PUMPKIN (Cucurbita pepo) Powdery Mildew; Podosphaera xanthii

R. J. Precheur, Department of Horticulture and Crop Science J. Jasinski, Department of Extension R. M. Riedel, Emeritus, L. H. Rhodes, M. Kelly and A. Trierweiler, Department of Plant Pathology The Ohio State University, Columbus, OH 43210

Evaluation of pumpkin varieties for resistance to powdery mildew under a standard disease control program, 2007.

Plots were established 30 May on a Crosby silt loam soil, and Brookston silty clay loam (pH 6.1, OM <2%) at the Western Branch Research Station, Ohio Agricultural Research and Development Center, South Charleston, OH (Clark Co.). Plots consisted of single 30-ft rows of pumpkins hand transplanted 4 ft apart in rows 10 ft apart. Transplants were 10 days old grown in 72 deep cell trays using Metro Mix 360. Each variety was replicated four times in a randomized complete block design. One day, prior to planting, the insecticide Admire 2 F (16 oz/treated A) was applied to the transplants for cucumber beetles. Fertilizer (0.49 t/A each of 11-52-0, 0-0-60 and 46-0-0 (N-P-K) was applied broad cast preplant on 29 May. All plots were side dressed in a band application just prior to vine tip with a 28% N solution (25 lb/A) on 9 Jul. Strategy 2.1 SC at (5 pt/A) + Dual Magnum II, (1.3 pt/A) + Roundup Weathermax 4.5 EC (32 oz/A) was applied preplant for weed control on 29 May. During the season weeds were controlled by cultivation and hand weeding. For control of cucumber beetle feeding on fruit rind, Pounce 3.2 EC (8 oz/A)was applied to all plots at on 21 Jun, 1 and 25 Aug. Fungicide applications for all plots were Cabrio EG (16 oz/A) on 25 Jul, Manex 4F (1.6 qt/A) + Nova 40 W (5 oz/A) on 2 Aug, Quadris opti (3.2 pt/A) on 9 and 24 Aug, Bravo Weather Stik 6F (3pt/A)+ Procure 50 WS (6 oz/A first spray, 8 oz/A) on 16 Aug, 14 Sep and Pristine 38 W (18.5 oz/A) on 4 Sep to control powdery mildew and fruit rots. Fungicides and insecticides were applied at 55 psi and 50 gal/A with a tractor-mounted, PTO driven sprayer with a 12 ft boom carrying 7 Teejet TXVS-18 cone jet nozzle tips spaced 20 in apart. On 17 and 24 Jul, 7 and 21 Aug, and 4 Sep, nine leaves were chosen at random per plot to determine the percentage of leaf coverage of powdery mildew on the upper and lower surface of the leaves. Data from all evaluation dates were used to calculate the area under the disease progress curve (AUDPC). The presence or absence of powdery mildew on pumpkin handles was also recorded. Pumpkins were harvested on 11 Sep and graded into marketable orange fruit. All plots were trickle irrigated to maintain 1 in. of water per week. Rainfall for Jun, Jul, Aug, and Sep was 2.92, 2.44, 3.2 and 1.94 in., respectively.

The evaluated varieties of pumpkin are listed in order of ability to control powdery mildew on the lower leaf surface. Powdery mildew development on the foliage was first observed the last week of Jul. On 7 Aug, percent leaf infection was as high 30% on the upper leaf surface after applications of Cabrio, Manex and Nova. Varieties Mr. Wrinkles and RPX1295 had significantly higher mildew severity levels than HMX 6685, HMX 6686, 20 Karat Gold, small types and mini pumpkins. The mini varieties Gold Dust and Gold Speck had the lowest percent severity. By, 4 Sep, the standard fungicide program controlled powdery mildew on the upper leaf surface and % severity for all varieties was less than 8%. There was no significant difference in severity among varieties except for PXT 13056567 which had significantly higher percent leaf infection than HMX 6685, HMX 6686, SSX 5078, Gold Dust and Gold Speck. AUDPC values on the upper surface for Mr. Wrinkles and RPX1295 were significantly higher than HMX 6685, HMX 6686 the small types and mini pumpkins. Powdery mildew severity was16% or less on lower leaves during early assessments. Percent leaf infection was 1.25% or less for 6 of the entries. Near harvest, powdery mildew on the lower surface ranged from 9.8 to 79% infection and only HMX 6685, HMX 6686, Gold Dust and Gold Speck had significantly lower % infection than all other varieties except SSX 5120 and SSX 5078. AUDPC values for the lower leaf surface were similar to mildew resistance observations at the last assessment. Presence or absence of powdery mildew on handles was not significantly different among varieties. Foliar virus symptoms were not observed until just before and after harvest. The fruit produced by all varieties had good size, shape and color. Differences in fruit number/A, t/A and average fruit size are mostly influenced by variety. An attractive variety like Mr. Wrinkles would have to be grown with a good disease control program while HMX 6685, HMX 6686, small types and mini pumpkins evaluated could be grown with minimum fungicide input.

