By Tony Keinath, Clemson Plant Pathologist
Despite some unusually cold weather in January and February, Alternaria black spot is active on overwintered brassicas. Although the brassica Alternaria fungus (Alternaria brassicicola) present in South Carolina supposedly prefers warm temperatures, I doubt that old information is accurate today. Growers should be on the lookout for tan to gray to black spots ¼ to 1 inch in diameter on leaves. Longer, narrower spots are also found on the top or bottom of the main rib of collard and kale leaves. The number of spots per leaf varies.
Fortunately, three fungicides provide good control of Alternaria black spot on leafy brassica greens, based on a trial done on ‘Oldenbor’ kale at Clemson Coastal REC from September to October 2025. Priaxor, Quadris Top, and Miravis Prime clearly reduced leaf spotting symptoms and increased the weight of healthy leaves without spots compared to control plants sprayed with water.
Another takeaway from this trial is that Priaxor, Quadris Top, and Miravis Prime remain active in the plant longer than Inspire Super does. At least, that’s my interpretation of the difference between the performance of Inspire Super based on disease symptoms and on based on yield. Because of the risk of black spot developing or continuing to develop postharvest on chopped, bagged leaves or on bunched leaves that are misted on grocery store shelves, we used very strict grading when sorting harvested leaves. Many of the leaves in the Inspire Super-treated plots had very small spots that together were less than the size of a dime (about 1% of the leaf area) and were graded as not marketable quality.
One issue with all three recommended fungicides is that they have limits on the number of applications and, more importantly, on how many times they can be sprayed in a row. Miravis Prime and Quadris Top must be rotated 1:1 with another fungicide, while Priaxor can be sprayed twice before rotating. In this trial, I used Badge X2 copper as the rotation partner. In commercial fields, potassium phosphite could be rotated to provide protection against downy mildew. Note that Quadris and Quadris Top will control both black spot and downy mildew. Zampro controls downy mildew, but note that it has no effect on black spot.
| Week 1 | Week 2 | Week 3 |
| Miravis Prime | Badge X2 | Miravis Prime |
| Priaxor | Priaxor | Badge X2 |
| Quadris Top | Badge X2 | Quadris Top |
The organic-approved fungicides Oso and Badge X2 were ineffective in this trial. Organic growers should consider other management options. Oldenbor tends to be one of the curly kale cultivars more susceptible to black spot. In addition, in other research I’ve done, disease increases between the first and second harvests on cropped kale when diseased leaves from the first harvest are left in the field.
The South Carolina Grower 