 PA91 20 EA374 56 CH581-13 96 RA762 21 CK52 57 CH586-12 97 PA871 22 CK64 58 CHS9l-36 98 RA872 23 CK69 59 CH592-46 99 FR16 24 CK75 60 CH593-9 100 ER20 25 OGll 61 CH606-1l 101 FR21 26 CG12 62 CH663-8 102 H60 27 CG13 63 BB7 103 H84 28 CG14 64 MS71 104 H93 29 CG15 65 M575 105 H98 30 CG16 66 MS76 106 H100 31 CGl7 67 M8200 107 H102 32 0618 68 H95 108 H103 33 CLl 69 H99 34 1672 70 W6QA+ 35 M874 71 w548 36 ‘W117HT+ 72 ‘W552C 73 w562 74 w570 75 CH753-4 76 CH671-28 ‘a‘Maturitybased on southern MiChigan growing conditions. b + represents a check entry, an established line used for maturity placement. 62 .«4 cm sows cwxumefluw Hm>o~ wa on» on an Ho>wa am on» on acouommwc mayonnamacmaw mum vacuum came so mums cm>am o How menu: a cm can; smegma «a ammo ems we» .mh msoum How nonwa mm so .ov uncum you nosed ca .MH macaw now mmcHH mm umpo pomMum>m mum memo: m e.mm h.o~ m.em o.o~ Aao.ov m.em m.em e.ma m.ma Amo.ov 0mg m.me m.em m.mw ~.oh e.ma om.o «w.m¢ am.h¢ a¢.vm «e.mm m.h mm.o H.mm e.mo m.mn H.mh e.ma oo.o CC uommuw 5m: H.¢m m.em ~.oh e.mh ms o.Hm e.mm m.mh m.mm we am.~v an.m¢ e.mo o.Hh ma e.ma mm.o «e.mw «m.me m.me m.me ms «H.5v «m.me «4N.mm «av.om we m.mw c.5w «ao.om naam.mm ma m.h mm.o m.mm m.me H.wh H.n> m5 w.on ~.Hn m.mh H.om we m.me c.5o m.ew mo.m> ma e.ma oo.o 3v 3; EB RENE: m umnmw< m wash «a wash a wash macaw sumac unusumouu muaucunz cofiumuomuoocH sadnesamwua mmaH mama .mwassum camau mama saw «was an mucmeummuu chamusauauu o» manna :aoo nausea no «macawmu sauna sense .N manna 63 .umou omens magmas m.emocso on» we Hgoa am on» no ”Eon—mums mflucmommmsmmm uoc mum nouuofl c9580 m 5H3 hummus fine no 3mm pan new» 55% a now now sump a Low meow: m a m.ea a... «.ma a m.ma n ha a... m.aa a «Am «my oooaao can: a m.Ha oo m.me one 0.0a as m.«m n m.ma oo «.qm oon m.«a as «.am «amm n m.me o m.aa oon a.oa oon a.oa n m.me o «.ma one m.Ha oon m.«a seam a «.mm a m.mm so s.sm a m.mm a m.mm o m.mm ops m.sm a m.mm o«aa n m.sa ooo m.me oon a.oa ooo m.ma n a.«a ooo «.mm one m.sa ooo m.ma «mam a a.am ooo m.ma as m.«m as m.Hm a a.«m ohm a.om am «.am am «.am mama a omsmsa a mass cases: 3983 mama a «Am 0. m.«a a am a m.mm a m.ma m «Am cc oooauo sass so m.ma as 0.0m on a.oa a «.sm as m.ma so a.«m so a.aa no a.mm «ama so «.ma a m.mm as m.ma am m.ma as m.ma as «.mm oaa m.ma ooo m.ma Hsmm n a.aa as o.om o m.«m a m.«m n m.ma am m.mm o a.ms ooo m.aa o«mm as H.aa so a.ma am m.ma o m.mm om e.ma no m.sm son m.ma as m.«m «mam a 4.Hm a m.mm as m.ma am a.am a m.mm a m.mm ohm o.om am m.mm mama 8 E E E oooaao saw: so as so m.m Hooosoo oooaao can: so as so m.m Hooosoo assess Aas\ma am.ov mucosoaoso smsaossmmoa Aas\mx am.ov osasomouo smwasssaaos ooosoam as mass m ossn «amH m.moaosom osoaa mama osa «ams sh mososooooo sasmossumoo oo moans»; sooo ooososm so omsommoo ossom ososm .m magma 64 ,Pioneer 3320 in 1982 than the 15 cm incorporation. In 1983, Pioneer 3320 and Pioneer 3747 were statistically the same in stand reduction, and both had greater stands than the other hybrids when averaged over all treatments (Table 3). Inbred corn lines did not show a significant shoot height response to trifluralin at either incorporation depth when expressed as a percent of control (Table 4). There was a tendency for a greater reduction in shoot height by the trifluralin at the 15 cm incorporation depth (Table 4). Shoot height was significantly reduced both years by the incorporation of 0.56 kg/ha of trifluralin to 15 cm when expressed as a percent of control and averaged over all hybrids (Table 5). Individual hybrids did not show significant responses to trifluralin at either incorporation depth. Inhibition of shoot height tended to decrease as the season progressed for the hybrids (Table 5) and the inbred lines (Table 4), suggesting recovery from early trifluralin injury. Trifluralin at 0.56 kg/ha at both incorporation depths significantly injured all inbred lines both years as measured by visual injury (Table 6). The early maturity group was injured the most of the three maturity groups and the injury persisted later in the season. Overall trifluralin injury decreased as the season progressed both years (Table 6). Visual injury to the corn hybrids by 0.56 kg/ha trifluralin at both incorporation depths was significant both years averaged over all hybrids (Table 7). Trifluralin incorporated at both depths visually injured the hybrids to the same degree in 1982. In 1983, 65 .mn macho now mocha mm no .mv macaw sou nonma ov .MH macaw now mocma mm uo>o ammono>c who memo: m m.nm q.o¢ e.mm m.mm Aao.ov a.a~ 5.0m H.om m.mm Amo.ov emu m.ms m.me m.me H.vo e.ma om.o m.ma m.mo m.mh m.mh m.m wm.o AMV uoomwo 5oz v.ah m.ma m.mb a.