|
MANAGING POWDERY MILDEW IN PUMPKIN WITH RESISTANT VARIETIES
Margaret Tuttle McGrath and Jane F. Davey
Department of Plant Pathology, Cornell University
Long Island Horticultural Research and Extension Center
3059 Sound Avenue, Riverhead, NY 11901-1098. mtm3@cornell.edu
and
Bob Precheur, Mac Riedel, Andy Wyenandt, Jim Jasinski, and Celeste Welty
Dept. of Horticulture and Crop Science, Departments of Plant Pathology Southwest Extension IPM, and Entomology, Ohio State University, Columbus, OH 43210-1087
and
Timothy E. Elkner
Penn State Cooperative Extension
1383 Arcadia Rd., Rm. 1, Lancaster, PA 17601-3184
and
Walter R. Stevenson and R. Vaughan James
Plant Pathology Department, University of Wisconsin
1630 Linded Drive, Madison, WI 53706-1520
and
Mark Hutton and David Handley
University of Maine Cooperative Extension
P.O. Box 179, Highmoor Farm, Monmouth, Maine 04259
|
Powdery mildew is a common disease of pumpkin, as well as other cucurbit crops, which reduces yield when not adequately managed. The characteristic white, powdery fungal growth is readily recognizable on foliage. Infected leaves usually wither and die. Premature loss of leaves can result in reduced market quality because fruit ripening prematurely before achieving full color and handles may be shriveled or rotten. Size and/or number of fruit can be reduced when powdery mildew is severe. Severe disease can also lead to imperfections on fruit rind such as speckling and oedema. In addition, powdery mildew infection predisposes plants to other diseases, in particular, gummy stem blight/black rot.
Resistant varieties are becoming an increasingly important tool for managing powdery mildew in pumpkin as the number of resistant varieties available to growers increases and as fungicide resistance continues to challenge effective chemical control. The first powdery mildew resistant (PMR) pumpkins, Merlin and Magic Lantern, were commercialized in 1998 and the next, Mystic Plus, in 2000. Recently, several new PMR varieties of pumpkin, as well as winter squash, have been released each year. Effectively managing powdery mildew with fungicides necessitates products able to provide control on the underside of leaves through systemic, translaminar or volatile activity. Unfortunately, all such materials have been at risk for resistance development. Strains of the powdery mildew fungus resistant to QoI fungicides (FRAC Group 11; aka strobilurins; Amistar, Quadris, Cabrio, and Flint) are believed to now occur throughout the US. Resistance to MBC fungicides (aka benzimidazoles; Topsin M and Benlate) are likely still widespread in the US. They were common on Long Island in 2004. QoI and MBC resistances are qualitative, thus resistant strains are fully insensitive to these fungicides. Resistance to the DMI (demethylation inhibiting) fungicides (Bayleton, Nova, and Procure) is quantitative; pathogen strains exhibit a range in fungicide sensitivity depending on the number of genetic changes they possess that affect the fungicide’s ability to function. Moderately resistant strains likely are common in the US now. These are fully insensitive to Bayleton and have reduced sensitivity to low rates of Nova and Procure.
PMR pumpkin varieties vary in their susceptibility to powdery mildew depending on the number of genes for resistance they possess. The major gene for resistance in PMR varieties was obtained from a wild cucurbit at the Cornell Department of Plant Breeding. Varieties with this resistant gene from both parents (homozygous) usually develop less powdery mildew than those with resistance from one parent (heterozygous). In catalogues these are often, but not always, described as resistant and tolerant, respectively. The degree of powdery mildew suppression in PMR pumpkins and squashes usually is not as great as that in PMR melons and cucumbers. Some heterozygous PMR pumpkin varieties exhibit suppression of powdery mildew development for a few weeks, but become as severely affected as a variety without resistance by the end of the season. However, although leaves become severely affected by powdery mildew on these PMR varieties, they typically have less mildew on fruit handles than susceptible varieties. Also, initial disease suppression results in leaves dieing later and consequently more fruit with good color and solid handles at harvest. In addition to the major PMR gene, there are modifying genes with small affects that could account for the variation in susceptibility observed among PMR varieties. The resistance in PMR pumpkins and winter squash is not race-specific as it is in melons. However, the powdery mildew fungus has the potential to evolve the ability to overcome this specific major resistance gene in PMR pumpkins and squash. Such a new strain of the pathogen would be called a race.
