Effect of White Spruce Release on Subsequent Defoliation by the Yellowheaded Spruce Sawfly, Pikonema Alaskensis (Hymenoptera: Tenthredinidae)

Hand release of 22 5-year-old white spruce, Picea glauca (Moench) Voss, dramatically increased the amount of defoliation by the yellowheaded spruce sawfly, Pikonema alaskens is . The percent defoliation of the released trees was six times the defoliation in the control trees. A light overstory for young white spruce is suggested as a silvicultural method of reducing defoliation by this sawfly

Spatio-temporal modelling of forest monitoring data: Modelling German tree defoliation data collected between 1989 and 2015 for trend estimation and survey grid examination using GAMMs

Spatio-temporal modelling of tree defoliation data of German forest condition survey is presented. In the present study generalized additive mixed models were used to estimate the spatio-temporal trends of defoliation of the main tree species from 1989 to 2015 and to examine the suitability of different monitoring grid resolutions. Although data has been collected since 1989, this is the first time the spatio-temporal modelling for entire Germany has been carried out. Besides the space-time component, stand age showed a significant effect on defoliation. The mean age and the species-specific relation between defoliation and age determined the general level of defoliation whereas fluctuations of defoliation were primarily related to weather conditions. The study indicates a strong association between drought stress and defoliation of all four main tree species. Besides direct effects of weather conditions, indirect effects seem to play a further role. Defoliation of the comparably drought-tolerant species pine and oak was primarily affected by insect infestations following drought whereas considerable time for regeneration was required by beech following drought stress and recurring substantial fructification. South-eastern Germany has emerged as the region with the highest defoliation since the drought year 2003. This region was characterized by the strongest water deficits in 2003 compared to the long-term reference period. The present study gives evidence that the focus has moved from air pollution to climate change. Furthermore, the spatio-temporal model was used to carry out a simulation study to compare different survey grid resolutions. This grid examination indicated that an 8 x 8 km grid instead of the standard 16 x 16 km grid is necessary for spatio-temporal trend estimation and for detecting hot-spots in defoliation in space and time, especially regarding oak

Impact of pine looper defoliation in Scots pine

Widespread defoliation of forests caused by insects or fungi cause economic losses throughout the world. Successful outbreak management involves cost/benefit estimation and requires knowledge of potential yield losses. Currently, such knowledge is scarce. This thesis evaluates the significance of single-year defoliation by the pine looper moth (Bupalus piniaria L.) (Lepidoptera: Geometridae) and secondary attack by the pine shoot beetle (Tomicus piniperda L.) (Coleoptera: Scolytinae) for yield losses in Scots pine (Pinus sylvestris L.). In a seven-year study, tree mortality and growth losses were quantified after a B. piniaria outbreak with a subsequent T. piniperda infestation at Hökensås in 1996. Secondary attack by T. piniperda was also studied in a Scots pine stand at Fredriksberg, infested by Gremmeniella abietina (Lagerberg) Morelet. in 2001. Tree mortality at Hökensås mainly occurred in areas with an average defoliation intensity of 90-100%. Tree mortality averaged 25%, and the “defoliation threshold” for tree survival was found to be 90% defoliation. Tree mortality peaked two years after the defoliation event, which coincided with high levels of pine shoot beetles. Involvement of T. piniperda in tree mortality increased with time since defoliation, and tree susceptibility to beetle attack increased with increasing defoliation intensity and decreasing dominance status of trees. As foliage of trees recovered, fewer trees were susceptible to beetle attack, and ultimately, beetle attacks ended as breeding substrate was depleted. Tree susceptibility to beetle attack was a function of tree vigour and beetle density. Growth losses at the Hökensås site were a combined effect of pine looper defoliation and shoot pruning by T. piniperda. Radial, height and volume growth losses were proportional to defoliation intensity. Whereas radial growth was little affected by beetle-induced shoot pruning, height growth was severely affected by beetle-induced damage to leading shoots. Growth losses alone, excluding tree mortality, were large enough to economically justify control of the pine looper outbreak had the outbreak been prevented in 1996. At Fredriksberg, T. piniperda colonised trees that would have survived the damage caused by G. abietina. However, trees with 90-100% foliage losses died because of the damage caused by G. abietina alone, and tree survival seemed to require that trees retained at least 20% of full foliage

