Base water potential for germination of radiata pine and buddleia seeds adjusts in response to time, seed-bed water potential and supra-optimal temperatures

Hydrothermal germination models are mathematical models which predict germination time of seeds for a specified seed-bed temperature (T) and water potential (Ψ). In this paper, the commonly observed decline in seed germination at supra-optimal temperatures is investigated by fitting a hydrothermal time model to germination data from two unrelated plant species (Buddleia davidii and Pinus radiata). For both these species, reduced germination rates and germination percentages above optimum temperatures (20°C and 25°C for P. radiata and B. davidii, respectively) were successfully modelled by an upward shift in the seeds' base water potential (Ψb) during germination. The upwards shift in Ψb was shown to be an asymptotic function of time to germination, but with the rate increased by higher temperatures and moister seed-bed conditions. The physiological and ecological implications of this proposed model of the observed decline in germination at supraoptimal temperatures are discussed. Keywords: hydrothermal, model, Pinus radiata, Buddleia davidii

The impact of defoliation on nitrogen translocation patterns in the woody invasive plant, Buddleia davidii

The influence of defoliation on nitrogen (N) re-translocation and the source for N remobilisation by the invasive shrub, Buddleia davidii Franch. (buddleia) was determined. Eighty plants were grown over two growing seasons, and half were repeatedly defoliated by removing 66% of their leaf area. During the second season, the N supply was labelled with 15N (10 atom% enrichment), to distinguish the use of stored N (unlabelled) from N taken up by roots (labelled) for growth. Defoliation significantly decreased root (39%) and total biomass (26%). Old leaves were the main source of N for remobilisation which was accelerated and increased (by 50% in the second season) in response to defoliation. In spring, root uptake of N increased by 57% in defoliated plants. Thus, defoliation induced changes in N remobilisation and uptake as compensatory growth increased the demand for N. Continued leaf removal decreased the pool of stored N and caused a significant decline in biomass production, especially in roots (39%) and flowers (31%). This has important implications for the efficacy of defoliation as a control measure, as smaller roots suggest a reduced capacity for uptake of nutrients from the soil and reduced flower production may assist in reducing the invasive spread of the species. These findings clearly show that, although the success of B. davidii is associated, in part, with efficient remobilisation of N from storage, this advantage can be overcome by continued defoliation.

(93) Evaluating the Effectiveness of Prohexadione-Ca as a Plant Growth Retardant on Buddleia, Dianthus, Eupatorium, and Lilium

Prohexadione-Ca (ProCa) is a relatively new plant growth regulator (PGR) that inhibits internode length in rice, small grains, and fruit trees. However, little is known about its efficacy and potential phytotoxicity on floriculture crops and how it compares to other commercially available PGR chemicals. The effects of two foliar spray applications (2 weeks apart) of ProCa (500, 1000, or 2000 ppm), paclobutrazol (30 ppm), or a tank mix of daminozide plus chlormequat (2500 and 1000 ppm, respectively) were quantified on Dianthus barbatus L. `Interspecific Dynasty Red', Ageratina altissima R. King & H. Robinson (Eupatorium rugosum) `Chocolate', Lilium longiflorum Thunb. `Fangio', and Buddleia davidii Franch. `Mixed.' All plants were forced in a glass-glazed greenhouse with a constant temperature setpoint of 20 °C under a 16-h photoperiod. Two weeks after the second spray application of ProCa at 500, 1000, or 2000 ppm, plant height of Dianthus and Lilium was shorter than control plants by 56%, 60%, and 65% and by 6%, 26%, and 28%, respectively. However, ProCa bleached and reduced the size of Dianthus flowers. ProCa at 2000 ppm and daminozide plus chlormequat were effective at controlling the height of Eupatorium (64% and 53% reduction, respectively); however, leaves of Eupatorium were discolored and showed symptoms of phytotoxicity 1 week after the first ProCa application. Only daminozide plus chlormequat were effective on Buddleia. ProCa is an effective PGR for most of the crops we tested; however, its discoloration of red flowers and foliage may limit its application for commercial use.

