Turfgrass managers apply nonselective herbicides to control winter annual weeds during dormancy of warm-season turfgrass. Zoysiagrass subcanopies, however, retain green leaves and stems during winter dormancy, especially in warmer climates. The partially green zoysiagrass often deters the use of nonselective herbicides due to variable injury concerns in transition and southern climatic zones. This study evaluated zoysiagrass response to glyphosate and glufosinate applied at four different growing degree day (GDD)-based application timings during postdormancy transition in different locations, including Blacksburg, VA; Starkville, MS; and Virginia Beach, VA, in 2018 and 2019. GDD was calculated using a 5 C base temperature with accumulation beginning January 1 each year, and targeted application timings were 125, 200, 275, and 350 GDD5C. Zoysiagrass injury response to glyphosate and glufosinate was consistent across a broad growing region from northern Mississippi to coastal Virginia, but it varied by application timing. Glyphosate application at 125 and 200 GDD5C can be used safely for weed control during the postdormancy period of zoysiagrass, while glufosinate caused unacceptable turf injury regardless of application timing. Glyphosate and glufosinate exhibited a stepwise increase to maximum injury with increasing targeted GDD5C application timings. Glyphosate applied at 125 or 200 GDD5C did not injure zoysiagrass above a threshold of 30%, whereas glufosinate caused greater than 30% injury for 28 and 29 d when applied at 125 and 200 GDD5C, respectively. Likewise, glyphosate application at 125 or 200 GDD5C did not affect the zoysiagrass green cover area under the progress curve per day, whereas later applications reduced it. Glyphosate and glufosinate caused greater injury to zoysiagrass when applied at greater cumulative heat units and this was attributed to increasing turfgrass green leaf density, because heat unit accumulation is positively correlated with green leaf density. Accumulated heat unit-based application timing will allow practitioners to apply nonselective herbicides with reduced injury concerns.

Field studies were conducted in North Carolina to determine the critical period for Palmer amaranth control (CPPAC) in pickling cucumber. In removal treatments (REM), emerged Palmer amaranth were allowed to compete with cucumber for 14, 21, 28, or 35 d after sowing (DAS) in 2014 and 14, 21, 35, or 42 DAS in 2015, and cucumber was kept weed-free for the remainder of the season. In the establishment treatments (EST), cucumber was maintained free of Palmer amaranth by hand removal until 14, 21, 28, or 35 DAS in 2014 and until 14, 21, 35, or 42 DAS in 2015; after this, Palmer amaranth was allowed to establish and compete with the cucumber for the remainder of the season. The beginning and end of the CPPAC, based on 5% loss of marketable yield, was determined by fitting log-logistic and Gompertz equations to the relative yield data representing REM and EST, respectively. Season-long competition by Palmer amaranth reduced pickling cucumber yield by 45% to 98% and 88% to 98% during 2014 and 2015, respectively. When cucumber was planted on April 25, 2015, the CPPAC ranged from 570 to 1,002 heat units (HU), which corresponded to 32 to 49 DAS. However, when cucumber planting was delayed 2 to 4 wk (May 7 and May 21, 2014 and May 4, 2015), the CPPAC lasted from 100 to 918 HU (7 to 44 DAS). This research suggested that planting pickling cucumber as early as possible during the season may help to reduce competition by Palmer amaranth and delay the beginning of the CPPAC.

Experiments were conducted to examine the effects of low soil moisture on yellow nutsedge emergence in relation to thermal and chronological time and test the ability of thermal models generated previously to predict emergence under water stress. Unsprouted tubers from California and Arizona were planted in pots, buried at field sites in California and Arizona, and subjected to wet or dry treatments. Pots were monitored weekly to determine date of emergence and number of emerged shoots. The California genotype emerged 47 to 61 days after planting (DAP) in the dry treatment and 33 to 49 DAP in the wet treatment, depending on planting site. The range for the Arizona genotype was 51 to 76 DAP in the dry treatment and 43 to 61 DAP in the wet treatment. Days and degree-day intervals to first emergence differed between irrigation treatments and planting sites but interactions were not significant. All models were accurate in predicting emergence dates for genotypes in the wet treatment at the California site, while emergence in Arizona was underestimated by 9 d. Tubers subjected to the dry treatment needed a higher number of accumulated degree-day units before emergence occurred and had fewer emerged shoots as compared to the wet treatment. Degree-day models generated for yellow nutsedge under optimal conditions lack sufficient robustness to be predictive under water stress conditions.

