Tree Health Starts in the Roots

Root health is the most overlooked factor in pecan productivity. When trees decline, attention often turns to foliar nutrients, water availability, or soil fertility. Yet the real story begins belowground—within a complex system that most growers rarely see. Healthy soil and healthy roots are not synonymous. A pecan orchard can have biologically rich, well-structured soil and still suffer from root disease. Lumping soil and root health together oversimplifies an intricate biological relationship.

Pecan trees, like all woody plants, have two primary root systems: woody structural roots and fine absorptive roots. The woody roots anchor the tree and provide mechanical stability. When these fail, trees may uproot or snap at the base, but such failures are relatively rare compared with problems in the absorptive roots. These finer, non-woody roots form the living interface between the tree and its environment. They are the organs through which the tree takes up water and nutrients, and they are continually regenerated and lost throughout the season.

The absorptive root system consists of progressively finer orders of roots—each smaller and physiologically distinct. McCormack et al. (2015) proposed redefining fine roots into five orders. Orders 1 and 2 are the smallest, often less than a millimeter in diameter and shorter than an eyelash (Image 1). These roots lack bark and possess only a delicate epidermis that allows passive water entry through osmosis. They are metabolically active, high in nitrogen, and have high respiration rates. This combination makes them efficient absorbers of water and minerals, but also highly vulnerable to stress and infection. The first three orders of fine roots are also the primary site of mycorrhizal associations, where beneficial fungi enhance water and nutrient uptake and help protect the tree against some pathogens.

Two pathogens, Phytophthora spp. and Rhizoctonia solani, are the common culprits in absorptive root decline. Both thrive in warm, moist conditions and attack the finest roots where defenses are weakest. Infected roots become darkened, flaccid, and easily crushed or squished between the fingers. Healthy roots, by contrast, are firm, elastic, and typically light-colored at the tips where new growth is occurring. These pathogens cannot be distinguished by visual symptoms alone. Even experienced diagnosticians cannot reliably identify the causal organism without laboratory confirmation through culturing or molecular testing.

The high susceptibility of absorptive roots arises from both morphology and physiology. Their thin epidermis provides little physical defense, and their high nitrogen content makes them an excellent substrate for microbial growth. During drought, changes in the osmotic gradient cause sap to move out of the roots, leading to desiccation and fine cracking of the epidermis. Synthetic fertilizers, being salt solutions, can produce a similar effect, drawing sap out and stressing the roots further. These micro-injuries serve as entry points for pathogens, which are often chemotactic and move toward root exudates. When moisture returns, even under moderate soil conditions, previously drought-stressed roots are far more vulnerable to infection. This cycle is common in Texas pecan orchards, where alternating drought and rainfall or irrigation is routine.

A persistent management misconception arises when trees appear stressed: the reflex to “water and fertilize.” While well-intentioned, this approach can aggravate disease development. In plant pathology, the disease triangle describes how three factors—host, pathogen, and environment—interact. Adding water and nitrogen can strengthen all three sides: a vigorous host with excess nitrogen produces lush, succulent tissue more susceptible to infection; a saturated environment favors pathogens like Phytophthora; and nitrogen enrichment can stimulate pathogen and insect populations. What appears to be supportive care can, in reality, tip the balance toward disease.

Instead, pecan growers should focus on maintaining conditions that favor a balanced root–soil interface. Absorptive roots require both moisture and oxygen. Prolonged drought desiccates them; prolonged flooding suffocates them. Monitoring soil moisture within the active root zone—roughly the upper 12 to 18 inches in most pecan soils—helps prevent extremes. Mature trees benefit from a higher carbon-to-nitrogen ratio; slow-release, organic nutrient sources such as compost provide both carbon and nutrients, supporting root health more effectively than high-nitrogen, low-carbon, fast-release synthetic fertilizers. Avoiding unnecessary nitrogen applications during periods of poor drainage or after drought reduces both physiological stress and disease pressure.

When assessing root health in the field, a simple inspection can provide useful information. Carefully excavate a ten-inch area within three feet from the tree’s stem and expose fine roots. Healthy absorptive roots should appear evenly distributed and turgid, with white or tan tips indicating new growth in spring and fall. Diseased roots often appear darker, water-soaked, or threadlike, and may emit a sour or acrid odor if anaerobic conditions have developed. If substantial portions of the fine roots are discolored, degraded, or missing, sample collection and laboratory analysis are warranted. Diagnosis of Phytophthora and Rhizoctonia cannot be made by appearance alone.

Field diagnosis can guide management decisions. Where compaction or poor drainage is evident, physical remediation using air tools and integrating soil amendments can restore aeration and improve conditions for absorptive roots. Maintaining consistent but not excessive irrigation during root-active growth periods further supports root turnover and nutrient uptake.
While soil health alone does not guarantee root health, it remains a critical foundation. A diverse and stable rhizobiome—the microbial community surrounding roots—supports tree resilience. Beneficial fungi and bacteria outcompete pathogens, aid nutrient cycling, and help regulate root immune responses. Practices that preserve microbial diversity—such as minimizing unnecessary soil disturbance, avoiding overuse of broad-spectrum fungicides, and maintaining organic matter inputs—contribute to overall orchard stability.

Ultimately, root health drives tree health and nut production. Absorptive roots, nearly invisible but essential, determine whether a pecan tree can take full advantage of favorable soil and climate conditions. Recognizing that root and soil health are related but distinct allows growers to diagnose problems more accurately and manage orchards more effectively. The next time a tree looks weak or underperforming, resist the instinct to simply water and fertilize. Look deeper—literally—to the fine roots. Their condition tells the real story of tree health belowground.

 

Citations
McCormack, M.L., Dickie, I.A., Eissenstat, D.M., Fahey, T.J., Fernandez, C.W., Guo, D., Helmisaari, H.S., Hobbie, E.A., Iversen, C.M., Jackson, R.B. and Leppälammi‐Kujansuu, J., 2015. Redefining fine roots improves understanding of below‐ground contributions to terrestrial biosphere processes. New Phytologist, 207(3), pp.505-518.