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Identifying and Controlling Botrytis in Controlled Environment Tomato Production
Botrytis, also known as gray mold, is caused by a fungus known as Botrytis cinerea. This disease is known to be devastating to tomato crops grown in controlled environment agriculture (CEA). The fungus spreads rapidly when outdoor temperatures are cool and heating is used in the greenhouse.
June 2, 2021
Rutgers University has released an advisory on identifying and controlling Botrytis on controlled environment tomato production. Here are some of the most important things growers need to know.
About Botrytis
Botrytis, also known as gray mold, is caused by a fungus known as Botrytis cinerea. This disease is known to be devastating to tomato crops grown in controlled environment agriculture (CEA). The fungus spreads rapidly when outdoor temperatures are cool and heating is used in the greenhouse.
Botrytis is found everywhere and prefers to attack injured plant tissue, meaning any dying or dead tissue on the tomato crop is at high risk for infection.
Infection Symptoms
The fungus is known to attack the flowers, fruit, stems, and leaves of the crop, especially after the crop has been pruned. Infections can also occur in cracks and leaf scars. The spores remain dormant until they sense stress from the plant.
Lesions on stems can turn into concentric rings that wrap the stem, causing the crop to wilt.
How to Prevent the Spread
The fungus spores can remain dormant for about 12 weeks. The spores prefer a temperature of 64°F to 75°F with high humidity. Leaves do not need to be wet for an infection to occur.
Using a horizontal fan to maintain airflow and keeping humidity levels low can help mitigate any infection risk. This is especially important on warm summer days that are followed by cooler nights.
Be sure to keep your facilities clean from any organic debris. All pruning material should be removed immediately.
To learn more, click here.
Lead photo: Botrytis infection on tomato fruit, showing rotted tissue and spores. Photo: Shawn Butler, NCSU
How To Prevent And Identify Plant Diseases In Hydroponic Growing Systems
Depending on what kind of disease or virus your crops have, it’s possible the sickness could destroy your entire crop as it spreads from one to the next.
Plant diseases in hydroponic gardens can be detrimental if not properly taken care of. Depending on what kind of disease or virus your crops have, it’s possible the sickness could destroy your entire crop as it spreads from one to the next. In this article, we’re going to discuss how to identify and prevent plant diseases in hydroponic growing systems.
Preventing Plant Diseases
To prevent plant diseases from occurring in your hydroponic garden, you’ll want to follow these rules:
Promote good air circulation by adding fans to your growing area, spacing out plants, and pruning or removing dead or diseased plants.
Make sure your hydroponic system has good drainage by not overwatering and checking to see if there’s any standing or oversaturated water.
Try growing plant species that have been bred for growing indoors since they are made to be disease-resistant.
Prevent your plant’s stress by ensuring they have the necessary nutrients, and the correct temperature and humidity. Stressed plants can be more vulnerable to diseases.
Clean and sanitize your tools, growing media, and trays regularly.
Check for signs of plant diseases at least 1 to 2 times per week.
If able, allow for a one to two-month crop-free period once a year to eliminate all threats of disease.
Check for signs of pests because they can introduce and spread diseases amongst your plants.
Signs of Plant Diseases
Depending on what kind of disease your plant has contracted will determine the symptoms and signs to look out for. Plants are susceptible to viruses, diseases, fungi, and pythium. Once a pathogen enters your plants you’ll notice a development of galls, swellings or leaf curls, yellowing or stunted leaf, fruit, or root growth, or plant tissue die-off (wilting, rotting, browning, etc.).
Bacteria: If your plant has been contaminated by bacteria, you will notice a slimy, brown-colored coat on the plant’s roots. Try seeing if this brown coating is on your hydroponic reservoir’s walls, tubes, and water pump filter.
Fungi: Evidence of a fungal pathogen is when you notice powdery or fuzzy growths on the plant’s roots or leaves. These growths are typically gray, blue, white, or green colors.
Pythium: This type of disease is known for being the most deadly for hydroponic growing systems. Pythium will blacken the plant’s roots, ooze a foul-smelling odor, and halt the growth of the plant. This pathogen is highly contagious and can spread quickly to ruin entire crops.
Virus: While viruses in plants are rare, they can be fatal when they do occur. Viruses are typically brought about by outside insects or outdoor soil. When introduced to a virus, the virus will spread quietly through the crop and can hide dormant in plants waiting to come out later. If not treated, a viral plant infection can lead to the destruction of the entire crop.
Want to Learn More?
