A Systems Approach for Management of Pests and Pathogens of Nursery Crops

Nursery Production Systems Are Complex Systems Horticultural nurseries are exceedingly complex agricultural systems, making pest and pathogen management very challenging. Compared to crop monocultures, nurseries are characterized by extreme heterogeneity in plant material. The typical agricultural row crop contains a single cultivar of a single species, grown over hundreds or even thousands of acres, whereas a single horticultural nursery of 40 acres may grow upward of 500 different plant taxa in any given field season (Fig. 1). The typical agricultural crop is started from a uniform propagative material: seeds, clonally propagated tubers, or cuttings from a single source. In contrast, many nurseries propagate multiple species, each from a variety of sources including seeds, bulbs, tubers, cuttings, scions, grafted rootstocks, and tissue culture. This propagative material may originate from multiple sources including on-site production blocks and domestic and overseas markets and can be comingled in propagation blocks. Nurseries are also characterized by extreme spatial and temporal heterogeneity. Plants typically undergo repotting several times as they are transferred from micropropagation cells (tissue culture plantlets) or flats (seeds or cuttings), and are moved from the propagation house to production greenhouses to container yards or the field. Plants are densely packed in the early stages of growth, and are spread further apart as the canopies expand. Container stock is constantly moved from place to place in the nursery and comingled with other lots. Different plant species require different potting media with particular biological, chemical, and physical properties. Blocks of plants with similar water use are grouped together, but there may be several different irrigation systems (drip, microsprinklers, overhead spray) in a single nursery, and several different irrigation frequencies. In contrast, the typical monoculture row crop is grown in a fairly uniform growing environment, generally in a single soil type with similar physical, chemical, and biological properties, although slope and aspect may vary within the field. Cropping history, tillage, organic matter management, soil fertility, irrigation regime, sunlight, and plant spacing are also fairly uniform within monoculture crops. Unlike nursery crops, most agricultural crops stay in the same place once planted.