Foliar Fungicide Impact on Cotton in 2024

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Commercially available foliar fungicides (Table 1) were evaluated for the management of two emerging cotton diseases, target spot and areolate mildew. These diseases result in foliar leaf spots, powdery growth, and early defoliation. This trial was conducted in a research plot at the Upper Coast Plains Research Station located in Rocky Mount, NC. Foliar disease pressure was high in the area due to early-season drought conditions followed by hurricanes and heavy rains.

After the last treatments were applied, defoliation was assessed weekly, and foliar disease symptoms (lesions and white powdery growth) were assessed biweekly. The combined AUDPC from disease incidence and severity was calculated into a severity scale (1-10), with 1 being the lowest severity and 10 being the highest. The two center rows of each plot were harvested, and the adjusted yield (lbs of lint) was calculated from the plot yield (lb) and ratio of seed weight (lb) and lint weight (lb).

Fungicides reduced the impact of target spot and areolate mildew in cotton by reducing defoliation. Less defoliation was significantly correlated to higher yields (-0.067 and p-value <0.05). There were notable increases in yield with some of the tested fungicides (Table 2). However, the overall differences in disease, defoliation, and yield among the fungicide treatments were not statistically significant.

Table 1. Fungicide Products, Active Ingredients, Fungicide Resistance Action Committee (FRAC) Code, Rate, and Application Timing
Fungicide Active Ingredients FRAC Rate (fl oz/A) Application timing
Untreated
Revytek Mefentrifluconazole, Fluxapyroxad, & Pyraclostrobin 3, 7, &11 12 3rd week of bloom
Revylok Mefentrifluconazole & Fluxapyroxad 3 & 7 5.5 3rd week of bloom
Priaxor Fluxapyroxad, & Pyraclostrobin 7 & 11 6 3rd week of bloom
Miravis Top Pydiflumetofen, Difenoconazole 3 & 7 13.6 3rd week of bloom
Topguard EQ Flutriafol & Azoxystrobin 3 14 3rd week of bloom
Quadris Flowable Azoxystrobin 11 8 3rd week of bloom
Xyway Flutriafol 3 15.2 At Planting

Table 2. Disease severity, Defoliation, and Yield for Cotton Fungicide Applications
Fungicide Target spot severity scalea Aerolate mildew severity
scalea
Defoliation severity scaleb Yieldc (lint lb/acre) Yield Difference (%) Fungicide & Application Costsf
($)
Untreated 10 10 9.2 1476.95
Revytek 6.8 2.4 1.4 1615.71 +9.0 45
Revylok 6.7 4.9 4.7 1476.10 -0.1 31.5
Priaxor 3.4 2.2 1 1670.89 +12.3 28
Miravis Top 2.4 1.3 6.9 1418.50 -4.0 26.32
Topguard EQ 3.8 2.3 5.6 1513.14 +2.4 25.56
Quadris Flowable 4 2.6 8.2 1511.77 +2.3 20.94
Xyway 1.3 3.9 10 1334.23 -10.2 35

a Disease severity scales are standardized in at 1-10 scale from the combined AUDPC from biweekly incidence and severity assessments

b Defoliation severity scales are standardized in at 1-10 scale from the AUDPC from weekly severity assessments

c Yield (lbs of lint/acre) was calculated from the plot yield (lb) and ratio of seed weight (lb) and lint weight (lb)

d This reflected the estimated sum of the fungicide prices and application costs in North Carolina