Foliar Fungicides For Gray Leaf Spot (GLS) Control In Corn
Tests at the Research and Education Center
at Milan (RECM), Tennessee have shown a
high degree of control of gray leaf spot (Cercospora
zeae-madis) with two strobilurin fungicides
(Headline and Quadris). Each fungicide
was used at 6 oz/a with Penetrator Plus as an
adjuvant. Yield increases from the last two years
(2006 & 2007) ranged from an average of 27
bu/a on a GLS susceptible hybrid, 19 bu/a increase
on a moderately susceptible hybrid and
13 bu/a increase on a tolerant hybrid.
Eight row plots replicated four times on 30”
centers were planted no-till with three Pioneer
corn hybrids with varying levels of resistance to
GLS. They were: susceptible P 32T22, moderately
susceptible P 33R76 and P 33V14 for the
tolerant hybrid.
Each plot was split into two 4-row plots, so
that there was a treated and untreated side-byside
for each of the two foliar fungicides for all
three hybrids. This irrigated plot area has been
in no-till corn production for the past four years
with a high level of GLS each year. Each fungicide
was sprayed once at the VT (tassel stage)
with a Co2 tractor mounted sprayed using 20
gallons of water per acre. Yields were determined
by harvesting with a Almaco SPC 40 plot
combine. GLS ratings were taken on Aug. 6 in
2007 and July 7 in 2006 after the susceptible
hybrid had reached its highest rating for the unsprayed.
The GLS rating scale ranged from “0” to “10”
where 0 = no disease spots present and 10 = the
most disease possible. The two year average
GLS ratings for the susceptible hybrid was much
higher than for the other two hybrids ranging
from 5 for the sprayed to 8 on the unsprayed.
The two average GLS rating for the moderately
susceptible ranged from 2.75 for the sprayed to
4.75 for the unsprayed. The two year average for
the tolerant hybrid ranged from 1.25 to 2.0 for
the unsprayed. There were higher GLS ratings
for the test in 2007 than in 2006 but there was
a higher level of control of GLS in 2007.
Yields were higher in 2007 across all plots even
though there were more leaf spots. The two year
average yield improvement for Quadris was 28
bu/a for the susceptible hybrid, 27 bu/a for the
moderately susceptible and 17bu/a for the tolerant
hybrid. Headline’s two year average yield
increase was 26 bu/a for the susceptible hybrid,
11 bu/a for the moderately susceptible and 9
bu/a for the tolerant hybrid.
Both fungicides significantly controlled GLS
and increased yields but neither was significantly
greater than the other.
Three of the most important points to consider
when spraying fungicides for disease control are:
1. resistance to GLS, 2. over all weather conditions
especially after tassel, and 3. crop rotation
(corn after corn). Δ