Development of a grower‐conducted inoculum detection assay for management of grape powdery mildew

Management of grape powdery mildew (Erysiphe necator) and other polycyclic diseases often relies on calendar‐based pesticide application schedules that assume the presence of inoculum. An inexpensive, loop‐mediated isothermal amplification (LAMP) assay was designed to quickly detect airborne inoculum of E. necator to determine when to initiate a fungicide application programme. Field efficacy was tested in 2010 and 2011 in several commercial and research vineyards in the Willamette Valley of Oregon from pre‐bud break to véraison. In each vineyard, three impaction spore traps were placed adjacent to the trunk. One trap was maintained and used by the grower to conduct the LAMP assay (G‐LAMP) on‐site and the other two traps were used for laboratory‐conducted LAMP (L‐LAMP) and quantitative PCR assay (qPCR). Using the qPCR as a gold standard, L‐LAMP was comparable with qPCR in both years, and G‐LAMP was comparable to qPCR in 2011. Latent class analysis indicated that qPCR had a true positive proportion of 98% in 2010 and 89% in 2011 and true negative proportion of 96% in 2010 and 64% in 2011. An average of 3·3 fewer fungicide applications were used when they were initiated based on spore detection relative to the grower standard practice. There were no significant differences in berry or leaf incidence between plots with fungicides initiated at detection or grower standard practice plots, suggesting that growers using LAMP to initiate fungicide applications can use fewer fungicide applications to manage powdery mildew compared to standard practices.     

小麦品种多样性对白粉病及产量和蛋白质的影响

 对品种多样性控制小麦白粉病的效果以及对产量和蛋白质的影响进行了研究,为利用品种多样性控制白粉病提供理论依据和技术支持。采用SSR技术分析5个小麦品种的亲缘关系;2008年和2009年按组合所含品种数为2、3、4和5个进行组合,在田间种植混种组合和单播小区,人工接种白粉菌,比较各小区中小麦白粉病的AUDPC值、产量和蛋白质变化。结果表明,5个品种亲缘关系相对较近;2个品种混合时以抗感搭配较好,随着抗病品种比例增加控病效果增强;2008年混合种植中有防治效果的组合占54.55%,相对防效为10.02%~47.58%,2009年有防治效果的组合占23.08%,相对防效在1.85% 到18.96 % 之间;在适当的组合中,如京冬8号/轮选987、京双16/京411/京冬8号对小麦白粉病有控制效果,混种不会影响产量和蛋白质含量;当有大量能克服本地品种抗性的外来菌源时混合种植的控病效果降低。品种多样性可以用做防治小麦白粉病的一项措施。     

Effects of blast on components of wheat physiology and grain yield as influenced by fungicide treatment and host resistance

Two field experiments (Exp. 1 and Exp. 2) were carried out to assess the physiological performance and grain yield of wheat cultivars BR‐18 (moderately resistant) and Guamirim (susceptible) inoculated with Pyricularia oryzae in plots treated or untreated with Ópera (fungicide 13.3% epoxiconazole + 5% pyraclostrobin). Results from regression analyses indicated that spike and leaf blast severity at 10–14 days after inoculation (dai) were associated with greater yield losses (highest negative slope) than severity at 18–22 dai. Relative to untreated Guamirim, there were 0.3% and 16% increases in Exp. 1 and 2, respectively, for untreated BR‐18 (resistance alone). For fungicide treatment alone, the mean yield of Guamirim increased by 20% and 61% in Exp. 1 and 2, respectively, relative to the untreated fungicide control, whereas for the fungicide treated BR‐18, the mean yield increased by 26% and 83% in Exp. 1 and 2, respectively. Fungicide application and cultivar resistance resulted in higher measures of leaf health and photosynthetic performance in both spikes and leaves than in the untreated susceptible reference treatment. The results from this study may be useful in future efforts to develop crop loss models and management guidelines for wheat blast.     