~m an b.5h e.mm a.on H.om av m.mn n.am m.me m.me ma e.ma om.o o.a> m.me m.me H.a> an a.aa m.me v.mh m.mh we c.5a m.mw m.en mo.oa ma m.m mm.o .nnnxsooosoo ao awn... .u.u1«ooosoo so as... Asov Amsxmxc w umnma<_ m mash ma wash mm wean .mmoum. cameo acmeumouu moasooaz soaoaooaoooss sasmosaaaoa mama .momosom osoaa mama ass «ams sh mucosoaooo sasaoosamoo oo moans sooo ooossa mo oosomaoo osmaos oooso ososm .o manna .umou omens mamauaaa m.emucso ecu an Hm>mm am on» on ucoaouuao_mmucm0mmacmam uoc mac aouumH,coeeoo a cum: hummus came so oump men how» co>am a now now mump a now memo: m. 66 n a.a.a a a.mm 0. 4.2. a mam E oooaao can: a a.am one «.ma so a.mm a a.«a so a.aa no a.«a «amm a m.«m ooo a.ma a «.am a a.ma no m.ea a m.am ammm a a.aa o m.aa ooo m.mm o m.mm a a.aa no «.ma o«mm m m.aa ooo m.ma ono m.«m a a.oa no m.me as m.ma «mam a m.aa on m.«a ohm m.«m a m.ma no a.aa so m.mm mvmm a ommmmma a mass saunas amocOam mama 0. a.ma a m.am a «.mm a m.«a Cb oooaao can: a a.«a no m.ma so a.aa a o.aa a m.ma a a.om «amm as m.mm no m.ma a a.mm a m.ma a a.va a m.mm ammm no m.ma no a.ma as «.am a 4.4m o «.aa a a.aa o«mm a m.mm as «.«m a m.mm a m.mm a a.oa a m.me «mam no a.aa n «.mm a m.mm a m.me a a.ma a m.ma msmm Ame aaooosoo mo 3!!!! 8 lllluaaooosoo ao my oooaao can: so ma so m.m oooaao can: so ma so m.m saunas «mamas am.ov mososuoooo saamosauaaa «mamas am.qa,osmsomooo saaoosaaaoa ooosoam ma sass «« osss «ama mama o5 «ama sa 3:838» saaSsaaaoo B ooaoeas Eco noocOam mo uncommon unmaoc uoocm acumm m.moaosoa oaoaa .m manna 67 .3 6 5a: sofas aa agoa ma on... on 5... 5:. coins aa omoo 93 on» ma ao>oa am on» no ucoaoumaao maucmoauacmam mam uooumo cams .ao 3mm :23 o How memo: o .aa. @330 now mosaa am no .3 @395 now monaa 0v .ma @530 now monaa am ago pomcumza mum memo: m v.vm a.0~ m.mm m.ma m.«m 5.0a Aa0.0v 0.aa m.ma m.ma 0.aa N.ha N.va Am0.00 oma «0.0a «£0.0N «am.mm «m.ma «am.0m «£5.0m 0.ma wm.0 0.0a «m.mm cam.~m «a.«a ««N.mm «a0.h¢ m.m 0m.0 a.a h.a a.~ a.N m.m 0.0 0.ma 00.0 E oooaao saw: 0.0a «m.vN «wm.¢m m.m «ab.0m nam.mm an m.ma «N.hN ««¢.mm N.Na «am.mm «am.mm ow «a¢.am tam.hm «am.hm ««¢.mm «am.mv atm.0v ma 0.ma 0m.0 0.va «m.mm «av.mm 5.0 «a0.mm «aa.mv ah 0.va «m.«m aaa.mm m.ma «am.m~ «am.vv 0v 0.ha ««¢.aN ««¢.am a«N.MN «am.m¢ n««0.am ma m.m 00.0 0.0 m.m 0.N m.0 m.v m.m an a.a a.a e.m a.0 m.m a.m 00 ¢.a a.a h.a m.e 5.0a M0.Na ma 0.ma 00.0 ahsasar a 3.35): ass Esau: a.« omomaa a omsmaa a mass ma ”Emma «a Nana. m ossa. mooom fimoo 2333 3335. 53303005 saaMucamauu. mama mama .ooaosom oaoaa mama 05... mama ca mucmsnmouu caaMusamauu on mocaa 500 9055 no uncommon manna: among .0 manna Visual injury response of Pioneer corn hybrids to trifluralin treatments in 1982 and 1983 field studies.a :4 ,3 8 5+ 1982 Julypl4 June 9 asgfia l Trifluralin treatments (0 Pioneer Trifluralin treatment (0.56 kgéha) hybrid Control Main effect Main effect 7.5 cm 15 cm Control 15 cm (3 injury) (% injury) 68 .02 03.0.8 I‘I‘I‘CDN HHOOQ‘ .012 (6.0.0 0mm00 mmmom I-I ssfinfi 0mmmm O l O C O ONFNI‘ QED—0.0 00000 00000 fiDMUU \DmMVII-l Q'NQI-nl‘ Fir-IF! 88888 000mm amass afim88 0mococo ONOCDM NNM H Main effect 4.0 a 5.0 a 0.0 b 15.5 a 19.0 a 0.3 b 1983 Pioneer hybrid August 1 Julyf6 f5 €003 (U (U MVO‘MM 1010500 88m 8m commcom MNQC‘SI‘ Hv-Ir-lr-lr-l 88888 000QO O O I D C MMI‘MI‘ 'U'U'U'B'U 000000 000H0 (U mmmm mmcsoom P‘NNOI‘ Fit-1H a..a§ eases (‘NNI‘N HNNHr-l B§a§§ OLDMIDO I I O O U LONWNC HHHH Main effect 5.5 b 14.8 a 0.3 c 11.3 b 18.5 a C 1.0 69 .unou omens mamauaoe m.emocca mcu an ao>oa am may on acouomuap haucMOauacmam no: man amuuoa