Cultural management for plant health consists of tools or methods that modify the plant’s environment to suit the specific needs of the plant, such as irrigation, species or variety selection, and planting site preparation. Cultural management also includes post-planting physical treatments that limit the damaging influences of pest presence or severity. Through physical manipulation of the protected plant’s environment, many common pests can be reduced or eliminated by managing favorable environmental conditions of the threat.
Cultural management treatments also include pruning for removal of infected tissue (sanitation) or reduction of plant density (thinning). These treatments either directly remove disease sources or improve light and air penetration of the plant to eliminate dead air, in which diseases thrive.
Planting depth is a key component of the health of all plants, where instead of being placed and nurtured by natural selection, landscape plants are generally placed by humans with a shovel. Plants are inherently more stressed and prone to pest infestation when planted too deep (or too shallow) or when planted in the wrong environmental conditions such as persistent soil water content or direct sun exposure.
For example, arborvitae planted deep (buried root collar) in moist, poorly-draining soil are virtually guaranteed to fall victim to phytophthora root rot, which at best will devastate the aesthetic appeal of the plant and at worst will kill it outright. Soil moisture is also commonly regulated by irrigation and bed mulching, but both should be applied cautiously and professionally to avoid building excessively wet, stagnant soils that can choke the roots and the root-stem junction (root collar).
Root Collar Excavation and Cultural Management
Quite often, landscape plants and trees are planted in ways that inhibit establishment and growth: either too deep in the ground, too shallow with mounded soil, or finished with excessive mulch. These issues may seem minor, but planting technique is the most common cause of landscape plants’ failure to take proper root, establish, and thrive. Planting depth and mulch depth can lead to development of girdling roots (described below), insect and disease infestation of the root collar, and poor movement of resources up and down the plant. Root collar excavation makes use of hand tools or compressed air to carefully remove debris that has accumulated around the base of the plant to expose the stem portion that is supposed to be above ground. Once the root collar is exposed, further treatments may be necessary to restore the proper function of this critical tissue that transitions the plant from roots to stem.
Cultural Management and Girdling Root Removal
Girdling roots occur when developing roots wrap around and constrict other roots or the main stem of the plant, which severely inhibits proper circulation of water and nutrients between roots and the rest of the plant. Manmade structures (such as driveways, roads, and sidewalks) and soil conditions (such as large rocks or compacted soil) may cause lateral roots to grow back toward the stem of the plant, encircling the heart roots and the main stem. As all of these continue to grow, the lateral roots begin to strangle critical plant structures. With early detection, circling and girdling roots can be corrected over time, restoring full transport of resources, and dramatically extending the longevity of the plant. It is important to fully expose the root collar (described above) and investigate the extent of the girdling roots to provide the best recommendations. In general, girdling roots should be removed with consultation from a trained professional, since removal of too much girdling root tissue too quickly can be fatal to the plant.
Plants need healthy, biologically active, well-drained, and well-aerated soil to thrive. Unfortunately, most landscape plants are growing in compacted or otherwise unhealthy soil, with little or no pore space for oxygen and water penetration. Root zone invigoration makes use of an air spade, which directs compressed air to safely break apart heavy, compacted soil, with no damage done to the root system of the plant. This service helps to decompact thick clay soil and adds pore space for adequate water and air. Root-zone invigoration can be utilized on established trees as well as in preparation for new plantings, and gives the opportunity to amend the soil with nutrients, rich compost, and soil conditioners. For preferred and high-value plants or those that are beginning to show signs of decline, root-zone invigoration is the most thorough, most beneficial service that you can give individual plants.
Sanitation pruning is simply removing declining branches or other plant parts to prevent further spread of the active disease or insect pest. This is particularly important for diseases that cannot be effectively managed with chemical treatment alone. For black knot fungus in plums and cherries, sanitation pruning is one of the only options to control and suppress the disease, while chemical application can follow pruning to prevent new infection. In Leyland cypress trees, Seiridium canker can be treated with an intensive chemical treatment program; however, it is recommended that infected branches be removed to provide the greatest likelihood of disease control while reducing the total amount of fungicide needed. In spruces (especially blue spruces), cytospora canker is a significant threat, and no chemical treatments are particularly effective in suppressing the disease, while sanitation pruning or a combination of sanitation pruning and application of growth regulator substantially slows the spread. In apple and pear trees, fireblight is a common spring disease where most infections occur at bloom, through the open flowers. After infection, blossom clusters and shoots die, and there is no effective post-infection management to prohibit further spread of the disease other than to remove the dead tissue.
In general, it is recommended that sanitation pruning be done by professional plant health care specialists to ensure complete removal of the infected plant parts without unknowingly spreading the disease with contaminated pruning tools. Sanitation pruning has an immediately positive aesthetic impact given removal of dead and dying tissue, but also contributes to longer-term stress reduction and disease control by thinning plant canopies, permitting adequate light and air penetration that further suppresses disease development.
Corrective Pruning in Cultural Management
When trees or shrubs begin to encroach on your home, driveway, view, or neighboring plants, it may be time to consider corrective pruning for your landscape. Corrective pruning aims to meet the needs of the homeowner, while optimizing the health of the tree.
For example, many tree species are prone to development of codominant stems, where instead of growing a central leader, the leader branches, two main stems develop, and they compete with each other. These codominant stems create a very weak upper tree structure and are very likely to split apart in harsh weather. Corrective pruning of codominant stems consists of removing or reducing one of the stems, permitting the tree to resume growth around a strong central structure. Proper distribution of branch density also reduces likelihood of storm damage, while promoting uniform light and air penetration of the plant’s crown, improving photosynthesis and reducing disease pressure. For fruiting and flowering trees, the emphasis of corrective pruning is generally to encourage lateral growth (as opposed to upright growth) to promote development of dense, well-distributed flowers and fruit.
External support systems are often needed for newly planted and storm-damaged plants as well as species that have structures that lend themselves to damage (such as multi-leader softwoods like arborvitae). These systems can provide temporary or semi-permanent stabilization for trees, assist in reduction of plant stress and improvement of growth, and simplify management for the homeowner, landscaper, or plant health care technician.
For newly planted, windthrown, or unstable trees, ground anchors can literally save the life of the tree, allowing root growth and restabilization, followed by recommended removal of anchors after 2-3 years. Solid polypropylene chain-lock or woven polypropylene arbor-tie are very useful to secure stems of limber, leggy plants to stronger leads (or to vertical supports) to limit risk of splitting or other damage without girdling the supported stems. These supports can greatly reduce risk of structural damage while allowing the plants to develop strong, resilient stems. For extremely uniform, high-risk plantings (such as boundary screens or fruit trees), it can be beneficial to construct a full tight-wire trellis. This system provides full stability for the tree group without imposing on the aesthetic of linear tree groups.