In the United States, pumpkin (Cucurbita pepo) crops are grown primarily for wholesale processing and ornamental use. Pumpkin production in the United States increased 6.4% in 2005 from 2004 totaling 1.1 billion pounds (U.S. Department of Agriculture, 2006). In 2007, 2500 acres were harvested in New Jersey, accounting for ≈5% of U.S. production (Crop profile for pumpkins in New Jersey, 2007). Although considered a minor vegetable crop based on the numbers of acres produced each year in New Jersey, pumpkin crops play a critical role in keeping small roadside farm markets operational during fall months through agritourism events such as fall festivals, grade school farm tours, and u-pick operations.
Powdery mildew [Podosphaera (sect. Sphaerotheca) xanthii (Castagne) U. Braun & N. Shishkoff (also known as Sphaerotheca fusca (Fr.) S. Blumer and S. fuliginea (Schlechtend.:Fr.) Pollacci] is an important disease of cucurbit crops throughout the United States (Zitter et al., 1996). The pathogen may overwinter on crop debris; however, in most years, the pathogen is wind-dispersed into northern regions from southern states each production season (Zitter et al., 1996). The pathogen typically infects older leaves and stems first causing premature loss of foliage resulting in a reduction in yield as the size and number of fruit decrease (Mossler and Nesheim, 2003; Zitter et al., 1996). Premature defoliation can also lead to sunscald injury resulting in unmarketable fruit. Stems infected by powdery mildew before harvest will prematurely turn brown and shrivel reducing the postharvest longevity of marketable fruit.
Control of cucurbit powdery mildew begins with preventing nutritional stress (Pernezny and Stall, 2005), planting tolerant or resistant varieties such as cvs. Magic Lantern, Magician, or Gold Bullion (McGrath and Davey, 2006) and preventive fungicide applications (Alexander and Waldenmaier, 1999; Fitzgerald et al., 2005; McGrath and Shishkoff, 1999; Shamiyeh et al., 1999). Pumpkin breeding lines and cultivars have been consistently evaluated for cucurbit powdery mildew resistance, and in recent years, new cultivars with powdery mildew tolerance have been released commercially (Epinat et al., 1992; James and Stevenson, 2003, 2004, 2005, 2006; Kooistra, 1968; McGrath and Shishkoff, 2001; O'Brien, 1994; O'Brien et al., 1988).
Preventive fungicides, particularly those that are systemic or translaminar, are able to suppress the disease on abaxial (underside or bottom) leaf surfaces where conditions are more favorable for powdery mildew development (McGrath, 2001a). Effective control of powdery mildew depends on the timing of spray applications, the fungicide(s) used to control the disease, the age of the leaves, the presence of pathogen on the top or bottom surfaces of leaves, and pumpkin cultivar (Everts, 1999a, 1999b, 2002; McGrath and Staniszewska, 1994; McGrath, 1996a, 2001b). Some newer fungicide chemistries for cucurbit powdery mildew control have modes of action that target fungal growth and development at specific metabolic site(s) (McGrath, 2001a, 2005). In general, the more specific a fungicide's mode of action, the higher potential there is for fungicide resistance development. This is especially important in cucurbit powdery mildew where resistance to certain fungicide chemistries has already been detected (McGrath, 2001a).
Resistance to systemic fungicides has been researched and documented (Huggenberger et al., 1984; Kendall, 1986; McGrath, 1996b; O'Brien et al., 1988; Ohtsuka et al., 1988; Peterson, 1973; Schroeder and Provvidenti, 1969). The first case of fungicide resistance development in the United States was reported in cucurbit powdery mildew to the fungicide, benomyl (Schroeder and Provvidenti, 1969). Since that time, resistance in cucurbit powdery mildew to other fungicides in FRAC code 1 have been reported (McGrath, 1996b). In the late 1990s, a new class of fungicide, known as the strobilurins (FRAC code 11), were commercially released for the control of cucurbit powdery mildew. Cucurbit powdery mildew resistance to strobilurin fungicides [quinone outside inhibitors (QoI), FRAC code 11] was first reported in the United States in 2002 (McGrath and Shishkoff, 2003). Managing fungicide resistance has been an important aspect of managing cucurbit powdery mildew (McGrath, 2001a; McGrath and Shishkoff, 2003). Additionally, management of fungicide resistance in cucurbit powdery mildew has been studied and techniques developed to directly or indirectly detect it under field conditions (Cohen et al., 2004; Cushman et al., 2007; McGrath and Shishkoff, 2001). When such indirect techniques are used to measure fungicide resistance development, terms such as “field” or “practical” resistance have been used to describe the observable loss of chemical control. Indirect observations of fungicide resistance development are extremely important and useful for disease management because the observations can be used to make or adjust current fungicide recommendations in specific states or geographic regions.
