Introduction

The success and profitability of farming is largely dependent on the weather each growing season. In some cropping systems, the weather outside of the traditional growing season is also of concern, such as sub-zero temperatures in late winter desiccating the flower buds of stone fruit. With perennial crops, special attention needs to be given to the overall trends in weather over many years, as these crops are expected to grow and yield fruit for decades. These climatic considerations can help in understanding the needs of various crops as they perform differently from year to year. Perhaps the most influential climatic factor in agriculture is precipitation. And, often, too much precipitation poses a greater challenge than not enough.

In orchards, excessive rainfall can lead to oversaturated soils, flooding, and standing water. As a result, observations of plant disease caused by soilborne pathogens often coincide. The excessive free moisture in water-logged soils is problematic for many reasons, the first being stress brought on by the plant roots not having access to oxygen. This stress can increase a plant’s susceptibility to a host of diseases. For these diseases, free moisture acts to quickly move pathogens around the soil environment and to plant roots, rapidly increasing the number of affected plants. Although each disease is unique, the factors that cause these diseases and their symptoms are often analogous. When growers report these issues, observations tend to be similar: standing water in the area, a large number of affected plants, and rapid plant decline. Together, these suggest a root disease.

Blueberry Root Rot

This disease can be caused by two fungi, Pythium or Phytophthora. However, management for this disease will be the same for both pathogens. Blueberry Root Rot is usually an issue in low, poorly drained, and/or heavy-soiled (lots of clay) sites. In waterlogged soil, plants are not able to access oxygen. Excessive moisture in the soil causes the fine roots to turn black and rot. Even after the area drains, plants will have severely compromised root systems – affecting growth and development all season long. Symptoms include yellowing or reddening of leaves, defoliation, stunting, dieback, and plant death (Figure 1).

The best management strategy for this disease is proper site selection. However, with the rapidly and ever-changing climate, what seemed like an adequate site 10 years ago might be somewhat problematic today. Just a couple of days under water is enough to severely compromise a crop. Other options include improving drainage (be on the lookout for climate-smart agriculture grants from CT Department of Agriculture) or applying the fungicide Mefenoxam (Ridomil Gold). This material is primarily used at planting where this issue is anticipated, with a single reapplication allowed prior to conditions favorable for disease. However, it can also be used as a drench in established plantings (either type of application has a maximum of 7.2 pts/acre/year). It is important to note that this product will do nothing to help plants that are already exhibiting symptoms. More information in the New England Guide.

Phytophthora Root Rot in Apples

Like Blueberry Root Rot, apples are susceptible to the same pathogen, Phytophthora. In apples this pathogen can cause crown, collar, or root rot. Symptoms are similar to those in blueberry with discoloration of leaves, flagging, stunted/slow growth, and tree decline (Figure 2). It can often be confused with winter injury, nutrient deficiencies, or even Fireblight.

Management strategies are similar as well, with proper site selection and improving drainage being at the top of the list. Additionally, the Geneva series of rootstocks are all resistant to this disease, with G.16, G.41, G.935, and G.202 all being highly resistant. G.11 is moderately resistant. Stay away from M9, M26, MM 104, and MM 106 if at all possible, certainly in questionable sites. More information can be found here.

Black Root Rot of Strawberry

This root disease is a complex of a pathogen, lesion nematodes, and plant stressors that work together to compromise the strawberry crop. Pathogens involved in this disease complex are Rhizoctonia, Pythium, or Fusarium. Again, excessive rainfall creates the perfect conditions for this disease to thrive. Additional plant stress (nutritional or otherwise) makes plants more susceptible to this disease complex. As the name suggests, this complex causes fine feeder roots to rot and die, drastically restricting the plant’s ability to acquire water and nutrients (Figure 3). Often, growers are unaware of this issue until the warm, dry months of the summer, when compromised root systems and an increased demand for water cause plants to collapse.

Management for this disease depends on the specific site. In poorly drains sites, drainage is recommended (NRCS or other agencies may cost-share or pay for these drains entirely). Crop rotation is important as well – a rotation of at least three years away from strawberries for fields with known Black Root Rot issues in recommended. Ideal crops to rotate to are pumpkin, corn, or cover crops such as mustard. If replanting the same field, consider planting on mounds/hills or using raised beds. Reducing plant stressors whether they be nutritional, water-related, or pest-related should also be a priority. Additionally, there are many materials labeled for this disease including Abound (to be applied at planting), Rootshield (preventive), Double Nickel (for suppression), Actinovate AG (pre-plant, or via drip irrigation), and many more. Consult the New England Management Guide for more information and materials.

Conclusion

All told, most reports of root diseases occur in less-than-ideal locations. This includes low-lying areas, poorly drained soils, or heavy soils. Excessive rainfall makes these marginal sites highly unsuitable for plant growth. Going forward, growers should pay close attention to the impact of varying weather on their farms.

Resources

Connecticut Department of Agriculture. (n.d.). Grants. Retrieved December 13, 2024, from https://portal.ct.gov/doag/services/grants

U.S. Department of Agriculture, Natural Resources Conservation Service. (n.d.). Conservation in Connecticut. Retrieved December 13, 2024, from https://www.nrcs.usda.gov/conservation-basics/conservation-by-state/connecticut

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