coesco m spas uooumo same no mama new new» co>am a son now moan a mom memo: m a. a.m o m.e n 0.0 Amy uowmuo can: a m.m m m.m no m.a n 0.0 mamm m m.a no m.m n 0.0 n 0.0 aamm m m.m m m.m on m.a n o.o 0mmm m a.m m m.m n 0.0 n e.e mmmm m m.a no e.m n 0.o o 0.0 mamm mama J« ommmsa saunas umocoam mama muana oz mama 8 205.9: as 888 saw: so ma so a . m 85:8 332 «mn\mx am.00 ucmaumouu camousaMamw aoocoam mama .ha umnmd¢ 82.388 .5 manna 70 trifluralin incorporated to the 15 cm depth caused significantly greater visual injury than at the 7.5 cm depth or the control when averaged over all hybrids (Table 7). Pioneer 3320 displayed the most visual injury in 1982 when averaged over all the trifluralin treatments, but there were no significant differences among the lines in 1983. There was a tendency for reduced visual injury as the season progressed both years (Table 7). Inbred corn lines showed significant stunting with 0.56 kg/ha trifluralin incorporated to 15 cm in 1982 but not in 1983 (Table 8). The death of potential stunted plants due to the harsher environmental conditions in 1983, as shown in the lower stands in Table 2, possibly accounting in these results. Trifluralin at 0.56 kg/ha at both incorporation depths significantly stunted the hybrid corn both years when averaged over all hybrids (Table 9). A slight, but significant, increase in stunting occurred when trifluralin was incorporated to 7.5 cm compared to the 15 cm in 1982. Pioneer 3320 had the largest percent of stunted plants both years, when averaged over all trifluralin treatments (Table 9). Trifluralin tolerance index values for 1982 (Table 10) and 1983 (Table 11) show the wide tolerance range found in the 108 inbred lines. The relative rank of an individual inbred line varied between 1982 and 1983, apparently in response to the different environmental conditions of the two years. The tolerance index value of a given inbred line is dependent on the depth of trifluralin incorporation into the soil (Tables 10 and 11). .4. so soas oosoos ma aoooa aa oso on .4 so soaz cosmos ma poo» oma on» an aw>oa am on» on acouomuao maucooamacmam mum uoouum same so mono co>am m sou menu: 0 71 .am mooum now mocaa mm so .av mocha now wocaa ca .ma acoum now wmcaa am uo>o commuo>o can mean: a .mCaa ooanca anacoauumm may now monao>m on» on aamu no somehow cm can» whoa mums has» mucmam cuoo may no newcomm on» ma ooumoam>o was mcaucsum m m.em o.oa aao.o0 m.aa a.a amo.ov ems m.a «a.aa e.ma am.o a.a m.m m.m am.o m.a e.m m.ma oo.o 8 888 can: a.a m.m am m.m «40.Na 0v m.a o««a.«a ma a.aa am.o a.a m.a am a.a m.a as m.m a.a ma m.m am.o o.« om.« am m.a a.a aw m.« n«.« ma m.ma oo.o nuaooossoo man: unaooossoo man: asov aas\mxv mama .om panama «ama .ma omsmsa macaw, sumac ososooooo moausunz scauMHOQuooca caamacauaya «.moaosom oaoaa mama can mama ca mucmeumoau caanusamauu op mosaa choc counca mo oncomnoa moauccum .a magma 72 .omoo omsoo mamaoass m.aaosso oso my ao>oa mm oso om osoooaaao mau:80auacmam uoc mam amuuoa coseoo c spa: pooumo same so mono new new» co>am u now now mono a now memo: o .oaunmn anacoauumm may now ommuo>m may we aaau mm ucooaom cm can» mama mum: one» nonmam choc «nu mo scooumm on» no ooumcam>o was mcauccumm. a a.a a m.a a m.a amt oooaao saw: a a.a one a.a m m.aa mo m.a mamm n «.« on m.a ole «.4 o a.a ammm a «.m ooo «.m no a.aa oo m.a o«mm no m.m oua a.a m.m m.m ooo m.« «amm no m.m cum m.a oua m.a o a.a momm mama .0m banana panama amocOam 0. m.m a a.a. o m.a E oooaao same a m.m oon «.v n m.a o a.a «amm n «.« con m.« oon a.« no m.a ammm a a.a a m.«a a m.«a oo a.a o«mm n «.v on m.m n m.a mo a.a «mam n a.« no m.a a m.a no a.a mvmm nmv aav oooaao can: so ma so am». aooosoo saunas Nammmx am.ov osmsomooo saaaosawaoe ooosoam mama .ha um1m1¢ «.moaoooa oaoaa mama can mama ea mucmEDmoau eaaMucamauu ou moaabmn coco uoocOaA mo oncomnou meaucsum .m manna 73 Table 10. Ranking of tolerance index values of inbred corn lines that were treated with 0.56 kg/ha trifluralin at two incorporation depths in a 1982 field study.a Inbred Incorporation Inbred Incorporation Line Codeb depth 7. 