Editor’ s Note: The following research involving zucchini (Cucurbita pepo ‘ Raven F1’ ) and powdery mildew (Podosphaera xanthii) was performed and reported here by Purdue’ s D. Egel, S. K. Saha, S. Johnson, S. Monroe, D. Nowaskie, and M. Restrepo.

On July 12, zucchini were direct seeded into a field at the Southwest Purdue Agricultural Center in Vincennes, Indiana, which was managed for the fifth consecutive year organically. Individual row plots consisted of 30-ft rows on 6-ft centers. Zucchinis were planted 3.0-ft apart with 10 plants per plot. Each row was mulched with 4-ft wide x 0.16 in. black plastic (Visqueen 4020). The experimental design was a randomized complete block with four replications. Treatment plots were separated in the row by 10-ft unplanted buffers. OMRI (Organic Materials Research Institute) listed fungicides were applied weekly from July 22 to August 31 with a CO2 backpack sprayer with 4 flat fan nozzles Tee-Jet 8002VS spaced 19 inches apart applying 10 gal per acre at 30 psi. The plots were examined for symptoms of disease on August 20, 27 and September 3 using the Horsfall-Barratt ratings system. Zucchini were harvested on August 19, 20, 23, 25, 27, 30 and September 1. Rainfall totals for June, July and August were 4.79, 10.67 and 1.54 inches respectively.

Symptoms of powdery mildew were first observed on August 20. Only data collected on August 27 are shown below since this is the only date on which significant differences were observed. The only harvest date for which significant differences were observed was September 1. Only Champ DP and Milstop treatments had significantly lower levels of powdery mildew than the untreated check. While the total number of zucchinis harvested was not significantly different between treatments, on September 1, zucchinis treated with Champ DP had significantly more fruit than any other treatments except Serenade Max.

Treatment, rate/Az	Disease Severity 27 Aug (%)y		Number of zucchini/A
	Leaf top	Leaf bottom	1 Sep	Total
Untreated check. . . . . . . . . .	18.8 ax	37.5 a	968 b	12,269
Serenade Max 3 lbs. . . . . . .	15.0 ab	37.5 a	1,041 ab	11,132
Oxidate 90 fl ozw. . . . . . . . .	12.0 ab	30.3 ab	653 b	10,333
Milstop 2 lbs. . . . . . . . . . . .	5.7 bc	12.0 c	726 b	11,543
Champ DP 3 lbs . . . . . . . . .	2.3 c	18.8 bc	1,525 a	14,593
P-value	0.0125	0.0525	0.0965	0.1189

^z Fungicides were applied approximately weekly from 9 until 31 Aug, except Oxidate which was applied twice weekly.
^y Plots were rated for severity of powdery mildew using the Horsfall-Barratt scale and converted to percent using the ELANCO tables.
^x Means within each column with a letter in common are not significantly different (Fisher’s Protected LSD), P=0.05 for disease severity leaf top and P=0.1 for disease severity leaf bottom and number of zucchinis on 1 Sep.
^w Oxidate was mixed in a dilution of 1:100 with water, the resulting rate per A appears above.