Testing of Fungicides for the control of Mycosphaerella on Eucalyptus

Published Date: January 26, 2022

Fungicides are used for the control of mycosphaerella is a fungus that infects the leaves and stems of several Eucalyptus species. And causing them to fall prematurely. The loss of photosynthetic leaf tissue could result in a steady drop in vigor. Because of the growing worry about this fungal infection affecting Eucalyptus delegatensis seedlings in the nursery. The effort was done to develop a fungicidal treatment that could be applied every two weeks or even more frequently.

Eucalyptus globulus is a kind of eucalyptus. Labill is plantation species that are farmed for structural and appearance-grade timber, pulp, and paper product in temperate locations around the world. A rapid spread of monoculture plantations, mainly of E. globulus, has resulted in a hardwood plantation. One of the most devastating fungal diseases of Eucalyptus species is Mycosphaerella leaf disease(MLD). Despite the fact that other Eucalyptus species, such as Eucalyptus nitens and Maid, are less vulnerable to MLD. E. globulus is grown due to its high pulp output, density, and strength.

Effects of Mycosphaerella leaf disease (MLD) on the growth and wood quality of Eucalyptus globulus

Pathogenic Hemibiotrophic Mycosphaerella species are disseminated via wind-borne ascospores and splash-dispersed conidia. Germination of ascospores necessitates a high level of humidity or free water, which can be provided by dewfall or rainfall. MLD is most harmful to young foliage, especially newly emerging leaves, with resistance rising with leaf age and ontogenetic transition to adult foliage. Although adult foliage infection is uncommon, certain growth effects have been observed at levels less than 15%. Although severe defoliation has the potential to kill trees, no data has been gathered on the amount of infection on the leaves or stems that will cause branch or tree death or senescence.

Geeken Chemical Testing of Fungicides for the control of Mycosphaerella on Eucalyptus
Mycosphaerella

In some countries, E. globus is present. Although E. globus is native. Significant MLD epidemics have occurred, resulting in tree loss and the need for some plantations to be re-established due to poor growth. However, vast swaths of E. globus have been identified. Over the last 25 years, globulus has been successfully produced with rapid growth rates and short rotations. As far as E. globus is concerned, these crops have been remarkably disease-free. The pathogen E. globus is not native. There are no co-evolved diseases in native forests to infect plantation forests. However, surveys show that the incidence and severity of Mycosphaerella are increasing in the key growth areas. MLD-induced growth reductions may be visible in the future in all areas where E. globus grows.

MLD causes two types of non-lethal damage

MLD causes two types of non-lethal damage: necrosis (leaf or shoot spotting/blighting) and defoliation. However, the possibility of stem abnormalities because of the pruning of infection-killed branches. It could be the third component of MLD damage. In addition to producing productivity losses, has the potential to alter stem form and quality. As well as increase the tree’s susceptibility to other pests and pathogens, as has been found with significant insect defoliation.

Tree Growth Response

  • There are two basic kinds of tree growth responses to defoliation or treatment. The first is a type 1 reaction. In which a short-term drop in growth is detected after damage. But does not persist over time, and growth rates revert to those of undamaged trees. As a result, a type 1 growth response up to a threshold degree of injury.For example, a type 1 reaction was observed up to 72% damage by Mnesampela privata.
  • The second sort of response is a type 2 response. In which growth decreases are endlessly reduced and growth trends are permanently divergent from those of unaffected trees. Damage severity, frequency of occurrence, tree species, age of the tree when the damage occurs, and nutritional state. These are all factors that influence growth responses. A type 2 response beyond that threshold may be feasiblea type 2 response was observed beyond this damage threshold. Similarly, trimming more than 80% of E. nitens leaves. Resulted in long-term growth impacts.At the provenance level, some short-term growth impacts have been observed.