5 cm Line Code depth 15.0 cm 19 PA373 0.21 19 PA373 1.49 5 A666 0.81 20 PA374 8.25 20 PA374 1.41 7 ND100 16.73 36 W117HT+C 5 . 64 98 PA872 17 . 15 18 RA329 6.04 8 ND240 18.95 57 C8586-12 8.43 9 ND241 19.69 16 ND474 9.17 18 RA329 21.30 15 ND408 9.60 29 CG15 21.90 68 H95 9.67 15 ND408 21.92 34 M872 9. 8 106 H100 22.64 48 NY821 LERF 10.09 36 wul7HT+ 23.36 35 M874 12.67 35 M874 24.44 99 FR16 12.75 45 A1499 25.26 50 NYRWB 13.09 16 ND474 25.90 24 CK75 13.51 47 NY378 26.30 25 CGll 13.69 88 M040 27.15 83 B77 13.86 5 A666 27.40 45 A3499 14.00 14 ND376 27.55 13 ND301 14.03 80 B68 27.62 29 0015 14.75 97 PA871 29.35 2 00109+ 15.27 69 H99 29.87 86 M014W’ 15.92 34 M872 30.75 91 N139 15.94 4 A665 31.10 100 FR20 15.98 13 ND301 31.52 30 CG16 16.66 90 N132 31.80 95 PA91 16.84 2 00109+ 32.02 69 H99 16.98 71 'w548 32.78 54 FR19 17.57 25 C011 33.26 1 CN105+ 17.75 102 H60 34.12 17 RA326 17.86 53 PA405 34.45 14 ND376 18 . 41 72 WSSZC 34 . 62 49 NYD410 18.49 10 ND245 34.83 55 CH9 18.63 24 CK75 34.86 27 0G13 18.72 37 A6l9+ 35.28 31 0017 19.03 31 CG17 35.42 59 CHS92-46 19.26 33 CLl 35.64 53 PA405 19.39 74 ‘W570 35.66 28 CGl4 19.69 84 B79 35.77 88 M040 19.95 108 H103 35.96 71 'w548 20.05 40 A634 36.70 41 A635 20.08 32 0G18 37.16 70 W64A+ 20.20 41 A635 37.17 42 .A659 20.87 28 0Gl4 37.45 74 Table 10. (Continued) Inbred Incorporation Inbred Incorporation Line Code depth 7.5 cm Line Code depth 15.0 cm 98 PA872 21.08 75 CH753-4 37.94 101 FR21 21.14 48 NY821 LERF 38.44 61 08606-11 21.22 95 PA91 38.77 39 885 21.68 73 ‘W562 38.84 26 CG12 21.83 86 M014W 38.90 52 NYRW23 22.27 27 0Gl3 38.93 7 ND100 22.30 62 C8663-8 38.96 102 860 22.41 44 M042 39.08 65 M875 23.64 11 ND246 39.28 32 CGl8 23.72 68 H95 39.45 73 ‘W562 24.51 83 877 39.48 107 H102 24.67 99 FR16 39.81 90 N132 24.79 101 FR21 40.13 9 ND241 24.91 26 CG12 40.47 64 M871 25.03 55 CH9 41.49 4 A665 25.37 107 8102 42.03 38 A632+ 25.38 54 FR19 42.52 105 H98 25.55 6 A671 43.25 97 PA871 25.64 3 A661 43.67 106 H100 25.81 60 CHS93-9 43.69 51 NYRWZO 25.84 67 M8200 43.70 72 w552C 26.27 49 NYD410 43.72 58 08591-36 26.78 94 08514 44.22 80 868 26.78 85 884 44.32 47 NY378 27.54 17 RA326 44.33 44 .M042 27.89 50 NYRW3 44.64 84 879 27.92 79 N28HT+ 45.06 79 NZBHTW 28.25 39 885 45.54 60 08593-9 28.45 105 898 45.68 33 CLl 28.48 38 .A632+ 45.75 63 887 29.23 77 873+ 45.76 76 C8671-28 29.76 87 M020W’ 46.29 75 CH753-4 29.87 91 N139 46.31 81 875 30.13 23 CK69 46.48 94 0H514 31.11 82 876 46.76 8 ND240 32.04 64 M871 46.78 78 M017+ 33.07 42 .A659 47.27 37 A619+ 33.31 51 NYRWZO 47.55 74 w570 34.77 100 FR20 47.56 6 A671 34.92 30 CG16 48.56 46 AY562 34.92 78 M017+ 49.17 103 884 34.97 12 ND300 49.41 40 A634 35.14 58 CHS91-36 49.52 77 873+ 35.51 59 08592-46 50.03 89 M042 35.75 46 AY562 50.28 75 Table 10. (Continued) Inbred Incorporation Inbred Incorporation Line Code depth 7 . 5 cm Line Code depth 15. 0 cm 11 ND246 36.18 22 CK64 50.33 82 876 36.29 81 875 51.09 22 CK64 36.84 56 C8581-13 51.97 56 C8581-13 36.88 52 NYRW23 51.98 96 RA762 37.13 89 M042 52.59 67 M8200 38.07 92 N152 53.19 66 MS76 38.70 96 RA762 53.98 23 CK69 39.15 1 CN105+ 54.08 10 NDZ45 39 . 86 70 W64A+ 58 . 06 43 A670 40.87 57 C8586-12 58.31 12 ND300 41.37 63 887 58.45 62 CH663-8 41.60 61 CHGO6-1l 59.54 108 8103 42.51 43 .A670 60.45 93 08509A 43.69 21 CK52 60.74 87 M020W 43.79 76 08671-28 61.13 104 H93 44.29 103 884 63.18 3 A661 47.16 65 M875 63.87 21 CK52 47.88 104 H93 64.39 92 N152 48.40 66 M876 65.17 85 884 60.72 93 OHSO9A 66.68 Main effect (3?) 24.99 40.29 a value 0 equals lowest ranking; the higher the value, the better the inbred line performed. b code is from the 1982 IRMIE trial. 0 + represents a check entry, an established line used for maturity placement. 