As cotton gets closer to blooming, scouts should be on the lookout for target spot and defoliation starting in the lower canopy.
The warm, wet weather the Mid-South has been experiencing could promote target spot in cotton fields, especially those fields that saw the disease in 2016 and are irrigated. Additional factors that increase target spot risk include higher planting rates, excessive N rates, narrow row spacing, vigorous growth, as well as hot, humid weather. Some facts about target spot:
- Target spot is caused by the fungal pathogen Corynespora cassiicola which causes lesions with irregular concentric rings. More concerning than the lesions of target spot is the premature defoliation it causes, which both lesions and defoliation start in the lower canopy. See image 1 and 2. Additional information/images of target spot and other foliar diseases of cotton can be found on the mobile friend guide at guideutcrops.com.
- No variety resistance has been identified but target spot is more severe where a dense canopy is allowed to develop.
- While the disease is responsive to fungicides, lint yield responses from fungicide applications have been variable. Generally, Tennessee research trials have shown one or two applications at or around the third week of bloom can increase yields over the untreated check by reducing disease incidence and reducing defoliation.
- Fungicides labeled for target spot in cotton include: Elatus (5-7.3 fl oz/a), Headline (6-12 fl oz/a), Priaxor (4-8 fl oz/a), Quadris (and generic azoxystrobin products, 6-9 fl oz/a), Stratego YLD (5 fl oz/a), and Twinline (7-8.5 fl oz/a)
- Fungicide applications applied after physiological cutout (NAWF 5) may decrease defoliation but are not recommended because they will often fail to protect yields.
Whether cotton would benefit from a fungicide application to protect yield from target spot needs to be assessed on a field by field basis. As with other diseases higher risk fields include those that are continuous cotton and irrigated. Also the effect target spot has on yield will be influenced by when the disease first develops, what growth stage the field is at, and weather conditions. Uncertainties include estimating yield loss from amount of target spot or defoliation.
Please tweet foliar cotton disease pictures along with county and state to @cottondisease