Fungal and Virus Diseases

Anthracnose

Anthracnose is the primary reason why mangoes, avocadoes and some other fruit trees fail to fruit or develop blackened fruit that drops prematurely. Anthracnose is a fungal disease that is exacerbated by rain and high humidity. During dry weather the disease is virtually absent. Application of copper based sprays immediately prior to flowering and during early fruit set and/or use of biodynamic preparations such as casuarina tea can help reduce the effects of anthracnose. Some fruit tree varieties also possess inherent resistance to anthracnose.

Black Spot on Pawpaw

Adequate nutrition is as much a tool in disease control as the use of sprays. Plants deficient in potassium, phosphorous and magnesium are more susceptible to attack by black spot and powdery mildew. Simply increasing the potassium (sulphate of potash and/or lucerne mulch), phosphorous (rock phosphate or chicken manure) and magnesium levels (Epsom salts) helps to make plants more resistant to disease. Pawpaws are most susceptible to black spot disease during the cooler months. Spraying with sulphur or copper based compounds prior to the onset of the cool weather and watering with liquid seaweed can help reduce the severity of infestations.

Citrus Melanose

This disease typically affects more mature trees or plants that have a canopy of foliage that hangs close to the ground. Mulch trees with a feeding mulch such as lucerne. This will help to prevent spores splashing up onto the foliage when it rains. Lift the lower branches so that foliage is well clear of the ground. Spray trees with copper based compounds after all fruit has been harvested, thoroughly wetting the foliage, trunk and branches. Repeat applications each year until no further evidence of disease exists. Improve general tree health with additional nutrients and water.

Damping off Fungus

This disease affects germinating seeds and young seedlings. It is transferred via water and affects the water conducting tissues of the plant. Use new seed raising mix or clean compost. Wash all pots and tools in hot, soapy water then allow to dry in the sun before use. Make sure that plants do not sit in water. There is no cure for affected plants and they should be disposed of so as not to infect neighbouring stock. Note that newly planted seedlings can appear to suffer from a similar condition, but this is typically the result of over watering or planting into a soil containing excessive amounts of fertiliser or overly rich compost and manure.

Passionfruit Virus

At the end of the growing season after production of a bountiful crop, passionfruit vines can look tired and in need of a well earned rest. In some cases, vines will show characteristic mosaic leaf yellowing that indicates presence of a virus disease. Such diseases are often present in plants from an early age, but only begin to gain the upper hand when the vine is occupied with fruit production or stressed in some way. Affected vines may continue to grow, flower and fruit in coming seasons, but will always lack vigour. Unfortunately there is no cure for virus affected plants. Given their rapid growth rate, high productivity and short lifespan, passionfruit vines are best replaced every few years. Unfortunately there is no cure for virus affected plants. Given their rapid growth rate, high productivity and short lifespan, passionfruit vines are best replaced every few years.

 

Authored by: 
Annette McFarlane
Sourced from: 
www.annettemcfarlane.com
Date sourced: 
16/02/2013