Greenhouse Diseases: Phytophthora

Gloxinia showing symptoms of phytophthora. Photo: R.K. Jones, North Carolina State University, Bugwood.org

Phytophthora is a serious disease of floriculture crops, and it is especially difficult to control once it has become established. It is one of several organisms that cause root and crown rots. Phytophthora is closely related to Pythium, which also causes root rot. 

While there are a wide variety of plants that are susceptible to Phytophthora, some are more likely to be infected than others. Poinsettia, rhododendron (azalea), fuchsia, vinca, gloxinia, lantana, African violet, begonia and ornamental peppers are among the more common hosts of the disease. There are several species of Phytophthora, and they are host-specific, meaning each species will only affect certain types of plants.

Symptoms To Watch For
Infected plants will display symptoms of wilting and overall decline, including dark lesions, known as cankers, at the crown of the plant. The cankers impede the flow of water and nutrients between the roots and leaves. When they become large enough to encircle the stem, the plant dies. Plants with soft stems, such as pansies, will pull off at the soil line when tugged gently. When the plant is removed from the pot, the roots will be brown and rotted, as opposed to the normal healthy white color. Symptoms can appear any time during the production cycle, from very young plants to finished, and the disease is also a problem in the landscape. It is important to obtain positive identification of the disease from a laboratory, since symptoms can be similar to those of other diseases.

Prevention
Prevention of Phytophthora is especially important, because it is difficult to eradicate once infection begins. It produces several different types of spores that allow it to persist through a variety of environmental conditions. Oospores and chlamydospores can survive on pots, floors, media and other surfaces, while zoospores can actually swim for tiny distances (a few inches) on a film of water. Sporangia spread through the air. In addition, plants may be infected and infectious even before they show symptoms, which may not appear until the plant is stressed.  High temperatures can cause a latent or mild problem to become severe. Warm, wet conditions are ideal for the development and spread of Phytophthora. Recirculating water in irrigation systems can also spread the disease.

Control
Sanitation is of paramount importance. Remove plant debris and clean and disinfect potting surfaces, tools and pots. Sanitize the propagation area. Keep plants on benches away from contact with the ground and use potting mixes with excellent drainage and porosity. Cuttings should be inspected upon arrival for signs of disease. Remove diseased plants immediately and follow recommended protocols of preventative fungicidal sprays.

Resources:

Daughtrey, Margery. Phytophthora Crown Rot on Pansy. Floricast. Greenhouse Grower. GreenhouseGrower.com/video/c:0/822/

Hausbeck, Mary and Blair Harlan. Greenhouse Disease Update for Phytophthora Root Rot. Michigan State University Extension, Department of Plant Pathology. msue.anr.msu.edu/news/greenhouse_disease_update_for_phytophthora_root_rot

Gillman, Dan. 2011. Seedling Root and Crown Rots. University of Massachussetts Amherst. http://extension.umass.edu/landscape/fact-sheets/seedling-root-and-crown-rots

Vincelli, Paul and Don Hershman. 2005. Plant Pathology Fact Sheet. Controlling Phytophthora Root Rot in Greenhouse Ornamentals. University of Kentucky Cooperative Extension Service. http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-H-9.pdf

 

 

 

Leave a Reply

More From Disease Control...
Cart-with-RFID-Tag

November 24, 2017

How RFID Technology Can Help With Plant Cart Tracking

One of the biggest hassles in the greenhouse is keeping track of all those shipping carts. Improved RFID technology for cart tracking may be one solution to help keep profit losses due to lost or damaged carts at a minimum.

Read More
Growing-Media-Symposium-Tour

November 13, 2017

International Growing Media Symposium Comes to the U.S.

This International Symposium, with representatives from 21 countries, covered new market opportunities, generated innovative ideas, and offered first-hand information to more than 150 attendees.

Read More
Parasitized aphid mummies, ladybird beetle larvae

November 11, 2017

OHP Announces Two New Ornamental Pest Management Tools

OHP recently added two new crop protection tools to its profile of biosolutions: a biological insecticide, and an ornamental fungicide.

Read More
Latest Stories
Researchers Study Rose Varieties

October 17, 2017

Rose Rosette Update: Research into Detection and Manage…

Halfway through a five-year, $4.6 million grant to combat rose rosette disease in the U.S., a national research team is encouraged by the amount of information learned, but admits having a way to go before finding how to overcome the deadly problem.

