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Botrytis fruit rot, also known as gray mold, is a common problem for home and commercial growers when growing strawberries. It can destroy an entire crop left unchecked.
Sometimes you don’t even know your plant is infected until it’s too late to do anything about it.
Keep reading to learn more about Botrytis fruit rot and how to save your strawberries from this all-too-common disease.
Contents
What is Botrytis fruit rot?
To find the proper treatment for botrytis fruit rot, you need to understand the disease and how it spreads.
Botrytis rot is caused by a fungus called Botrytis cinerea. Although it infects your fruit in the spring, symptoms usually appear during the harvest season.
It is most active when the weather is cool and wet, but it can be present, hiding dormant, even when conditions are less than ideal. This is why you should be aware of the symptoms that may appear early in the growth process.
A few sprigs of Botrytis cinerea are more difficult to treat than others because they have become resistant to fungicides, but the symptoms are the same.
The first symptoms usually appear within two to four weeks of infection, or the fungi may go dormant and reappear as the fruit begins to ripen.
Symptoms include small light brown spots that grow and coalesce. These can eventually cover the entire fruit. If the disease is left untreated, the brown spots will develop a coating of gray mold.
If you start to see spots, examine the stem of the fruit. You may see light brown lesions forming there.
Once gray mold begins to grow, it can also infect nearby fruit on strawberries or other species. That’s why you need to act quickly if you see symptoms.
The lifespan of botrytis rot
The disease may lie dormant on the leaves before showing apparent symptoms. It can also produce growths called sclerotia, which can survive in the soil for years, even in the absence of strawberries. The sclerotia act as food storage for the fungus.
This means you can re-infect plants years later. And since Botrytis can live on many other species, not just strawberries, it can find alternate hosts.
This disease can also lie dormant for some time before showing any signs. It can infect plants in early spring, hang around without symptoms during the summer and “suddenly” appear in the fall.
As mentioned, the fungus needs cool conditions, between 65-75°F, to grow, spread and reproduce. It also needs humidity. High humidity, lots of rain, and excessive irrigation all contribute to the spread of this disease.
Prevention of fruit rot due to Botrytis
It can be difficult to tackle the Botrytis mushrooms because it has different strands. One may be resistant to common fungicides in your area, and one may be suitable for drier conditions than another.
You should start by changing the growing conditions to see if you can treat the disease without applying chemicals.
A fungicide can impact soil quality and can create resistant fungi, so it’s a good idea to try treating the disease without chemicals to begin with.
Here are some tactics to try:
1. Limit nitrogen
Studies show that nitrogen can increase the presence of fungi like Botrytis. This is because nitrogen causes an abundance of leaf growth, which reduces air circulation. When the weather turns cold and damp, the conditions are perfect for gray mold to take over.
Limit nitrogen use during the growing season and monitor the amount of leaves. Test your soil before fertilizing to make sure you’re not adding too much of something your soil doesn’t need.
2. Increase air circulation
Space several strawberry plants well apart to increase air circulation. Most cultivars should be spaced about 18 inches apart. Planting strawberries in raised beds can also increase air circulation.
To avoid high humidity levels, add additional mulch to the top layer of soil to ensure that moisture is not trapped.
3. Plant in full sun
Strawberries need full sun to grow well. Choose a spot in your garden that is not shaded by walls or other plants. Sunnier locations help any excess moisture dry out faster.
4. Control weeds
Weeds can cause problems for strawberries. Remove them from your gardens. Don’t just pick them by hand or cut them with scissors. You have to dig up all the weed in order to remove the roots. Otherwise, the weeds will grow back.
Mulching is also an effective method of minimizing weeds, with the added benefit of helping moisture stay in the soil so you don’t have to water as often.
5. Remove damaged fruits and leaves
Not only is it important to get rid of weeds, but you also need to remove any damaged fruit or leaves. Removal of dead tissue will help protect the fruit from exposure to Botrytis fungus, as the disease enters through damaged areas.
Check and remove damaged parts daily. You should also avoid damaging the fruit when mowing, weeding or pruning near the plants.
6. Harvest strawberries regularly
Harvesting your strawberries as soon as they are ripe will limit the continual spread of mold. The harvest season usually only lasts 3-4 weeks, so you don’t need to be vigilant for too long.
You usually know a strawberry is ready to pick when the fruit is bright red. Strawberries are delicate, so be careful when picking them. The easiest way to pick fruit is to pull it out with your fingers.
A simple pull should remove the berry, then you can place it in a container or bag. Or you can cut the stem. Remember not to put too many strawberries in a small box as this will cause them to bruise.
If you notice mold, discard the infected berries and save the healthy fruit. Be careful not to pick unripe strawberries that are still pale and hard.
7. Water properly
Remember that this fungus needs moisture to propagate. That’s why you should do your best to keep strawberries from getting wet and staying wet.
A straw mulch under the plants can help reduce splashing, and you should always water at ground level, not on the leaves. Keep plants well spaced to improve air and water circulation in the morning so moisture can evaporate quickly.
Chemical treatment options
If all of the above fails, fungicides are the next best solution for Botrytis fruit rot. It is a complex disease to manage and requires careful factory treatment.
Apply treatment when fruit begins to sprout. You may need to try several different products before you find one that adequately controls the disease.
In some areas, you can request a Botrytis fungus test from your local agricultural office to find out what will be most effective in treating it.
Botrytis cinerea is resistant to the following fungicides: pyraclostrobin, iprodione and fenhexamid.
If you spray your strawberry plant in the early stages of growth and again during harvest season, you should be able to prevent the disease from developing further.
Biofungicides
Biofungicides are a great way to treat Botrytis rot because they are effective and less damaging to the surrounding environment.
Here are some biofungicides suitable for Botrytis fruit rot:
Most of the time, Botrytis fruit rot treatment involves trial and error by experimenting with various fungicides.
Storage
Once infected, store the berries in a cool, dry place to delay rotting.
After harvesting your berries, place them in the refrigerator to keep them fresh. Eat them as soon as possible.
Another option is to wash and store the strawberries in the freezer and mix them into smoothies, jams or desserts.
The most important thing is that you store your strawberries in a dry place so they don’t rot quickly.
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