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- Author or Editor: W.L. Tedders x
Twenty-one days of foliar feeding in late spring by the blackmargined aphid [Monellia caryella (Fitch)] on a mature ‘Stuart’ pecan tree [Carya illinoensis (Wang.) K. Koch] reduced soluble sugars and starch in leaves to 82% and 79%, respectively, of the aphid-free control. Chlorophyll levels were unaffected. Sugars were reduced to 75% of the control in both 1- and 2-year-old branches. Starch in 1-year-old branches was reduced to 71%, but was unchanged in 2-year-old branches.
Fungal leaf scorch, a potentially devastating disease in pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards, was influenced substantially by irrigation and genotype. Three years of evaluating 76 pecan cultivars revealed that all cultivars exhibited scorch symptoms and that at least three classes of scorch susceptibility existed. Severity of symptoms was also much greater in nonirrigated than irrigated trees, and there were substantial differences in the concentrations of free nitrogenous compounds and free sugars in leaves between irrigated and nonirrigated trees.
Feeding injury by pecan aphids on fully expanded pecan [Carya illinoensis (Wangenh) K. Koch] seedling foliage reduced net CO2 exchange within 2 weeks of infestation and was dependent upon aphid density and species. Increasing aphid population levels resulted in increasing reductions in net photosynthesis. Carbon exchange rates after a buildup and subsequent rapid decline of either Monellia caryella (Fitch) or Monelliopsis pecanis (Bissell) populations resulted in a 50% reduction in net photosynthesis and 25% reduction in dark respiration. This effect can persist at least 12 weeks after the cessation of aphid infestation. Such leaves exhibit aphid-induced clogging of the phloem with callose and other substances. Such clogging may be associated with the commonly observed aphid population decline in pecan orchards. Observations indicate that the influence of aphid feeding on leaf photosynthetic physiology may impair pecan productivity.
The heavy levels of sooty mold commonly present on pecan [Carya illinoensis (Wangenh.) C. Koch] foliage in the autumn prompted an evaluation of its influence on net photosynthesis (Pn) of pecan leaves. Extra heavy sooty mold levels were observed to block light penetration to the leaf surface by up to 98%. Heavy mold levels suppressed leaflet Pn by up to 70% with suppression due to a blockage of photosynthetically active radiation (PAR). An observed 4°C increase in abaxial leaf surface temperature may also contribute to this suppression. The results indicate a possible need to introduce sooty mold control methods into orchard management programs.
Severe economic losses in pecan crop productivity result from phytophagous stink bugs and coreid bugs (Hemiptera) feeding on the kernel. Discriminating hemipteran damage from other late seasonal kernel disorders is often inconclusive. Two additional markers of hermipteran damage have been distinguished and can be used as unequivocal evidence of the feeding activity of these insects regardless of the source of the nuts. Staining pecan nuts with red fluorescent dye differentiates the microscopic hemipteran punctures from the natural markings on the shell. Additional confirmatory evidence can be obtained by recognition of the stylet sheaths connecting the packing material on the shell interior to the seed coat of the kernel. These anatomical evidences of hemipteran feeding should facilitate research studies to evaluate the role of hemipteran attack with late seasonal pecan kernel disorders.
Feeding activity by several species of phytophagous stink bugs and coreid bugs (Pentatomidae and Coreidae) on the fruits of pecan [Carya illinoensis (Wangenh.) C. Koch] causes severe economic losses in nut yield and kernel quality. Verification of late-season damage by these insects to pecan nuts has been possible only after examination of the condition of the kernel. Staining nuts with a red fluorescent tracing dye resulted in a differential contrast between the surface of the shell and sites of hemipteran punctures. This technique can be used with the aid of a dissecting microscope to identify hemipteran bug damage by examining the exterior of the shell. Stylet sheaths connecting the packing material on the shell interior to the seedcoat of the kernel have been identified and can be used as confirmatory evidence of hemipteran attack.
Annual legume ground covers were evaluated in pecan (Carya illinoinensis) orchards to supply nitrogen and increase beneficial arthropods. Treatments were established at two sites, each with 5 ha of a `Dixie' crimson clover (Trifolium incarnatum) /hairy, vetch (Vicia villosa) mixture and 5 ha of grass sod. Data indicated that the legume mixture supplied over 100 kg·ha-1 N to the pecan trees. Beneficial arthropods were greater in orchards with legume ground covers than in orchards with a grass groundcover. Lady beetles and green lacewings were the most important spring predators, and green lacewings were the most important fall predator. The Species distribution on the ground covers differed from that in the canopy. Coleomegilla maculata lengi, Hippodamia convergens and Coccinella septempunctata were the most abundant lady beetle species in the legume ground covers, and Olla v-nigrum, Cycloneda munda, and Hippodamia convergens were the most abundant species in the pecan canopies. Beneficial arthropods appeared to suppress injurious pecan aphids.