Residues of two fungicides (dodine and fenarimol) and two insecticide/acaricides (amitraz and formetanate) on pear (Pyrus communis L.) leaves were reduced by over-tree sprinkler irrigation applied 24 or 72 hours after pesticide treatment. The difference in residue persistence following over-tree irrigation applied at 24 vs. 72 hours after pesticide treatment was significant only for fenarimol. Residues on leaves from nonirrigated trees at 96 hours post-treatment had declined 24% to 57% from initial levels. Over-tree irrigation further reduced residues by 14% to 47%. For all compounds except dodine, foliar residues measured at 96 hours post-treatment were reduced from initial levels to a greater extent by factors other than over-tree irrigation. Chemical names used: dodecylguanidine monoacetate (dodine); α-(2-chlorophenyl)-α-(4-chlorophenyl)-5-pyrimidinemethanol (fenarimol); N'-(2,4-dimethylphenyl) -N-[[(2,4-dimethylphenyl) imino]methyl] -N-methylmethanimidamide (amitraz); N,N-dimethyl -N'-[3[[(methylamino) carbonyl]oxy]phenyl]methanimidamide (formetanate).
Roots of most of the primitive Pynus species were infested with pear root aphid Eriosoma pyricola Bak. and David., and increase or decrease in number noted 30 days later. Although seedling populations varied somewhat, P. amygdaliformis, P. elaeagrifolia, P. syriaca, P. betulaefolia, P. calleryana, P. koehnei, P. ussuriensis, and P. nivalis can be considered resistant. P. communis, P. cordata, P. gharbiana, P. pashia, P. Fauriei, and P. pyrifolia were either susceptible or very variable in resistance. Only P. bucharica, P. dimorphophylla, and P. mamorensis had no resistant seedlings in the lots tested. Interspecific hybrid populations were predictable though variable in resistance.
Field and laboratory studies of host preference and resistance of Pyrus species and cultivars to the pear psylla, Psylla pyricola, were conducted in Southern Oregon from 1964–1968. Asian species were generally less attractive to oviposition than those from Asia Minor, North Africa or Europe. Attractiveness of P. pyrifolia and P. communis cultivars was higher than for P. ussuriensis.
Susceptibility of Pyrus was based on differences between total egg deposition and resulting nymphal populations. Using this nymph/egg ratio the results indicated that Asian material was more resistant than material from Asia Minor or Europe. The Asian species P. fauriei and P. calleryana exhibited both a high degree of unattractiveness to oviposition and resistance to nymphal development.
Overtree irrigation of pear trees following application of pesticides by speedsprayer resulted in lowering most insecticide deposits by 30-90%. Addition of a spreader sticker to pesticide sprays did not reduce pesticide loss.
Handgun treatments of abamectin and oil applied between mid-June and late August caused distinct epidermal rings where drops of spray liquid dried on the surface of pear fruit (Pyrus communis L.). The severity of epidermal injury was related to the concentration of oil in the abamectin spray mixture (abamectin applied without oil caused no fruit damage). Of six pear cultivars tested, `Anjou' was most susceptible to injury, followed by `Cornice' and `Bartlett'. `Sensation Red Bartlett', `Bosc', and `Seckel' showed little or no phytotoxicity symptoms from abamectin and oil treatments with oil concentrations from 0.125% to 2.0% (v/v). On sensitive cultivars, the concentration of oil should not exceed 0.25% (v/v) when combined with abamectin to reduce the risk of epidermal injury. Oil at 0.25% provides for adequate leaf penetration of abamectin and results in commercially acceptable spider mite (Tetranychus urticae Koch) control. Chemical names used: avermectin B1 (abamectin).
Overhead sprinkler systems are not new to orchard management but have been used almost exclusively for irrigation. However, economic considerations would encourage a modification of this one-purpose system into multi-purpose usage. Potentially, with the correct physical arrangements of pumps, pipes, risers, and nozzles it would be possible not only to irrigate, but to have frost protection and summer environmental and pest control as well. The present paper examines the latter two uses of an overhead sprinkler system and the effects of the system on the pear tree.
Differential population levels of pear psylla (Psylla pyricola Foerster) and of twospotted spider mite (Tetranychus urticae Koch) were established in ‘d’Anjou’, ‘Bartlett’, and ‘Bosc’ pear (Pyrus communis) trees by application of selective insecticides and acaricides. Numbers of psylla or mites counted were used to calculate psylla days and mite days by averaging numbers per leaf on successive sampling dates and multiplying this average by the number of days between samples. The N concentration of apparently uninjured shoot leaves of ‘d’Anjou’ and spur leaves of ‘Bartlett’ were negatively related to mite days. The reduction in N induced by mites on ‘d’Anjou’ shoot leaves was large enough to affect fertilizer recommendations based on foliar N. Phosphorus concentration was negatively related to mite days in both shoot and spur leaves of ‘d’Anjou’, but not in other cultivars. Other leaf nutrients were not consistently affected. Densities of the pear psylla were not correlated with foliar mineral nutrient concentrations, although high population levels were not established in this study.
Dilute sprays of 4, 8 and 16% Volck Supreme oil at dormant and repeated at delayed dormant to mask pear trees against psylla, Psylla pyricola (Foerster), oviposition delayed bloom slightly, while 2% applications in the Meld advanced bloom less than 1 day. Dormant pear branches dipped under laboratory conditions in oil at concentrations of 8% and higher caused injury to vegetative buds and slight injury to flowering buds. Single and repeat field applications of oil at 2, 4 and 8% caused no reduction of fruit set or cropping of ‘Anjou’, ‘Bartlett’, ‘Cornice’, ‘Bose’, and ‘Seckel’ pear trees, and in some cases increased fruit set on ‘Anjou’ trees. Hormonal analysis of oil-treated buds indicated a slight increase of gibberellin (GA) and a reduction of abscisic acid (ABA) levels.
Three consecutive annual nitrogen applications on trees of ‘Bartlett’ pear (Pyrus communis L.) at 120 kg/ha increased leaf N, shoot growth, number of expanded shoot leaves, crop density, fruit size, and yield compared to no N. N application without butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide) increased late bloom and fruit russet associated with pear psylla honeydew. Daminozide at 2 g/liter sprayed twice annually for 3 years, 30 and 50 days after bloom with or without N application, reduced minal growth, number of expanded shoot leaves, late bloom, fruit size, density of psylla nymphs, (Psylla pyricola Foerster) and fruit russet from psylla honey dew. The effects of N and daminozide on tree growth, fruit size, and yield, as well as on psylla density, varied from year to year. Daminozide can reduce shoot growth of pear and subsequently reduce psylla densities and resultant damage but with some reduction in fruit size.