Most growers would concede that a high-value fruit crop such as peach requires the best land you've got (i.e., good air and soil drainage) for consistent, reliable production. However, with limited suitable land available to buy or lease, urban encroachment pressure, and the concern to minimize unproductive (i.e., fallow) land in an operation, grower decisions about where and when to replant are complicated. The decision to replant on a “good” site that has been in peaches before, perhaps continuously for many years, may dramatically impact future profitability.
It is best to consider that a peach orchard is an ecosystem (a biological community of interacting organisms and their physical environment). Peach is a “susceptible host” in this ecosystem because it is subject to many living (biotic) insults. Long-term monoculture of peach actually causes many organisms to build up over time. For example, fungal pathogens that build up on-site include Armillaria, Phytophthora, and Verticillium. Nematodes such as ring, dagger, rootknot, and lesion may also accumulate over time. Other pathogens and insects may build up off-site on nearby alternate host plants, in abandoned orchards, etc. (i.e., Prunus necrotic ring spot virus, X-disease, and plum curculio). These may serve as a reservoir for future problems!
Dr. Guido Schnabel, Fruit Pathologist at Clemson University, examines a peach replant site with a history of Armillaria root rot disease. Root grafting facilitates rapid spread of the disease down the tree row of closely spaced (6 foot) trees. Photo courtesy of Desmond Layne
The physical (abiotic) soil environment can also be impacted adversely by long-term peach monoculture. Specifically, vital mineral nutrients and soil organic matter may be depleted. Soil acidity at deeper soil depths may increase. The soil structure may be altered so that compaction adversely affects aeration and water drainage, causing an unfavorable environment for root development. Long-term application of persistent herbicides can also cause residual problems that may compromise tree growth.
Because this ecosystem (both biotic and abiotic factors) has changed over many years of peach production, it may be very difficult for new, young trees to establish a strong root system. Young trees that are stressed may be more susceptible to winter injury and pathogenic attack, causing premature decline and death. As a grower, you need to decide whether the replant site is worth renovation, or whether abandonment (from peaches at least) is a better idea.
If you decide to renovate a replant site, a long-term plan is advisable. If you already own the land and you know the orchard history, this may be easier than if the land is to be leased (or bought) and only a limited site history is available. A good first step is to map the orchard one year before it is removed. A best-case scenario is that the orchard is mapped every several years throughout its life to note if/when and where trees die. This may help track disease spread and determine “hot spots” that may need special treatment or avoidance in the future. The map should make note of healthy, dying, dead, or missing trees. Compass direction and GPS coordinates would be helpful if possible. It is also good to note any low spots or topographic changes, drainage channels, and adjacent habitats (i.e., alternate hosts, etc.).
The next step in the plan is to determine the cause of tree death. You can make appropriate notes on the map by using a relevant legend. Diagnosis may require the help of a knowledgeable county agent, consultant, or Extension specialist, but many problems are rather easy to detect. It is necessary to determine whether the trees were killed by a soilborne disease, poor soil drainage/waterlogging, winter injury, insects (i.e., borer, scale), nematodes (i.e., peach tree short life), rodents, or tractor blight.
Soil sampling from the overall site and “hot spots” will assist in determining if plant parasitic nematodes are present and fumigation is warranted. If you decide to fumigate, you should consult with a licensed custom applicator and adhere to state regulations. One can also determine if soil pH adjustment and/or nutrient and organic matter amendments are necessary. If the site is poorly drained or there are low spots, you could consider installing tile drainage or using raised beds. The cost of modifying the site with heavy equipment should be carefully considered.
Prior to replanting, the goal should be to modify the old orchard ecosystem and make it more suitable for peaches. If you can keep the land fallow for two years, some pathogen populations will decrease significantly. Removal of trees and working the soil to remove dead root pieces is usually helpful. However, if Armillaria is present, infected root pieces may be deep in the soil and impossible to extract. They present a future problem that should be seriously considered.
Rotation with cover crops such as wheat, rye, or sudex can be used to build organic matter. Soil amendments (i.e., lime, nutrients) should be added based on soil test results. Hard pans should be shattered and raised beds prepared if necessary. If a reliable and sufficient water source is available, installation of a microsprinkler irrigation system may prove invaluable, especially to help get the trees off to a good start should natural rainfall be inadequate.
Finally, by reducing inoculum, modifying and improving the soil and site, and making provisions for supplemental irrigation, it is possible to give the trees every advantage to get off to a good start. Selection of the appropriate rootstock and cultivar for your climate is vital. Only buy trees from a reputable nursery that produces robust trees with a strong, healthy root system. They may cost a little more, but we’re talking about a long-term investment that will hopefully provide a good return over the long run!
This column by Dr. Desmond R. Layne, “Replant Site Considerations” appeared in the March 2008 issue of The American Fruit Grower magazine on pages 68-69.