As a result of the importance of understanding and managing fungicide resistance, an industry-led group, known as the FRAC, was established in the early 1980s (Fungicide Resistance Action Committee, 2006). FRAC committees have been established throughout Europe, North and South America, and Japan to manage and monitor fungicide resistance development. In 2002, the NA-FRAC (North American Fungicide Resistance Action Committee) was established to 1) coordinate and identify resources for contact between government, universities, and the public on fungicide resistance management issues; 2) assist in the creation of new working codes in North America for other areas of chemistry as they are needed; and 3) serve as a spokesman for the industry's view on fungicide resistance management (Fungicide Resistance Action Committee, 2006).
Each year, the FRAC committee updates and publishes a list of FRAC codes, which contain most of the fungicides and fungicide chemistries in which mode of action and resistance risk are known (Fungicide Resistance Action Committee, 2006). As of 2006, there were 43 numbered and three-lettered FRAC codes for the ≈93 listed chemical groups and 181 common names of fungicides (Fungicide Resistance Action Committee, 2006). Accordingly, fungicides listed within a given FRAC code may share a similar mode of action and, therefore, may have: 1) similar risks for resistance development; 2) similar use patterns on single or multiple crops; and 3) exhibit the potential for cross-resistance development. Of the 43 numbered and three-lettered FRAC group codes in 2006, fungicide resistance was common, known, reported, or described in 54% of the FRAC groups and resistance management recommended or required for 52% of the groups.
In recent years, fungicide resistance has been detected in important diseases of vegetable crops grown in the eastern United States, including the mid-Atlantic region (Louws and Driver, 2001, 2005; Norton, 1982; Van der Meer et al., 1978). Unfortunately, some growers become concerned about managing resistance only after it has developed, although it is more important to recognize the primary goal of resistance management is to delay its development rather than to manage resistant strains (McGrath, 2001a). The large number of fungicide chemistries available and the differences in modes of action can make it very difficult for vegetable growers to develop and follow fungicide resistance management programs on their farms. In many cases, fungicides within a given FRAC code are listed for the control of the same pathogen, which can lead to confusion by vegetable producers when it comes to developing a seasonal fungicide application program for specific diseases. For example, gummy stem blight caused by Didymella bryoniae (Auersw.) Rehm [syn. Mycosphaerella melonis (Pass.) Chui & J.C. Walker] is an important disease in cucurbit crops in the United States. In the mid-Atlantic region, resistance in the gummy stem blight fungus to azoxystrobin has been documented (Everts, 1999b) and FRAC code 11 fungicide chemistries such as azoxystrobin and pyraclostrobin are currently recommended control options, although both fungicides have a high risk for fungicide resistance development. Although both chemistries are still effective in some areas in the mid-Atlantic region, it is very important for growers who have resistance on their farm to know which fungicides belong to FRAC code 11 so that these fungicides are used in tank mixes and/or in rotations with other fungicide chemistries (i.e., FRAC codes) and not used in alternation with each other.
Because development of fungicide resistance in a production field can be difficult to measure without specific laboratory methods, a cucurbit grower could be unknowingly selecting for a resistant fungal population through the improper use of certain fungicide chemistries (McGrath, 2001a). The successful management of fungicide resistance in highly mobile pathogens such as cucurbit powdery mildew may require regional cooperation. Otherwise, growers using high-risk fungicides exclusively may select resistant strains and thereby reduce the efforts of growers using a resistance management program (McGrath, 2001a).
