Forty Buxus accessions from the U.S. National Arboretum National Boxwood Collection were evaluated as potted plants and detached leaves for susceptibility to Calonectria pseudonaviculata (Crous et al.) L. Lombard et al., and nine boxwood cultivars were evaluated against both species of Calonectria causing boxwood blight, C. pseudonaviculata and C. henricotiae. Accessions of B. harlandii Hance, B. sinica (Rehder and E.H.Wilson) M.Cheng, and B. microphylla Siebold and Zucc. had less disease than B. microphylla ×sempervirens, and all had fewer lesions per plant than the 20 B. sempervirens L. accessions evaluated. Variation within species was observed. Of the individual accessions, B. sinica var. aemulans (accession 60705*H), B. sempervirens (36365*J), and B. harlandii (18834*H) were least susceptible, with <10 lesions per plant. B. sempervirens ‘Scupi’ (9548*H), B. microphylla ‘Compacta’ (4899*CH), B. sempervirens ‘Arborescens’ (57953*H), B. sinica var. insularis ‘Pincushion’ (51898*H), and B. microphylla var. japonica ‘Jim Stauffer’ (72213*H) each had <20 lesions. These rankings differ from previous studies that used detached leaf and unrooted cutting assays. Normalizing to account for plant size effects on inoculation and disease increased variability for individual accession rankings but did not result in significant differences in the most and least susceptible accessions or species ranking. Nine boxwood cultivars evaluated against both pathogen species exhibited a range of susceptibility against four pooled isolates each of C. pseudonaviculata and C. henricotiae. Although small differences in disease severity were observed on boxwood inoculated with the two pathogens, there was no interaction of cultivar and pathogen species, suggesting that a cultivar rated resistant to one species was resistant to the other. These results may aid boxwood breeders to develop resistance to boxwood blight.
Todd L. Mervosh and James A. LaMondia
The effects of terbacil herbicide on strawberry (Fragaria ×ananassa Duch. `Honeoye') yield and black root rot disease were determined in field plots at two locations in Connecticut over 4 years. Terbacil treatments at up to four times the maximum label dosage caused some temporary foliar chlorosis but did not affect the health of structural or perennial roots and associated feeder roots. Development of secondary root growth (perennial roots) was not influenced by terbacil. Terbacil had no effect on the quantity of lesion nematodes [Pratylenchus penetrans (Cobb) Filip & Schur. Stek.] extracted or the amount of the fungal pathogen Rhizoctonia fragariae Husain and McKeen isolated from strawberry roots. At both locations, R. fragariae was common on plant roots by the fourth year. Terbacil treatments did not affect strawberry yields in terms of number or weight of ripe berries per plot. Our results indicate that terbacil does not contribute to black root rot or decreased yields in `Honeoye' strawberry. Chemical name used: 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4-(1H,3H)-pyrimidinedione (terbacil).
James A. LaMondia, Richard S. Cowles and Lorraine Los
Surveys mailed to strawberry growers in 1999 determined the state of nematode and root weevil awareness and practices for their management. Based on the survey response, 41 fields representative of various practices were selected for sampling throughout Connecticut. Adult black vine weevils (Otiorhynchus sulcatus) were found in only 3 fields, but notched leaves characteristic of their feeding were found in 40 fields, indicating a greater prevalence than perceived by growers. The percentage of notched leaves was positively correlated with years in production, suggesting that it took some time for the flightless weevils to migrate into and to increase to damaging numbers in fields. In fields older than 2 years, bifenthrin insecticide reduced leaf feeding compared to untreated fields or to fields treated with endosulfan or azinphos-methyl. Lesion nematodes (Pratylenchus penetrans) were detected in 31 fields and were present in about 58% of plants. When present, nematode numbers were greater in the margins of poor areas than in adjacent healthy plants (735 vs. 428 per g root, respectively). Lesion nematode numbers were also greater in replanted strawberries than rotated fields (760 vs. 304, respectively). Soil fumigation with methyl bromide, but not methyl dithiocarbamate or the combination of 1,3-dichloropropene and chloropicrin, reduced nematode densities in the following strawberry crop. Based on an economic model, nematodes reduced accumulated profit over 4 fruiting years by more than the percent loss of fruit yield. Beneficial insect pathogenic nematodes, predominantly Heterorhabditis bacteriophora and Steinernema feltiae, were found in 75% of fields to which commercially obtained nematodes had been applied, and to 14% of the remaining fields. Presence of naturally occurring insect pathogenic nematodes in strawberry fields may control root weevil populations and lead to more years of productivity.