The disease known as Downy Mildew is one of the most common diseases affecting basil plants. It is caused by a fungus called Fusarium oxysporum f. sp.
cubense (FPC). The spores are usually found growing on dead or dying foliage, which then becomes infected when it dries out and gets wet again after rain. When the plant is not pruned properly, the soil moisture level may become too low and cause the roots to dry out. If this happens, the root system will eventually die due to lack of water. Once this occurs, the leaf area at the base of each stem will turn brown and fall off leaving only a few white spots left on them. The affected areas are often near where new growth begins to appear. The fungus can spread throughout the whole plant if not controlled.
Symptoms: Leaves turn yellowish with dark spots. They may curl up and drop off completely. The affected parts may wilt and die, but they will regrow quickly.
Affected plants will have a “dead” look to them, especially during hot weather months.
Treatment: Prune the plant back and dispose of the infected portions. Fungicides will not work on this type of fungus. Rich soil high in organic content will help prevent it from infecting your plant.
Plants that are grown in direct sunlight can get a condition known as sunburn. This occurs when the parts of the plant are directly exposed to sunlight without any protection from wind or other natural elements.
Sources & references used in this article:
Diseases of basil and their management by A Garibaldi, ML Gullino, G Minuto – Plant Disease, 1997 – Am Phytopath Society
Fresh basil production guidelines for Hawai’i by RT Hamasaki, HR Valenzuela, DM Tsuda… – 1994 – scholarspace.manoa.hawaii.edu
Reduction of fusarium wilt of hydroponically grown basil by Fusarium oxysporum strain CS-20 by DR Fravel, RP Larkin – Crop protection, 2002 – Elsevier
The role of bacteria in periodontal disease by BG Bibby – Oral Surgery, Oral Medicine, Oral Pathology, 1953 – oooojournal.net
Basil Downy Mildew (Peronospora belbahrii): Discoveries and Challenges Relative to Its Control by CA Wyenandt, JE Simon, RM Pyne, K Homa… – …, 2015 – Am Phytopath Society
Pests and diseases of sweet basil after methyl bromide phase out: the northern Italian experience by A Minuto, A Bogliolo, G Minuto, N Vovlas… – … on Chemical and Non …, 2009 – actahort.org
Diversification of diseases affecting herb crops in Israel accompanies the increase in herb crop production by A Gamliel, O Yarden – Phytoparasitica, 1998 – Springer