Venturia inaequalis, the causal agent of apple scab, overwinters in apple leaves on the orchard floor. To develop a control strategy based on the prevention of the maturation of overwintering pseudothecia, a sampling of fungi colonizing dead apple leaves was conducted from different orchard floors in Quebec during the spring and fall of 1993. A total of 345 different isolates were obtained, from which fifteen genera have never been previously recorded as colonizers of apple leaves in North America. Small differences were detected in genera richness among orchards but the fungal composition of each orchard was fairly unique. Different tests on growth on amended media and leaf decomposition demonstrated that leaf degradation is not a reliable parameter alone to screen antagonist against V. inaequalis. No significant relation between growth on amended media, leaf rheology and ascospore inhibition was detected. However, 40 fungi reduced significantly ascospore production more than 87% compared to the control (V. inaequalis only). Of these antagonists, 30% decomposed apple leaves, suggesting that competition for the substrate is involved in the mode of action of at least one third of the antagonits detected. Other possible modes of antagonism are discussed.

Thesis (PhD(Agric))--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The apple industry in South Africa currently relies entirely on chemical fungicides to control apple scab, caused by Venturia inaequalis. In this dissertation, alterative management strategies against V. inaequalis were tested for the first time in South Africa. New information on the behaviour of the sexual winter phase of V. inaequalis in different climatic conditions was found and sources of asexual inoculum overwintering in apple orchards were identified. The effect of leaf shredding on fruit and leaf scab incidence and severity was tested against a non-shredded, non-sprayed negative control, a positive control that followed a commercial fungicide programme and a combined treatment of a commercial fungicide programme with leaf shredding, from 2010 to 2013. Reductions in fruit and leaf scab incidence and severity in the leaf shredding treatment were significantly lower compared to the negative control. Quantitative real-time polymerase chain reaction (qPCR) of airborne ascospores trapped using volumetric spore traps was used to measure the reduction in airborne ascospores in the shredded plots, and confirmed the efficacy of shredding found by comparing scab incidence and severity on fruit and leaves. Shredding twice during leaf-drop increased the efficacy of the treatment. Results indicate that leaf shredding should be integrated into scab management strategies in future. However, practical considerations unique to South African orchards, e.g. timing of leaf shredding relative to leaf-drop and orchard layouts, need to be addressed. Pseudothecial densities (PD, number of pseudothecia per fertile lesion) and ascal densities (AD, number of asci per pseudothecium) were compared between in Koue Bokkeveld (KB), a cold winter region, and Elgin (EL), a warm winter region experiencing climate warming, in 2012 and 2013. Scabbed leaves were detached during leaf-drop and overwintered in their region of origin and in the other region. The PD in leaves collected in KB and overwintered in KB was significantly higher than for leaves collected in EL and overwintered in EL, and leaves collected in KB and overwintered in EL. These results agreed with what was expected, as temperature during pseudothecial formation (i.e. the first four weeks after leaf-drop) was significantly lower in KB than in EL. However, the PD for leaves collected in EL and overwintered in EL did not differ significantly from EL leaves overwintered in KB. AD values in all treatments did not differ significantly from one another. Results suggest that factors other than temperature may be involved in controlling PD, e.g. the EL population may include strains not present in the KB population, with higher optimal temperatures for pseudothecial formation. Apple buds and pygmy apples were collected and tested for presence, number and viability of conidia in 2010, 2011 and 2012. Pygmy apples are small, late season fruit that remain attached to the tree throughout winter, especially in regions with warmer winters where trees do not experience sufficient chilling to complete dormancy. High conidial numbers were found on outer bud tissue and low numbers on inner bud tissue, but viable conidia were only found on inner bud tissue, using microscopy, and generally in orchards with high scab levels in the previous season. Molecular methods using PCR-RFLP and qPCR confirmed the presence of high amounts of V. inaequalis DNA in outer bud tissues, although calculated conidial amounts were higher than data obtained when using microscopy, which could indicate presence of mycelia not detected during microscopic examination. Higher numbers of conidia with higher percentage viability were found on pygmy apples, which are a more likely source of asexual inoculum in South African apple orchards than the low number of viable conidia on inner bud tissue. