Boxwood (Buxus spp.) is the most commonly cultivated woody ornamental shrubs in landscape settings and nursery production. Boxwood is grown for its attractive evergreen foliage and versatility in both formal and informal gardens. Meeting the high demand for boxwood plants worldwide has become challenging in recent years as the boxwood industry has been negatively impacted by a growing number of serious diseases and arthropod pests. Globally, the most common arthropods of concern are boxwood leafminer (Monarthropalpus flavus, Diptera: Cecidomyiidae), boxwood psyllid (Psylla buxi; Hemiptera; Psyllidae), Eurytetranychus buxi (Acari: Tetranychidae) and the invasive moth, Cydalima perspectalis (Lepidoptera: Crambidae). Moreover, major diseases of boxwood include boxwood blight (Calonectria pseudonaviculata, Hypocreales: Nectriaceae), Volutella blight (Pseudonectria buxi, Hypocreales: Nectriaceae), and Phytophthora root and crown rot (Phytophthora spp., Peronosporales: Peronosporaceae). These pests and diseases can lead to significant economic losses to growers and can decimate plants in landscape settings. Here we have reviewed recent research advances focused on the description and management of boxwood arthropod pests and diseases. Boxwood arthropod pests and diseases can be managed by implementing integrated arthropod pest and disease management strategies such as sanitary and cultural practices, genetic resistant cultivars, biological and chemical control methods. This information is provided to aid nursery producers, landscape industry professionals, and other stakeholders in developing integrated arthropod pest and disease management plans for boxwood.
Phytopythium vexans (de Bary) Abad, de Cock, Bala, Robideau, A. M. Lodhi & Levesque is an important waterborne and soil inhabiting oomycete pathogen causing root and crown rot of various plants including certain woody ornamentals, fruit, and forest trees. Early and accurate detection of Phytopythium in the nursery production system is critical, as this pathogen is quickly transported to neighboring healthy plants through the irrigation system. Conventional methods for the detection of this pathogen are tedious, frequently inconclusive, and costly. Hence, a specific, sensitive, and rapid molecular diagnostic method is required to overcome the limitations of traditional identification. In the current study, a loop-mediated isothermal amplification (LAMP) assay was developed for the identification of P. vexans. Several sets of LAMP primers were designed and screened, but PVLSU2 was found to be specific to P. vexans as it did not amplify other closely related oomycetes, fungi, and bacteria. Moreover, the developed assays were sensitive enough to amplify DNA up to 102 fg per reaction. The real-time LAMP assay was more sensitive than traditional PCR and culture-based methods to detect infected plant samples. In addition, both LAMP assays detected as few as 100 zoospores suspended in 100 mL water. These LAMP assays are anticipated to save time in P. vexans detection by disease diagnostic laboratories and research institutions and enable early preparedness in the event of disease outbreaks.
Phytopythium was initially grouped with closely related species of the Pythium group, which German botanist Nathanael Pringsheium first described in 1858. Later with the progress in studies of this group, the clade K (Ovatisporagnium) of the genus Pythium was concluded to be more closely related to the genus Phytophthora than Pythium. Ovatisporangium in the Pythium group was then replaced by the term Phytopythium. Hence, the genus Phytopythium is relatively new and is different from Pythium (Bala et al. 2010; Lodhi et al. 2020; Tkaczyk 2020). It exhibits intermediate morphological features between Phytophthora and Pythium but is unique in having internally proliferating papillate sporangia and cylindrical or lobate antheridia (De Cock et al. 2015). Phytopythium helicoides (Abad, De Cock, Bala, Robideau, Lodhi & Levesque) and Phytopythium vexans (Abad, De Cock, Bala, Robideau, Lodhi & Levesque) are two closely related emerging oomycete plant pathogens in the Phytopythium group. Several other names have been provided to P. helicoides in the past such as Pythium helicoides (Drechsler 1930) and Ovatisporangium helicoides (Azizi et al. 2013) whereas P. vexans (Ivors et al. 2008) was called Pythium vexans and Ovatisporangium vexans (Uzuhashi et al. 2010).
Phytophthora root rot caused by Phytophthora cinnamomi Rands is one of the major diseases of flowering dogwoods (Cornus florida L.). The severity of root rot disease increases when the plants are exposed to flooding conditions. A study was conducted to determine the efficacy and timing of application of different fungicides, biofungicides, host plant defense inducers, and fertilizer to manage Phytophthora root rot in month-old seedlings in simulated flooding events for 1-, 3-, and 7- days. Preventative treatments were drench applied 3 weeks and 1 week before flooding whereas curative treatments were applied 24 hrs. after flooding. Dogwood seedlings were inoculated with P. cinnamomi 3 days before the flooding. Plant height and width were recorded at the beginning and end of the study. At the end of the study, plant total weight and root weight were recorded and disease severity in the root was assessed using a scale of 0-100%. Root samples were plated using PARPH-V8 medium to determine the percentage recovery of the pathogen. Empress Intrinsic, Pageant Intrinsic, Segovis, and Subdue MAXX, as preventative and curative applications, were able to suppress the disease severity compared to the inoculated control in all flooding durations. All treatments, with the exception of Stargus as preventative application 3 weeks before flooding and Orkestra Intrinsic as curative application, were able to suppress the disease severity compared to the inoculated control for 1-day flooding event. Aliette and ON-Gard were effective in the first trial when applied preventatively in both 1 week and 3 weeks before flooding but not in the second trial. Signature Xtra was effective as preventative application but not as a curative application. Interface was effective as curative application but not as preventative application. The findings of this study will help nursery growers to understand the performance of fungicides, biofungicides, host-plant defense inducers, and fertilizer in different time intervals and repeated applications to manage Phytophthora root rot in flooding conditions.
Boxwood is one of the most popular evergreen shrubs in the United States, the production of which is currently challenged by boxwood blight, an emerging threat that has spread across 30 states. A thorough understanding of boxwood production, plant health, management practices and economic impact could aid in answering the needs of the nursery industry in managing this disease. An online modified Delphi survey was conducted to identify grower perceptions on processes, programs, and practices to limit or prevent the entry and spread of boxwood blight disease. The expert panel consisted of 29 nursery producers who represented a significant portion of boxwood production nationally. The panel members rated boxwood blight as the third most problematic disease with a potential to be number one in the future. Boxwood transplants were perceived as the main source of boxwood blight outbreak, followed by cutting tools, nursery equipment, containers, plant debris, irrigation water, worker hygiene, and other crops. According to the panel responses, cultural control methods, inspection, and quarantine of incoming plant material, scouting, and sanitization were the most important practices that can limit or prevent plant diseases during boxwood production. The panel members did not agree that the composted manure could influence the spread of plant disease in boxwood production, although this has been verified by the findings of various previous research experiments. Panel members were very familiar with scouting and employee training, best management practices, and the boxwood blight cleanliness program. This study documents the key components, practices, and procedures in boxwood production that could influence the spread of boxwood blight in nurseries and could be further verified by sampling and laboratory assays to specify the critical control points in the production process.
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