Read More
Botrytis Symptoms on Leaves

October 17, 2017

How One Grower is Battling Botrytis with a New Biologic…

CropKing in Lodi, OH, recently began using a new beneficial fungus in its fight against Botrytis in its greenhouse tomatoes. So far, the results have been promising.

Read More
BASF Pageant

September 29, 2017

New Fungicide Provides Production and Postharvest Disea…

Pageant TR from BASF controls seven key diseases, and can be used both in the greenhouse and in trucks that are on their way to a retail site.

Read More
Ascochyta in chrysanthemum

September 27, 2017

14 Common Chrysanthemum Diseases to Monitor

Penn State University Extension features a section on its website devoted to diseases commonly found in chrysanthemums.

Read More
Boxwood Blight

September 19, 2017

Concerned About Boxwood Blight? Here Are Some Updated M…

AmericanHort’s Horticultural Research Institute has released an updated version of its boxwood blight Best Management Practices document.

Read More
Powdery mildew on rosemary. Photo credit: SHS Griffin

September 9, 2017

Howler Biological Fungicide from AgBiome Gains EPA Appr…

Howler provides preventive, long-lasting activity on a broad spectrum of soilborne and foliar diseases, with no special handling or storage required.

Read More
Aphids

July 7, 2017

New Tools for Your Crop Protection Arsenal in the Green…

Over the past few months, crop protection companies have developed several new products designed to help you manage a wide range of insect and disease pests. Here’s a look at some of them.

Read More
Primula acaulis, Botrytis, Disease, Griffin Greenhouse Supplies

May 30, 2017

BioWorks Launches New Biofungicide for Botrytis Control

BotryStop was developed for the control of pathogens such as Botrytis, Sclerotinia, and Monilinia in several crops, including ornamentals.

Read More
Botrytis Blight Geranium

May 10, 2017

A Refresher on Botrytis Management in the Greenhouse

When the weather is moist and humid, susceptible greenhouse plants may need to be protected from Botrytis cinerea, a fungus that causes leaf spots, blighting, and stem cankers.

Read More
Downy mildew sporulation on underside of leaf

May 5, 2017

New Bactericide/Fungicide from BioSafe Systems Helps Ma…

BioSafe Systems has introduced PerCarb, a broad-spectrum bactericide/fungicide for use in greenhouse fruits and vegetables, as well as other crops.

Read More
Pythium

March 27, 2017

Florida Ornamental Growers Took a Hit in 2016 Thanks to…

While damage figures from the 2015-2016 winter rains are still being compiled, researchers have found that Phytophthora and Pythium caused severe destruction in many plants.

Read More

March 20, 2017

AgBiome’s New Zio Biofungicide Receives EPA Regis…

The new biofungicide is the first product from AgBiome, and will be marketed by SePRO Corp. in the ornamentals market.

Read More

February 26, 2017

AgBiome Will Enter the Ornamentals Market With a New Bi…

AgBiome, a young company with teammates steeped in decades of experience in the crop protection world, sees an opportunity to bring products to market that fill the existing gaps in plant protection. The company has partnered with SePRO to market and distribute Zio, a biological fungicide expecting EPA registration this spring.

Read More
Tomato Spotted Wilt Virus on Osteospormum

February 23, 2017

4 Pathogens to Prepare For in 2017

Early detection of disease and virus symptoms in the greenhouse is critical. One expert says there are a few pathogens in particular that growers should be monitoring.

Read More
Boxwood Blight

February 7, 2017

Boxwood Blight Detection in Illinois Has Growers on Ale…

Symptoms of boxwood blight, which can spread quickly in production facilities, include leaf spots, stem cankers, and defoliation.

Read More
downy-mildew-impatiens-feature

December 24, 2016

How Agronomic Programs Can Help You Successfully Manage…

To prevent problems before they start, make an agronomic program an essential part of your production plan.

Read More

December 19, 2016

Funding Allocated for Several Horticulture Pest Researc…

The USDA Animal and Plant Health Inspection Service has allocated millions in funding to research plant pests such as boxwood blight, downy mildew, and phytophthora.

Read More
Phytophthora On Poinsettia

November 23, 2016

Tips On How To Prevent Aerial Blight Spread In Poinsett…

According to Michigan State University experts, certain species of the pathogen Phytophthora, which is typically thought of as a root rot, can also cause issues above-ground.

Read More