If there’s one fungus to really be afraid of, that’s the Fusarium. This term encompasses a broad spectrum of fungi that constitute potential threats to crops. However, like with any other plague, this one can also be prevented. If prevention fails, though, there’s nothing you could do to save your plants from a horrible death. Here’s all you need to know about them, about their spreading capacity, and about the best way to keep them at bay.
The term Fusarium refers to a group of filamentous fungi that usually live in the soil. Of all the different organisms that make up this group, one is especially dangerous. This species, known as Fusarium oxysporum, is an ascomycete fungus. Among others, it's characterized by the production of septate mycelium and an unknown sexual life cycle.
A highly resistant fungus that spreads rapidly
Fusarium is a long-lived fungus that can survive in the soil indefinitely and that's, precisely, what makes it such a dreadful threat. Not only can this strong pathogen live in soil, though, it can also be found in other kinds of substrates as well as in crop residues. Even in unfavorable conditions, such as in dry or water-soaked soils.
The asexual airborne spores known as conidia are famous for their resistance to extreme conditions, meaning no water or moisture is needed for them to survive. Besides, they cover long distances with the help of air currents and dust. It's true that water is not necessary for their survival. However, its presence improves their structure making them stronger and more resistant. In other words, a nutrient-rich damp environment will keep them active for years.
Don't forget either that the spores can reach our crops transported by many terrestrial insects.
What triggers their propagation?
A primary risk factor is the temperature. This type of fungus thrives at warm temperatures (82°F). Fusarium is famous for its resilience, though, which means infection can happen even in low temperatures if the following circumstances occur:
- The use of an infected substrate or soil mix may greatly contribute to its spreading. This fungus can spend years active in the soil. It's very difficult to tell whether the one we've picked is contaminated or not.
- Excessively high moisture levels and temperatures will cause the fungus to become stronger and live longer. Make sure the soil's temperature remains lower than 86ºF and that the irrigation water and nutrient solution you use stay below 75ºF.
- The lack of light also favors the spread of Fusarium oxysporum, so appropriate lighting, whether it's natural or artificial, will definitely hold off this nasty fungus.
- Poor soils with low levels of some nutrients, such as nitrogen, or with high levels of others, say potassium, are a hotbed of these pathogenic organisms. Use nutrients wisely.
Detecting a Fusarium infection
A Fusarium outbreak happens when airborne spores reach the substrate. Once there, they produce mycelial colonies and the contamination process kicks off, from bottom to top. If the plant's got any wounds, then it's more exposed to a rapid attack of Fusarium for it can work its way into the plant much more easily. First, it will attack vascular tissues and then the rest.
Early detection is key, but symptoms take long to become visible, so by the time we spot them it's always too late. It's essential to remain vigilant and act quickly at the slightest hint of trouble. These are the most common symptoms of a Fusarium oxysporum infection:
- The appearance of lower stem vascular tissue decay will reveal the presence of Fusarium in your plants. Pay attention to the coloring. If you notice some yellowing or browning, then start looking for other signs.
- Check the lowest and oldest leaves for the emergence of small spots or for tips that curl upwards. Over time they'll turn chlorotic (yellow in color) and necrotic, although still attached to the plant.
- Lignification of the stems: if we cut a stem, we'll see it's brownish inside.
- Root rot: the many hairs that make up the root system become necrotic as well. They gradually turn brownish with decaying tips, causing the wilting of the plant, particularly during peak sunshine.
Prevention is the only effective strategy
If any of your plants has already received the visit of the so-dreaded Fusarium oxysporum, that's bad news. The best you can do to prevent this from happening is to make sure you follow these steps:
1- Be scrupulously clean. Carefully clean any tool you use from the very start until the drying phase is over. Remember to wash your hands before working on your plants and, if anyone happens to visit you, make them do exactly the same.
2- Use a quality substrate. This way you'll keep the fungus at bay. If, even so, it manages to work its way into your grow, it won't live as long. A lack of nitrogen or an excess of potassium can make them thrive. Don't forget that. Alternatively, we recommend using clay soil for the bacteria contained therein are effective against Fusarium.
3- As mentioned before, high temperatures can trigger the outbreak and affect the spreading capacity of this pathogen, so try to keep the substrate temperature below 82ºF. Outdoor growers should use light-colored pots, as light as it's possible, so they better reflect sunshine and don't absorb any heat. Dark colors raise the temperature sharply when in direct contact with sunshine.
4- The kingdom of fungi is full of allies. Trichoderma harzianum, for example, will help you protect the roots from the attack of Fusarium while improving the absorption of nutrients and water, which will greatly benefit roots making them stronger against other potential threats.
5- If your grow is already infested, we recommend removing ALL the affected plants as quickly as possible, as well as the substrate used for growing them.
With these tips, the presence of the so-dreaded Fusarium should be less worrying. Keep an eye on your plants and take good care of them. If you follow our tips, we're sure it won't be necessary for you to even come up with a strategy against it.