I was at the grocery store the other day and nothing catches my eye (and my sweet tooth) like raspberries and blueberries on sale. In October, these tasty, anti-oxidant beauties are coming from South America or a cooler climate in North America. My local food guilt usually gives me pause for purchasing them out of season, but the frozen blueberries leftover from my garden this summer just don’t hit like the fresh ones from Peru. Either way, what else will slow me from sticking that clamshell in my cart is evidence of grey fuzz on any of the fruit. This fuzz isn’t harmful to humans, but it does impact the fruit quality. Let’s learn about why!

 

The Grey Fuzz is Grey Mold

One of the few times the mycologists have it, grey mold is a type of fungus called Botrytis cinerea, and it looks grey and moldy! What we’re seeing as grey fuzz is really the reproductive structures, called conidia. It is a huge issue in the fruit and greenhouse production industries because it degrades the quality of crops, but also in your own kitchen! Fruit becomes deformed and tastes like dirt. Your annuals can get ugly leaf spotting or totally rot out. What makes this so insidious is that it is a necrotrophic fungus, meaning it kills its host tissue to feed on the dead cells. This is why it causes soft, rotting spots (blight) on flowers, leaves, and fruits. 

Keeping Grey Mold At Bay

The fall brings cooler, wetter weather, which can increase the prevalence of grey mold. Unfortunately for us, grey mold is ubiquitous in the environment, but it prefers cooler temperatures and high humidity, and especially wet conditions. The spores of Botrytis are easily spread by air currents, splashing water, or even human and insect activity. Grey mold has a wide host range, as well. Hundreds of species have been shown to be susceptible to grey mold under the right conditions. The key is staying vigilant during ideal conditions to make sure you can keep this fungus at bay. 

In The Refrigerator

The berries on our refrigerators can be targets for this fungus because they are sugary and less protected than vegetative parts of plants, and the insides of our refrigerators are a perfect ecosystem for this fungus! Before you put your berries in

your cart, inspect them for any fuzz or damaged fruit. Just because you don’t see the grey fuzz yet, doesn’t mean there isn’t already Botrytis growing. If it is only a little bit, you can remove the damaged, fuzzy berries when you get home and just plan to eat them as soon as possible. Once you bring them home, the key here is reducing moisture around the berries. Refrigerate the berries as soon as you get home, but don’t wash them until just before you eat them!

 

In the Seed-Starting Tray

It is so rewarding to start your own seedlings for your garden, but grey mold can also impact you there. “Dampening off” is a disease that attacks young seedlings, causing the stem to rot at or near the soil line, leading to the seedling collapsing and dying. It typically happens before or just after the seedling emerges from the soil. It is caused by several fungi, but the species will depend on the environmental conditions you are growing your seedlings in. In cool, wet conditions, you have the perfect environment for grey mold.

There are cultural practices that you can use to help prevent grey mold and sanitation practices you can use before and after an infestation to keep infection down. Keep the humidity down around your seedlings by increasing ventilation and using fans to keep the air moving around your seedlings (just make sure you are keeping the media moist!). Avoid overhead watering that can get the leaves wet and provide ideal breeding ground for Botrytis. Finally make sure to keep seedlings spaces so that air can move and seedlings are not touching each other.

If Botrytis shows up, remove and destroy any dead or dying plant material immediately. There are fungicides and sanitizers that are approved for treating Botrytis; though it is recommended to wait to use these until it is confirmed that you have Botrytis present. Once confirmed, it is recommended to sanitize surfaces, pots, tools and seeds before and after use in production areas known to have had Botrytis in the past. Contact you local N.C. Cooperative Extension Office for a list of control options appropriate for your growing conditions.

 

In the Garden

You can also find grey mold in the garden, and it is worth being on the lookout for it when the days are cool and wet, and still. For garden prevention, the focus should be on site selection, cultural practices, and maximizing air flow. Start by planting susceptible crops, like strawberries or tomatoes, in sunny, well-drained sites so the foliage dries quickly after rain. Improve air circulation by pruning plants to open the canopy and using stakes or cages to keep fruit and foliage off the wet ground. Furthermore, apply a clean mulch (like straw, particularly for strawberries) to prevent developing fruit from touching moist soil. Finally, practicing good sanitation is critical: remove all crop debris from the garden bed at the end of the season, as the Botrytis fungus can easily overwinter in plant residue and soil.

Amanda Bratcher is the Horticulture Agent for North Carolina Cooperative Extension in Lee County