can serve as alternate hosts for Cronartium ribicola , the causal agent of white pine blister rust (WPBR). This disease was introduced into North America over 100 years ago and has caused major mortality to native five-needle pines. Once the Ribes
Todd A. Burnes, Robert A. Blanchette, Jason A. Smith, and James J. Luby
Abigail J. Walter, YongPing Duan, and David G. Hall
Huanglongbing, one of the most devastating diseases of citrus, is associated with the bacterium ‘Candidatus Liberibacter asiaticus’ vectored by the Asian citrus psyllid, Diaphorina citri, in North America. Murraya paniculata is a common ornamental plant that is an alternate host of both the psyllid and bacterium. We tested M. paniculata and Citrus sinensis grown together in the same field for their titer of ‘Ca. L. asiaticus’. We found the bacterium in both M. paniculata and C. sinensis, but the titer was four orders of magnitude lower in M. paniculata. We also assayed D. citri from laboratory colonies reared on either ‘Ca. L. asiaticus’-infected M. paniculata or infected Citrus spp. Psyllids reared on infected M. paniculata also carried bacterial titers five orders of magnitude lower than psyllids reared on infected Citrus spp. These observations imply resistance to huanglongbing in M. paniculata.
Harold A.A. Gibbs
Xanthomonas campestris pv. vesicatoria (Xcv) recovered from Commelina benghalensis L., caused bacterial spot disease in cultivars of pepper and tomato susceptible to the pathogen. This is the first reported case of a dicot-infecting Xc pathovar infecting a monocot plant, represented here by a member of the Family Commelinaceae. Laboratory strains of the pathogen that included 81-23, 81-23M13, 82:4, 2595, and P6AD4, known to be pathogenic to pepper and tomato, promoted bacterial spot symptoms on leaves of C. benghalensis L. Of the 63 field isolates recovered from infected C. benghalensis L., 30 gave biochemical and physiological reactions consistent with Xcv pathogens, whereas 10 of the latter promoted bacterial spot disease in the test cultivars resulting in the identification of seven pathogenic races, including P2, P5, P6, P5T1, P5T2, P6T2, and P6T3. Bacterial spot disease symptoms developed on stems only when C. benghalensis L. was spray-inoculated with strains 81-23, 81-23M13, and P6AD4. Bacterial concentration increased in planta by as much as 103 per lesion of the leaf, whereas growth of the same strains was restricted in the stem of this weed. Growth of these three strains was, however, significantly (P ≤ 0.05) lower on NYGA amended with C. benghalensis L. stem extract than on NYGA amended with leaf extract. The ability of the bacterial spot pathogen to infect the stem of C. benghalensis L. has serious implications for management of bacterial spot disease in fields populated with this weed since stems of this plant infected with the pathogen continue to grow vegetatively and disperse throughout all fields in which it is found.
Michele R. Warmund, Jeanne D. Mihail, and Kaley Hensel
, teliospores, and basidiospores develop on Carex spp. ( Mims, 1981 ). At least 13 species of sedge have been reported as an alternate host for P. sambuci ( Afshan and Khalid, 2009 ; Arthur, 1962 ). Pycnia are the first signs observed on elderberry leaflets
Marie-José Côté and Lisa Leduc
Common barberry ( Berberis vulgaris L.) is an alternate host for black stem rust of wheat, Puccinia graminis Pers. The shrub provides a means for the pathogen to reproduce after the winter and then spread to new cereal plants in the spring
J.S. Caldwell, J.P. Amirault, and A.H. Christian
Eighty-two vegetable growers responded to a survey on pests, beneficial insects, and cover crop use sent in Winter 1993–94 to 314 members of the Virginia Assn. for Biological Farming (VABF) and participants at the 1993 Virginia Sustainable Agriculture Conference. Respondents reported 68 occurrences of insect pests on 99 vegetable crops and herbs. Six insects (flea beetle, squash vine borer, stink bug, cucumber beetles, and Mexican bean beetle) comprised 70% of the occurrences. Squash vine borer and cucumber beetles on cucurbits comprised 24% of all pest occurrences. Insect pests attacked summer squash on 57% and cucumber on 49% of the farms. Average severity of squash vine borer damage was 3.8 (range 0–4, where 0 = no damage and 4 = death or destroyed). Average severity of cucumber beetle damage was 3.0 (severe). Squash vine borer was not observed by farmers on non-cucurbit alternate hosts. Cucumber beetles were observed on horse nettle (10%) and wild nightshades (6%), but on no other plants in most cases (61%) when found on cucurbits. The most frequently observed beneficial insects were lady beetles (64% of the farms), preying mantises (42%), wasps (29%), assassin bugs (18%), and spiders (15%). Only 29% of the farms had purchased beneficial insects, with assassin bugs (10%) and lady beetles (7%) the most common types. Vetches, clovers, rye, and buckwheat comprised 69% of the responses on 23 types of cover crops and mulches used.
