DISEASE
 
   NAME
     Leaf Nematodes
     Aphelenchoides species

Description
These microscopic size soil borne nematodes attack leaves by entering through the stomates but are restricted by the veins. The nematode can resurface and move around the leaf in water, infesting other parts of the leaf.  

Leaf Nematode (Aphelenchoides ritzema-bosi) enters the plant when the stems and wet allowing the nematode swim to the stomates in the leaf. The leaf forms yellowish to brown spots that are contained by the veins but merge eventually turning the entire leaf brown then dieing. It infects greenhouse and outdoor Chrysanthemum and Penstemon species.

Stem Nematode (Ditylenchus dipsaci) enters through the stomates in young shoots and working upwards as thew stem grows causing the leaves to become malformed. Flowers fail to open, stems may grow sideways and the plant becomes stunted, dieing prematurely. The main host is Phlox species but not all are affected. 

Symptoms
Infested fronds of ferns turn brown to black and may die prematurely. Other softer foliage plants such as Chrysanthemums form yellow spots initially that are constricted by veins. These areas become dark brown turning black in severs attacks with the leaf withering and collapsing. 
 
Source and Dispersal
The nematodes remain active in plant material for up to 18 months. They are dispersed by infected plant cuttings or soil and travel along a film of water on the outside of the plant. They can also be dispersed by splashing water from the soil or from another plant.

Favoured Conditions
Humid cool conditions are preferred, as in after periods of rain or following overhead watering. They also prefer over crowded fernery stock. 

Affected Plants
A wide range of plants are affected these include, Australian native plants in the Asteraceae family or Anigozanthos and Lophostemon species. Ferns such as Asplenium, Blechnum and Pteris species are also susceptible.
 
  Plumeria acutifolia

Many ornamentals, perennials, annuals, trees and shrubs are also attacked include;
Begonia, Bergenia, Chrysanthemum, Coleus, Cyclamen, Gloxinia, Impatient, Penstemon, Plumeria and Saintpaulia species.

Ficus and Philodendron species are occasionally attacked by the leaf nematode (Aphelenchoides fragariae) forming angular markings that are water soaked at first, and then turning brown appearing on the leaf surface.

Non-chemical Control
Heavily infected plants and infested parts should be removed and burnt. Infected plant parts may be immersed in hot water at 45 deg for up to 15 minutes. This can only be used in local infestations and the immersed period varies according to the species.
Be certain to propagate from uninfected plant material and avoid replanting with susceptible species.

Chemical Control
Application of a systemic pesticide such as Fenthion are effective, but must be used as soon as the damage appears and repeated fortnightly. 
Note
Always read the label for registration details and direction of use prior to application of any chemicals.