R. M. Riedel, and Mary Stuart
Department of Plant Pathology,
and Mark Schmittgen,
Department of Horticulture & Crop Science
The Ohio State University
Columbus, OH 43210

Plots were established on Crosby silt loam (pH 6.5, OM < 2%) at the Waterman Farm, Ohio State University, Columbus, OH (Franklin Co.). Pumpkins were seeded 2 ft apart in single 40 ft rows on 1 Jul. Treatments were replicated 4 times in a randomized commplete block design. Plots received 80 lb/A N preplant. Fungicides were applied at 65 psi and 60 gal/A using a gasoline-powered, tractor-mounted sprayer with a one-row boom carrying 5 Delavan HC-8 tips. Foliage was rated for Powdery Mildew development on 18 Sep. Fruit stems (handles) were rated for Powdery Mildew at the same time. Fruit harvest was not taken because of fruit theft from the plots prior to rating on 18 Sep. Rainfall for Jul, Aug, and Sep was 5.88, 0.89 and 4.99 in. , respectively.

Powdery Mildew was first observed in the plots on 5 Aug. Development was severe. Virus symptoms were severe by early September. All chemical treatments were better than check in terms of Powdery Mildew (PM) control on foliage.. Standard PM control programs, Bravo Ultrex plus Benlate and Bravo plus Topsin M, gave comparable control of PM which was significantly better than Bravo Ultrex or Bayleton used alone. CGA-219417, Sulfur, RH 0611, and RH 3866 all gave signigicantly better control of PM on foliage than the standard fungicide treatments. Control of PM with Microthiol, Reach, Bravo Ultrex + Bayleton, Terranil 90 DF + Bayleton, Terranil 6L + Bayleton and TRA-0019 + Bayleton was excellent though they were not significantly different from the standard fungicide treatments. Those fungicides that gave good control of foliar PM tended to protect the handles, also. It was impossible to statistically analyze these data, however, because so much of the ripe fruit had disappeared prior to Sep 18.

Chemical Control of Powdery Mldew on Pumpkin

Treatment and rate/A	Foliar rating*	Stem rating**
untreated control	5.3 a	+-
CGA-219417 75WP 0.33 lbs	1.0 g	---
Microthiol 80DF 4 lbs	1.8 e f g	---
Benlate 0.5 lbs + Bravo Ultrex 1.8 lbs	2.3 d e	----
Topsin M 70WSB 0.375 lbs + Bravo Ultrex 1.8 lbs	2.0 d e f	---
Maneb 75DF 1.5 lbs	2.8 c d	++--
Bravo Ultrex 1.8 lbs	3.5 b c	----
Reach 4 pts	1.5 e f g	---
Sulfur 6L 4 pts	1.0 g	-
Bravo Ultrex 1.8 lbs + Bayleton 8 oz	1.5 e f g	----
Terranil 90DF 1.66 lbs + Bayleton 8 oz	1.5 e f g	---
Terranil 6L 2pts + Bayleton 8 oz	1.3 f g	----
TRA-0019 3pts + Bayleton 8 oz	1.5 e f g	----
RH 0611 62.3W 2.5 lbs	1.0 g	---
RH 3866 (NOVA) 2.5 oz	1.0 g	----
Bayleton 50DF 4 oz	3.8 b	----
LSD (P=0.05)	0.98

* 1 = no or a trace of mildew, 2=1 25%, 3=26 50%, 4=51-75%, 5=76-100% foliage with fungal colonies and 6=necrotic leaves.
** Stem rating indicates development of Powdery Mildew (PM) on fruit stems (handles);
"+" = PM present,
"-" = PM absent