We examined the relationship between temperature and emergence of yellow nutsedge tubers to generate predictive models for the arid southwestern United States. Field experiments were conducted in California and Arizona to obtain phenological and temperature data needed to generate degree-day models. The effect of air temperature on emergence was tested with available programs using four methods to calculate degree-days (single sine, double sine, single triangle, and double triangle). Separate models were tested for each genotype examined (Arizona source and California source) as no one model was a good predictor of emergence when data were pooled. Results indicate that there is year to year variation in model accuracy but predictions of date of emergence can be made to within 2 d of actual emergence. This information can be used to schedule cultivations to reduce early yellow nutsedge competition in the field.

Velvetleaf has been a major concern of Southern cotton growers, yet information on its competitiveness and seed production in cotton is lacking. Experiments were conducted in 1997 and 1998 at the Central Crops Research Station in Clayton, NC, to evaluate density-dependent effects of velvetleaf interference and seed production dynamics in conventional tillage cotton. Velvetleaf at densities of up to 3.5 plants m−1 of row did not influence cotton height until at least 4 wk after planting. Velvetleaf height increased as plant density increased throughout the season in 1997, but it was not affected until 9 wk after planting in 1998. Because of differences in environmental conditions, velvetleaf and cotton achieved maximum height later in 1998 than in 1997; however, velvetleaf seed production and cotton yields were higher in 1998 than in 1997 regardless of velvetleaf density. Velvetleaf density had no effect on the fresh weight, dry weight, and stem diameter of velvetleaf plants in 1997. But in 1998, all these parameters decreased significantly with increasing velvetleaf density. Velvetleaf seed production in 1998 was nearly twice that in 1997. Averaged over velvetleaf densities, the greatest number of seed were produced between nodes 6 and 20 in 1997 and between nodes 1 and 10 in 1998. In both years, cotton yield loss increased with velvetleaf density. Maximum yield loss was 84% at 3.5 velvetleaf plants m−1 of row. Yield losses of 5 and 10% were caused by 0.2 and 0.4 velvetleaf plants m−1 of row (1,930 and 4,110 plants ha−1), respectively, in 1997 and by 0.03 and 0.08 velvetleaf plants m−1 of row (360 and 850 plants ha−1), respectively, in 1998. To understand better the applicability of these results, we hypothesized that environmental variation caused differences in measured responses between 1997 and 1998. Therefore, kriging methods were used to fit correlations between observed rainfall and growing degree days (GDD) each year at the experiment site. Results based on climate data from 4 yr at 110 sites indicated that inference space was higher for GDD than for rainfall. The conditions observed at the experiment site in 1997 were deemed most appropriate for the recommendations made in the surrounding area.

Knowing when weed species are likely to emerge can aid in developing effective integrated weed management programs. When using nonresidual herbicides such as glyphosate for weed control, treatment timing is critical. This study characterized the emergence patterns of common lambsquarters, common sunflower, common waterhemp, eastern black nightshade, ivyleaf morningglory, shattercane, and woolly cupgrass in soybean, in relation to common glyphosate application timings. Approximately 90% or more of common lambsquarters, common sunflower, and common waterhemp seedlings emerged before the end of May, both in 2000 and 2001. Both ivyleaf morningglory and shattercane emerged from late April to mid-August, allowing these species to avoid glyphosate applications timed to prevent early-season weed competition. Avoidance through periodicity in emergence underscores the importance of integrating multiple tactics to ensure that difficult to manage weeds are not selected for in this management system.

The viability of freshwater turtle populations is largely dependent on the survivorship of reproducing females but females are frequently killed on roads as they move to nesting sites. Installing artificial nesting mounds may increase recruitment and decrease the risk of mortality for gravid females by enticing them to nest closer to aquatic habitats. We evaluated the effectiveness of artificial nesting mounds installed in Algonquin Park, Canada. Artificial mounds were monitored for 2 years to determine if turtles would select them for nest sites. We also simulated turtle paths from wetlands to nests to determine the probability that females would encounter the new habitat. A transplant experiment with clutches of Chrysemys picta and Chelydra serpentina eggs compared nest success and incubation conditions in the absence of predation between artificial mounds and natural sites. More turtles than expected used the artificial mounds, although mounds comprised a small proportion of the available nesting habitat and the simulations predicted that the probability of females encountering mounds was low. Hatching success was higher in nests transplanted to artificial mounds (93%) than in natural nests (56%), despite no differences in heat units. Greater use than expected, high hatching success, and healthy hatchlings emerging from nests in artificial mounds suggest promise for their use as conservation tools.