To obtain information growers need on relative tolerance and yield to select PMR varieties most suitable for their operation, evaluations have been conducted in ME, NY, OH, PA, and WI over the past 3 years. Pumpkins were either transplanted or direct-seeded into black plastic mulch or bareground in June. Cultural practices recommended for each area were followed. Fungicides for powdery mildew were applied to achieve an integrated management program except in WI. Powdery mildew developed naturally. Severity was assessed repeatedly. Other diseases were also assessed in some locations. Fruit number, weight and quality were determined. References to full reports on the individual studies are listed at the end.
Among the 39 PMR varieties and experimental lines evaluated, powdery mildew was least severe on Gold Dust, Bumpkin, Touch of Autumn, Hobbit, Magician, Gladiator, and experimental lines from pumpkin breeding programs at Outstanding Seed Company, Harris Moran Seed Company, Cornell University and University of New Hampshire. Relative to varieties without PMR genes, percent control achieved with PMR pumpkins ranged tremendously – from 0% (eg no control) to 100% (complete control) (Table 1).
Variation was detected in susceptibility to other diseases among the varieties and experimental lines evaluated. Super Herc (HMX 3692), Gold Gem, Gold Medal, and Pro Gold 510 were highly susceptible to anthracnose while Wee-B-Little was highly resistant in the Ohio State pumpkin variety trial in 2003. Magic Lantern and Merlin were shown in another project to be more susceptible to bacterial wilt than the susceptible varieties Harvest Moon and Howden (*). Research is underway to determine if this occurs with other resistant varieties.
* http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Cuc_AttrBeetle.htm
Average fruit weight of the PMR varieties and experimental lines evaluated ranged from 0.5 to 26.5 (Table 2). Additional information about yield can be found in the full reports on these experiments (web sites listed below). Some reports also have descriptions of horticultural characteristics and photographs. Harris Moran pumpkins generally had good color and appearance. In the NY 2004 experiment, fruit of 03RPX764 was the most popular among growers and others who selected their top 3, Scarecrow was second, and Sorcerer was third. Other pumpkins receiving high ratings were Howden, Magic Lantern, Magician, and HMX 2689.
An integrated program, consisting of a reduced fungicide program applied to a PMR variety, is recommended for managing powdery mildew in pumpkin to improve control and to minimize chance of selection of pathogen races able to overcome the genetic resistance in the plant or the action of fungicides. Fewer fungicide applications are needed with a PMR variety because powdery mildew often starts to develop later in PMR than susceptible varieties and the spray interval can be increased from 7 to 14 days without affecting control. Routine scouting is needed when growing PMR varieties not only to determine when powdery mildew has started to develop, and thus fungicide treatment is warranted, but also to detect other diseases. Some fungicides used for powdery mildew on susceptible varieties have broad-spectrum activity and thus will control additional diseases that may consequently not be detected when growing susceptible varieties.
