Controlling Fusarium Wilt

Fusarium Wilt is caused by a soil-borne fungus species called Fusarium. Oxysporum. This dreaded plant pathogen affects a wide variety of hosts of any age and poses a serious threat to more than 20 economically important food crops including:

Chilli, tomato, green- and blackgram, citrus, banana, cucurbits, groundnut, potato etc.

Favorable Conditions for Fusarium Wilt

Fusarium Wilt thrives at warm soil temperatures and can live indefinitely in soil without any access to living host plants. As a result, an eradication of this disease is currently impossible. Once it’s in the soil, it can remain for decades.

Light and sandy soils, acidic soils, the use of nitrate (NO3) based fertilizers and the presence of plant parasitic nematodes, such as root knot nematodes, support the development of Fusarium Wilt. On one hand, the infection of the roots is favored by cool, humid conditions in spring. On the other hand, the expression of symptoms is most severe in warm dry periods, when the plants' need for water increases.

Damage Symptoms

Fusarium oxysporum includes many different species, which generally produce symptoms such as wilting, chlorosis, necrosis, premature leaf drop and browning of the vascular system.The most common symptom is wilting, which can cause massive losses.

Mode of infection

There are two basic types of spread: Distribution over short distances through water splashes and planting equipment, and over long distances through infected transplants and seeds. Fusarium Oxysporum infects a healthy plant with mycelium or germinating spores that penetrate the root tips, root wounds or lateral roots of the plant. After the plant dies, the fungus penetrates all tissues, sporulates and continues to infect neighbouring plants.

Preventative Measures

• Completely remove / destroy crop residues and affected plants
• Purchase resistant seed varieties / transplants
• Rotation away from susceptible crops for 3-5+ years will reduce disease (weed management must be undertaken during this period)
• Use clean propagation materials (read more about hot water treatment)
• Disinfect tools, machinery and irrigation water (here is some information on farm hygiene)
• Ensure there is adequate soil drainage
• Apply nitrogen in the form of nitrate instead of ammonium
• Fumigate the infected soil with hydrogen peroxide and keep the pH of the soil at 6.5-7.

Biological Control

The fungus Trichoderma viride and Trichoderma harzianum are proven biocontrol agents to control this disease in an environmentally friendly way. Bacteria like Pseudomonas fluorescens and Bacillus subtilis work as a catalyst for Trichodermaviride and also control some species of nematodes.

Soil application:

• Mix 2 kg/Acr each of Trichoderma viride, Trichoderma harzianum, Pseudomonas fluorescens and Bacillus subtilis in 200 kg of farmyard manure separated, from each other.
• Cover them with gunny bags and keep for 7 days.
• Moisten these gunny bags slightly every day so that they can reproduce rapidly.
• Mix all these four batches together with FYM or compost on the 8th day.
• Spread the mix all over the field.

Seed treatment:

• 4 to 5 gm per kg of seeds as per standard wet treatment.
• Seedling root dipping: at 10 gm per litre prior to planting.
• After planting: Alternately use 1 kg each of Trichoderma sp + Pseudomonas & amp; Trichoderma sp + Bacillus at an interval of 8 days.

Chemical Control

There is no chemical control measure that completely eliminates a Fusarium infection, but some can stop an infection for up to a few days by using various fungicides. However, this control measure only makes sense for short duration cultures. Prothioconazole is the only commercially available fungicide with proven efficacy. Azoxystrobin, prothioconazole and thiophanate-methyl led to the highest values for reduction of Fusarium wilt and did not cause phytotoxicity in watermelons.