Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 73-77). Also available via the Internet.

The process of diagnosing the foliar nutrient status of Fraser fir [Abies fraseri (Pursh)Poir.] Christmas trees and prescribing fertilizers is not well understood. Agricultural researchers have established critical yield levels for agronomic crops that are objective measures of crop quality and have associated these yields with nutrient status; however, Christmas tree quality is subjective and not well associated with nutrient status. A nutrient-sensitive tree response factor that reflects tree quality is needed for a proper diagnosis. The purpose of this study was to determine the relationship between nutrient balance and indices of tree quality and to evaluate how nutrient balance and tree quality can be manipulated by fertilizer inputs based on the Diagnosis and Recommendation Integrated System. In 1984 a factorial N, P, pH, fertilizer source, and fertilizer frequency trial was installed in northwestern North Carolina. A randomized complete block design with factorial combinations of all five factors was used. After three years, the fertilizer trial was analyzed to study the effects of fertilizer additions on foliar nutrient balance and tree quality. Several tree response factors were measured in the fall after dormancy. Statistical methods such as correlations and multivariate discriminant analysis were used to determine which response factors were correlated with foliar nutrients and which factor most governed tree quality. DRIS indices were calculated for six independent plots of different fertility treatments. Basal diameter (BD) was the strongest discriminator of tree quality and was used as a substitute for yield in the DRIS analyses. The importance of nutrient intensity was demonstrated since significant nutrient / dry matter ratios were calculated for N, P, K, and Mg. Balance was shown to be important since the indices for N, K, and Mg were a function of the four other nutrient ratios other than dry matter, and the P and Ca indices were a function of three nutrient ratios other than dry matter. Nutrient balance was also shown to be important by the significant relationship of BD as a function of the nutrient balance index (NBI). When NBI had a relatively small value, large BD trees were produced; as NBI values increased, BD decreased. Fertilizer additions that created nutrient imbalances also decreased BD, in spite of the high nutrient intensities found in the foliage. These results show that nutrient balance in Fraser fir foliage, as well as nutrient intensity, is important for producing optimal Christmas tree quality. / Master of Science

Fraser fir [Abies fraseri (Pursh) Poir.] is an important Christmas tree species in Virginia. Because it is responsive to fertilization, and because most Fraser fir growers fertilize their crop, a scientifically-based nutrient diagnosis and fertilizer recommendation system is needed. The objective of this study was to develop and test DRIS norms for Fraser fir Christmas trees grown in Virginia for the ultimate purpose of establishing a nutrition diagnosis and fertilizer prescription system. A total of 107 Fraser fir plantations were sampled for foliage, soil, and diameter measurements. These plantations represented the range in site conditions and management practices for Fraser fir Christmas trees grown in Virginia. Foliage was analyzed for N, P, K, Ca, Mg, Zn, Mn, Fe, Cu, and B. Soil was analyzed for extractable macro- and micronutrients. DRIS norms were developed from these data using standard DRIS procedures. A total of 42 nutrient ratios were significant discriminators of tree performance as measured by variation in ground line diameter. The norms were tested using sixth year data from a factorial fertilizer trial. Nutrient limitations due to both deficiencies and imbalance were detected and correctly diagnosed using the newly-derived norms. A complete validation is required, but this preliminary test showed that these norms are useable and useful in their present form. In the process of developing and testing the norms, modifications to traditional DRIS methods were used to meet the special conditions of this crop. DRIS symmetry was maintained by including non-significant ratios, but setting their standardization functions equal to zero. This reduced the influence of the non-discriminating nutrient ratios on the DRIS analysis. Norm ranges as opposed to discrete norms (ratio means) were used to correct for the influence of extremely variable micronutrient ratios on the DRIS analysis. Soil norms did not enhance diagnoses over and above using foliar norms alone. This is due to soil sampling variation, poor correlations of extractable nutrients with tree performance, and an incomplete understanding of fertilizer reactions and uptake chemistry in a variety of soils. Each crop presents unique challenges in the application of DRIS. DRIS should not be naively applied without investigating these problems. The DRIS norms established in this study, and the modifications to standard DRIS methods, provide a sound scientific basis upon which to build a nutrient diagnosis and fertilizer recommendation system for Fraser fir Christmas trees grown in Virginia. / Master of Science

Procerum root disease (PRD), caused by Leptographium procerum (Kendr.) Wingf., is the most serious problem facing Christmas tree growers of eastern white pine, (Pinus strobus L.). Limited studies have shown an association between PRD affected trees and insect infestations, and L. procerum has been recovered from field collected insects. The objectives of this study were to demonstrate the association of L. procerum with the life cycle of potential insect vectors and determine if the insect associates could transmit the fungus to healthy trees. To study the association of PRD with potential insect vectors, PRD symptomatic trees from 4 Christmas tree plantations were excavated and examined monthly, June - September in 1988 and 1989, and April - September 1990. Potential insect vectors were collected weekly in baited pit-fall traps placed in: 1) paired plots placed in asymptomatic and symptomatic areas of PRD symptomatic plantations, 2) plots in plantations where PRD was absent, 3) plots in the headlands of plantations, 4) plots in forested areas and 5) one plot in an urban setting. Trees in the plots were also inspected for evidence of weevil feeding and for development of PRD. Larvae of two weevil species, Hylobius pales (Herbst.) and Pissodes nemorensis Germ., were recovered from 52, 42, and 43% of PRD symptomatic eastern white pine in 1988, 1989, and 1990, respectively. Hylobius pales and P. nemorensis contaminated with L. procerum were recovered from all plots. The proportion of H. pales contaminated with L. procerum was 73.0% in 1988, 86.5% in 1989 and 72.9% in 1990 while the proportion of P. nemorensis contaminated with the fungus was 17.8, 21.2 and 14.2% in 1988, 1989 and 1990, respectively. Over the three year period of the study, the proportion of PRD infected trees in the symptomatic paired plots rose from 3.6 to 29%. None of the trees in the asymptomatic plots became symptomatic. Transmission of L. procerum was determined by caging field collected and artificially infested H. pales and P. nemorensis on eastern white pine seedlings for 24 hours. To determine if transmission of the fungus during oviposition leads to contamination of the brood,field collected H. pales adults were allowed to feed and oviposit on fresh white pineee bolts. Feeding by artificially infested H. pales adults resulted in transmission of L. procerum 90 and 98% of eastern white pine seedlings in 1989 and 1990, respectively. Field collected H. pales adults transmitted the fungus to 58 and 68% of seedlings in 1989 and 1990, respectively. Artificially infested and field collected P. nemorensis adults transmitted L. procerum to 100 and 28% of the seedlings respectively. All bolts oviposited on by field collected H. pales became colonized by L. procerum and 100% of the weevils that emerged from them were contaminated with the fungus. The results from this study confirms the rules for insect transmission of a plant pathogen. / Ph. D.