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse appelbedryf is tans afhanklik van chemiese swamdoders vir die beheer van die appelskurf patogeen, Venturia inaequalis. In hierdie proefskrif is alternatiewe bestuurstrategiëe vir die eerste keer in Suid-Afrika ondersoek. Nuwe inligting te opsigte van die gedrag van die geslagtelike winterfase van V. inaequalis, is onder verskillende klimaatstoestande ingewin en bronne van die oorwinterende ongeslagtelike inokulum in appelboorde, is identifiseer. Die invloed van blaarversnippering op die voorkoms en erns van appelskurf op vrugte en blare, is vanaf 2010 tot 2013 ondersoek en met ʼn negatiewe kontrole (onversnipperde blare sonder spuitprogram), ʼn positiewe kontrole (ʼn kommersiële swamdoderspuitprogram is gevolg) en gekombineerde behandelings (kommersiële swamdoderspuitprogram en blaarversnippering) vergelyk. Daar was ʼn betekenisvolle verskil in die voorkoms en erns van skurf op vrugte en blare met blaarversnippering teenoor die negatiewe kontrole. Kwantitatiewe intydse polimerase kettingvermeerderingsreaksie (kPKR) van luggedraagde askospore, vasgevang in volumetriese lokvalle, is gebruik om die afname van luggedraagde askospore in versnipperde behandelings te meet. Die doeltreffendheid van versnippering as behandeling, is bevestig deur die voorkoms van appelskurf te vergelyk met die ernstigheidsgraad daarvan op vrugte en blare. Die uitvoer van blaarversnippering twee keer gedurende die blaarvalperiode het die effektiwiteit van hierdie behandeling verhoog. Hiervan kan dus afgelei word dat blaarversnippering voordelig sal wees vir die bestuur van appelskurf en in toekomstige bestuurspraktyke ingesluit moet word. Praktiese oorwegings, uniek aan Suid-Afrikaanse boorde, soos boorduitleg en die tydsberekening van blaarversnippering teenoor blaarval, moet egter in ag geneem word. Pseudothesiale digtheid (PD; die aantal pseudothesia per vrugbare letsel) en askale digtheid (AD; die aantal aski per pseudothesium) is gedurende 2012 en 2013 vir die Koue Bokkeveld (KB), 'n koue winterstreek, en warm winterstreek Elgin (EL), 'n winterstreek wat klimaatsverwarming ervaar, vergelyk. Blare, met skurf, is gedurende blaarval gepluk en oorwinter in hul gebied van oorsprong, asook in die ander klimaatstreek. Blare wat in KB versamel is en in KB oorwinter het, se PD was aansienlik hoër as dié wat in EL versamel is en in EL oorwinter het, sowel as dié wat in KB versamel is en in EL oorwinter het. Hierdie resultate stem ooreen met wat verwag is, om rede die temperatuur gedurende pseudothesiale vorming, d.w.s. die eerste vier weke na blaarval, aansienlik laer in KB as in EL was. Die PD van blare wat in EL versamel en daar oorwinter het, het egter nie betekenisvol verskil van blare wat in KB oorwinter het nie. Die AD-waardes tussen behandelings verskil nie noemenswaardig nie en word as onbeduidend beskou. Die verkrygde resultate dui aan dat daar ander faktore as temperatuur betrokke is by die beheer van PD, bv. die EL-skurfpopulasie, waar die warmer klimaat meer optimaal is vir pseudothesiale vorming, rasse wat nie in die KB-bevolking teenwoordig is nie, mag insluit. Appelknoppe en dwerg-appels is gedurende 2010, 2011 en 2012 versamel en vir die teenwoordigheid, aantal en lewensvatbaarheid van konidiospore getoets. Dwergappels is klein laatseisoen appeltjies wat reg deur die winter aan die boom bly hang; veral in die streke met warmer winters waar die bome nie die nodige koue ervaar om dormansie te voltooi nie. Met behulp van mikroskopie is ʼn hoë aantal spore op die buitenste knopweefsel en lae getalle in die binneweefsel bespeur; maar lewensvatbare spore is net in die binneweefsel van knoppe waargeneem, wat hoofsaaklik afkomstig is van boorde wat hoë vlakke van appelskurf in die vorige seisoen ervaar het. Molekulêre tegnieke, PKR-RFLP en kPKR, is gebruik vir bepaling van V. inequalis DNA hoeveelhede op die buitenste knopweefsel. Hoër getalle konidiospore is met die molekulêre analise gevind, as dié verkry met mikroskopiese ondersoek en dui op die moontlike teenwoordigheid van miselium wat nie met visuele waarneming sigbaar was nie. Meer konidiospore met 'n hoër vlak van lewensvatbaarheid is op dwerg-apples gevind en dit is moontlik 'n meer waarskynlike bron van ongeslagtelike inokulum in Suid-Afrikaanse appelboorde, as die lae getalle van lewensvatbare konidiospore op die binneweefsel van die appelknoppe.