We at the Nick Greens Grow Team have a plethora of knowledge covering hydroponic growing. Join our new Patreon page so you can get behind the greens, which is a behind the scenes look at growing food inside a closet and on kitchen counters. Learn every process of how to hydroponically grow strawberries, lettuce, green onions, kale, cucamelons, lemon cucumbers, and microgreens. We upload how-to and informational videos twice a week.
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Canada Requires Romaine From Parts of California To Be Tested For E. Coli
Effective October 7, 2020, the CFIA will require importers to either provide proof that romaine lettuce destined for import into Canada does not originate from counties in the Salinas Valley, or provide an official certificate of analysis from an accredited laboratory confirming that the lettuce has below-detectable levels of E. coli
Thanks in part to imported products, Canadians can enjoy fresh produce year-round. From 2016 to 2019, romaine lettuce from California was linked to outbreaks of E. coli illnesses in the USA and Canada. Food safety investigations by Canadian and US authorities identified the Salinas Valley growing region as a recurring source of the outbreaks.
To mitigate risk in the event of another outbreak this fall, the Canadian Food Inspection Agency (CFIA) is implementing temporary import measures aimed at preventing contaminated food from entering the marketplace.
Effective October 7, 2020, the CFIA will require importers to either provide proof that romaine lettuce destined for import into Canada does not originate from counties in the Salinas Valley, or provide an official certificate of analysis from an accredited laboratory confirming that the lettuce has below-detectable levels of E. coli.
CFIA is working closely and collaboratively with the US Food and Drug Administration to identify and respond to any potential outbreaks and continues to put in place effective preventive controls.
The testing applies to romaine lettuce as well as mixed salads containing romaine and will be required until December 31, 2020.
The program adds an extra layer of controls to the food safety measures in place under the Safe Food for Canadians Regulations (SFCR).
On January 15, 2020, SFCR requirements came into force for most businesses in the fresh fruits or vegetables (FFV) sector that import, export or engage in interprovincial trade.
Under the SFCR, FFV businesses are required to obtain a Safe Food for Canadians licence and maintain:
preventive controls that address food safety hazards;
preventive control plans that document risks to food and how they are addressed; and
traceability documentation that tracks the movement of food one step forward and one step back in the supply chain.
Additional safeguards
Canada maintains specific import requirements to minimize potential hazards associated with romaine. For example, the importation of leafy greens from California is limited to products supplied by certified members of the California Leafy Greens Marketing Agreement (LGMA). LGMA certified members must adhere to food safety requirements subject to regular audits by the California Department of Food and Agriculture.
In addition, the CFIA has a regular monitoring program for E. coli O157:H7 in fresh vegetables and is also testing 1,000 more samples of lettuce and products containing lettuce per year.
For more information, read the CFIA's guidance Import requirements for romaine lettuce from the United States.
Source: Canadian Food Inspection Agency (CFIA)
Quick Facts
The CFIA plays a critical role in safeguarding a healthy food supply system, ensuring the foods Canadians eat are safe and facilitating the trade of food and food products internationally.
More than 50,000 shipments of romaine lettuce or salad mixes containing romaine lettuce were imported into Canada from June 2019 to July 2020.
Romaine is associated with elevated food safety risks. In Canada, there have been seven documented outbreaks of illnesses associated with romaine lettuce, and 16 recalls of romaine lettuce or products containing romaine lettuce due to E. coli O157:H7 from 2010 to 2019.
Under this new requirement, romaine from Salinas must be tested in a laboratory accredited by the Standards Council of Canada (SCC), the Canadian Association for Laboratory Accreditation (CALA) or another accreditation body that is a signatory to the International Laboratory Accreditation Cooperation (ILAC) Mutual Recognition Agreement (MRA).
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Scientists Develop ‘Probiotics’ To Help Plants Fight Disease Without Pesticides
With concern about the impacts of pesticides on human health and the natural world growing, and disease resistance leading farmers to increase their use, the team is hoping to find a chemical-free solution
Enhancing a plant’s immune system with ‘probiotics’ could help it to fight off pests and diseases without the need for pesticides, according to scientists at the University of Sheffield. At the university's Institute for Sustainable Food, a study was launched, funded by a £1.5 million grant from the Biotechnology and Biological Sciences Research Council, into how beneficial bacteria protect plants’ health – in a similar way to gut bacteria in humans.
With concern about the impacts of pesticides on human health and the natural world growing, and disease resistance leading farmers to increase their use, the team is hoping to find a chemical-free solution.