Impact of Simulated Insect Defoliation and Timing of Injury on Cabbage Yield in Minnesota

In 1992 and 1994, field studies were done to assess the tolerance of transplanted cabbage to simulated insect defoliation and to determine if the defoliation level and growth stage at which defoliation begins influences final yield. In both years, 6 defoliation levels ranging from 0-100% were applied to transplanted cabbage at 4 time intervals. The time intervals began at transplanting, pre-head and head stages and continued until either head stage or harvest. For both years, the only time interval with significantly higher yield than the trans- plant to harvest interval (longest interval) was the head to harvest interval (shortest interval) and significant yield loss occurred only when defoliation was \u3e12.5%. Results suggest that transplanted cabbage can withstand relatively low levels of defoliation before yield loss occurs but that yield loss is also related to the duration over which defoliation occurs. In early growth stages, to protect yield, pest management practices should focus on reducing the interval over which damage occurs. The use of cultural practices that delay the onset of defoliation or allow avoidance of pests could protect yield. These strategies may include using transplants to shorten the time from planting to harvest or using planting dates that allow significant plant growth (i.e., head stage) before defoliators are able to infest the crop and cause significant damage. In addition, management strategies that reduce pest populations can also protect yield but at the head stage should switch to managing pests to protect marketability by reducing aesthetic damage and head contaminants

Response of Lowland Rice Plants to Simulated Insect Defoliation in West Africa

Field experiments were conducted to investigate the impact of simulated insect-caused defoliation on irrigated rice. Defoliation levels tested were 0% (control), 25% defoliation at 21 days after transplanting (dat), 25% defoliation at 41 dat, 25% defoliation at 21 and 42 dat, 50% defoliation at 21 dat, 50% defoliation at 42 dat, 75% defoliation at 21 dat, 75% defoliation at 42 dat, 75% defoliation at 21 and 42 dat, 100% defoliation at 21 dat, and 100% defoliation at 21 and 42 dat. Tiller height, total number of tillers, percent panicle-bearing tillers, weight of 100 grains, and grain yields were recorded. The rice plant when defoliated just before tillering or in the tillering stage has the ability to compensate for defoliation damage. No yield losses occurred at 25% defoliation. Defoliation of 100% had a significant effect on the total number of tillers and on grain yield. Yield losses at 100% defoliation over the 3 years of the study averaged 40% in the 21 dat treatment and 55% in the 21 and 42 dat treatment. The implications of the development of cultural practices to manage lowland rice defoliating insects are discussed

Effects of Light and Nutrients on Tomato Plant Compensation for Herbivory by \u3ci\u3eManduca Sexta\u3c/i\u3e (Lepidoptera: Sphingidae)

This preliminary study examined how two resources (light and nutrients) influence the ability of tomato plants to show growth compensation for defoliation by the tobacco homworm (Manduca sexta). Growth rate and biomass of plants grown under high and low levels of light and nutrients, and exposed to 4 levels of defoliation by Manduca sexta were measured. Nutrients affected plant growth rate much more strongly than did light. Light and nutrients, however, each influenced how herbivory affected plant growth. Defoliation significantly decreased growth rate only under conditions of low light and high nutrients. Biomass, on the other hand. was low under all resource treatments except high levels of both light and nutrients, and defoliation significantly decreased biomass only under high levels of both resources. Thus, plants appeared to compensate for damage. in terms of biomass, only under conditions of either low light and/or low nutrients

Effect of defoliation height on regrowth of timothy and meadow fescue in the generative and vegetative phases of growth