Powdery Mildew Severity and Marketable Yield

	Powdery Mildew Severity (% of leaf coverage)^z						Marketable Yield^y
	Upper leaf surface			Lower leaf surface			Total fruit (no./A)	Total yield (t/A)	Avg wt/fruit (lb)
Variety	7 Aug	4 Sep	AUDPC^x	7 Aug	4 Sep	AUDPC
HMX 6685^v….	6.4 cd^w	0.5 cd	128.7 bcd	1.1 c	9.8 g	127.4 f	1786 cd	17 abcd	20 def
HMX 6686^v …	5.6 cd	1.6 abcd	130.2 bcd	1.2 c	13.8 fg	159.3 f	2897 bcd	24 a	16.8 fgh
RPX 1626^u…...	13 abcd	0.6 cd	213.6 abcd	1.1 c	38.5 ed	412.9 ef	2752 cd	19 abc	13.8 h
SSX 5120^t……	15.9 abcd	1.8 abcd	308.2 abcd	7.5 abc	31.5 ef	621.5 de	1159 d	21 ab	35.8 a
20 Karat Gold^u.	7.2 cd	4.4 abcd	173 bcd	6.2 abc	58.2 bc	1005.9 bdc	2028 cd	16 bcde	15.7 gh
Midas Touch^s...	23 abc	4.8 abcd	427.8 ab	15.4 ab	63.8 abc	1045.2 abc	1979 cd	21 ab	22 cde
Gold Medal^u….	9.5 bcd	3.6 abcd	200.3 abcd	3.9 abc	68.4 abc	1051.3 abc	1883 cd	20 ab	22 cd
Hannibal^s……..	21.9 abcd	4.3 abcd	394.1 abc	7.7 abc	74.5 ab	1202.1 abc	1979 c	17 abcde	17.4 fgh
Mr. Wrinkles^t...	30.2 a	4.8 abcd	529.9 a	16.2 a	66.7 abc	1224.9 abc	1738 cd	22 ab	26.1 b
RPX 1295^u…...	28.2 ab	6.2 abc	509.6 a	14.7 ab	66 abc	1262.7 ab	1690 cd	17 abcde	20 def
PXT 13056567^r	14.7 abcd	7.1 ab	329.1 abcd	16.6 a	74.2 ab	1352.6 ab	1207 d	15.2 bcdefg	25.1 bc
Gold Challenger^u…..	15.2 abcd	4.3 acd	290.5 abcd	15.3 ab	79 a	1408.8 a	1786 cd	16 abcdef	18.1 efg
Small Types
SSX 5078^t…....	3.7 cd	0.33 d	66.7 cd	1.0 c	27 efg	232.7 f	5987 ab	11 cdefgh	3.6j
HMX 5683^v.....	4.6 cd	1.4 bcd	99.9 bcd	0.7 c	62.3 abc	644.1 de	4538 abc	9 efgh	4 j
Mini Pumpkins
Gold Dust^u…...	2.5 d	1.2 cd	52.7 d	0.5 c	9.8 g	85.4 f	26,264 e	7 gh	0.5 j
Gold Speck^u….	3.1 d	0 d	52.9 d	2.9 bc	15 fg	188.1 f	24,864 e	5 h	0.4 j
LSD 0.05%	19.4	5.7	333.2	12.9	18.3	387.3	3141	8.2	3.7

z Powdery Mildew Severity is the average of 9 leaves per plot by 3 raters.

y Marketable Yield includes only good orange fruit of proper size, shape and free of defects.

x AUDPC = area under disease progress curve, 5 evaluations.

w Column numbers followed by the same letter are not significantly different at P=0.05 determined by Fisher’s protected LSD.

v Obtained from Harris Moran Seed Company

u Obtained from Rupp Seeds Inc.

t Obtained from Sakata Seed Company

s Obtained from Siegers Seed Company.

r Obtained from Seminis Seed Company