Infestation

About: Infestation is a research topic. Over the lifetime, 8308 publications have been published within this topic receiving 82305 citations.

Importance of seed-borne inoculum in the etiology of the Ascochyta blight complex of field peas (Pisum sativum L.) grown in Victoria.

Abstract: Fungi associated with the ascochyta blight complex of field peas were isolated from 436 of 691 seedlots tested. Of the fungi detected, 94.8% of isolates were Mycosphaerella pinodes, 4.2% Phoma medicaginis, and 1.0% Ascochyta pisi. The levels of infestation of seed varied considerably from year to year and between seedlots, depending on the amount of rainfall between flowering and maturity. Within a particular pea-growing region, the level of seed-borne infection was often highest in seed from crops harvested latest. In addition, crops sown early were usually more severely affected by disease than late-sown crops, and this resulted in higher levels of seed infection. There was no correlation between the level of seed infestation by M. pinodes and the severity of ascochyta blight; however, where the level of seed infection was high (>11%) there was a significant reduction in emergence, which caused a reduction in grain yield. It may therefore be possible to use seed with high levels of seed-borne ascochyta blight fungi, provided the seeding rate is increased to compensate for poor emergence.

Effect of period and level of infestation of the fall armyworm, Spodoptera frugiperda, on irrigated maize yield.

Abstract: The effect of period and level of infestation by the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), on irrigated maize, Zea mays L., yield was determined. Two applications of the insecticide chlorpyriphos (336 g[ai]/ha) applied directly to the whorl produced yields equivalent to treatments with three applications. FAW infestation of 100% caused 45% yield reduction. A linear regression model (yield[g/plant] = 87.84 - 0.384 (% plants infested by FAW)) explained 46% of the yield variation. The economic injury level (EIL) was calculated as 2% of the plants infested. This low EIL is due to currently high subsidies provided pesticides in Nicaragua. The impact of pesticide subsidies on EIL's is discussed.

Survey of ixodid ticks in domestic ruminants in Bedelle district, Southwestern Ethiopia.

Abstract: A survey aimed at determining the status of ticks in cattle, sheep and goats in Bedelle district (Southwestern Ethiopia) was carried out from November 2007 to April 2008. Out of the total 330 animals examined, 314 (95.2%) were found to be infested (harbouring of at least a single tick). High rates of infestations were recorded across all three host species. Factors like month of collection, age and sex of host species did not show significant association with infestation rates. A total of 5,507 ticks belonging to three genera (i.e. Amblyomma, Boophilus and Rhipicephalus) were collected during the study period of which six species were identified. The species of ticks encountered comprise of Amblyomma cohaerens (44.1%), Amblyomma variegatum (13.8%), Amblyomma lepidum (1.2%), Boophilus decoloratus (24.9%), Rhipicephalus evertsi evertsi (14.3%) and Rhipicephalus lunulatus (1.7%). As about 86.7% (4,772) of the ticks were collected from cattle, it was recognised that this could be an evidence of host preference where cattle are serving as principal host while sheep and goats serve as alternative hosts. The role of ecological factors and little attention paid by livestock owners for treatment of animals against ticks are suggested to result in the abundance of ticks. Acaricide spraying should be strategically applied to control ticks. Better result could be achieved if an emphasis is being put on spraying cattle. Studies on tick-borne diseases, involvement of wildlife species as well as related factors are recommended as they may provide a valuable basis for designing and launching an all-round control programme in the country.

Maize response to corn leafhopper (Homoptera: Cicadellidae) infestation and achaparramiento disease

Abstract: To determine the effect that the timing of infestation of Dalbulus maidis (DeLong & Wolcott), a vector of 3 maize pathogens, known collectively as “achaparramiento,” has on stunt symptoms and maize yield, we conducted a field trial in the Sebaco Valley of Central Nicaragua. Achaparramiento has caused severe yield losses in maize throughout Central America. Six periods of D. maidis infestation were created using exclusion cages of finemesh screening. The treatments were natural infestations of D. maidis during 0-10, 10-20, 20-30, 30-40, 0-40 d after plant emergence, and no D. maidis infestation. The treatments were repeated on 3 planting dates. During the season, population densities of D. maidis varied from 4 to 8 per plant for the 1st planting date, from 1 to 3 per plant in the 2nd planting date, and from 2 to 8 per plant in the 3rd date. Planting date had a significant effect on plant height, the number of ears, and the yield per plant, but not on disease symptoms or the length of the ears. The timing and duration of D. maidis infestation affected disease symptoms, plant height, and yield: earlier periods of D. maidis infestation produced more pronounced disease symptoms, shorter plants, and lower yields than treatments with late D. maidis infestation. Plant infested 10-20 d after plant emergence had significantly lower yields than plants infested 30-40 d after plant emergence, and plants infested 30-40 d after plant emergence did not have Significantly different yields from plants that were not infested. The yield reduction was caused by smaller ears, not a reduction in the number of ears. The results demonstrate that a management program for reducing the effects of maize stunting diseases caused by the 3 pathogens should be focused on tactics that reduce D. maidis levels from seedling through midwhorl stage of maize growth.

Yield Evaluation of Maize Cultivars across Environments with Different Levels of Pink Stem Borer Infestation

Abstract: Yield under infestation by the pink stem borer [Sesamia nonagrioides (Lefebvre)] has been proposed as the best estimator of maize (Zea mays L.) performance under pink stem borer attack. Yield is a complex trait that greatly interacts with the environment. Several methods could be used to study the genotype x environment (GE) interaction. The objective of this work was to study the GE interaction for yield of 49 maize hybrids in five different environments by the Site Regression (SREG) and factorial regression methods. Locations presented different levels of natural infestation by the pink stem borer. The biplot obtained by applying the SREG method allowed visual cultivar evaluation. The factorial regression method incorporated genotypic and environmental covariates that enhanced biological interpretation of GE interaction. Hybrid A637 × EP42 would be recommended in northwestern Spain under medium and high natural infestation by the pink stem borer because it showed high and stable yielding ability. Genotypic and environmental covariates explained approximately 75% of the GE interaction variation, but other genotypic covariates could be introduced in the model to reduce GE residual variation to a nonsignificant level. In general, GE effects for grain yield were mainly due to earliness, vigor effects, and environmental yield limiting factors such as the mean of minimum temperature and percentage of air humidity.