Chemical control of Didymascella thujina on Western red cedar in forest nurseries

Didymascella thujina causes a serious needle blight in nursery stock of Western red cedar. It may be controlled by cycloheximide applied at a concentration of 85 ppm of active ingredient and at a rate of 100 gal/acre (1123 1/ha) at the end of March and again at the end of April. In south Wales and south-west Scotland a third application may be needed in mid-June. Other fungicides tested were not effective against this disease.     

Ectomycorrhizal fungal communities of pedunculate and sessile oak seedlings from bare-root forest nurseries

In this study, we present the detailed molecular investigation of the ectomycorrhizal (ECM) community of Quercus petraea and Quercus robur seedlings grown in bare-root forest nurseries. In all tested oak samples, mycorrhizal colonization was nearly 100%. Morphological observation and molecular investigations (sequencing of fungal ITS rDNA) revealed a total of 23 mycorrhizal taxa. The most frequent and abundant fungal taxa were Hebeloma sacchariolens, Tuber sp., and Peziza sp.; from the detected fungal taxa, 20 were noted for Q. petraea and 23 for Q. robur. Depending on the nursery, the species richness of identified ECM fungal taxa for both oak species ranged from six to 11 taxa. The mean species richness for all nurseries was 5.36 and 5.82 taxa per Q. petraea and Q. robur sample, respectively. According to the analysis of similarity, ECM fungal communities were similar for Q. petraea and Q. robur (R = 0.019; p = 0.151). On the other hand, detected fungal communities were significantly different between nurseries (R = 0.927; p < 0.0001). Using the Spearman rank correlation, it was determined that the ectomycorrhizal diversity (in terms of richness, the Shannon diversity, evenness, and Simpson dominance indices) is significantly related to the soil parameters of each nursery. We conclude that individual nursery may be considered as separate ecological niches that strongly discriminate diversity of ECM fungi.     

Isobutylidene diurea and other nitrogen fertilizers for seedlings and transplants ofPicea sitchensis in two English forest nurseries

Summary Three slow-release nitrogen fertilizers — medium- and coarse-sized granules of IBDU (isobutylidene diurea) and formalized casein — were applied before sowing or transplanting to Sitka sprucePicea sitchensis, and their effects on growth compared with that on plots not given N or given four topdressings of ‘Nitro-Chalk’ (the source of N used in practice). The comparisons were made at two sites: a very sandy podsol and a sandy loam with better nutrient retention. The experiments with seedlings were continued for four years, those with transplants for three, and the same treatments were applied to the same plots each year. Responses to ‘Nitro-Chalk’ were large, especially during wet seasons. Formalized casein was always as effective as ‘Nitro-Chalk’ for transplants. IBDU (especially the coarse fraction) was almost as good as formalized casein for transplants at both sites and equalled it for seedlings on the sandy loam. For seedlings on the sandy podsol, both particle sizes of IBDU became steadily less effective in succeeding years, and no satisfactory reason can be offered for this decline.     

Observations on the population dynamics and vertical distribution of trichodorid nematodes in a Scottish forest nursery

The population dynamics of Trichodorus primitivus, T. velatus and Paratrichodorus pachydermus was followed between April 1974 and March 1977 in a forest nursery growing young Sitka spruce (Picea sitchensis) trees. Soil samples taken at 10 cm intervals between 0–50 cm indicated that nematode and root distribution were not correlated and numbers of T. velatus were greatest between 0–29 cm and T. primitivus between 30–49 cm. After 3 yr trichodorid numbers between 0–19 cm had increased and those between 40–49 cm had decreased. The sex ratio of T. primitivus and T. velatus males to females was 1:1.6 and 1:1.5 respectively while for P. pachydermus it was 1:1.0. The ratios of adults to larvae varied with depth, the proportion of T. primitivus and T. velatus larvae increasing with depth but for P. pachydermus the greatest larval to adult ratio was in the top 10 cm. No consistent seasonal fluctuations were observed in the populations of all three species although larval numbers were proportionally greater than adult numbers in the summer and autumn of 1975 and 1976.     

Chemical Communicators in Nematodes

Chemical signals released by one organism and perceived by another organism are classified as semiochemicals. Semiochemicals are divided into pheromones, which elicit intraspecific responses, and allelochemics, which elicit interspecific responses. Nematodes utilize and (or) recognize signals from both categories of semiochemicals. The existence of pheromones, specifically sex and aggregation pheromones, has been demonstrated in numerous plant and animal parasitic and free-living nematodes. Sex pheromones have been isolated and purified from Nippostrongylus brasiliensis and Heterodera glycines, and epidietic pheromones have been shown to be responsible for initiation of dauer juvenile formation in Caenorhabditis elegans. Allelochemics cause interspecific responses in insects and other invertebrates but are only postulated to occur in nematodes. Food-finding behavior of nematodes is almost certainly caused by host-released allelochemic messengers. Understanding of the behavioral responses and the chemical messengers that affect bioregulation of various processes in nematodes will influence future management strategies.