Morpholine management strategy
Morpholine fungicides may be used to control powdery mildew
(Erysiphe cichoracearum) on cucurbits
(Photo: David Mitchel, www.nifg.org.uk)
(Revised December 2004)
Introduction
These guidelines are designed to avoid or delay the development of resistance to the morpholine group of fungicides in New Zealand. They have been developed from previously published information (Beresford et al. 1996) in consultation with the New Zealand agricultural chemical industry (AGCARM) and are based on recommendations from the Fungicide Resistance Action Committee (FRAC) in Europe.
Morpholine product perspective
Morpholine fungicides have protective and systemic activity and a site-specific mode of action that inhibits sterol biosynthesis. The mode of action is different from that of the demethylation inhibitor (DMI) fungicides, which are also classified as sterol biosynthesis inhibitors. Morpholines are useful for controlling powdery mildew diseases on a wide range of crops and for controlling a range of cereal foliar diseases (Table 1). The morpholine fungicides, fenpropimorph and tridemorph, that were previously available in New Zealand, are no longer available and two further ones, fenpropidine and spiroxamine (Impulse), are under evaluation for use in New Zealand.
Current status of morpholine resistance
There are at present no records of morpholine resistance in New Zealand, and evidence from overseas suggests that although resistance can be selected in the laboratory, this group of fungicides is not at a high degree of risk from resistance development. Morpholines have been used for more than 25 years in Europe for barley powdery mildew control and there are no reports of loss of efficacy in the field (Hollomon 1994). For wheat powdery mildew, there is evidence of a decrease in sensitivity to fenpropimorph in Europe, but no reported control problems (Readshaw & Heaney 1994). Tridemorph is used for control of black sigatoka disease (Mycosphaerella fijiensis) in bananas, but a recent survey found no evidence of sensitivity changes in South and Central America (Cronshaw et al. 1994).
| Pathogen | Disease | Crops |
|---|---|---|
| Horticultural crops | ||
| Erysiphe cichoracearum | Powdery mildew | Cucurbits |
| Sphaerotheca fuliginea | Powdery mildew | Cucurbits |
| Uncinula necator | Powdery mildew | Grape |
| Cereal Crops | ||
| Blumeria graminis | Powdery mildew | Wheat, barley |
| Leptosphaeria nodorum | Glume blotch | Wheat, barley |
| Mycosphaerella graminicola | Speckled leaf blotch | Wheat |
| Puccinia coronata | Crown rust | Oat, ryegrass seed crops |
| Puccinia hordei | leaf rust | Barley |
| Puccinia graminis | Stem rust | Wheat, oat, ryegrass seed crops |
| Puccinia recondita | Leaf rust | Wheat |
| Puccinia striiformis | Stripe rust | Wheat |
| Pyrenophora teres | Net blotch | Barley |
| Rhynchosporium secalis | Scald | Barley |
Resistance prevention strategy
Do not apply excessive numbers of applications of morpholine fungicides. Adhere to manufacturers' recommendations for application rate and timing for specific products. Reduced-rate applications should be avoided. Apply morpholines preventatively when disease levels are low.
Implementation recommendations
Product labels should include a statement indicating that there is a risk of resistance development if excessive numbers of morpholine applications are made.
Acknowledgements
This resistance management strategy has been compiled with assistance from Jack Richardson (Agcarm Inc.) and Max Moore (Bayer CropScience).
References
Beresford R, Cromey M, Grbavac N, Smith B 1996. Morpholine resistance management strategy. In: Bourdôt GW, Suckling DM ed. Pesticide resistance: prevention and management. New Zealand Plant Protection Society, Rotorua, New Zealand. Pp. 142-143.
Cronshaw K, Lorenz G, Mappes D, 1994. Monitoring results of Mycosphaerella fijiensis to tridemorph. In: Heany S, Slawson D, Holloman DW, Smith M, Russell PE, Parry DW ed. Fungicide Resistance. British Crop Protection Council Monograph No. 60. Pp. 315-321.
Hollowmon DW 1994. Do morpholine fungicides select for resistance? In: Heany S, Slawson D, Holloman DW, Smith M, Russell PE, Parry DW ed. Fungicide Resistance. British Crop Protection Council Monograph No. 60. Pp. 281-289.
Readshaw AE, Heaney SP 1994. Fenpropimorph sensitivity in Erysiphe graminis f.sp. tritici, survey of northern France 1991-1993. In: Heany S, Slawson D, Holloman DW, Smith M, Russell PE, Parry DW ed. Fungicide Resistance. British Crop Protection Council Monograph No. 60. Pp. 297-302.
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