76 Table 11. Ranking of tolerance index values of inbred corn lines that were treated with 0.56 kg/ha trifluralin at two incorporation depths in a 1983 field study.a Inbred Incorporation Inbred Incorporation Lineb CodeC depth 7.5 cm Line Code depth 15.0 cm 22 CK64 1.07 22 CK64 0.16 107 8102 1.75 107 8102 0.87 80 868 2.83 16 ND474 1.19 16 ND474 3.74 51 NYRWZO 2.66 74 8570 4.07 80 868 4.48 47 NY378 4.89 15 ND408 5.26 15 ND408 5.33 9 ND241 6.33 58 CH59l-36 6.12 74 '8570 6.91 23 CK69 6.41 47 NY378 9.69 57 08586-12 7.36 23 CK69 10.08 68 895 7.37 36 ‘W117HTWd 10.31 94 08514 7.47 8 ND240 10.61 51 NYRWZO 8.09 52 NYRW23 12.01 59 CHS92-46 8.38 7 ND100 13.39 88 8040 9.48 14 ND376 14.72 91 8139 9.93 10 ND245 15.53 8 ND240 10.68 18 RA329 16.53 86 M014W' 10.73 27 0013 16.99 13 ND301 11.45 12 ND300 17.26 97 PA871 11.77 11 ND246 18.13 60 CHS93-9 12.02 45 AY499 18.92 36 Wll7HT+ 12.11 17 PA326 19.80 56 08581-13 12.15 49 NYD410 19.93 24 CK75 12.29 61 C8606-ll 21.28 95 RA91 12.68 54 FR19 21.63 52 NYRW23 12.76 13 ND301 22.19 54 F819 13.23 34 M872 23.20 27 0013 13.65 86 M014W’ 23.35 11 ND246 14.14 42 A659 23.76 9 ND241 14.55 48 NY821 LERF 24.02 50 NYRWB 14.78 60 CHS93-9 24.18 61 08606-11 14.81 69 H99 24.28 89 M042 14.88 43 A670 24.61 7 ND100 15.75 24 CK75 24.71 96 PA762 16.53 57 08586-12 25.56 99 8816 16.54 19 RA373 25.86 92 8152 16.57 76 CHG71-28 25.88 90 8132 16.72 21 CK52 26.11 76 CH67l-28 16.88 25 0011 26.57 55 CH9 16.89 55 CH9 26.72 87 MOZOW’ 17.06 5 A666 26.82 48 NY821 LERF 17.90 90 8132 27.98 69 H99 18.05 6 A671 28.15 77 Table 11. (Continued) Inbred Incorporation Inbred Incorporation Line Code depth 7.5 cm Line Code depth 15.0 cm 5 A666 18.11 37 .A619+ 28.16 18 PA329 18.25 3 A661 28.33 45 A3499 18.27 59 CHS92-46 28.48 3 A661 19.04 88 M040 28.70 46 A1562 19.27 46 A¥562 29.42 106 H100 20.04 50 NYRW3 31.73 81 875 20.10 35 M874 32.34 83 877 20.14 106 H100 32.77 14 ND376 20.46 91 N139 32.82 25 0611 20.72 98 PA872 33.64 35 M874 20.77 97 EA871 34.16 17 PA326 20.90 56 08581-13 35.09 103 884 21.33 105 898 35.21 19 PA373 21.56 31 0617 35.42 2 00109+ 21.72 2 00109+ 35.46 1 CN105+ 21.78 41 A635 35.76 67 M8200 21.80 85 884 35.93 85 884 22.15 96 RA762 35.96 49 NYD410 22.27 87 M020W 35.99 75 08753-4 22.32 1 CN105+ 36.25 65 M875 22.72 95 PA91 36.63 29 0615 22.94 29 0615 37.25 53 RA405 23.49 89 M042 37.37 34 M872 24.37 53 PA405 38.33 101 FR21 24.87 99 FR16 38.55 100 FR20 25.42 58 08591-36 38.77 26 C612 26.72 82 876 38.85 78 M017+ 27.47 26 0612 39.35 12 ND300 27.51 77 873+ 39.48 10 ND245 28.76 33 0L1 39.51 44 M042 29.68 4 .A665 39.56 70 W64A+ 29 . 72 67 M8200 39 . 72 21 CK52 29.78 40 .A634 40.02 31 C617 29.91 94 08514 40.62 42 A659 30.32 101 FR21 40.81 84 879 30.39 92 N152 41.59 37 .A619+ 32.20 103 884 42.07 43 A670 32.42 83 877 43.27 38 A632+ 32.89 38 A632+ 43.51 104 H93 32.93 44 M042 43.61 93 08509A 33.15 68 H95 44.24 82 876 33.28 100 FR20 44.66 28 0614 33.29 32 0618 45.58 98 PA872 33.29 75 CH753-4 46.24 77 873+ 33.32 20 RA374 46.28 Table 11 . (Continued) Inbred Incorporation Inbred Incorporation Line Code depth 7.5 cm Line Code depth 15.0 cm 32 0618 33 . 56 63 B87 46 . 48 64 MS71 33 . 89 65 MS75 46 . 98 41 A635 34 . 41 30 C616 47 . 29 63 B87 34 . 48 104 H93 48 . 91 72 W552C 34. 93 28 C614 50. 25 62 08663-8 35 . 28 39 885 50 . 41 66 1676 35. 79 79 N28HT+ 50 . 81 105 H98 36 . 26 84 B79 50 . 88 30 0616 38 . 77 93 (11509A 51 . 02 40 A634 38 . 97 81 B75 51 . 50 33 cm 39 . 25 78 [4017+ 53 . 53 102 H60 40 . 88 73 W562 53 . 91 4 A665 41 . 19 62 08663-8 54 . 47 20 PA374 41 . 62 66 $876 54 . 83 6 A671 42. 59 102 H60 55. 02 39 885 47 . 91 72 W552C 55 . 07 79 N288T+ 51 . 94 64 M871 56 . 02 73 W562 52 . 32 70 W64A+ 56 . 16 71 W548 58 . 13 71 W548 58 . 52 Main effect (3?) 22.39 32.04 a Value 0 equals the lowest ranking; the higher the value, the better the inbred line performed. b Line 108, code 8103, did not germinate, therefore it could not be ranked. C Code is from the 1982 IRMIE trial. 5 + represents a check entry, an established line used for maturity placement. 