Kim E. Hummer and Stan Pluta
In the late 1800s a European disease called white pine blister rust, Cronartia ribicola Fisher, was introduced into the United States. By 1937 this disease had naturalized and was firmly established in native Ribes across the country. White pine blister rust causes economic damage to white pines and infects leaves of some Ribes late in the summer after harvest. Ribes serve as obligate alternate hosts for this disease. Our objective was to determine which Ribes species were susceptible to white pine blister rust under field conditions in Corvallis, Ore., where inoculum is naturally present. In 1995 and 1996, 57 Ribes taxa from North and South America, Europe, and Asia, were evaluated in mid-August and mid-September for presence of white pine blister rust. Susceptibility was determined by the rust infection of the abaxial leaf surfaces. Rust infection was rated on a scale from 1, no infection observed, to 9, severe infection covering almost the entire surface of at least three or more leaves. Data from 1995 indicated that 22 Ribes taxa were susceptible to white pine blister rust, while 35 others had no infection. The 1996 data will be reported. Species without infection may offer resistance genes to breeders who wish to develop rust-resistant commercial fruit cultivars.
Kim E. Hummer
The center of diversity for white pine blister rust (WPBR) (Cronartium ribicola J.C. Fischer) most likely stretches from central Siberia east of the Ural Mountains to Asia, possibly bounded by the Himalayas to the south. The alternate hosts for WPBR, Asian five-needled pines (Pinus L.) and Ribes L. native to that region have developed WPBR resistance. Because the dispersal of C. ribicola to Europe and North America occurred within the last several hundred years, the North American five-needled white pines, Pinus subsections, Strobus and Parya, had no previous selection pressure to develop resistance. Establishment of WPBR in North American resulted when plants were transported both ways across the Atlantic Ocean. In 1705, Lord Weymouth had white pine (P. strobis L.), also called weymouth pine in Europe, seed and seedlings brought to England. These trees were planted throughout eastern Europe. In the mid-1800s, WPBR outbreaks were reported in Ribes and then in white pines in eastern Europe. The pathogen may have been brought to Europe on an infected pine from Russia. In the late 1800s American nurserymen, unaware of the European rust incidence, imported many infected white pine seedlings from France and Germany for reforestation efforts. By 1914, rust-infected white pine nursery stock was imported into Connecticut, Indiana, Massachusetts, Minnesota, New Hampshire, Ohio, Pennsylvania, Vermont, and Wisconsin, and in the Canadian provinces of Ontario, Quebec, and British Columbia. The range of WPBR is established in eastern North America and the Pacific Northwest. New infection sites in Nevada, South Dakota, New Mexico and Colorado have been observed during the 1990s.
Brent A. Holtz
Pistachio (Pistacia vera) was successfully introduced into California and initially touted as a tree nut crop with no disease or insect pests. Unfortunately, these expectations were dashed as a number of diseases and pests followed commercial plantings, making plant protection practices integral to production. Verticillium wilt (Verticillium dahliae) devastated early plantings but is now controlled with the use of resistant rootstocks. Botryosphaeria blight (Botryosphaeria dothidea) and alternaria late blight (Alternaria alternata) are recently arrived foliar fungal diseases that blight fruit clusters and defoliate trees, respectively, and multiple fungicide applications are needed for control. The conversion to low volume irrigation systems, specifically to drip or buried drip, has reduced disease. Pruning out botryosphaeria blight infections has reduced overwintering inoculum and disease, while current research aims at accurately predicting infection events to increase fungicide efficacy. A number of hemipteran insect pests have been associated with epicarp lesion: spring treatments have been replaced with dormant carbaryl and oil applications which are less toxic to beneficial insects while controlling phytocoris (Phytocoris californicus and P. relativus) and soft scale pests. Early season insect damage can be tolerated because trees compensate by maturing a higher percentage of remaining fruit kernels. Some mirid (Calocoris spp.) pests can be effectively reduced by eliminating alternate hosts in an effective weed control program. If lygus (Lygus hesperus) populations are present, weeds should not be disturbed from bloom until shell hardening to prevent movement by insects into the trees where feeding can result in epicarp lesion. Stink bugs (Pentatomidae) and leaffooted bugs (Leptoglossus clypealis and L. occidentalis) can penetrate the hardened shell and cause internal nut necrosis along with epicarp lesion. Trap crops are used to monitor pest populations in order to develop treatment thresholds. Degree-day based timing of treatments increase insecticide efficacy for the control of navel orangeworm (Amyelois transitella) and obliquebanded leafroller (Choristonuera rosaceana), but navel orangeworm populations are more effectively managed by destroying unharvested over wintering fruit. Bacillus thuriengiensis sprays, liquid-lime-sulfur, and biological control show promise in controlling obliquebanded leafroller.
Ebrahiem M. Babiker, Stephen J. Stringer, Barbara J. Smith, and Hamidou F. Sakhanokho
., 2010 ; Rebollar-Alviter et al., 2011 ; Zheng et al., 2017 ). T. minima is a heteroecious fungus requiring both primary and alternate host plants to complete its life cycle ( Hiratsuka 1965 ). In the northern United States, the disease cycle begins