Management of pests and diseases for Tree Tomtoes

1.1. Fungal diseases

The major fungal diseases include anthracnose (Glomerella cingulata), powdery mildew (Erysiphe sp., Oidium sp.), and verticillium wilt, a soil-fungal disease which can affect tomato, potato, and eggplant (Morton, 1987; Prohens and Nuez, 2005; Orwa et al., 2009). Other fungal diseases of tamarillo are ascochyta disease, black spots disease, etc.

1. Powdery mildew

The fungus grows on the plant and produces spores that appear as white powder on the surface of leaves; which is the characteristic symptom of the disease. If not controlled, the disease can cause defoliation of the whole plant.

Management:

• Avoid overcrowding of plants.
• Application of a sulphur based fungicide like Thiovit/Thionil at 40g/20L of water with 2 weeks spray interval. Spray benomyl (e.g. benobest) at 40g/20L water in alternation with the above product.

b) Verticillium wilt

The fungus infects plant through the roots and then travels up the plant stem. Leaves, stems and fruit are all affected by the disease. Affected leaves become yellow gradually. Other disease symptoms include leaf necrosis and wilting and internal brown discoloration of the stem, which help to distinguish it from other causes of yellowing, such as virus, nematodes, root rot.

Management:

Crop rotation for about 3-4 years is recommended to prevent this disease. Care is needed also not to transmit the pathogen through soil movement on tools and boots.

c) Ascochyta disease

This disease is characterized by dry circular and concentric rings which are black or dark brown in colour, mainly on older leaves. 

Management:

• Application of a sulphur based fungicide like Mancozeb or Copper oxychloride 40g/20L of water with 2 weeks spray interval.

 

1.2. Bacterial diseases

Bacterial diseases can also attack tamarillo but they are not an important problem. However, bacterial wilt, bacterial canker of tomatoes (Corynebacterium michiganense), bacterial blast (Pseudomanas syringae and P.solanacearum) and crown canker (Agrobacterium sp.) have been shown to cause damage (Prohens and Nuez, 2005).

There is no direct control measure for bacterial diseases; proper hygiene is required to prevent these diseases. The affected plants should be removed and burned. 

1.3. Viral diseases

Tamarillo is susceptible to a number viruses including tamarillo mosaic virus (TaMV), Potato aucuba mosaic virus (PAMV), alfalfa mosaic virus (AIMV), tomato spotted wilt virus TSWV), arabis mosaic virus ArMV), tobacco strick virus (TSV), and tomato aspermy virus (TAV).

Symptoms:

All virus will cause loss of yield and “mottling” on the fruit (this does not affect eating quality). Symptoms are most severe on young or unhealthy plants, and will be worst if several viruses have infected the plant at once.

Management:

• Good orchard hygiene, pruning and burning infected plants and a good pest management program will help to reduce pests and diseases.
• However once a plant is infected there is no treatment – prevention is the only solution. Thus, It is important to have good control over aphids and whiteflies as they are carriers of viruses.
• Weed control is also important as some weeds such as chickweed and deadly nightshade can harbour viruses that infect tamarillos. Weeds also compete for light, water and nutrients especially when tamarillos are young.

1.4. Aphids and whiteflies

Different species of aphids attack tamarillo but the green peach aphids (Myzus persicae) are the most important. They are vectors of several viruses that affect tamarillo such as cucumber mosaic virus (CMV) and potato virus ‘Y’ (PVY).

Whiteflies secrete honey dew over the leaves and fruit. This can lead to the appearance of sooty mould, which leaves fruit unsalable. They also transmit viral diseases.

Prevention:

• A complete crop break will help ensure complete eradication of the pest and prevent carry-over into subsequent crops.
• Use pest-free planting material.
• Keep recently received plants isolated to monitor closely and prevent the spread of any potential infestation.
• Field sanitation to destroy weeds which may act as refuge and alternative hosts.
• Where possible, protect seedlings from infection by growing them under 60 mesh screening.
• Conserve natural enemies: parasitic wasps (Hymenoptera) in the family Aphelinidae, lady bird bettle, etc.

Monitoring:

• Thoroughly inspect plants before planting for all stages of the pest, particularly on the underside of leaves. They are usually found on young leaves.
• Monitor throughout the growing season with yellow sticky traps.
• Check for the presence of whiteflies by agitating plants to encourage flight by adults and inspect the leaves for immature “stage”

Direct control:

• Begin treatment immediately if any life stages of the pest are detected to ensure prompt eradication.
• Application of insecticidal soaps and oils is effective in controlling aphids and whiteflies. Spraying water underneath the leaf also help to kill adults and reduce the number of eggs laid.

• Chemical control can be achieved using Lambda-Cyhalothrin at 1 ml/1l of water at 14 days interval. Alternate   the above pesticide with any one of the following: imidacloprid, acetamiprid, abamectin, nimbecidine (1 ml/1l of water) at 14 days interval.