Clark S. Throssell

2,4-D Rate Response, Absorption, and Translocation of Two Ground Ivy (Glechoma hederacea) Populations'

Ground ivy is a stoloniferous, perennial weed that persists in lawn turf. With the widespread use of 2,4-D on turf sites, the development of 2,4-D–tolerant ground ivy is a possibility. Ground ivy populations showed a highly variable response to foliar 2,4-D application. Ground ivy from Nebraska (NE) was tolerant to 2,4-D, whereas Ohio (OH) ground ivy was susceptible. The 2,4-D–susceptible OH population absorbed 37% more foliar-applied 14C–2,4-D than the 2,4-D–tolerant NE population. Although OH and NE populations total translocation of applied 14C was similar and averaged 5%, the OH population translocated 42% more toward the apical meristem of the primary stolon than the NE population, primarily because of the OH populations higher 14C–2,4-D absorption. The variation in response to 2,4-D found between these two populations occurred after exposure of roots to 2,4-D, but the effect was less pronounced. These results suggest that the difference in foliar uptake may partially contribute to differences in response to 2,4-D between these two populations. Likewise, differences in acropetal translocation may contribute to the differential sensitivity of 2,4-D–tolerant and –susceptible ground ivy populations. Nomenclature: 2,4-D; ground ivy, Glechoma hederacea L. #3 GLEHE. Additional index words: Dose response, ecotype, herbicide, resistance, root uptake, tolerance. Abbreviations: DAT, days after treatment; HAT, hours after treatment; LCO, lawn care operators; NE, Nebraska; OH, Ohio.

Ground Ivy (Glechoma hederacea) Populations Respond Differently to 2,4-D or Triclopyr

Ground ivy is an invasive, perennial, broadleaf weed common in turf sites. A recent survey of lawn care professionals suggests ground ivy populations respond differently to herbicides. Our study was conducted to determine the variation in response among and within ground ivy populations to 2,4-D or triclopyr application. Ground ivy populations were sampled from nine sites in the United States and Canada. Leaf width, petiole length, and internode length varied by population by as much as 31, 36, and 45%, respectively. In a greenhouse study, applying 4.5 kg/ha 2,4-D or 0.9 kg/ha triclopyr to all populations resulted in a phytotoxic response that varied according to population by as much as 47% for 2,4-D and 31% for triclopyr. Random-amplified polymorphic DNA analysis identified 52 genotypes in the nine populations, and these genotypes varied in response to 2,4-D application in some populations. Difficulty in control of ground ivy with 2,4-D or triclopyr may be because of the presence of ecotypes and biotypes. Nomenclature: 2,4-D; triclopyr; ground ivy, Glechoma hederacea L. #3 GLEHE. Additional index words: Biotype, ecotype, herbicide screening, resistance, tolerance. Abbreviations: DAT, days after treatment; FW, fresh weight; LCO, lawn care operator; RAPD, random-amplified polymorphic DNA; RFW, regrowth fresh weight.

Turf Safety to Dithiopyr of Newly Seeded Kentucky Bluegrass (Poa pratensis)1

Abstract: Competition from large crabgrass is often responsible for the establishment failure of spring-seeded cool-season turfgrasses. The objective of this study was to determine how soon after seedling emergence dithiopyr could be applied without causing unacceptable damage to Kentucky bluegrass. Dithiopyr at 0.28 and 0.56 kg/ha was applied at various times prior to seeding and after emergence of Kentucky bluegrass in the field and greenhouse. Dithiopyr damaged Kentucky bluegrass seedlings in the greenhouse when applied earlier than 10 d after emergence (DAE) at 0.28 kg/ha and 14 DAE at 0.56 kg/ha. In the field study with heavy large crabgrass infestation, no significant phytotoxicity or long-term thinning occurred with any application of dithiopyr after emergence of Kentucky bluegrass. Dithiopyr applied as early as 3 DAE improved cover of Kentucky bluegrass by reducing competition from large crabgrass. When seeding is done early in spring before large crabgrass germination, dithiopyr could be applied at 0.28 kg/ha 10 DAE or at 0.56 kg/ha 14 DAE without risk of injury. Dithiopyr could be applied as early as 3 DAE on sites with heavy large crabgrass pressure or to late spring seedings when large crabgrass is germinating because the risk of turf thinning is warranted given the benefit of reduced large crabgrass competition for the desired turf. Nomenclature: Dithiopyr; large crabgrass, Digitaria sanguinalis (L.) Scop. #3 DIGSA; Kentucky bluegrass, Poa pratensis L. ‘America’, # POAPR. Additional index words: Preemergence herbicides. Abbreviations: DAE, days after emergence; POST, postemergence; PRE, preemergence; WAE, weeks after emergence.