Deadhead Common Diseases

In our “Taking Out The Top Five” article, Greenhouse Grower asked the technical experts from our industry’s leading chemical companies for tips on insect prevention, diagnosis and treatment.

This month, we’re using that same mold, but we’re now seeking out advice to tackle some of the most common diseases growers face worldwide. Keep in mind diseases do vary with climate, geography and crop. This top five list of common plant infections includes botrytis, powdery mildew, pythium, phytophthora and fusarium.

“If any growers are making a diagnosis for the first time, it is highly recommended that growers make clear notes and take pictures of the symptoms that were found,” advises Vijay Choppaktla, plant pathologist and director of research for BioSafe Systems. “Send infected plant samples or pictures to the nearest plant disease diagnostic laboratory for disease confirmation.” These services can be provided to growers at a minimal cost.

Botrytis

As a lover of humidity, botrytis is initially noticed as a general blight (a browning and collapse of tissue) on the leaves and flowering parts of a plant, says Nancy Rechcigl, a Syngenta field technical manager who specializes in ornamentals. “The telltale fuzzy spores are not produced until humidity reaches 85 percent or greater.”

Jeff Dobbs, director of technical service at OHP, Inc., also has some advice: “If conditions look favorable, be prepared to increase ventilation to keep flowers and leaves dry and space them out.”

Plants that have moisture (specifically condensation) on their foliage for more than four hours at a time are the ones most at risk of botrytis, which can be common with warm days and cool nights.

“Before you begin any concentrated removal of infected plants and plant parts from the growing area to prevent additional spread, be sure to first get a fungicide spray on first,” Rechcigl says. “When you dispose of the material, make sure the bag or container you put the waste in can be closed before you walk through the rest of the greenhouse. Using open dumpsters allow spores to dislodge and blow around freely.”

Also remember to use a fungicide application after any pruning has been done. And dead plant tissue also serves as an ideal host for botrytis reproduction.

“Growers that are proactive rather than reactive reduce disease pressure by applying fungicides starting the first week,” says John Schwartz, market manager for BioSafe Systems turf and ornamental division. “With this practice, growers actually eliminate mounting pressure every time they apply.”

BASF’s Steve Larson agrees. Larson is the national ornamentals account manager for BASF. He believes many growers are starting too late with preventative treatments.

“Prevention is much cheaper than curative,” he says. “Once you see symptoms, the disease is established and you may end up throwing away some plants.”

Powdery Mildew

Easily identifiable by the white powdery spore growth on the upper surface of the leaves, powdery mildew can sometimes be mistaken for downy mildew infection when the mildew happens to develop first on the underside of the leaves, says Syngenta’s Rechcigl.

Unlike botrytis, free moisture on plants does not favor powdery mildew, but actually limits its development. It does however enjoy a relative humidity of 70 percent or higher and cooler temperatures, 62 to 72 degrees. When the temperature reaches 85 degrees and above, you will see powdery mildew stop developing.

“High night humidity is congenial for establishment of powdery mildew,” says Choppaktla of BioSafe Systems.

By the time growers react to powdery mildew, there is already plant injury that cannot be reversed, says Schwartz of BioSafe Systems. “This also weakens the plants and leaves them susceptible to other diseases and insect injury.”

Emphasizing a “detective frame of mind,” any chance Schwartz has to “get a down and dirty view” of his plants with the Bausch & Lomb 10X magnifying lens his grandfather passed onto him is his best defense against a full blown epidemic.

Choppaktla agrees and recommends that scouting be done every three days to at least once a week.

Rechcigl says it’s good to start a preventative fungicide program on a 14-day schedule when environmental conditions are conducive to disease development. “If powdery mildew does break into your crop and you have an active infection, you’re going to want to reduce that interval down to seven days.”

Pythium

When it comes to pythium, don’t rely on visual observations only, Larson says. Send suspect samples to a qualified pathologist.

“Pythium is one of the most common causes of root rot or damping off, but it usually doesn’t leave many clues as to its identity,” says Dobbs of OHP, Inc.

Since pythium attacks a plant’s root system that results in a plant wilt, growers can mistakenly respond to this visual sign by additional irrigation. “Additional water is the last thing a pythium plant needs,” adds Larson.

Pythium symptoms can commonly misguide growers to believe they have another root disease on their hands like fusarium, phytophthora and rhizoctonia, and a broad spectrum formula fungicide will be necessary, Choppaktla says.

Ideal conditions for pythium include poor water aeration, water logged media and cool temperatures. Allow plants to dry down between irrigations. It’s important to also monitor the level of soluble salts in the growing media. “High soluble salt in the growing media can injure roots and make them susceptible to infection,” says Rechcigl. “If you’re using a lot of liquid fertilizer on a constant basis, it’s important to check that routinely and leach when necessary, because salts can build up in the media and cause root burn.”

Lastly, water sanitation can play a role in the introduction of pythium, especially for those growers using recycled water sources (e.g., ponds). The filtration/sanitation system may need to be improved or if one is not in place, one should be considered.

Pythium and phytophthora belong to the same class of fungi-like organisms called Oomycetes. They thrive in familiar conditions and produce symptoms that are very similar to each other, says Choppaktla. This commonality reinforces the importance of lab diagnosis in order to accurately treat the disease. There are also test kits available for growers to make accurate, on-site identification, says Dobbs.

Fusarium

A disease common in chrysanthemums and cyclamen, fusarium can overwinter in the soil, festering in the waste of infected plants, says Dobbs. Once it has established itself, it can be extremely difficult to completely remove fusarium from the soil.