The use of a biofungicide on the perfect stage of V. inaequalis on leaf litter is one potential way to reduce the number of fungicides used to control apple scab. The previous in vitro screenings of Quebec mycoflora have shown that several isolates are able to significantly reduce the primary inoculum of the pathogen. Among the screened fungi, P176A and P130A, reduced over 98% of the ascospore production and were as effective as Athelia bombacina. However, because in vitro tests are generally poor predictors of in vivo assays a re-evaluation of the antagonists was done under field conditions. Eight fungal isolates, leaf shredding, and two comparative treatments (A. bombacina, 5% urea) were applied to intact scabbed leaves in October 1994 and 1995. After the treatments, the leaves overwintered on the orchard ground until the next spring. In April, samples of treated leaves were randomly selected and placed in spore traps to collect the ejected ascospores during rainfall. Since the primary inoculum was ejected during a four-month period, antagonism was based upon ratings taken throughout the whole ejection season. To evaluate the effect of incubation conditions on the antagonistic performance we incubated separately, in vitro and in vivo, sterile leaf disks which were artificially inoculated with V. inaequalis and fungal isolates. (Abstract shortened by UMI.)

vi, 128 leaves : photos, tables ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Pathology, 1978

Mite pest problems in Utah apple orchards became generally serious about 1944, when DDT was first used extensively to control Codling moths, Carpocapsa pomonella (Linn.) (Jorgensen, 1967}. Since then several investigators (Pickett et al., 1946; Lord, 1949; Pickett, 1955; Lord, Herbert, and MacPhee, 1958) have examined the influence of various spray programs on apple orchard fauna, while still others (Clancy and Pollard, 1952; Morgan, Anderson, and Swales, 1958; Oat-man and Legner, 1962) have conducted related studies with widely used broad spectrum pesticides on apple mites and their predators. All seem to lend credence to the theory that mite pest problems on apples resulted primarily from the reduction or elimination of natural enemies with pesti-cides. Still other factors as m9ntioned by Huffaker, van de Vrie, and McMurtry (1970) may have profound effects on, or be a principal cause of mite outbreaks in some situations. Presently, integration of natural and chemical control methods for mites seems essential. Van Den Bosch and Stern (1962) and Jorgensen (1967) redefined the control target when they emphasized that in the development of an integrated control program, the entire ecosystem, rather than isolated pest species, must be of primary concern.

No description available.

No description available.

No description available.

No description available.