The objectives of this study were to evaluate the effects of cultivar resistance and five different fungicide programs on fungicide resistance development in cucurbit powdery mildew in pumpkin production.
Alexander, S.A. & Waldenmaier, C.M. 1999 Evaluation of fungicides for control of powdery mildew in pumpkin, 1998 Fungic. Nematic. Tests. 54 224
Baumler, S. 2004 Development and evaluation of molecular diagnostic systems for QoI fungicide resistance in fungal phytopathogens Technical University of Munich Bavaria Thesis.
Cohen, R. , Burger, Y. & Katzir, N. 2004 Monitoring physiological races of Podosphaera xanthii (syn. Sphaerotheca fuliginea), the causal agent of powdery mildew in cucurbits: Factors affecting race identification and the importance for research and commerce Phytoparasitica 32 174 183
- Search Google Scholar
- Export Citation
Cohen, R. Burger, Y. Katzir, N. 2004 Monitoring physiological races ofPhytoparasitica Podosphaera xanthii(syn. Sphaerotheca fuliginea), the causal agent of powdery mildew in cucurbits: Factors affecting race identification and the importance for research and commerce 32 174 183
Crop profile for pumpkins in New Jersey 2007 28 Jan. 2008 <http://www.pestmanagement.rutgers.edu/njinpas/CropProfiles/pumpkinCP.pdf>.
Cushman, K.E. , Evans, W.B. , Ingram, D.M. , Gerard, P.D. , Straw, R.A. , Canaday, C.H. , Wyatt, J.E. & Kenty, M.M. 2007 Reduced foliar disease and increased yield of pumpkin regardless of management approach or fungicide combinations HortTechnology 17 56 61
Epinat, C. , Pitrat, M. & Bertrand, F. 1992 Genetic analysis of resistance of five melon lines to powdery mildews Euphytica 65 135 144
Everts, K.L. 1999a Integrated pumpkin disease management using a cover crop, host resistance and reduced fungicide application Phytopathology 89 S25 [abstr.].
Everts, K.L. 2002 Reduced fungicide applications and host resistance for managing three diseases in pumpkin grown on a no-till cover crop Plant Dis. 86 1134 1141
Fitzgerald, C.B. , Everts, K.L. & Newell, M.J. 2005 Evaluation of pumpkin cultivars under conventional and reduced risk fungicide programs, 2004 Biol. Cult. Tests Control Plant Dis. 20 V009
Fungicide Resistance Action Committee 2006 28 Jan. 2008 <http://www.frac.info/frac/index.htm>.
Huggenberger, F. , Collins, M.A. & Skylakakis, G. 1984 Decreased sensitivity of Sphaerotheca fuliginea to fenarimol and other ergosterol-biosynthesis inhibitors Crop Prot. 3 137 149
James, R.V. & Stevenson, W.R. 2003 Evaluation of pumpkin and squash varieties for resistance to powdery mildew—Hancock, WI, 2002 Biol. Cult. Tests Control Plant Dis. 18 V002
James, R.V. & Stevenson, W.R. 2004 Evaluation of pumpkin and squash varieties for resistance to powdery mildew—Hancock, WI, 2003 Biol. Cult. Tests Control Plant Dis. 19 V003
James, R.V. & Stevenson, W.R. 2005 Evaluation of pumpkin and squash varieties for resistance to powdery mildew—Hancock, WI, 2004 Biol. Cult. Tests Control Plant Dis. 20 V005
James, R.V. & Stevenson, W.R. 2006 Evaluation of pumpkin and squash varieties for resistance to powdery mildew—Hancock, WI, 2005 Biol. Cult. Tests Control Plant Dis. 21 V012
Kendall, S.J. 1986 Cross-resistance of triadimenol-resistant fungal isolates to other sterol C-14 demethylation inhibitor fungicides Br. Crop Prot. Conf.-Pests Dis. 2 539 546
Kuck, K.H. & Mehl, A. 2003 Trifloxystrobin: Resistance risk and resistance management Pflanzenschutz-Nachrichten Bayer 56 313 325
