The Plant Destroyer Every Gardener Should Know: Phytophthora

What's killing this plant?

Phytophthora Lives Up to It's 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 effect 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" — is Greek for "Plant Destroyer," and unfortunately, it lives up to this ominous reputation.

So What Is Phytophthora?

Phythophthora is actually a group of fungal-like organisms. Together, this group of pathogens is one of the most destructive plant pathogens in the world. The most well-known type is Phytophthora infestans, which was responsible for the Irish potato famine that led to thousands of deaths by starvation in the 1840s and is still prevalent 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.

The Secret Life of a Plant Destroyer

What makes Phytophthora particularly insidious is its ability to remain dormant in your soil for years, completely undetected. 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, we may expect to see more cases of it in wetter years than in times of drought.

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

These pathogens are remarkably versatile destroyers, capable of causing multiple types of plant damage:

• Blights that cause leaves and stems to wither and die rapidly

• Wilts that make plants droop despite adequate watering

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

• Root rots that destroy the plant's foundation from below ground

• Dieback that kills branches and shoots progressively

• Discoloration: Blackening or browning of the crown or stems. Leaves may turn purple, brown, or reddish.

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 quickly. Don't leave them sitting directly on bare soil, which can harbor the pathogen.

Prevent the Spread

It often spreads from plant to  plant. To minimize this risk, remove all dead limbs and leaves and then assess if the plant is salvageable or not.

Treat the Plant

It's important to note that there is no chemical treatment for 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. The goal is to help repair and restore the soil's natural ability to fight off harmful pathogens.

Here's how:

1. Use a combination of Microgro Liquid AF and Liquid Molasses. Use 1 ounce of each per gallon of water.

2. Spray the entire plant, and water the solution into the soil. Do this every 1 to 4 weeks (depending on severity) until you no longer see signs of infection.

3. Treat the area with Microgro Bio-Innoculant. Be sure to treat 6ft. to 8ft. out from the center of the infected plant.

4. If multiple plants around the property have signs of Phytophthora Root Rot treat the entire property. Each 25lb bag covers 2,500 sq. ft.

Before You Replace Plants

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

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

• Spirea

• Weigela

• Hypericum

• Abelia

• Artemesia

• Beautyberry

• Camellia

• Jerusalem Sage

• Forsythia

• Honeysuckle

• Mimosa Trees

• Quince

• Gingko

• Crape Myrtles

What If It's Not Phytophthora?

This treatment will cure 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. While Phytophthora will not affect your grass, it can be 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 the pathogen, 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 fertilizations, 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.