KENTUCKY: Tobacco black shank, caused by the Oomycete pathogen Phytophthora nicotianae, is giving growers a run for their money this year. One of the most yield-robbing diseases in tobacco, black shank overwinters and survives in soil for at least four to six years, making prevention key to combating this pathogen.

Spread

It’s important to understand how this pathogen spreads in order to prevent it. The University of Kentucky explains that black shank can be spread through water or soil movement, via tractor tires, cultivators, fertilizer spreaders, contaminated tools and even workers’ boots.

Symptoms

Symptoms of black shank start as wilting during the heat of the day, though early on plants may appear to recover overnight. Later, plant leaves become yellow (chlorotic), as seen in the photo above, and don’t recover from wilt even under conditions of adequate moisture. These plants are often stunted and have blackened tissue within the stem at the root-stem interface. In late stages of the disease, plants die back completely and in severely affected fields, yields are significantly reduced, according to the University of Kentucky.

Management

Experts recommend that growers should begin implementing tactics now to manage black shank. The University of Kentucky recommends that growers be proactive, using the following three-pronged approach:

1. Crop rotation. Rotate fields away from tobacco for three to five seasons to reduce levels of the black shank pathogen. While it can never be truly eradicated from fields, black shank can be significantly reduced by growing non-host crops over several seasons.
2. Resistant varieties. For fields with any history of black shank, choosing a resistant variety is key. In Kentucky, two different races of the black shank pathogen are common and unless specific farm populations have been tested, the most conservative approach is to choose a variety that’s resistance to both races.
3. Fungicides. Apply fungicides in transplant water as well as soil-directed sprays. Fungicides available for application in transplant water include Ridomil Gold® SL and Orondis® Gold 200 (combine to form Orondis Ridomil Gold SL). At first cultivation and layby, Ridomil Gold SL and Orondis Gold 200 may be used. Post-transplant applications are most effective when directed at soils using drop nozzles followed by cultivation to move the fungicide into the root zone.

Combining the active ingredient oxathiapiprolin with the proven, trusted performance of mefenoxam, Orondis Ridomil Gold SL offers control that growers can rely on. As the only active ingredient in FRAC Group U15, oxathiapiprolin is not cross-resistant to any other fungicide and offers built-in resistance management when included in a season-long Oomycete disease control program. Growers can speak with their Syngenta representative to learn more about Orondis Ridomil Gold SL in tobacco.

A well-executed fungicide program and good management practices can help Kentucky tobacco growers reduce the spread of black shank, setting themselves up for a more profitable season.

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