“Things like yellowing or chlorosis of the foliage can be mistaken for fertility issues like nitrogen deficiency,” Lookabaugh says. “Early on, you can also see plants that are slightly stunted. So when you look out across your greenhouse bay, you’ll be able to pick out a couple of plants that look a little stunted, but otherwise healthy.”
Different root diseases — including, but not limited to, Pythium, Fusarium, Rhizoctonia, Phytophthora and Thielaviopsis — present differently and can lead to other issues for the plant like increased susceptibility to pest outbreaks.
“In general, these issues all go hand in hand,” Lookabaugh says. “If you have insect damage — say, a high whitefly population on poinsettias — and it’s already stressing the poinsettia, that’s just going to open you up to more problems like root diseases. Looking at it the other way, when you have a root problem, it stresses out a plant and makes it more susceptible to other diseases and pests that could be more damaging than they might be on their own.”
Photos courtesy of BASF
Identifying root diseases
According to Lookabaugh, Pythium can cause plants to wilt during the day only for them to recover overnight and appear fine at first glance. However, she says that over time, the wilting will become irreversible.
“The roots will appear brown and they can be water-soaked,” she says. “If you take your fingers and run them along the root, that outer cortex will actually slough off between your fingertips. And if you pull the plant out of the pot, you will likely see that the roots haven’t grown past their initial plug.” She says rot from Pythium can extend up the stem of the plant and destroy it. Lookabaugh adds mums, snapdragons and poinsettias are three of the crops most susceptible to Pythium.
Like Pythium, Phytophthora can cause stunting, chlorosis and root rot, but also a noticeable lack of vigorous growth. According to Lookabaugh, the first sign of disease is often a plant not looking as good as it should. African violets, gerbera daisies and woody ornamentals are among the crops most susceptible to Phytophthora.
Lastly, there’s Rhizoctonia — a disease that often presents itself right at the soil line in a pot or plug. Lookabaugh says that it’s particularly dangerous to plants in flats for one reason.
“When Rhizoctonia presents in flats, it can spread very rapidly,” she says. “The entire crop could be lost to disease in just a few days.” Like Pythium, it also presents by plants not growing as vigorously as they should. Seedlings can also emerge apparently healthy but then collapse right at the soil line.
To learn more about these diseases, others such as Fusarium and Thielaviopsis and how they can lead to other issues, Lookabaugh recommends reaching out to technical service reps like herself and/or local extension specialists.
Preventing root disease
According to Lookabaugh, there are two main things to focus on to prevent root disease: timely fungicide applications and sanitation.
For fungicides, Lookabaugh says a good place to start is a drench application. At the beginning of a growing cycle, applying a drench can prevent disease. However, its effectiveness will fade over time. Repeat applications may be necessary to maintain control throughout the production cycle.
“Most applications wear off within 14-28 days and pathogens can then become active again,” she says. “Waiting until symptoms appear to treat is risky because the plant may be already too far gone to reverse the damage.”
To prevent that from happening, Lookabaugh says it’s key to apply preventative fungicides on schedule and with the right product.
“If you are growing a crop that is susceptible to a specific disease or have a history of disease in your greenhouse, you want to stick to a strict, preventative fungicide schedule,” Lookabaugh says. “You want to rotate your fungicides so you’re utilizing different modes of action to reduce the risk of fungicide resistance and also maximize efficacy.”
BASF products Lookabaugh recommends include:
- Pageant®, which she advises using at sticking to increase rooting and strong root systems
- Empress®, a product Lookabaugh suggests using as a tank mix when transplanting to continue helping the plant root faster and protect against major root diseases
- Orkestra®, which also helps with root growth and recently became available for use in California and offers control of Thielaviopsis
As for sanitation, Lookabaugh says it is also key to stay on a regular schedule and be consistent with efforts to keep a growing area clean. That can include, but is not limited to, sanitizing growing areas, cleaning benches deeply between crop cycle, sanitizing pots when they have to be reused, treating water if it’s being recirculated and cleaning up any debris where a pathogen can ‘hang out.’
One other step Lookabaugh recommends is buying disease-free material from companies with a reputation for cleanliness. Chances are that if a company is known for having disease-free material, it will be pest-free too.
“Buy from reliable sources that are known for having healthy plants,” she says. “And do everything you can to promote fast rooting.”
What to know about vegetable expansion
For growers who are considering expanding into vegetable production, Lookabaugh says the diseases are largely the same as in ornamental production.
“It’s pretty much the same diseases — Pythium, Phytophthora, Rhizoctonia, etc. — and all of them can be problematic with vegetables and vegetable transplants,” she says. “Tomatoes and peppers seem to be most notably the most susceptible, with Pythium most common with tomatoes.”
For establishing robust roots in vegetable crops, Lookabaugh offers the following tips:
- Start strong. Apply products like Pageant® early in production to promote healthy roots and early disease prevention.
- Have strong sanitation protocols in place and use disease-free plant material, as well as pathogen-free growing media.
- Maintain strong fertility programs.
- For vegetable transplants, Lookabaugh says managing insects and pests is especially important — making scouting especially important.
“It’s the same logic as ornamental crops,” she says. “Any time your plant is struggling or it’s stressed, it is more vulnerable to disease and pest pressures.”
Overall, Lookabaugh has direct advice for growers looking to update their program.
“Always rotate with different modes of action,” she says. “And know what product your using does. What controls Pythium will not control Rhizoctonia and vice versa. Consider a tank mix with multiple modes of action to prepare yourself with any root disease you might encounter.”