| [Image: Tight lock of cotton] |
| [Image: Picture of Phomopsis boll rot] |
| [Image: Picture of boll rot symptom] |
Symptoms
Symptoms of boll rot are variable. Most often brown to black lesions are visible on the surface of the boll. Some lesions are covered with fungal growth. Often locks of infected bolls do not open properly, causing a condition referred to as “tight-lock.” The lint from infected bolls is stained yellow, brown or black and does not fluff properly. With some boll rot organisms, external symptoms are not visible, but the fiber and seed inside the boll are destroyed. Under conditions of high humidity or free moisture, yield losses caused by boll rots can be severe. Insect injury will contribute to yield losses caused by boll rot.
Causal agent and disease development
Boll rots are caused by a number of fungi and by the bacterial blight pathogen. Some of the most common species of fungi are Fusarium, Phytophthora, Phomopsis and Aspergillus. Boll rots are more severe on tall, rank cotton or on cotton exposed to frequent rain or overhead irrigation late in the season during boll development. These conditions provide the high humidity and free moisture on the bolls that encourage fungal growth. Insect injury will also increase the incidence of boll rot.
Control
Attempts to control boll rots with fungicides have not been successful because of the broad spectrum of fungi involved, the failure to get adequate coverage and the inability to time the applications properly. Boll rots are best managed by avoiding excessive nitrogen and improper irrigations that promote rank growth. Avoid overhead irrigation during boll development. Controlling insects that feed on bolls will reduce boll rots. Skip row planting reduces boll rots by permitting more air movement between the rows, reducing humidity and promoting drying of the foliage and bolls.