How to Identify and Control Fusarium Wilt Disease in Your Garden

The height of the summer gardening season is a busy time. It’s time to prune, fertilize, and water. As you check your vegetable plants, it’s crucial to pay attention to how they look. Are leaves turning yellow? Are they wilting?

If you notice signs of wilting or yellowing, how do you know if your plants need more water or fertilizer? Are your plants just wilting from the heat, or is it something more nefarious, such as fusarium wilt?

We’ll cover how to identify verticillium and fusarium wilt. And share helpful methods to control these fungal diseases.

Fusarium wilt is a vascular disease that affects a wide range of plants. Various species of the fungus Fusarium cause it. These fungi live in the ground and enter a plant through damaged roots. When a plant becomes infected with Fusarium, the fungus blocks the plant's vascular system. The vascular system is the tissue that transports water and nutrients throughout the plant.

As a result, the infected plant starts to wilt because it can't receive enough water and nutrients to sustain itself. Even when watered, the plant won’t recover. Then, the leaves turn yellow. At first, just one side of the leaf or one side of the plant turns yellow. The plant may eventually die if the infection is severe.

Commonly affected crops include tomatoes, eggplant, peppers, cucumbers, and watermelon.

Verticillium wilt is very similar to fusarium wilt. Both diseases are caused by pathogens in the soil and affect the plant’s vascular system. We’ll include verticillium wilt in this guide since the symptoms and control methods will be the same.

The first symptom of both verticillium and fusarium wilt is leaf wilting. Even with additional water, you’ll notice that the leaves droop. This can be tricky at first because extra watering can help temporarily. However, as the wilt disease progresses, the xylem becomes more clogged, and the plant won’t be able to transport water and nutrients throughout the vascular system.

You’ll soon notice yellow leaves. Often, just one side of the leaf is affected, and then one side of the plant, but eventually, the whole plant will turn yellow.

How do you know if you’re dealing with fusarium wilt or some other issue? While it may look like under watering at first, wilt diseases will have some unique symptoms. One sign is the way that the leaves turn yellow. The yellowing will usually start at the bottom of the plant and just one branch. When plants wilt from not enough water, the whole plant will wilt. You may also notice that just one half of the plant turns yellow.

To positively identify disease in your plants, you can peel back the very outer layer of the stem. The inside xylem will be brown. The dark color is caused by the fungus blocking the vascular system.

Once you have identified fusarium or verticillium wilt, you will need to remove the infected plants. Once a plant has a wilt disease, it won’t get better. Sometimes, the plant will limp along for a while, but eventually, the whole plant will die.

Fusarium and verticillium wilt are challenging to control because they can live in the soil for years. However, there are some steps you can take to help control how badly it affects your garden. Creating a healthy garden starts with the soil. Having the right nutrients and beneficial microorganisms will increase your chances of success.

One way to control fusarium wilt is to heat the soil hot enough to kill the pathogens. Solar solarization is a simple process of placing sheets of plastic over moist soil and letting the sun's heat cook the ground. It can take two to four weeks at temperatures above 99ºF for the fungal pathogens to die. Soil solarization can also help control pests and weeds. 

Colorado State University Extension has a Soil Solarization Fact Sheet that explains how to use this process in your home garden. Soil solarization is a safe and organic way to help control fusarium wilt. The hotter you get the soil temperature, the quicker and more effective it will be. Contact your local university extension for specific solarization tips in your growing area.

Cover crops are excellent for improving your soil. Yellow mustard is an especially beneficial cover crop because of its biofumigation properties. 

Yellow mustard can be used as a cover crop for controlling fusarium and verticillium wilts. It is best planted in the late summer so it can develop enough biomass to be effective. It will take about ten weeks for it to grow to the flowering stage. 

Once the yellow mustard plant starts flowering, you can mow it down and chop it up. Then, immediately til it into the soil. Breaking up the plant releases the chemical compounds that can kill the wilt pathogens. You will need to water the soil well and keep it moist. Wait at least three weeks for the gasses to release into the soil and disperse before planting additional crops. Soil temperature needs to be at least 50 ºF.

Infected soil can be tracked from place to place. To control the spread of disease, it is essential to clean your gardening tools. Use a 10% chlorine bleach solution to clean all seed-starting equipment and supplies. Also, don’t use regular garden soil to start seeds; use sterile soil-less growing media.

It is also important to control weeds as some are host plants for fusarium wilt. Use clean weeding tools, mulch, and cover crops to help control weeds in your garden.

Pests and diseases are a natural part of gardening, but fusarium wilt can be alarming to home gardeners. However, there are methods for managing it. By growing cover crops, using soil solarization, and employing good garden hygiene, you can control verticillium and fusarium wilt in your garden.