Phosphonate Treatment Effects on Phytophthora Root Rot Control, Phosphite Residues and Phytophthora cactorum Inoculum in Young Apple Orchards.

Phytophthora root rot, caused by Phytophthora cactorum, is an economically important disease on young apple trees. Limited information is available on the effect of different phosphonate application methods and dosages on disease control, fruit and root phosphite concentrations, and soil and root pathogen inoculum levels. Evaluation of phosphonate treatments in three apple orchard trials (two in the Grabouw and one in the Koue Bokkeveld region) showed that foliar sprays (ammonium or potassium phosphonate), trunk sprays and trunk paints, were equally effective at increasing trunk diameter in one trial and yield in a second trial over a 25-month period. Foliar ammonium and potassium phosphonate sprays (12 g of phosphorous acid/tree), and two different dosages of the ammonium phosphonate sprays (∼4.8 g or 12 g of phosphorous acid/tree) were all equally effective at improving tree growth. The addition of a bark penetrant (polyether-polymethylsiloxane-copolymer) to trunk sprays did not improve the activity of trunk sprays. The low dosage ammonium phosphonate foliar spray (∼4.8 g a.i./tree) was the only treatment that, in general, yielded significantly lower root phosphite concentrations than the other phosphonate treatments. Root phosphite concentrations were significantly positively correlated (P < 0.0001) with an increase in trunk diameter and negatively (P < 0.0001) with P. cactorum root DNA quantities. Phosphite fruit residues were <31 ppm for all treatments, with the trunk paint treatment (80 g of phosphorous acid/tree applied annually) yielding significantly lower residues than the higher dosage foliar sprays (∼12 g a.i./tree). Twenty-one months posttreatment, most of the phosphonate treatments in all of the trials similarly significantly reduced P. cactorum DNA quantities estimated directly from roots, but not from soil based on soil baiting DNA analysis. Pathogen quantities in fine feeder roots did not differ significantly from those in higher-order roots (<5 mm diameter). P. cactorum DNA quantities estimated using DNA quantification directly from roots were significantly correlated (P < 0.0001) with those obtained through root leaf baiting DNA analysis and, to a lesser extent, with soil leaf baiting DNA quantities (P = 0.025).

Determining Mancozeb Deposition Benchmark Values on Apple Leaves for the Management of Venturia inaequalis.

Apple scab, caused by Venturia inaequalis, is the most common fruit and foliar disease in commercial apple production worldwide. Early in the production season, preventative contact fungicide sprays are essential for protecting highly susceptible continuously unfolding and expanding young leaves. In South Africa, mancozeb is a key contact fungicide used for controlling apple scab early in the season. The current study developed deposition benchmarks indicative of the biological efficacy of mancozeb against apple scab, using a laboratory-based apple seedling model system. The model system employed a yellow fluorescent pigment that is known to be an effective tracer of mancozeb deposition. A concentration range of mancozeb (0.15 to 1 times the registered dosage) and fluorescent pigment concentrations was sprayed onto seedling leaves, which yielded various fluorescent particle coverage (FPC%) levels. Modeling of the FPC% values versus percent disease control yielded different benchmark values when disease quantification was conducted using two different methods. Thermal infrared imaging (TIRI) disease quantification resulted in a benchmark model where 0.40%, 0.79%, and 1.35 FPC% yielded 50, 75, and 90% apple scab control, respectively. These FPC% values were higher than the benchmarks (0.10, 0.20, and 0.34 FPC%, respectively) obtained with quantitative real-time PCR (qPCR) disease quantification. The qPCR benchmark model is recommended as a guideline for evaluating the efficacy of mancozeb sprays on leaves in apple orchards since the TIRI benchmark model underestimated disease control. The TIRI benchmark model yielded 68% disease control at the lowest mancozeb dosage, yet no visible lesion developed at this dosage. Both benchmark models showed that mancozeb yielded high levels of disease control at very low concentrations; for the qPCR benchmark model the FPC% value of the FPC90 (90% control) corresponded to 0.15 times that of the registered mancozeb concentration in South Africa, i.e., 85% lower than the registered dosage.