Today, many fruits and vegetables – particularly tomatoes and soft fruits like strawberries – are grown hydroponically (without soil) in vast greenhouses and polytunnels covering 948 hectares in the UK. This enables farmers to grow high-value produce out of season – but because the plants are grown in sterile conditions, any diseases that do find their way inside can devastate entire crops.
By introducing beneficial bacteria to these greenhouse environments, the University of Sheffield scientists hope to prevent these outbreaks – helping to improve productivity and avoid food waste.
Looking at tomato plants, the team will use a combination of genetics and biochemistry to gain a thorough understanding of how roots interact with beneficial microbes in the soil. This knowledge will then be applied to develop plant versions of probiotics – methods of adding good bacteria to growing systems that will support the tomatoes to fight off pests and diseases using their own enhanced immune systems.
Scientists at the Institute for Sustainable Food have already developed synthetic foam ‘soils’, which can grow two to 10 times more produce than natural soil, relieving pressure on agricultural land and increasing the potential for urban farming. By injecting these probiotics into the foam, they hope to create ideal growing conditions for a whole range of herbs, fruits, and vegetables to be grown year-round.
"Scientists have learned a lot in recent years about how beneficial bacteria in our guts keep us healthy – and we believe the same is true for plants.
By investigating how tomato plants interact with good bacteria in the soil through their roots, we hope to be able to develop plant probiotics to boost their immune systems and help them fight diseases without the need for harmful pesticides.
Coupled with our synthetic foam soils, this completely new approach could help farmers to grow healthy and sustainable fruits and vegetables out of season and in the urban areas where most people live," says Professor Duncan Cameron.
Source: The University of Sheffield.
Publication date: Wed 3 Jun 2020
How Do You Stop Diseases On Controlled Environment Edible Crops?
Controlling the environment is a key component of preventing diseases on edible crops.
As an increasing number of growers start growing edible crops in controlled environment structures they may be facing some diseases that they haven’t encountered before. For ornamental plant growers who are adding edible crops, they will not have as many or as effective chemical controls as they have access to with their ornamental crops.
“Growers currently don’t have a good complement of products for edible crops being grown in greenhouses or other controlled environment structures,” said Michigan State University plant pathologist Mary Hausbeck. “And if there are chemical controls available, growers may want to spray all of their herbs together. For instance, if the rosemary needs to be sprayed to protect against Botrytis, it’s wise to make sure that other nearby herbs are also listed on the fungicide label. Otherwise, growers need to make sure that their employees who are going to be spraying know which herbs they can and cannot spray with a particular product. Fungicides labels can be complicated.”
Hausbeck said growers should be cautious about using pesticides in greenhouses and other controlled environment structures like warehouses, vertical farms and plant factories.
“Previously, EPA required that use in greenhouses had to be specifically stated on a pesticide label in order for greenhouse growers to use it. But states varied in their interpretation and so usage was determined on a state-by-state situation. Several years ago EPA determined that if the label doesn’t restrict use in greenhouses, then a pesticide can be applied to a greenhouse-grown crop. In Michigan, our state agency views greenhouses and other controlled environment structures similarly. Just make sure that the label doesn’t prohibit the use of a fungicide in a greenhouse.”
Optimizing environmental control
Because of the limited number of chemicals available to greenhouse growers of edible crops, Hausbeck said it is critical for growers to use environmental control to limit disease.
“Environmental control has to be part of the equation,” she said. “Powdery mildew, downy mildew and Botrytis have a tremendous capability to reproduce in large numbers via spores. A microscope is needed to see one spore, but when there are many spores, the eye can see the fuzziness of the mildew or grey mold on the plants. The spores are moved around the greenhouse via air currents.
“Powdery mildew and downy mildew tend to be specific as to what plants they will infect. Powdery mildew is a problem on tomatoes, cucurbits and peppers. Downy mildew can be a problem on basil, cucumber and lettuce. Botrytis has a much broader host range.”
Botrytis is in a lot of growing environments because it can take advantage of plant tissue whether it is alive or dead. Downy mildew and powdery mildew won’t colonize dead plant tissue that is lying on the floor or sitting in a trash pile. Botrytis will infect plant parts that are still attached or have been discarded.
Powdery mildew, downy mildew and Botrytis prefer cooler temperatures.
“Occasionally I have seen Botrytis sporulate in coolers,” Hausbeck said. “Older leaves that are mature and are senescing may be in direct contact with moist growing media and may lead to Botrytis infection. Plants growing in a moist environment with high humidity and extended periods of leaf wetness are at particular risk of Botrytis infection. For instance, Botrytis can cause stem blight on rosemary and other herbs leading to significant losses.”
Hausbeck said Botrytis has a fairly broad temperature range in which it can infect plants.
“Growers who effectively use environmental control to keep conditions dry and unfavorable for Botrytis can get by without fungicides,” she said. “Botrytis needs leaf wetness to infect plants. Moisture is key.
“At 80-85 percent relative humidity even a small drop in temperature can lead to Botrytis issues. If the relative humidity is maintained at a low level, Botrytis won’t be successful in becoming established. Growers should do everything possible to keep Botrytis at low levels.”
Botrytis can cause stem blight on rosemary leading to significant losses.
Photo courtesy of Mary Hausbeck, Mich. St. Univ.
Botrytis can also come in as a secondary problem. It may become a problem as a result of the plants undergoing an environmental stress that results in some leaf browning. Botrytis can take advantage of this dead tissue.
Hausbeck said Botrytis can be an issue with rosemary propagated by vegetative cuttings.
“Growers should try to lower the humidity immediately following taking cuttings from rosemary stock plants for 24 to 48 hours,” she said. “Botrytis infection can occur on the wounded stems of stocks plants leading to dieback. Growers can raise the temperature in the greenhouse by a degree or two to reduce the relative humidity. Growers should try to drop the humidity below 70 percent or as low as possible depending on the circumstances of the greenhouse. They should also provide good air movement around the plants. Having good airflow movement around the plants helps to prevent all types of diseases, including Botrytis, bacterial diseases, powdery mildew and downy mildew.
“It doesn’t take a lot of expensive technology to keep the relative humidity low and the plants dry. Avoid overwatering and keep the leaves dry by watering at a time of day when they can dry rapidly. Keep the air in the greenhouse moving so that there aren’t pockets of high humidity. Ensure there is good drainage so there is no standing water on the greenhouse floors. In areas of the greenhouse where there is standing water, the relative humidity in these areas can be increased by as much 15 percent.”
Correctly identifying the disease
Hausbeck has encountered times when some of the problems growers have reported were caused by environmental stress.
“In some cases growers have been able to send me really good pictures and I can make a diagnosis based on the photos,” she said. “If it appears the plants have a potential disease I’ll recommend that growers send samples to a diagnostic lab. There are some symptoms that don’t look like a pathogen at all. I ask the growers about their growing systems and to describe when the symptoms first appeared and the pattern they are seeing across the crop.”
Having good airflow movement around plants applies to preventing all types of diseases, including basil downy mildew. Photo courtesy of Mary Hausbeck, Mich. St. Univ.
Hausbeck said as more edible crops are being grown, she expects to see some “oddball” diseases showing up that she hasn’t seen before.
“Some of these are fungal pathogens,” she said. “I have seen Septoria, which is a fungal leaf blight, on a couple of herbs. As herbs are being grown in greater volume, it’s likely that we are going to see more problems develop just by the sheer amount of plant material being grown. It’s important for growers to recognize in some situations this is still a relatively new arena for plant disease.
“We don’t know everything about the range of crops that can be impacted and what the disease symptoms might look like. If growers see a problem with a crop they really should connect with a diagnostic lab sooner than later. In the case of a disease problem, the recommendation may be to toss the plants and not try to save them because there isn’t a good complement of fungicides. Growers may sit on a crop trying to nurse it along with different growing regimes, not recognizing that it is a pathogen that is destroying their crop. This could result in costing them more time and more money.”
More control options available
Hausbeck and her laboratory at Michigan State have developed a reference chart for “Registered Products for Common Greenhouse Diseases on Vegetables and Herbs.”
“We have compiled this “cheat sheet” for products that can be used on edible crops,” she said. “We have grouped the crops according to brassica, cucurbit, leafy greens, fruiting and herbs. It is only meant to be used as a guide. Growers must read the pesticide labels carefully.
“What we have learned is that there is not a blanket product that can be used on all herbs. If a product can be used on herbs, it may or may not include basil. The situation is getting better with these crops and registered products in terms of having more options.”
For more: Mary Hausbeck, Michigan State University, Plant Biology Laboratory; hausbec1@msu.edu; https://veggies.msu.edu.
Hort Americas works with a wide variety of vendors that help controlled environment gorwers manage the climate inside their greenhouses and vertical farms. Learn more about fan, ventilation equipment and other products available from Hort Americas.
This article is property of Hort Americas and was written by David Kuack, a freelance technical writer in Fort Worth, TX.