Diseases of Vegetable, Ornamental and Spice Crops

NUTMEG

1. LEAF SPOT AND SHOT HOLE
Symptoms:

• The initial symptoms of the disease appear as sunken spots surrounded by a yellow halo.
• Later, the central portion of the necrotic region drops off resulting in shot hole symptoms.
• Die back symptoms are also observed in some of the matured branches.
• On young seedlings, drying of the leaves and subsequent defoliation are observed.

Pathogen:

• The disease is caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.
• Pathogen, disease cycle and epidemiology have been described under Large Cardemom.

Management:

i) Collect and destroy the infected plant debris.
ii) Apply prophylactic sprays of Bordeaux mixture (5:5:50) and repeat 2 or 3 times at 14 days interval

2. THREAD BLIGHT
The disease manifests in two types:

a. White thread blight:

• The first is a white thread blight wherein fine white hyphae aggregate to form fungal threads that traverse along the stem underneath the leaves in a fan shaped or irregular manner causing blight in the affected portion.

b. Horse hair blight:

• The symptoms of this disease appear as fine black silky thread of the fungus form an irregular, loose network on the stems and leaves.
• These strands caused blight of leaves and stems.
• However, these strands hold up the detached, dried leaves on the tree, giving the appearance of a bird’s nest, when viewed from a distance.

Pathogen:

• White thread blight is caused by Marasmius pulcherima while horse hair blight is caused by Marasmius equicrinus.

Disease cycle and epidemiology:

• These fungi perennate as mycelium in dried up leaves.
• These diseases are severe under heavy shade.

Management:

i) Follow phytosanitation and shade regulation practices.
ii) With the initiation of the disease spray the crop with Bordeaux mixture (5:5:50).

3. FRUIT ROT
Symptoms:

• On immature fruits, the symptoms of the disease appear as splitting and rotting of fruits which ultimately drop prematurely.
• In case of fruit rot, the infection starts from the pedicel as dark lesions and gradually spreads to the fruits, causing brown discolouration of the rind resulting in the rotting.
• In advanced stages, the mace also rots emitting a foul smell.

Pathogen:

• The disease can be due to both physiological and pathological regions.
• The fungi associated with this disease are Phytophthora spp. and Diplodia natalensis Pole-Evans.

Management:

i) Spray the crop with Bordeaux mixture (5:5:50) when the fruits are half mature.

Other diseases of importance are:

• Die-back (Diplodia spp.)
• Dry rot (Stigmina myristicae)
• Root rot (Fomes noxius and F. lamaoensis)