79 vConsidering both incorporation depths, the 10 most trifluralin tolerant inbreds in 1982 were: CK52, N152, A670, H93, MS76, 884, 884, 08509A, ND300, and 08581-13. In 1983, the 10 most tolerant inbreds were: w548,‘W562, NZSHT, H60, 885, 08663-8, M871, CGl6, A665, and MS76. The 10 least trifluralin tolerant inbreds in 1982 were: PA373, PA374, A666, PA329, w117HT, ND408, ND474, PA872, 0615, and MS74. In 1983, the 10 least tolerant inbreds were: CK64, 8102, ND474, 868, W570, NYRW20, ND408, NY378, CK69, and ND240. Hybrid corn trifluralin tolerance index values also show a range, although not as large as for the inbreds (Table 12). The relative rank of a hybrid varied with 7.5 to 15 cm incorporation depth and with year. EHSCUSSION Environmental factors can modify the response of a corn hybrid to trifluralin, as described in Chapter 2 of this thesis. The growing season in East Lansing, Michigan in 1982 was the third coolest on record, while the 1983 season was the third warmest according to the 0.8. weather Bureau. The difference in environment between the two years complicates data interpretation. There was variability in tolerance of individual inbreds and hybrids from 1982 to 1983, but several important conclusions are evident. The corn lines tested displayed a wide range of tolerance to 0.56 kg/ha trifluralin. The hybrids showed from 5 to 30 percent visual injury, with an average of 16 percent. The inbreds ranged fran 10 to 90 percent visual injury (data not presented), with an average of 39 80 Table 12. Ranking of tolerance index values of Pioneer corn hybrids that were treated with 0.56 kg/ha trifluralin at two incorporation depths in 1982 and 1983 field studies.a 1982 Pioneer Incorporation Pioneer Incorporation hybrid depth 7.5 cm hybrid depth 15 cm 3320 37.81 3320 69.33 3572 52.20 3382 75.97 3382 59.01 3572 79.64 3747 61.78 3747 80.43 3541 80.95 3541 92.73 Main effect (if) 58 . 35 79 . 62 1983 3382 55.51 3541 57.29 3320 59.78 3382 57.44 3572 62.52 3572 59.26 3541 68.66 3747 63.86 3747 78.81 3320 67.27 Main effect (3?) 65 . 06 61 . 02 a‘Value 0 equals lowest ranking; the higher the value, the better the hybrid performed. 81 percent. This data agrees with Davis et al. (5), who found 0 to 70 percent injury in 52 corn lines. The visual injury decreased as the season progressed, indicating recovery from the trifluralin injury. Injury tended to persist longer with deeper incorporation, as the roots could not escape the herbicide as rapidly. Trifluralin also persists longer at deeper incorporation depths (16, 20). A small degree of injury was noted in the controls, which may be due to sensitivity of some inbreds and hybrids to the alachlor and simazine used as weed control agents (1, 7, 15). This injury should only be additive, as was found for alachlor in Chapter 2 and for other herbicides applied with trifluralin as reported in the literature (11, 14). The early maturity inbreds tended to show.more injury and a greater stand reduction than other maturity groups. This finding suggests that these inbreds may be inherently more sensitive to trifluralin as a group or that they stop root growth sooner and do not escape trifluralin as readily as other maturity groups. Differences in the two mechanisms of tolerance can be seen when comparing the response to the two depths of trifluralin incorporation. Trifluralin incorporation to 7.5108 reduced plant stand more than did 15 cm incorporation in the inbreds both years and the hybrids in 1982. However, the 15 cm incorporation treatment reduced shoot height as a percent of control more than the 7.5 cm incorporation treatment in the hybrids both years. The inbreds showed this tendency also, but due to a large standard deviation, the effects were not significant. The 15 cm trifluralin treatment also increased stunting in the inbreds in 1982. In 1983, many of the 82 plants that would have been stunted died due to environmental conditions, as reflected in the lower 1983 percent stand. Individual corn inbreds and hybrids responded differently to the trifluralin at the two incorporation depths, suggesting that two mechanisms are involved in tolerance. These differences can be seen nost clearly in the tolerance index values. It is an injury rating method that is less subjective than a visual injury rating. A.high tolerance index value for a corn inbred or hybrid to the 7.5 cm trifluralin incorporation depth would suggest tolerance due to rapid downward root growth, while a high tolerance index value to the 15 cm trifluralin incorporation depth would suggest a high physiological