“Know your crop,” stresses Larson. If the crop has shown a receptiveness to this disease in the past, start early and consider a preventative “sprench” (spray/drench) program that gets down to the crown of the plant.

Unfortunately, once the symptoms of a vascular disease like fusarium appear, it may be too late for the plant. It can cause root, crown and stem rot by growing into the vascular system and blocking movement of water and nutrients into the upper canopy.

When further investigating the symptoms, cut into the stem, says Rechcigl. “You’ll notice a reddish-brown streaking in the vascular tissue that’s very indicative of a fusarium infection.”

Leave a Reply

Latest Stories
Lighting Book Light Management in Controlled Environments

April 24, 2017

“Light Management in Controlled Environments̶…

An expanded update to “Lighting Up Profits,” this new lighting book unlocks the secrets of managing light to enhance greenhouse crop production.

Read More

April 24, 2017

Ian Baldwin Offers Examples From Grower-Retailers on Pr…

In March, Baldwin wrote a blog advising grower-retailers to consider raising their prices this spring. The post inspired a number of creative suggestions.

Read More
OHP PGR App

April 23, 2017

OHP Redesigns Its PGR Calculator App

The new version contains many of the same features as the previous version but now runs faster and works on all iOS device environments.

Read More
Kaylee South

April 22, 2017

American Floral Endowment Announces Winners of 2017 Pau…

Four students pursuing careers in horticulture now have scholarships to help them along the way, thanks to the American Floral Endowment.

Read More
Jim Zampini

April 21, 2017

Nursery Industry Leader Jim Zampini Dies at 85

Jim Zampini, a nationally recognized nurseryman and one of the leading figures in the thriving Lake County, OH, nursery industry for more than six decades, passed away on April 15 at the age of 85.

Read More
Begonia Spectre Silver Terra Nova Nurseries

April 20, 2017

Terra Nova Nurseries Releases Two New, Attractive Begon…

Stardust is the latest addition to Terra Nova Nurseries’ existing T Rex Begonia series, and Silver is the first introduction to the company’s new Spectre Begonia series.

Read More
GGS Cannabis Production

April 19, 2017

Suppliers Can Offer Technical Solutions for New Cannabi…

Here’s a look at how a few manufacturers have partnered with growers to make their transition into cannabis a smooth one, whether it’s through hands-on guidance or partnering with other industry leaders.

Read More

April 18, 2017

Cool Combos From CAST 2017 – Editor’s Choic…

With container gardening becoming more of a lifestyle among consumers than a trend, and breeders continuing to put more effort in container mixes and components, I feel I would be remiss if I didn't share some of the special combinations that not only caught my eye at California Spring Trials, but absolutely took my breath away and made me want to immediately get started gardening.

Read More
LumiGrow Growers Council

April 17, 2017

LumiGrow’s Latest Lighting Research Highlighted in Grow…

Industry leaders representing a broad range of vegetable, floriculture, and cannabis producers gathered to learn how to implement modern lighting strategies for their own production.

Read More
Danziger New Hires

April 16, 2017

Danziger Invests in Continued North American Business G…

As part of a new business structure for its North American market, Mike Fernandez has been appointed Market Manager North America for Bedding Plants and Perennials, and Kate Zvara was named as Key Account Manager and Retail Specialist.

Read More
Oregon Lean Nursery Consortium

April 15, 2017

How Oregon Growers Are Making Lean Improvements With He…

The Oregon Nursery Lean Consortium recently helped two Pacific Northwest growers realize significant productivity gains and labor savings.

Read More
Kemin Horticulture Trial

April 14, 2017

How to Trial a New Product Before You Use It in Your Gr…

Before you apply a new product on a plant, you want to make sure it is safe and effective. Technical experts from Kemin have compiled a five-step guide designed to help you measure the benefits of a new product you want to incorporate into your operation.

Read More
Venlo Greenhouse (Westbrook Greenhouse Systems Ltd.)

April 13, 2017

AmericanHort’s Production Technology Conference To Debu…

The AmericanHort Production Technology Conference is designed to give nursery and greenhouse growers a chance to get hands-on with the latest advancements in production technology and explore the return on investment potential of equipment purchases and upgrades.

Read More
Hydroponics Michigan State Web

April 13, 2017

Research Team Seeking Feedback From Hydroponic Growers

Are you a hydroponic grower of food crops? If so, Michigan State University and Iowa State University researchers are looking for your input.

Read More
Florida Flower Trials

April 12, 2017

Looking for Info on New Varieties for Hot Climates? Che…

The Florida Nursery Growers and Landscape Association’s Florida Flower Trials, which are focused on new and improved varieties able to thrive in the extremes of Florida’s climate, are a great opportunity to connect with national breeders.

Read More
Lupinus Staircase Series (Green Fuse Botanicals)

April 11, 2017

Begonias, Celosias Among Dr. Allan Armitage’s Favorites…

Check out some of Allan’s top picks from his final day at CAST 2017, which included visits to Green Fuse Botanicals and Floranova.

Read More

April 11, 2017

Jerry Halamuda of Color Spot Nurseries Retires

The co-founder of Color Spot Nurseries has retired, effective immediately, and has named a replacement.

Read More
Rex Begonia container mix at Green Fuse Botanicals

April 11, 2017

Green Fuse Botanicals’ Rex Begonias and First Looks; Fl…

Here are the highlights from Green Fuse Botanicals and Floranova on the last day of CAST 2017.

Read More