In order to increase the effectiveness of KNO₃ in controlling the late-season leaf disease complex, chlorothalonil (Bravo 720) was added to foliar applications on conventionally-tilled DPL 50 cotton plots. The plots were located in a field that tested low in available K on the Ames Plantation Experiment Station in 1993. Late-season leaf spots (mainly caused by Alternaria spp.) has caused much concern in Tennessee the last few years especially on soils testing low in K. Treatment included Bravo 720 at 2 qts./acre at mid-bloom, Bravo 720 at 0.5 qts./acre at boll set, a combination treatment of the two treatments above, and the combination treatments of Bravo 720 with KNO₃ (10.6 lbs./acre for each of two applications).

Plots were in a randomized complete block design and replicated four times. The center two rows of four-row plots 30 feet long were sprayed with a CO₂ applicator. Three TX8 nozzles per row (one over the row and a double 15" drop nozzle on each side) provided a treatment mixture of 24 gallons per acre.

Leaf spot ratings were made on August 30 and September 8 on a rating scale of 0-10, where 0 = no leaf spot and 10 = most possible disease before defoliation. Treatments of Bravo 720 at the 2 qt./acre and the combination treatments of 2 qts. and 0.5 qts./acre had significantly less leaf spot at both rating dates. Applying the combination of Bravo 720 and KNO₃ reduced leaf spots relative to double application of Bravo 720 alone.

Overall, yields were lower than expected. Treatment yields did not differ significantly from the untreated. However, a numerical increase in lint yield was noted as Bravo 720 rates increased and especially when KNO₃ was added to the Bravo treatment.