Stem diseases of blueberry (Vaccinium spp.) can cause significant crop loss as well as loss of entire bushes. Stem diseases are also more difficult to control with fungicides than foliar or fruit diseases. A screening program was initiated to test blueberry cultivars for resistance to two pathogenic fungi: botryosphaeria stem blight and phomopsis twig blight. An attached stem assay was developed to compare the host response with both fungi. The relative resistance of 50 blueberry cultivars was assessed using stem lesion lengths, analyzed on a log scale, taken at 4 weeks postinoculation. For Botryosphaeria stem blight, mean lesion length ranged from about 10 mm in resistant cultivars to about 140 mm in susceptible cultivars. The half-high cultivars Northsky, Northblue, and Chippewa, and the lowbush cultivar Putte were among the most resistant. Phomopsis twig blight lesions ranged in mean length from about 18 to 98 mm. Similar to results for Botryosphaeria stem blight, resistance was limited to half-high (`Northsky' and `Chippewa') and lowbush (`Blomidon', `Chignecto', and `Cumberland') cultivars. Individual cultivars resistant to one pathogen were not necessarily resistant to the other; although, overall, the resistances were correlated. Approximate 95% confidence intervals were established for all cultivars to predict mean performance across years. The cultivars tested varied in resistance, but the largest single factor affecting lesion length was the fungal isolate used for inoculations. These data enable us to identify cultivars resistant to both diseases that can be used for planting in problem areas, as well as selection of parental material for breeding cultivars with improved resistance.
James J. Polashock and Matthew Kramer
Mary C. Koelsch and Janet C. Cole
Vinca minor production in Oklahoma nurseries has declined in recent years due to foliar diseases. A study was conducted to determine whether several labeled and experimental fungicides control these foliar diseases in Vinca minor `Bowles'. This study was conducted outdoors under unusually mild and humid conditions, which were conducive factors for disease symptoms to occur throughout the season. Plants were sprayed at weekly intervals with the fungicides propiconazole (0.95 ml/liter), thiophanate methyl (1.58 ml/liter), thiophanate methyl/mancozeb (1.79 g/liter), triforine (3.95 ml/liter), CC 17461 (3.95 ml/liter), CGA 173506 (0.47/liter), or SAN 619 (0.79 ml/liter). Thiophanate methyl/mancozeb was the most effective of all chemicals at decreasing foliar dieback; however, no chemical completely controlled the disease symptoms throughout the season. Dry weights of plants treated with thiophanate methyl/mancozeb were greater at the end of the season than those of plants receiving the other fungicidal treatments.
H. Chris Wien
Flowering plants grown and marketed locally as cut flowers have become economically important in recent years, concentrating on species that are too delicate to ship long distances. Although the bulk of this production is done outdoors, extending the season at both ends by using high tunnels (unheated greenhouse structures covered with a single layer of polyethylene), has become popular. To determine the advantages and drawbacks of using high tunnels as season extension structures for cut flowers, variety trials of seven and four flower species were conducted in 2004 and 2005, respectively, both in a high tunnel and in an adjacent field. In the cool, rainy 2004 season, plants in the tunnel were ready for harvest 20 days sooner than the same varieties outside. Outside plants had 25% more stems than tunnel-grown plants, but there was no difference in average stem length. In the dry, warm season of 2005, tunnel-grown plants were 8 days earlier, and had 58% more stems, which were increased in length by 16% over field-grown plants. Lisianthus (Eustoma grandiflorum) and snapdragons (Antirrhinum) were grown in both seasons, and gave similar results both times. Tunnel-grown lisianthus showed a 34% increase in stems per plant, and an 8% increase in stem length, and the stems could be harvested 8 days earlier. Snapdragons were 9 days earlier in the tunnel both years, but tunnel-grown plants produced 22% fewer stems. Disease and insect pressures occurred in both locations, but pest species causing problems differed. With careful choice of species to be grown in tunnels, cut flower production in this environment can be optimized.
Josh A. Honig, Megan F. Muehlbauer, John M. Capik, Christine Kubik, Jennifer N. Vaiciunas, Shawn A. Mehlenbacher, and Thomas J. Molnar
0 to 5, according to a modified index adapted from Pinkerton et al. (1992) : 0 = no detectable EFB (includes presence of “sunken lesion” phenotypes where a few small sunken cankers that lack fungal stromata) = 0% of stems diseased; 1 = single canker
Joseph N. Wolukau, Xiao-Hui Zhou, Ying Li, Yong-Bin Zhang, and Jin-Feng Chen
. Foliar and stem disease indices for Cucumis melo L. (unless specified) germplasm in response to D. bryoniae inoculation from a plastic house screen. Table 1. ( continued )Foliar and stem disease indices for Cucumis melo L. (unless