Handbook of Vanilla Science and Technology

This fungus is very aggressive, it can attack any part of the plant and kill it in only a few days. The disease is distinguished by watery injuries of greenish to blackish color and causes general rotting of the infected tissue. One week after the infection, fine (thin) white filaments, the mycelium of the fungus, are observed (Wong et al. 2003; Anandaraj etal. 2005). Damage begins in the apical part of the plant and extends to the stem, leaves, aerial roots, and the rest of the plant. However, damage can be restricted to immature fruits or to specific plant parts. The disease can be confused with that caused by Fusarium,butPhytophtora is less aggressive and it differs in the formation of a mycelium on the injury and production of pin-head sized conidia (Anandaraj et al. 2005). The favorable conditions for the development of the disease are prolonged rains, poor soil drainage, excess shade, high plant density, and deficient control of weeds.

2.3.2 Damage

The disease causes high losses in production due to rotting, falling of fruits, and loss of plants.

2.3.3 Control

The incidence of the disease can be diminished by using the appropiate distance in between plants, from 1.5 to 2.0 meters between plants and from 2.0 to 2.5 meters between rows. The tutors should be pruned to allow from 30 to 50% or more of sunlight. Weeds should be controled. Infected plant parts should be removed and burned. Wong et al. (2003) recommend the monthly application of the following mixtures: Fosetyl-Al (2.5 g/L of water) + Carbendazim (2.0 g/L of water) and the mixture of Metalaxyl (2.5 g/L of water) + Benomyl (2.0 g/L of water).

2.4 ANTHRACNOSE (COLLETOTRICHUM SP.)

2.4.1 Description

The fungal pathogen Colletotrichum sp. attacks leaves, fruits, stems, and flowers. Characteristic of the disease are the small sunken dark coffee spots, irregular in color (Figure 2.2). It damages the leaves and the stem during the time called “nortes”, the season characterized by cold air and moderate rain (Curti-Diaz 1995; Hernández-Hernández 2005). In general the symptoms develop on the first five young leaves of the apical part of the plant.

Fig. 2.2 Anthracnose on leaves: initial, intermediate, and end stage.

Fruit damage (Figure 2.3) is pronounced during the humid and warm months. Although the symptoms are similar to those on the leaves, the pathogens can be considered different species or forms of the fungus, because they appear in different climatic conditions (Hernández-Hernández 2005). An excess of shade and high density of plants favors anthracnose development, as well as root rot and stem rot.

Fig. 2.3 Damaged fruits, ”pintos”, caused by Colletotrichum sp.

2.4.2 Damage

Damage of leaves and stems results in a reduction of new growth. Infected fruits fall prematurely before reaching their commercial maturity and the yields fall significantly, up to 50%.

2.4.3 Control

Anthracnose attack can be prevented by maintaining healthy root systems and adequate plant nutrition. Also, it can be prevented by applying any fungicide that contains copper oxychloride or mancozeb, in concentrations of 2 g/L with water or Bordeaux mixture (1 kg of lime + 1 kg of copper sulphate in 100 liters of water) before or immediately after the arrival of “norte”. To avoid burns it is important not to apply copper compounds on days with intense sunlight or during flowering and development of fruit. Young leaves and fruits affected with antracnose must be removed and buried outside the plantation to avoid further infection sources.

2.5 RUST (UROMYCES SP.)

2.5.1 Description

Rust is charactherized by the presence of yellow-orange spots on the leaves (Figure 2.4). As the disease advances, the pustules coalesce, eventually resulting in completely dried leaves. This fungal disease is more frequent in traditional production systems with little ventilation and excess shade, and in very rainy places.

Fig. 2.4 Symptoms of Uromyces sp. on a vanilla leaf.

2.5.2 Damage

Plants affected by rust stop growth and development. Therefore the disease eliminates the productive capacity and if it is not controlled in time, the resulting defoliation of the plants can destroy the vanilla plantation.

2.5.3 Control

Infected leaves should be removed and burned as soon as symptoms are observed. Also, it is important to increase the amount of light within the plantation and to make weekly applications of Bordeaux mixture, or other products that contain copper, in concentrations of 2.5 g/L of water.

2.6 ROTTING OF RECENTLY PLANTED CUTTINGS

2.6.1 Description