Fungicides for the control of Mycosphaerella on Eucalyptus

In an E. globulus plantation, sixteen plots (8 treated with fungicide and 8 untreated) were constructed. Due to the presence of an epidemic on the adjacent plantation prior to planting, trees were exposed to high levels of natural infection. With 24 measuring trees per plot, plots were randomly assigned. A five-tree buffer zone preceded and followed the measurement plot, with a four-tree buffer zone in between. Except for blocks A and B, which were in the same windrow, other blocks were separated by windrows. Due to size constraints in terms of aspect and soil type, these plots were planted in the same windrow.

Geeken Chemical Testing of Fungicides for the control of Mycosphaerella on Eucalyptus
Fungicides Spraying for the control of Mycosphaerella on Eucalyptus

Trees were fertilized with diammonium phosphate and urea at a rate of 100 kg ha-1. In December, all plots were aerially sprayed with the pesticide Fastac-duo (250 ml product ha-1) to control an over-threshold population of Chrysophtharta Agricola. It is a kind of Chrysophtharta (Coleoptera: Chrysomelidae). Between December and January, a tractor-mounted shrouded sprayer was used to apply a post-planting fungicide. Between the planting mounds, Roundup, and the surfactant Freeway were sprayed. And Lontrel with the surfactant Freeway was sprayed on the planting mounds. In Jan slashing between the planting, mounts were completed. Fungicide treatments began in June and continued every three weeks until the trees were too tall to spray by hand. The goal of the fungicide applications was to reduce Mycosphaerella infection rather than to test the fungicides’ viability. Hence a variety of fungicides were utilized throughout the study.

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Statistical analysis

In the exclusion trial, cumulative increments for height, diameter, and stem volume were calculated for treated and untreated plots. For each volume, height, and diameter, analyses of variance were performed in Genstat statistical tool, with time as a factor and initial height, diameter, or stem volume as covariates. Block was also taken into account while determining any site variations. Group regression analysis in Genstat® was used to find significant changes in slopes at each interval, with tree age as the explanatory variable and treatment as a grouping, to test the hypothesis that regression lines had the same slope. This was done again to see if the intercepts of regression lines for each era of growth were the same. On data from fungicide-treated and untreated plots spanning the following factors are being considered:

  • The trial period.
  • The period of greatest infection.
  • The period immediately following leaf phase change, linear regressions of total volume.
  • Increments in height, diameter, and stem volume were done.

Results

Damage assessment

Lesions appeared on young foliage in the early stages of infection, although infection was not severe enough to produce blighting and shedding of these leaves. Only minor levels of defoliation occurred throughout the winter months of June to January. Untreated plots exhibited only 6.8% defoliation, while treated plots had a mean (SE) of 3.9 percent (1.18). As fresh leaves grew on the outside of the crown during the first summer of the epidemic, inside leaves were prematurely shed, leaving a hollow inner crown. The summer months progressed, and the hollow crown’s branches began to senesce.

In May, there were substantial differences in the height of defoliation and branch senescence between fungicide-treated and untreated plots, with the mean height of defoliation for treated plots being 0.76 m and 1.26 m for untreated plots (0.04). At 24 months, the mean (SE) damage (Mycosphaerella index) in untreated plots was 22%, while damage in treated plots was 13%. As a result, MLD-related damage was decreased by 9% in plots that were treated. Fungicide application reduced mean defoliation by more than half throughout the peak infection.

Effects on Growth

Early in the trial, substantial decreases in damage were detected between treated and untreated plots, but significant reductions in height, diameter, and stem volume were not observed until the trees were 21 months old. Between January and August when the tree age was 14-21 months, an increase in mean (SE) crown damage from 17% to 22% resulted in diameter and height disparities of 8% and 7%, respectively, between treated and untreated plots. At 21 months of age, this resulted in a 17% reduction in volume, equating to 0.15 m3 ha-1.

Trees had immature foliage during this time. For the rest of the study, the differences in growth remained considerable for further 6 months. On the other hand, ontogenetic transition to adult foliage happened when trees were 21-24 months old. After the phase shift, there were no further reductions in stem diameter, height, or volume for the next six months, and the growth curves of the fungicide-treated and untreated plots were nearly identical. The slope of post-phase change regressions between stem volume in fungicide-treated and untreated plots and time did not change.

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