For more information on these experiments, see the following on-line reports:
NY http://www.longislandhort.cornell.edu/vegpath/2005/PMRPkin.pdf
OH http://vegnet.osu.edu/library/res05/pumpk05.pdf
http://vegnet.osu.edu/library/libr.htm#rr
PA http://capitalhort.cas.psu.edu/Research.html
WI http://www.plantpath.wisc.edu/wivegdis/index.htm
For photographs of the fruit of pumpkins evaluated go to:
OH http://vegnet.osu.edu/library/pumpic05.htm
Abbott & Cobb: http://abbottcobb.com/pumpkin/
Harris Moran: http://www.harrismoran.com/products/default.htm
Rupp Seeds: http://www.ruppseeds.com/divVegetable/default.htm
Sieger’s Seeds: http://www.siegers.com/shop/browse_species.asp?species_id=pump
Table 1: Percent control of powdery
mildew on leaves achieved in pumpkin varieties and experimental lines with
resistance to powdery mildew relative to varieties lacking resistance in
experiments conducted in ME, NY, OH, PA, and WI in 2003, 2004 and 2005 listed
in order of overall performance.
Pumpkin Variety or
Experimental Line |
Sourcez |
PM Reactiony |
Percent Control of Powdery Mildewx |
2005 |
2004 |
2003 |
OH-1w |
OH-2w |
NY |
WI |
OH |
NY |
PA-1v |
PA-2v |
WI |
OH |
WI |
ME |
XP6899 |
OS |
PMRR |
-- |
-- |
100 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
XP6888 |
OS |
PMRR |
-- |
-- |
100 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
NH1788 |
NH |
PMRR |
-- |
-- |
100 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
NH1799 |
NH |
PMR |
-- |
98 |
100 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
HMX
5684 |
HM |
PMRR |
-- |
98 |
-- |
93 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
HMX
4684 |
HM |
PMR |
-- |
98 |
-- |
91 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
NY01-605A |
NY |
PMRR |
-- |
-- |
100 |
-- |
-- |
88 |
-- |
-- |
-- |
-- |
-- |
-- |
Gold
Dust |
RU |
PMR |
-- |
-- |
-- |
91 |
-- |
-- |
98 |
92 |
-- |
-- |
-- |
-- |
Bumpkin |
MY |
PMR |
-- |
-- |
100 |
-- |
-- |
-- |
90 |
84 |
-- |
-- |
-- |
-- |
HMX
5681 |
HM |
PMR |
-- |
-- |
-- |
83 |
-- |
-- |
98 |
92 |
-- |
-- |
-- |
-- |
HMX
5683 |
HM |
PMR |
-- |
88 |
-- |
93 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
HMX
5680 |
HM |
PMR |
-- |
-- |
-- |
85 |
-- |
-- |
90 |
84 |
-- |
-- |
-- |
-- |
Touch
of Autumn |
RU |
PMR |
-- |
-- |
100 |
81 |
81 |
84 |
-- |
-- |
-- |
-- |
77 |
-- |
NY01-609 |
NY |
PMRR |
-- |
-- |
100 |
-- |
-- |
67 |
-- |
-- |
-- |
-- |
-- |
-- |
NH1755A |
NH |
PMR |
-- |
-- |
-- |
-- |
-- |
82 |
-- |
-- |
-- |
-- |
-- |
-- |
Hobbit |
SD |
PMR |
-- |
-- |
100 |
-- |
-- |
62 |
-- |
-- |
-- |
-- |
-- |
-- |
Magician
(HMX 0683) |
HM |
PMRR |
-- |
98 |
100 |
-- |
-- |
60 |
90 |
96 |
51 |
33 |
97 |
-- |
Gladiator
(HMX 2689) |
HM |
PMRR |
-- |
99 |
100 |
-- |