Post-defoliation carbohydrate stores, leaf area and the number of active meristems are important factors affecting the subsequent regrowth of grasses. Defoliation height affects the magnitude of all these factors. Timothy (Phleum pratense L.) and meadow fescue (Festuca pratensis Huds.) are the two most common pasture species in Finland, but little is known about their response to defoliation height. In this study the effect of three defoliation heights, 3, 6 and 9 cm, on the regrowth rates of timothy and meadow fescue in both the generative (June–July) and vegetative (August) phases of growth were examined in two one-year experiment in year 2000 and 2001. In addition, the main postdefoliation parameters were measured and their contributions to regrowth were studied. In June–July 2000 the regrowth rates, kg dry matter ha-1 d-1, of both species increased linearly by 19% by increasing the cutting height from 3 to 9 cm. In August 2000 the regrowth rates increased by 27% and the cumulative regrowth dry matter yield increased by 29%. In 2001 the defoliation height had no effect on the regrowth rates but the cumulative regrowth yield increased by 10% by increasing the cutting height. Meadow fescue produced 8–21% higher cumulative regrowth yields than timothy. In the reproductive phase, the regrowth rate of timothy is dependent on the population density of vegetative tillers but for meadow fescue population density did not have such importance. In vegetative phase there was no single factor essential for regrowth rates of either of the species

Effects of intensity and frequency of defoliation on a mixture of guinea grass (Panicum maximum cv. Coloniao) and Verano stylo (Stylosanthes hamata cv. Verano) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University

A study was conducted in a glasshouse to determine the effect of defoliation treatments comprising combinations of two intensities (7.5 cm and 15.0 cm cutting height) and three frequencies (2, 3 and 6 weeks) on production, botanical composition and crude protein of a Guinea grass (Panicum maximum cv. Coloniao) / Verano stylo (Stylosanthes hamata cv. Verano) sward. Total cumulative yield was reduced with more intense defoliation and decreased as the sward was defoliated more frequently. A similar response was observed for cumulative grass yield. In legume, cumulative yield was reduced at hard intensity but was not influenced by defoliation frequency. The proportion of the legume component in the sward was not influenced by defoliation intensity but increased with increasing defoliation frequency due more to depressed grass growth rather than a promotion in legume growth. Defoliation intensity and defoliation frequency had no effect on legume branch number. Similarly, branch size was not influenced by defoliation frequency but increased with less intense defoliation. Both defoliation intensity and defoliation frequency influenced grass tiller number. It was increased with more intense defoliation. The sward defoliated at moderate frequency resulted in the highest tiller number. Tiller number was not different between very frequent and infrequent defoliation. Intensity and frequency of defoliation also influenced average tiller size. It was reduced with more intense defoliation and decreased with increasing defoliation frequency. Percent crude protein content of both grass and legume was not influenced by defoliation intensity but was reduced with less frequent defoliation. The percent crude protein content in the legume which was more than double that in the grass indicates that Verano stylo has important contributions in the development and management of a legume-based tropical pasture

Interpretation and mapping of gypsy moth defoilation from ERTS (LANDSAT)-1 temporal composites

The author has identified the following significant results. Photointerpretation of temporally composited color Diazo transparencies of ERTS(LANDSAT) images is a practical method for detecting and locating levels of widespread defoliation. ERTS 9 x 9 inch images are essentially orthographic and are produced at a nearly constant 1:1,000,000 scale. This allows direct superposition of scenes for temporal composites. ERTS coverage provides a sweeping 180 km (110 mile) wide view, permitting one interpreter to rapidly delineate defoliation in an area requiring days and weeks of work by aerial surveys or computerized processing. Defoliation boundaries can be located on the images within maximum errors on the order of hundreds of meters. The enhancement process is much less expensive than aerial surveys or computerized processing. Maps produced directly from interpretation are manageable working products. The 18 day periodic coverage of ERTS is not frequent enough to replace aerial survey mapping because defoliation and refoliation move as waves

Sugar Maple Borer (Coleoptera: Cerambycidae) Activity Associated With Periods of Severe Defoliation

A perusal of previous research on sugar maple borer, Glycobius speciosus, in northern New York State strongly associates severe early and late season defoliation with increased borer damage. This re-examination of earlier work suggests foliage protection may be necessary when forest management objectives are concerned with wood volume and quality