January 2010. A problem on melons in Cambodia (seeds from Chia Tai, Thailand). Melon is a new crop, introduced recently by an NGO. However, farmers are facing many problems. It was thought that the plants are suffering from a fungus infection, possibly downy mildew. Symptoms occurred very quickly. This is the dry season; however, it was thought that the farmers are overwatering.
Symptoms of wilt:
A member thought the problem was caused by Verticillium wilt, a soil borne fungal pathogen. There are some important features of this pathogen on melon as given below:
Verticillium persists in soil and in decomposed plant material as resting structures called microsclerotia for more than 20 years. This soil-borne pathogen first attacks young plant roots, colonizes the xylem and phloem cells of the vascular tissue and then flows along with water and nutrient into the stems and leaves. As a result, plants wilt. Symptoms of Verticillium wilt differ from those of Fusarium wilt by a characteristic V-shaped interveinal yellowing, necrosis and dropping of leaves.
Another suggestion was anthracnose or, perhaps, downy mildew, as the leaves show large necrotic spots. There are resistant varieties to these pathogens, so the advice was to get the symptoms checked so that appropriate varieties could be chosen.
Fusarium solani was also suggested by Iran, as symptoms on melon were similar to those on bean in that country. The climatic conditions are the same as those in Cambodia.
Symptoms of blossom-end rot:
It was also suggested that the fruit were suffering from blossom-end rot. Blossom-end rot is not a disease; it is a physiological condition. Typically, it is caused by uneven watering/moisture and usually goes away later in the season. Its effects can be somewhat mitigated through proper watering techniques. Application of Dolomitic (not hydrated) lime can be helpful. If in doubt, have a soil test done first.
Also, one of the photos showed symptoms of virus, which one was hard to say from a photo as there are many infecting the crop. A suggestion of Zucchini mosaic virus was offered. And the pale blotches on the fruit may also be signs of virus.
Change the nos to positions of the photos
Virus. 7514 and possible 7488 are showing signs of virus. Perhaps the pale blotches on the fruit, too (7507). But that’s not the main problem.
Wilt (7445) and the associated symptoms on the leaves (7465 and 7466), perhaps caused by root damage (7452).
Fruit splitting 7496, 7497) ??? possibly, water related.
There is need to get the plants to a lab for isolation of fungi from the roots. Assistance was offered from the Plant Protection Division CARDI (Cambodian Agricultural Research and Development Institute).