The Efficacy of Semiselective Chemicals and Chloropicrin/1,3-Dichloropropene-Containing Fumigants in Managing Apple Replant Disease in South Africa.

Apple replant disease (ARD) is a biological phenomenon that is encountered when old apple orchards are replanted, resulting in tree growth and yield reductions in young trees. Three ARD orchard trials were conducted, which showed that semiselective chemicals (fenamiphos, metalaxyl, imidacloprid, and phosphonates) used independently, two fumigant formulations (33.3% chloropicrin and 60.8% 1,3-dichloropropene [Pic33-1,3D] and 57.% chloropicrin and 38% 1,3 dichloropropene [Pic57-1,3D]), and semiselective chemicals combined with Pic33-1,3D or Pic57-1,3D all contributed to significant increases in tree growth (trunk diameter and shoot length) relative to the untreated control 3 to 4 years postplanting. The treatments did not differ significantly from each other in improving tree growth. Yield was more indicative of treatment efficacy, but this varied between the three orchards. The Pic33-1,3D fumigant in combination with semiselective chemistries was the most consistent in significantly increasing cumulative yields. The Pic57-1,3D treatment was superior in increasing yields relative to the Pic33-1,3D treatment, because (i) it significantly increased cumulative yields in comparison with the Pic33-1,3D treatment in one orchard and (ii) in another orchard, a significant increase in yield was obtained with Pic57-1,3D relative to the control treatment but not with the Pic33-1,3D treatment. The quantification of ARD causative agents 20 months postplant showed that Phytophthora cactorum contributed to disease development in all three orchards; significant negative correlations existed between the quantity of P. cactorum DNA detected in tree roots and tree growth and less often, yield. In two orchards, only some of the treatments that significantly reduced the quantity of P. cactorum DNA in tree roots relative to the control also resulted in a significant increase in tree growth. Some of the aforementioned trends were also evident for Pratylenchus spp. root densities in two of the orchards. There was a significant positive correlation between P. cactorum root DNA quantities and Pratylenchus spp. root densities. Pythium spp. and "Cylindrocarpon"-like DNA quantities detected in tree roots typically were not indicative of treatment efficacy. However, a significant positive correlation existed between these two pathogen groups, suggesting complex interactions not associated with pathogen quantities per se.

Leptonic and charged kaon decay modes of the phi meson measured in heavy-ion collisions at the CERN super proton synchrotron.

We report on results of a measurement of meson production in central Pb-Au collisions at E(lab) = 158A GeV. For the first time in the history of high energy heavy-ion collisions, phi mesons were reconstructed both in the K+K- and the dilepton decay channels in the same experiment. This measurement yields rapidity densities near midrapidity, from the two decay channels, of 2.05 +/- 0.14(stat) +/- 0.25(syst) and 2.04 +/- 0.49(stat) +/- 0.32(syst), respectively. The shape of the measured transverse momentum spectrum is also in close agreement in both decay channels. The data rule out a possible enhancement of the phi yield in the leptonic over the hadronic decay channel of a factor 1.6 or larger at the 95% C.L. This rules out the discrepancy reported in the literature between measurements of the hadronic and dimuon decay channels by two different experiments.

Semihard scattering unraveled from collective dynamics by two-pion azimuthal correlations in 158A GeV/c Pb+Au collisions.

Elliptic flow and two-particle azimuthal correlations of charged hadrons and high-p(T) pions (p(T)>1 GeV/c) have been measured close to midrapidity in 158A GeV/c Pb+Au collisions by the CERES experiment. Elliptic flow (v(2)) rises linearly with p(T) to a value of about 10% at 2 GeV/c. Beyond p(T) approximately 1.5 GeV/c, the slope decreases considerably, possibly indicating a saturation of v(2) at high p(T). Two-pion azimuthal anisotropies for p(T)>1.2 GeV/c exceed the elliptic flow values by about 60% in midcentral collisions. These nonflow contributions are attributed to nearside and back-to-back jetlike correlations, the latter exhibiting centrality dependent broadening.

Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.

We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

Universal pion freeze-out in heavy-ion collisions.

Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda(f) reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider.