Problem Identifier / How to Treat and Prevent Botrytis

If you are looking for information on how to stop botrytis on cannabis, please see our article on bud rot.

What is Botrytis?

Gray Mold Botrytis Poinsetta
Botrytis cinerea, (gray mold) on poinsettia bract. PHOTO CREDIT Penn State Department of Plant Pathology & Environmental Microbiology Archives , Penn State University,

Botrytis is also referred to as gray mold and botrytis blight. Cannabis growers refer to it as bud rot. Botrytis attacks nearly any ornamental shrub or tree and numerous garden vegetables and perennials. You will generally see botrytis after summer or spring drizzles or rain. It typically appears on dying and dead flowers and foliage first. Botrytis cinerea causes botrytis blight. This fungus attacks the tender areas of the plants when the humidity level is high.

How to Identify Botrytis?

Look for symptoms of mold including gray mushy spots appearing on produce, flowers, stems and leaves. Gray fungus spores often form a coating over the plant when the levels of humidity are high. Plants and fruits become shriveled with hardened black fungal filaments located beneath the rotted areas. You will find gray mold close to the surface of the soil and in plant canopies’ densest areas.

Mold develops first on wilted flowers prior to spreading to other sections of the plant. It is often found in storage areas containing harvested or rotting vegetables and fruits. Look for:

  • Grayish mushy spots on produce, flowers, stems and leaves
  • Gray fungal spores
  • Rotting and shriveled fruit plants
  • Hard black mass of fungal filaments
  • Wilted flowers

Is Botrytis Harmful to Humans?

Most individuals do not experience any issues from mold, although this disease can result in allergic reactions. Winegrower’s lung results from pneumonitis hypersensitivity. Although this condition is not lethal, the uncomfortable symptoms may require treatment from a physician.

If you inhale large amounts of mold, lung inflammation can occur. Pneumonitis hypersensitivity can be easily prevented by ensuring you are not inhaling large amounts of dust. You should wear a mask if anywhere near mold and ensure all areas are kept as clean as possible.

How Does Botrytis Spread?

  • Development of mycelium
  • Production of conidiophores
  • Conidium/spores spread through the air
  • Rain
  • Infected plants nearby
  • High humidity levels
  • Penetration of aged or damaged tissue
  • Insect wounds to the plant
Botrytis Mold On Onions
Botrytis soil-line rot of onions. PHOTO CREDIT Howard F. Schwartz, Colorado State University,

If you allow infected plant debris to remain, there is a good chance gray mold will develop. Debris from past crops contains mycelium which can develop with an increase in temperature. This is common during early spring.

When bright light is present, conidiophore structures are developed by the mycelium. At the tip of each conidiophore are conidium, or spores, which begin to form. If the temperature and humidity suddenly decrease, the conidiophores will release the botrytis spores. This usually occurs early in the morning.

The spores are transported by air/wind. This enables botrytis to establish contact with the stems or leaves of your crops. Germination occurs, resulting in an attack of mold. When raindrops connect with an infected plant, the spore dissemination increases.

Insects can carry mold spores between plants, causing the infection to spread. Infection can also result from infected gardens or plants close to your crops. For germination of mold spores to occur, there must be enough nutrients and moisture – including organic materials and sugars.

Moisture can result from several different sources including plant condensation caused by leakage of plant sap due to damage occurring on the plant’s outer layer and air humidity levels above 95 percent. As spore germination takes place, germ tubes will start emerging from each spore. The widening at the end of each tube is called appressoria.

Botrytis On Grapes
Botrytis on grapes.

An infection then forms enabling mold to enter the tissue of the plant. Penetration of the tube into the tissue of the plant does not occur immediately. Specific enzymes must first be secreted for the elimination of the cellular barrier of the plant. This is called the cuticle and is the plant’s outermost waxy layer.

Healthy tissue usually has an extremely tough cuticle. This means the botrytis is most likely to penetrate aging, weakened or damaged tissue first. An infection can also begin through plant wounds and stomata. Botrytis can develop during any of the following conditions.

Botrytis Treatment

  • Apply Trifecta Crop Control
  • Good sanitation
  • Remove and destroy plant debris
  • Prune and destroy infected plant sections
  • Disinfect pruners
  • Avoid plant stress
  • Proper environmental conditions
  • Ensure good air circulation

Your first and most effective step for treating mold is applying Trifecta Crop Control Super Concentrate with a dilution of 2oz per gallon. Apply every 72 hours until the botrytis is under control. Then switch to 1oz per gallon for preventative maintenance each week. You must consider both weather conditions and relative humidity when applying as it may affect the frequency with which you need to apply.

Botrytis Mold On Blackberries
Botrytis on blackberries.

The next step is ensuring good sanitation. Start by picking up and destroying any debris located beneath the plant on the ground. This includes fruit, leaves, flowers and twigs. All heavily infected areas must be pruned and destroyed. You can help avoid spreading botrytis by using a solution of 90 percent water and 10 percent bleach for disinfecting your pruners after each cut you make.

All infected plant material needs to be destroyed by burying it beneath a minimum of one foot of soil. If allowed under the regulations for your area, the debris should be burned.

The natural defenses of healthy plants to botrytis are limited. This means you need to eliminate as many growing conditions as possible that can result in stress. Your plants need to be given the correct amount of fertilizer, water and sunlight.

When watering the soil directly, the foliage needs to be dry. To ensure good air circulation, prune your plants as required.

How to Prevent Botrytis on the Coast in a Greenhouse

  • Apply Trifecta Crop Control as preventative
  • Keep greenhouse dry and clean
  • Irrigate plants
  • Good air circulation
  • Eliminate overhead water drips
  • All containers for plant debris should have lids

Trifecta Crop Control Super concentrate is one of your best defenses against mold, mildew AND pests. Apply at 1oz per gallon once per week to prevent botrytis.

If you are growing indoors, plants need to be kept dry. Your plants should be irrigated during the early morning hours to ensure the foliage dries fast. Good air circulation is critical for preventing botrytis in coastal greenhouses. You can improve air movement by using HAF fans 24/7. Botrytis issues can also be prevented with proper plant spacing.

You need to remove all debris on or under greenhouse benches including spent flowers and fallen leaves. Be sure to put a lid on any container you are using for storage of discarded plant debris.

How to Prevent Botrytis Outdoors

Botrytis On Strawberries
A strawberry rachis completely engulfed by a gray mold fungus, Botrytis cinerea. PHOTO CREDIT Scott Bauer, USDA Agricultural Research Service,

Taking preventative measures to ensure your crops never get mold is the best way to prevent botrytis!

  • Use one ounce of Trifecta Crop Control Super Concentrate for each gallon of water sprayed weekly for mold prevention
  • Understanding the requirements of each plant
  • Ensure good airflow and circulation with proper spacing
  • Do not excessively prune
  • Use the correct amount of fertilizer
  • Keep an eye out for nutrient deficiencies

One of your best options for controlling mold outdoors is applying Trifecta Crop Control as a preventative at a dilution ratio of 1oz per gallon. In addition to preventing mold, our all-in-one formula will help prevent most troublesome pests and mildew.

Next, ensure you maintain proper environmental practices. Understand the requirements of every plant and crop. Plants need airflow, good circulation and the proper amount of light.

Do not excessively prune your plants, allow them to become too dry or overwater. Use the correct amount of fertilizer and be sure to keep an eye out for nutrient deficiencies.

How to Combat Botrytis in an Orchard

Adhere to the following practices to prevent and combat botrytis in orchards:

  • Apply Trifecta Crop Control Super Concentrate as a preventative
  • Good handling and hygiene
  • Remove discarded and rotten fruit
  • Do not store fruit long-term without the right mineral status
  • Treat water using chlorine

It may seem impossible to eliminate botrytis sources in orchards but taking preventative measures is always your best option. Again, the powerful anti-fungal properties of our food grade essential oils will help keep botrytis at bay.

Apply Trifecta Crop Control at a dilution rate at 1oz per gallon once per week. Relative humidity and weather conditions should be considered when determining the application any foliar. Contact us if you have questions!

You can also help control and prevent botrytis through good hygiene and crop handling. Find and remove all discarded fruit in your orchard. Take all rotted fruit from your bulk bins. Everything needs to be cleaned and scrubbed as you take it off your grader.

You can minimize botrytis contamination in your packhouses by keeping them clean. During harvest, make certain your pickers are supervised to prevent damage to the fruit or storing fruit already damaged. Any fruit stored long-term must have the proper mineral status. Use chlorine to treat your water to decrease botrytis in the water in your drench tanks.

What Crops are Most Affected by Botrytis?

  • Celery
  • Onion
  • Squash
  • Cucumber
  • Eggplant
  • Lima, kidney and snap beans
  • Tomato
  • Carrots
  • Lentils
  • Fruit trees
  • Grapes
  • Strawberries
  • Raspberries
  • Cannabis (See Bud Rot)

How Long Does It Take for a Plant to Recover from Botrytis?

Depending on the type of plant, temperatures, and humidity levels, recovery can take anywhere from a few weeks to several months.

Defeat Pests, Mold and Mildew… NATURALLY!

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