71 |
81 |
-- |
-- |
62 |
33 |
94 |
-- |
Gold
Bullion |
RU |
PMR |
-- |
-- |
100 |
-- |
48 |
73 |
74 |
74 |
-- |
-- |
88 |
-- |
Munchkin |
HM |
PMS |
-- |
-- |
-- |
-- |
-- |
-- |
71 |
79 |
-- |
-- |
-- |
-- |
Merlin |
HM |
PMR |
-- |
-- |
89 |
-- |
-- |
58 |
-- |
-- |
-- |
-- |
-- |
80 |
NH1771A |
NH |
PMR |
-- |
-- |
-- |
-- |
-- |
72 |
-- |
-- |
-- |
-- |
-- |
-- |
Magic
Lantern |
HM |
PMR |
-- |
84 |
94 |
-- |
-- |
26 |
62 |
80 |
32 |
-- |
90 |
80 |
Mystic
Plus |
HM |
PMR |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
80 |
03RPX763 |
RU |
PMR |
-- |
-- |
100 |
-- |
18 |
69 |
-- |
-- |
-- |
-- |
-- |
-- |
03RPX764 |
RU |
PMR |
53 |
-- |
100 |
-- |
23 |
68 |
-- |
-- |
-- |
-- |
-- |
-- |
Iron
Man (HMX 2690) |
HM |
PMR |
82 |
88 |
-- |
-- |
-- |
-- |
79 |
54 |
26 |
24 |
60 |
-- |
RPX
03515 |
RU |
PMR |
-- |
-- |
-- |
-- |
45 |
67 |
-- |
-- |
-- |
-- |
-- |
-- |
Scarecrow
(MSX6009) |
MY |
PMRR |
-- |
-- |
-- |
-- |
-- |
27 |
60 |
66 |
-- |
-- |
-- |
-- |
HMX
4682 |
HM |
PMR |
-- |
100 |
-- |
-- |
51 |
-- |
-- |
-- |
0 |
-- |
-- |
-- |
Harvest
Princess |
MY |
PMR |
-- |
-- |
-- |
-- |
-- |
-- |
75 |
16 |
-- |
-- |
-- |
-- |
Aladdin |
HM |
PMR |
86 |
0 |
-- |
-- |
-- |
-- |
20 |
70 |
32 |
-- |
-- |
-- |
MSX
6078 |
MY |
PMR |
-- |
-- |
-- |
-- |
-- |
-- |
42 |
38 |
-- |
-- |
-- |
-- |
HMX
3694 |
HM |
PMR |
-- |
-- |
-- |
-- |
53 |
-- |
-- |
-- |
24 |
-- |
-- |
-- |
Harvest
Time |
AC |
PMR |
-- |
-- |
-- |
-- |
37 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
MSX
6074 |
MY |
PMR |
-- |
-- |
-- |
-- |
-- |
-- |
13 |
58 |
-- |
-- |
-- |
-- |
Super Herc
(HMX 3692) |
HM |
PMR |
-- |
-- |
-- |
-- |
45 |
-- |
-- |
-- |
35 |
6 |
51 |
-- |
RPX
03516 |
RU |
PMR |
-- |
-- |
-- |
-- |
29 |
63 |
-- |
-- |
-- |
12 |
-- |
-- |
Wee-B-Little |
RU |
PMS |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
24 |
-- |
-- |
King
Midas |
SI |
PMS |
-- |
-- |
-- |
-- |
18 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
Phat Jack |
SI |
PMS |
-- |
-- |
-- |
-- |
18 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
Pro
Gold 510 |
AC |
PMS |
-- |
-- |
-- |
-- |
12 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
Oktoberfest |
SI |
PMS |
-- |
-- |
-- |
-- |
9 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
Apprentice |
HM |
PMS |
-- |
-- |
-- |
-- |
-- |
-- |
13 |
0 |
-- |
-- |
-- |
-- |
RPX
1002 |
RU |
PMS |
-- |
-- |
-- |
-- |
7 |
-- |
12 |
0 |
-- |
6 |
-- |
-- |
Mother
Lode |
RU |
PMS |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
25 |
Sorcerer |
HM |
PMS |
-- |
-- |
0 |
-- |
-- |
14 |
-- |
-- |
-- |
-- |
0 |
30 |
Racer |
JO |
PMS |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
25 |
RPX
1003 |
RU |
PMS |
-- |
-- |
-- |
-- |
1 |
-- |
13 |
0 |
-- |