Littell, R.C. , Milliken, G.A. , Stroup, W.W. , Wolfinger, R.D. & Schabenberger, O. 2006 SAS for mixed models 2nd Ed SAS Institute Inc Cary, NC
Louws, F.J. & Driver, J.G. 2001 Evaluation of pepper lines for resistance to Phytophthora crown and root rot and TSWV incidence, 2000 Biol. Cult. Tests Control Plant Dis. 18 V008
Louws, F.J. & Driver, J.G. 2005 Evaluation of pepper lines for resistance to Phytophthora crown and root rot incidence, 2004 Biol. Cult. Tests Control Plant Dis. 20 V021
McGrath, M.T. 1996a Successful management of powdery mildew in pumpkin with disease threshold-based fungicide programs Plant Dis. 80 910 916
McGrath, M.T. 1996b Increased Resistance to triadimefon and to benomyl in Sphaerotheca fuliginea populations following fungicide usage over one season Plant Dis. 80 633 639
McGrath, M.T. 2001b Alternative fungicides to Bravo evaluated on pumpkin cultivars differing in susceptibility to powdery mildew, 2000 Fungic. Nematic. Tests. 56 V77
McGrath, M.T. 2005 Occurrence of resistance to QoI, DMI, and MBC fungicides in Podosphaera xanthii in 2004 and implication for controlling cucurbit powdery mildew Resistant Pest Management Newsletter. 14 36 40
McGrath, M.T. & Davey, J.F. 2006 Comparison of powdery mildew resistant pumpkin under a reduced-fungicide program, 2005 Biol. Cult. Tests Control Plant Dis. 21 V021
McGrath, M.T. & Shishkoff, N. 1999 Evaluation of biocompatible products for managing cucurbit powdery mildew Crop Prot. 18 471 478
McGrath, M.T. & Shishkoff, N. 2001 Resistance to triadimefon and benomyl: Dynamics and impact on managing cucurbit powdery mildew Plant Dis. 85 147 154
McGrath, M.T. & Shishkoff, N. 2003 First report of the cucurbit powdery mildew fungus (Podosphaera xanthii) resistant to strobilurin fungicides in the United States Plant Dis. 87 1007
McGrath, M.T. & Staniszewska, H. 1994 An IPM program for powdery mildew in pumpkin that includes timing of chemical control and fungicide resistance considerations. (abstr.) Phytopathology 84 545
O'Brien, R.G. 1994 Fungicide resistance in populations of cucurbit powdery mildew (Sphaerotheca fuliginea) N.Z. J. Crop Hort. Sci. 22 145 149
O'Brien, R.G. , Vawdrey, L.L. & Glass, R.J. 1988 Fungicide resistance in cucurbit powdery mildew (Sphaerotheca fuliginea) and its effect on field control Aust. J. Exp. Agr. 28 417 423
Ohtsuka, N. , Sou, K. , Amano, T. , Ojima, M. , Nakazawa, Y. & Yamada, Y. 1988 Decreased sensitivity of cucumber powdery mildew (Sphaerotheca fuliginea) to ergosterol biosynthesis inhibitors Ann. Phytopathol. Soc. Jpn. 54 629 632
Pernezny, K. & Stall, W.M. 2005 Powdery mildew of vegetables. Florida Cooperative Extension Service document PP-14 29 Jan. 2008 <http://edis.ifas.ufl.edu/pdffiles/VH/VH01400.pdf>.
Shamiyeh, N.B. , Straw, R.A. , Mullins, C.A. & Follum, R.A. 1999 Foliar fungicides for control of diseases on pumpkins, 1998 Fungic. Nematic. Tests 54 233 234
U.S. Department of Agriculture 2006 Vegetable 2005 Summary 28 Jan. 2008 <http://usda.mannlib.cornell.edu/usda/nass/VegeSumm/2000s/2006/VegeSumm-01-27-2006.pdf>.
Van der Meer, Q.P. , Van Bennekom, J.L. & Van der Giessen, A.C. 1978 Gummy stem blight resistance of cucumber (Cucumis sativus L.) Euphytica 27 861 864
Zitter T.A. , Hopkins D.L. & Thomas C.E. 1996 Compendium of cucurbit diseases The American Phytopathological Society St. Paul, MN