Phytophthora Root Rot in North Texas: Symptoms, Prevention and Treatment

What's killing this plant?

Phytophthora Lives Up to Its Name as The Plant Destroyer

Sometimes it starts as a yellowing of the foliage. You might notice bleeding cankers on the trunk or branches. The roots of your plants rot away, causing the plant to decline slowly over several years, or the entire top may suddenly turn brown and die. And it can affect a wide range of trees, shrubs, and perennials in your garden. But what is it? And how do you fix it?

Phytophthora—pronounced “fy-TOFF-thor-uh”—comes from Greek words meaning “plant destroyer,” and it often lives up to that ominous name.

So What Is Phytophthora?

Phytophthora is a genus of oomycetes, commonly called water molds. Together these organisms cause some of the world’s most destructive plant diseases. One of the best-known species is Phytophthora infestans, which caused the potato late-blight epidemic associated with the Great Irish Famine and remains an important potato and tomato pathogen today.

These microscopic enemies are water-loving pathogens that can devastate gardens, crops, and natural ecosystems. While invisible to the naked eye, their impact is anything but subtle.

Recently planted lavender quickly succumbed to Phytophthora after only about a week. Notice that one section of the plant has dieback while the rest of the plant still looks healthy. Without treatment, the entire plant will eventually die.

The Secret Life of a Plant Destroyer

Some Phytophthora species can survive in soil or infected plant material for years without producing obvious symptoms. Like a sleeper agent, it waits patiently until conditions become favorable. When moisture levels rise and temperatures are right, these pathogens spring into action with devastating efficiency. In other words, outbreaks are generally more likely during wet periods or where irrigation keeps the soil saturated.

Perhaps most remarkably, Phytophthora produces swimming spores — tiny reproductive units that can actually propel themselves through waterlogged soil and standing water. These aquatic invaders can also spread through water splash, irrigation systems, and even on gardening tools, making them incredibly effective at colonizing new areas.

What to Watch For

Phytophthora can cause several types of damage:

• Blights: leaves and stems to wither and die rapidly

• Wilts: plants droop despite adequate watering

• Cankers: create sunken, diseased areas on stems and branches

• Root rots: feeder roots become dark, soft, or decayed

• Dieback: ranches and shoots die progressively

• Discoloration: Crowns or stems may turn brown or black, while foliage may become yellow, purple, brown or reddish.

These symptoms can also result from overwatering, drought stress, planting too deeply, root injury or other diseases, so it's important to confirm the cause before treating your valuable plants.

Holly bush infected with Phytophthora.

Managing the Threat in Your Garden

While it's impossible to completely eliminate Phytophthora from infected soil, smart gardening practices can significantly reduce the risk of outbreaks:

Focus on Drainage

Since these pathogens thrive in wet conditions, improving soil drainage is your first line of defense. Avoid overwatering and ensure your garden beds don't become waterlogged. Where possible, select plants that are less susceptible to infection.

Water Correctly

Adjusting irrigation frequency, amount, and timing based on the weather and the needs of your plants helps prevent soil saturation, which in turn, minimizes disease outbreaks.

• Avoid wetting plant trunks and foliage. Water splashing on foliage can spread Phytophthora spores and infect above-ground tissues.

• Always use clean, uncontaminated water sources.

• Ensure that your containers drain freely. Don't leave them sitting directly on bare soil, which can harbor the pathogen.

Prevent the Spread

As mentioned earlier, Phytophthora can spread through contaminated soil, water, plants, containers, and tools. Remove infected plant debris, avoid moving soil from affected areas and clean soil from tools and footwear before using them elsewhere. Severely affected plants may need to be removed.

Treat the Plant

It's important to note that there is no chemical treatment that reliably eliminates Phytophthora. However, if the condition is not too far advanced, there's a good chance that you can help the plant fight off an attack with our recommended organic program, along with corrected drainage and improved irrigation. The goal is to help repair and restore the soil's natural ability to fight off harmful pathogens.

Our approach to fighting phytophthora root rot is to introduce beneficial bacteria into the plants and soil to attack and kill the phytophthora organisms.

Here's how:

Application 1: As soon as possible after the disease is identified, drench the foliage of infected plants and surrounding soil with a combination of MicroLife's MicroGro Liquid AF and Liquid Molasses. Apply 1lb per 100 square feet of MicroLife's MicroGro Bio-Inoculant to the soil in the infected bed and around other vulnerable plants. Prune out dead foliage from infected plants to make it easier to monitor any additional progress of the disease. If further deterioration appears, consider repeating the liquid application after 2 or 3 weeks.

Application 2: Two to three months after Application 1, apply 1 lb. of Bio-Inoculant per 100 square feet to the soil in the infected bed and around other vulnerable plants.

Application 3: One year after the original application, repeat application 1.

After this Phytophthora-infected rose bush was treated with Marshall Grain's recommended program, it began to produce new healthy growth.

Before You Replace Plants

Before planting anything in areas where plants have been infected, treat it with the MicroGro Bio-Inoculant.

Replace plants with varieties that are less susceptible. Some examples are:

• Spirea

• Weigela

• Hypericum

• Abelia

• Artemisia

• Beautyberry

• Camellia

• Jerusalem Sage

• Forsythia

• Honeysuckle

• Mimosa Trees

• Quince

• Ginkgo

• Crape Myrtles

What If It's Not Phytophthora?

Several root diseases and environmental problems can produce similar symptoms. This treatment will often correct most types of fungal root rot in shrubs and trees even if it is not Phytophthora. However, it will not cure Take all Root Rot in lawns. Marshall Grain recommends a different solution for this problem. While Phytophthora typically does not affect your grass, it can still spread through the soil under your grass.

The Bottom Line

Phytophthora brilliantly illustrates why proper drainage and water management are so crucial in gardening. Excessive soil moisture and poor drainage create ideal conditions for Phytophthora diseases. Proper watering reduces the chance of spreading diseases and keeps plants healthy and resilient against Phytophthora and other root rot diseases.

By managing your garden's conditions you can coexist with these pathogens while protecting your beloved garden.

Let Us Do It For You

Marshall Grain offers customized landscape maintenance services, including fertilization, planting, weed control, and mulching, as well as treatment for Phytophthora disease*. Give us a call to discuss how we can help you today.

*Please note we do not offering mowing services.