Using Acaricides in Combination with Phytoseiulus persimilis Athias-Henroit to Suppress Tetranychus urticae Koch Populations

Acaricides are often used to suppress populations of the twospotted spider mite, Tetranychus urticae Koch. Problems associated with acaricide use have led some ornamental producers to incorporate releases of the predaceous mite Phytoseiulus persimilis Athias-Henriot into pest management programs. Our objective was to determine if acaricides could be used with P. persimilis to suppress T. urticae. Ten acaricides were tested against T. urticae on infested Buddleia × davidii ‘White Profusion’ cuttings. Abamectin, chlorfenapyr, Gowan 1725, horticultural oil and neem oil suppressed T. urticae populations 3, 7 and 14 d after application. Bifenthrin suppressed T. urticae populations 7 and 14 d after application, and hexythiazox suppressed T. urticae populations 14 d after application. Azadirachtin, pyridaben and spinosad did not suppress populations. Acaricide applications followed by release of P. persimilis reduced T. urticae populations, but suppression with acaricides followed by predatory mite release was not significantly greater at all times than with acaricide applications alone, or with predator releases without previous acaricide application. Results demonstrate that efficacy is variable among the acaricides tested and that acceptable levels of T. urticae suppression can be achieved with acaricides and P. persimilis.

Time of Pruning Effects on Cold Hardiness of Butterfly Bush

A study was conducted over a two-year period to determine how time of pruning affects cold hardiness of butterfly bush (Buddleia davidii (Franchet) ‘Royal Red’). Plants were pruned in November, January, or March, and pruned and non-pruned plants were exposed to six freezing temperatures two weeks after pruning treatments were applied. In addition, plants pruned in previous seasons were included in subsequent freezing treatments. Plants were rated for injury 2 or 3 weeks after treatment (WAT), and for mortality at 6 WAT. In fall 2001, at −6C (21.2F), injury ratings were higher in pruned than non-pruned plants. At all other treatment temperatures, injury to pruned and non-pruned plants was similar. In fall 2001, mortality increased with decreasing temperatures and was higher in pruned plants than in non-pruned controls, regardless of treatment temperature. In winter and spring 2002, injury and mortality increased with decreasing temperatures, but were not affected by pruning treatments. In fall 2002, temperature decreased as injury rating and mortality increased, regardless of pruning treatment and pruned plants had a higher injury rating and mortality than non-pruned across all temperatures. In winter 2003, injury rating and mortality increased with decreasing temperatures and pruning did not affect either. Spring 2003 plants, which had deacclimated prior to freeze treatment, were not affected by pruning or freezing treatments.

Drought Stress Increases Densities but Not Populations of Two-spotted Spider Mite on Buddleia davidii `Pink Delight'

Two experiments were conducted to determine the effect of drought stress on the susceptibility of Buddleia davidii Franch. `Pink Delight' to the two-spotted spider mite (Tetranychus urticae Koch). In the first experiment, drought stress was imposed by withholding water until predawn xylem pressure potential fell below -1 MPa. Shoot growth was 75% less in drought-stressed than in nonstressed plants. Mite population densities were not affected, but noninfested leaf area was 14% higher, and degree of mite damage was lower, in nonstressed plants. Evidently, the greater amount of new growth in nonstressed plants leads to lower spider mite densities by diluting populations. In a second experiment, nonstressed B. davidii `Pink Delight' plants were watered every 1 to 2 days and drought-stressed plants were watered every 3 days. Spider mite populations were monitored by sampling newly expanded and mature foliage. Mite populations on mature foliage were not affected by stress, but stressed plants grew less and had larger spider mite populations on their newly expanded foliage than did nonstressed plants.

Effects of Dolomitic Lime on Growth and Nutrient Uptake of Buddleia davidii ‘Royal Red’ Grown in Pine Bark

Buddleia davidii Franch. ‘Royal Red’ was grown in pine bark amended with 0.0, 2.4, 4.7 or 9.5 kg/m3 (0.0, 4.0, 8.0, or 16.0 lbs/yd3) dolomitic lime. Growth characteristics responded quadratically to dolomitic lime with those plants receiving 2.4 kg/m3 having the greatest shoot and root dry weights and inflorescence numbers. Plants grown in 4.7 kg/m3 had the greatest shoot lengths. Concentrations of Ca and Mg in leaves of plants grown in containers without dolomitic lime amendment were below that recommended for normal growth of B. davidii. Leaf concentrations of N, S and Mn showed quadratic responses to dolomitic lime additions. Media pH and concentrations of NO3, Al, B, Mn and P also showed quadratic responses. Media Zn concentrations showed a linear response. Although all dolomitic lime amendments tested improved growth of Buddleia davidii ‘Royal Red’, the incorporation of 2.4 kg/m3 produced maximum growth and inflorescence quantity.