tolerance. Inbreds and hybrids low in both were very sensitive to trifluralin. While there were differences between incorporation depths with the tolerance index there were also differences between years. Based on results presented in Chapter 2, the differences between years were probably due to the differences in temperature between the 1982 and 1983 growing seasons. Hybrid corn tolerance to trifluralin was shown in Chapter 2 to increase or decrease as growing temperatures changed. Inbred corn lines appeared to respond in the sane manner. A.range of corn tolerance to 0.56 kg/ha trifluralin.was found in 108 inbreds and 5 hybrids. Individual inbreds and hybrids responded differently to the trifluralin incorporation depths of 7.5 or 15 cm. These responses suggest two separate mechanisms for trifluralin tolerance in corn. 10. 11. 12. 13. 14. 15. 83 LITERATURE CITED Andersen, R. N. 1964. Differential response of corn inbreds to simazine and atrazine. weeds 12:60-61. Anderson,'w. P. 1977. weed Science: Principles. west Publishing, New YOrk. 598 pp. Burnside, 0. C. 1972. Telerance of soybean cultivars to weed competition and herbicides. weed Sci. 20:294-297. Burnside, 0. C. 1974. Trifluralin dissipation in soil following repeated annual applications. weed Sci. 22:374-377. Davis, J. L., J. R. Abernathy, and A. F.‘Wiese. 1978. Tolerance of 52 corn lines to trifluralin. Proc. South. weed Sci. Soc. 31:123. Fink, R. J. 1972. Effects of tillage method and incorporation on trifluralin carryover injury. Agron. J. 64:75-77. Francis, T. R. and A. S. Hamill. 1980. Inheritance of maize seedling tolerance to alachlor. Can. J. Plant Sci. 60:1045—1047. Geadelmann, J. L. and R. N. Andersen. 1977. Inheritance of tolerance to Hoe 23408 in corn. Crop Sci. 17:601-603. Hacskaylo, J. and‘V. A. Amato. 1968. Effect of trifluralin on roots of corn and cotton. ‘weed Sci. 16:513-515. Helling, C. S. 1976. Dinitroaniline herbicides in soils. J. Environ. Qual. 5:1-15. Horowitz, M. and G. Herzlinger. 1973. Interactions between residual herbicides at low concentrations. weed Res. 13:367-372. Jacques, G. L. and R. 6. Harvey. 1979. Persistence of dinitroaniline herbicides in soil. 'Weed Sci. 27:660-665. Idgnowski, E. M., and E. G. Scott. 1971. Trifluralin and root growth. Plant Cell Physiol. 12:701-708. Marriage, P. 8. 1974. Lack of interaction of herbicides in annual grasses. Can. J. Plant Sci. 54:591-593. Narsaiah, D. B. and R. 6. Harvey. 1977. Differential responses of corn inbreds and hybrids to alachlor. Crop Sci. 17:657-659. 16. 17. 18. 19. 20. 84 Oliver, L. R., and R. E. Frans. 1968. Inhibition of cotton and soybean roots from incorporated trifluralin and persistence in soil. weed Sci. 16:199-203. Parka, S. J. and J. B. Tepe. 1969. The disappearance of trifluralin from field soils. weed Sci. 17:119-122. Sagaral, E. 6. and C. L. Foy. 1982. Responses of several corn (Zea mays) cultivars and weed species to EPTC with and without the antidote R-25788. weed Sci. 30:64-69. Savage, K. E. 1973. Nitralin and trifluralin persistence in soil. 'weed Sci. 21:285-288. Savage, K. E. and w. L. Barrentine. 1969. Trifluralin persistence as affected by depth of soil incorporation. ‘Weed Sci. 17:349-352. CHAPTER4 SUMMARY AND CINCLUS IONS Trifluralin1 carry-over injury to corn (Z_e_a_ _m_aE L.) is becoming a nore connon problem. Conservation tillage methods appear to increase the probability of carry-over injury. The occurrence of injury has been sporadic and unpredictable. The first study evaluated conditions under which trifluralin injury to corn was most likely to occur. In addition, a range of corn hybrids were tested to determine if genetic variability exists for trifluralin tolerance. Experinents were conducted in controlled environment chambers and greenhouses to test conditions that could modify trifluralin tolerance. Several corn hybrids were found to be more sensitive to trifluralin at 15 C than at 25 0. Soil moisture differences were not as strong a nodifier of trifluralin tolerance as temperature, but did interact with certain hybrids to alter their response to trifluralin. The addition of phosphorus and alachlor [2-chloro—2' ,6'-diethy1-_N_- (methoxymethyl)acetanilide] did not alter corn tolerance to trifluralin. Significant differences were found in genetic tolerance of corn to trifluralin within a group of 13 hybrids. The trifluralin tolerance of specific hybrids changed when they were exposed to different environnental conditions. 