The anthocorid, Orius insidiosus (Say) is a common polyphagous predator in Virginia apple orchards, particularly in orchards under reduced pesticide programs. The purpose of this research was to contribute to the basic knowledge of the biology and ecology of O. insidiosus in Virginia orchards and to evaluate the potential for its incorporation into IPM programs currently being developed. Egg and nymphal development of O. insidiosus was studied at 17°, 23°, 29°, and 35°C. Nymphs were supplied with an excess of the European red mite, Panonychus ulmi (Koch). There was a linear relationship between development rate (l/Days) of O. insidiosus and temperature. Developmental threshold temperatures were calculated as 10.2°C for the eggs; 8.9°, 7.5°, 10.7°, 12.5°, and 9.9°C for nymphal instars 1-5 respectively; and 10.0°C for total nymphal development. Mean degree-days (DD) requirements were 75.8 for eggs; 45.0, 38.0, 27.8, 28.8, and 64.9 for instars 1-5 respectively: 201.7 DD were required for total nymphal development. Nymphal development was also studied using aphids and pollen as food sources. Mean time (days ± S.E.) for total nymphal development at 23°C was 19.0 ± 0.0 with aphids and 20.0 ± 0.5 with pollen. As already mentioned, O. insidiosus is a polyphagous predator. Extensive laboratory and field observations established a number of small, soft-bodied insects and mites as well as the eggs of several lepidoptera are acceptable as prey. O. insidiosus also feeds on other beneficial species including predaceous thrips and mites. O. insidiosus falls prey to a number of other general orchard predators, particularly spiders, chrysopids, and other predaceous Heteroptera. During 1977-1978, the population dynamics of O. insidiosus along with a complex of predators and pests in orchards under three different pesticide programs was studied. O. insidiosus underwent 2-3 generations per year in Virginia orchards, depending on the availability of prey. Adults overwintered in the orchard, but most migrated into the orchard during May-early June from other areas. O. insidiosus first responded to aphid populations, but as this prey became scarce in late June, O. insidiosus fed on the European red mite whose populations were usually building up at that time. This study indicated that O. insidiosus responded numerically to increasing mite densities. Numerous weeds and crops serve as alternate sites for 0. insidiosus populations. Corn and alfalfa are often adjacent to orchards in Virginia and apparently serve as a reservoir for O. insidiosus throughout the season. Thistle (Carduus spp.) harbors large numbers of O. insidiosus which prey on thrips. These natural and cultivated alternate sites may be important to the management of O. insidiosus populations. Since pesticides are an important component of an IPM program for apples, the relative toxicity of 14 compounds (2 rates of each) to adult O. insidiosus was evaluated. Common cover-spray materials, aphicides, miticides, new materials such as synthetic pyrethroids, and fungicides were tested. Generally, O. insidiosus tolerated many of the compounds being considered for use in our developing IPM programs--especially at the lower rates. The functional response of O. insidiosus to densities of the European red mite was studied at 18.3°, 23.9°, 29.4°, and 35.0°C. Prey densities ranged from 5-80 mites/ cage. Mite consumption was recorded during five, three-hour intervals during the day. O. insidiosus did exhibit a functional response and increasing temperatures resulted in increased feeding at most prey densities. The data provided a good fit to both the type-2 and type-3 functional response models. The interspecific interactions of 5th instar O. Insidiosus and 2nd instar larvae of another mite predator, Leptothrips mali (Fitch) was studied in the laboratory. L. mali is a potential prey for O. insidiosus, but has a defensive anal secretion which repels predator attacks. Most contacts between well fed O. insidiosus and L. mali resulted in mutual avoidance. Most attacks by O. insidiosus were unsuccessful, especially if the approach was from the rear. Contact with the thrips' anal secretion resulted in immediate repelling of O. insidiosus with subsequent cleaning activity lasting 1-3 minutes. This study supports earlier work that indicated these two predators were compatible, especially in the presence of another food source such as the European red mite. / Ph. D.