With the rapid expansion of Georgia’s (USA) blueberry (Vaccinium sp.) industry in the past 2 decades (Fig. 1), the demand for rooted cuttings increased exponentially. This prompted many growers to begin propagating cuttings both for their own use and for sale to other growers. The first published accounts of blueberry propagation were made in a bulletin from the US Department of Agriculture Bureau of Plant Industry entitled “Experiments in Blueberry Culture” by F.V. Coville (1910). Coville (1921) later published “Directions for Blueberry Culture, 1921,” laying out the basic procedures for the propagation and production of blueberries as a horticultural crop. In the intervening years, little changed in blueberry propagation methods (Cline and Mainland 2008; Haralson et al. 2021). Many recommendations have been made based on Coville’s work, but no preferred method has been established for either propagation per se or disease management during propagation. Thus, it is not surprising that growers and nursery operators in Georgia have applied a wide range of methods that combine elements from many different sources, resulting in wide variation in propagation methods (Haralson 2009).
Blueberry propagation is achieved primarily by rooting either softwood or hardwood cuttings, although softwood cuttings are used almost exclusively in Georgia. For hardwood propagation, cuttings measuring 4.5 to 5.5 inches long with a diameter of 1/4 to 1/2 inch are taken from the previous season’s growth in late January to early February (Haralson et al. 2021). Softwood cuttings can be taken in May to early June and late July to early August in Georgia. Softwood cuttings are cut from apical shoots from the current season’s growth and should measure between 4.5 and 6 inches in length (Cline and Mainland 2008; Haralson et al. 2021). An advantage of softwood is the speed at which rooting occurs; softwood cuttings can be rooted in 6 to 8 weeks (Haralson et al. 2021), compared with hardwood stock that can take as long as 6 months to produce a rooted cutting. In addition, hardwood cuttings also generally have lower rooting percentages and are at higher risk for stem blight (Botryosphaeria dothidea), as compared with softwood cuttings. However, softwood cuttings are subject to numerous plant diseases (Haralson et al. 2021, 2022). Registered chemical control options are limited (Haralson et al. 2013); therefore, using best-management cultural practices is important to disease suppression during propagation.
Although softwood cuttings are the primary choice for propagation material in Georgia, many different propagation systems and methods are used by growers (Haralson et al. 2022). Propagation systems can be separated into two main types: open and closed. A closed system is defined by an enclosed growing environment such as a greenhouse or shade-house, whereas an open system is exposed to the natural outdoor environment. Preliminary farm visits (2000–05) indicated that a range of growing media, containers, and pest management practices are used in blueberry propagation.
Diseases have been a particularly difficult challenge for blueberry propagation (Haralson et al. 2013, 2021, 2022). In other regions, the four main diseases affecting blueberry cuttings are Cylindrocladium root rot [Calonectria ilicicola (Cylindrocladium parasiticum)], Phytophthora root rot (Phytophthora cinnamomi), Pythium root rot (Pythium sp.), and Rhizoctonia root rot (Rhizoctonia sp.) (Cline 2004; Haralson et al. 2013; Schilder and Cline 2017). In Georgia blueberry nurseries, the predominant pathogens are C. ilicicola and Rhizoctonia sp., with water molds (Phytophthora and Pythium species of the Oomycete class) so far contributing little to plant losses from disease (Haralson et al. 2021). C. ilicicola is spread primarily through contaminated plant material or propagation substrate, and reuse of propagation media has been strongly linked to Cylindrocladium root rot in Georgia and North Carolina, USA, rooting beds (Cline 2004; Haralson et al. 2022). Likewise, a similar trend was observed in Georgia for Rhizoctonia root rot (Haralson et al. 2022).
With regard to fungicide use, efficacious fungicides for blueberry propagation are limited due to lack of US Environmental Protection Agency registrations. Fludioxonil (Cannonball WG; Syngenta Crop Protection, Greensboro, NC, USA) is registered for use against Rhizoctonia and Calonectria, but this may be the only currently registered fungicide with a blueberry propagation use pattern on the label. Azoxystrobin (Abound FL, Syngenta Crop Protection), which is known to have activity against Rhizoctonia, is registered for use on blueberry, but it is not registered specifically for a propagation use pattern. The use pattern language is often debated when selecting fungicides, but a conservative approach to fungicide use would dictate that the use pattern must be on the label to allow for a legal application, especially for enclosed structures.
To better understand the diverse methods of propagation found in Georgia and as a baseline for developing best-management practices, a survey was conducted in 2007 to document production and disease management methods in use. To further document changes in the industry and production practices following the first survey and subsequent efforts to educate producers regarding disease management practices, a second survey was conducted in 2022.
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