1 a,3,_a,-trifluoro-2,6-dinitro-N,N_-dipropyl-p-toluidine (TREFLAN) 85 86 Differences in trifluralin tolerance exhibited by particular hybrids from field reports and from the experiments above suggested two mechanisms of tolerance. The container experiments tested for physiological tolerance, since the roots could not escape the trifluralin residues. In the field, rapid downward root growth through a trifluralin layer to non-treated soil below could also provide morphological tolerance. A second study was conducted to test a larger range of corn genetic material for trifluralin tolerance and to attempt to determine if there are two:mechanisms contributing to trifluralin tolerance in corn. Field experiments were conducted in 1982 and 1983 with 108 corn inbred lines and 5 hybrids. Trifluralin was incorporated to 7.5 or 15 cm depths. Hybrids showed from 5 to 30 percent visual injury in response to the trifluralin, while the less vigorous inbred lines showed from 10 to 90 percent visual injury. Early maturing inbreds were found to be injured more than later maturing lines. Shallow trifluralin incorporation reduced stand, while deep incorporation reduced shoot height and increased stunting. Individual inbred lines and hybrids also responded differently to the two incorporation depths. Some inbred lines and hybrids displayed tolerance suggesting rapid root growth while others displayed tolerance suggesting high physiological tolerance. Environmental differences between the 1982 and 1983 growing seasons also modified individual inbred line and hybrid response to trifluralin. In conclusion, the research indicated that many factors interact to influence the expression of corn tolerance to trifluralin carry-over residues. Such factors as soil temperature and moisture, 87 trifluralin residue amount and depth of incorporation, corn maturity, and the amount of genetic tolerance due to physiological and/or morphological traits can alter the manner in which corn responds to trifluralin. ‘With so many factors involved, accurate predictions of trifluralin carry-over on a field by field basis would be very difficult. However, the inbred lines identified as being very sensitive to trifluralin can be avoided for use in producing hybrids. The best solution to the problem of trifluralin carry-over would be to utilize the genetic variability identified in these studies to breed for trifluralin tolerance in corn. Inbred lines have been identified that have good tolerance due to one or both mechanisms. By using these inbred lines to produce hybrids, the potential exists to produce a hybrid that will tolerate trifluralin carry-over residues with no injury. This advance should be readily achievable, since several hybrids tested showed little injury to 0.56 kg/ha trifluralin. In addition, the lines with rapid downward root growth may produce hybrids with more stress tolerance, due to early deep rooting. If corn trifluralin tolerance could be advanced to a level where trifluralin could be safely used as a weed control agent, the cost of corn production would decrease and problem grass weeds could be controlled cheaply and effectively. APPENDIX hybrids.a Root fresh wt dry wt (9) (9) ioneer (301' n wt (9) dry Shoot (9) fresh wt (cm) length l moisture level, and temperature on four P 1n, 801 (C) Temperature (% field capacity) hybrid moisture teraction of triflural Pioneer Soil 1n ( kg/ha) The Trifluralin Table A1. Effects compared to be 88 0 (DO) TO) 0) .8811.81.181.§8188.88881 mmmmmmmoamomomhwwm 101‘th NQMWInMV‘DMI‘VI-DMO‘MWMGMVMCMF I O D I O 00000H000000000000000H00 'OAEPI-I 'E a: 4:10.}: 5}" (P 5.21.0"?! 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