Spring rains can create growing conditions that are devastating to most landscape plants. Wet soils are favored by a group of pathogens called water molds, or oomycetes, which cause a range of root and stem diseases.

Water molds are found in most soils, but plant stress and high pathogen numbers can lead to severe disease. One common water mold is Phytophthora. This pathogen is common in Kentucky and has recently been diagnosed causing root rot on numerous plants, such as blueberry, arborvitae, and Colorado blue spruce.

Phytophthora Facts

• Symptoms vary greatly due to disease severity and host characteristics.

• Roots are concealed, so disease often goes undetected until plants begin to decline or upper plant parts wilt (Figure 1) as a result root reduction (Figure 2).

• Disease often begins during rainy spring weather, but it is typically not noticed until hot dry weather initiates wilting.

• Aboveground infections may result in symptoms ranging from yellow mottling of leaves to water-soaked lesions on leaves or succulent stems. Woody tissues may develop cankers, often near the soil line.

• Free water is required to allow for "swimming" spores to move to new sites of infection.

• Spores are spread by splashing water and movement of contaminated soil particles.

• The pathogen can produce survival structures that allow it to lie dormant during hot dry seasons or during winter.

Management

Most Phytophthora diseases can be prevented or managed using cultural practices. Consider the management tips below to prevent infections or to help manage infected nursery or landscape plants.

• Improve drainage through management of surface water, limited irrigation, diverting downspouts, or planting in raised beds.

• Disinfest tools and containers.

• Dispose of infested potting media.

• Inspect plants prior to purchase or during production to insure that plants are healthy prior to installation.

• Do not compost infected plant material.

• Remove plant debris and other sources of inoculum.

• Mulch plants to reduce spore splash.

• Use resistant cultivars whenever possible.

Phytophthora spp. are not true fungi, so not all fungicides will be effective against these pathogens. Fungicides must be specifically labeled for oomycetes. Homeowners can utilize fungicides containing phosphorus acid to protect plants from infection or suppress disease development. Commercial production fungicides include products containing cyazofamid, etridiazole, mefenoxam, or phosphorus acids. For additional information on fungicide use, please contact a local UK Cooperative Extension Service agent. Always follow label directions when utilizing fungicides.

For more information, contact the Pulaski Co Extension office at 606-679-6361 and request various resources on this topic. You may also contact us through our Facebook account.

Become a fan of Pulaski County Horticulture on Facebook, follow @hortagentbeth on Twitter and/or kyplants on Instagram. You can also find Pulaski County Horticulture on YouTube.

The Pulaski Co Extension office is open to the public on a regular basis, Monday through Friday 8am to 4:30pm.

The Lake Cumberland Master Gardeners have pine straw mulch for sale at the Pulaski County Extension office. It is sold in bales for $7 per bale (over 50, $6 per bale). We encourage purchasing and pickup on Tuesdays.

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