Late-Season Leaf Spot Control in Cotton with Chlorothalonil and Potassium Nitrate

M. A. Newman, D. D. Howard


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.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 273
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998