The epidemiology of powdery mildew on concord grapes

ABSTRACT Vitis labruscana 'Concord' is a grape cultivar widely grown in the United States for processing into juice and other grape products. Concord grapes are sporadically but sometimes severely damaged by the grape powdery mildew pathogen, Uncinula necator. Although the foliage is often reported to be moderately resistant to powdery mildew, severe fruit infection occurs in some years. We observed the seasonal development of powdery mildew on leaves, rachises, and berries of unsprayed Concord grapevines. Inoculations of flower and fruit clusters revealed a brief period of berry susceptibility and a protracted period of rachis susceptibility. The rachis remained highly susceptible to infection, and the severity of rachis infection increased throughout the growing season until the rachis formed a periderm shortly before harvest. In contrast, berries were nearly immune to infection within 2 weeks after fruit set. Rachis and berry infections were detected before the disease was observed on foliage, and the incidence of rachis and berry infection often exceeded disease incidence observed on foliage until after fruit acquired substantial ontogenic resistance. Excellent control of fruit infection, and adequate control of leaf infection, was achieved by two fungicide applications targeted at the peak period of fruit susceptibility. Although Concord is thought to be moderately resistant to powdery mildew, the rachis is highly susceptible, and may be the avenue by which prebloom infections make their way onto the developing fruit. Late-season infection of the rachis neither spread to the fruit, nor did it cause fruit to drop prematurely, and may be of little economic consequence on fruit destined for processing. Although fruit of V. vinifera cultivars have been reported to remain susceptible to infection until berry sugar levels reach 8 to 15%, Concord fruit become nearly immune to infection nearly 6 weeks before this stage of development. Because powdery mildew does not become conspicuous on foliage until late summer, it is generally regarded as a late-season problem on Concord grapes, and previous management programs have reflected this belief. However, the greatest contribution to control of fruit infection is due to fungicides applied during the peak period of fruit susceptibility, from bloom until shortly after fruit set, long before the disease is observed on foliage.     

Evaluation and QTL mapping of resistance to powdery mildew in lettuce

Lettuce (Lactuca sativa) is the major leafy vegetable that is susceptible to powdery mildew disease under greenhouse and field conditions. Quantitative trait loci (QTLs) for resistance to powdery mildew under greenhouse conditions were mapped in an interspecific population derived from a cross between susceptible L. sativa cultivar Salinas and the highly susceptible L. serriola accession UC96US23. Four significant QTLs were detected on linkage groups LG 1 (pm‐1.1), LG 2 (pm‐2.1 and pm‐2.2) and LG 7 (pm‐7.1), each explaining between 35 to 42% of the phenotypic variation. The four QTLs are not located in the documented hotspots of lettuce resistance genes. Alleles for the disease resistance at the four QTLs originated from both parents (two from each), demonstrating that even highly susceptible accessions may provide alleles for resistance to powdery mildew. These QTLs appeared to operate during limited periods of time. Results of the field trials with F_2:3 and F_3:4 families derived from a Soraya (moderately resistant) × Salinas cross demonstrated effective transfer of resistance to powdery mildew in this material. An integrated rating approach was used to estimate relative levels of resistance in 80 cultivars and accessions tested in a total of 23 field and greenhouse experiments. Generally, very low resistance was observed in crisphead‐type lettuces, while the highest relative resistance was recorded in leaf and butterhead types. Comparison of two disease assessment methods (percentage rating and the area under the disease progress steps, AUDPS) for detection of QTLs shows that the two approaches complement each other.     

Characterization of resistance mechanisms activated by Trichoderma harzianum T39 and benzothiadiazole to downy mildew in different grapevine cultivars

Downy mildew, caused by Plasmopara viticola, is one of the most destructive diseases of grapevine and is controlled with intense application of chemical fungicides. Treatment with Trichoderma harzianum T39 (T39) or benzothiadiazole‐7‐carbothioic acid S‐methyl ester (BTH) has been previously shown to activate grapevine resistance to downy mildew and reduce disease symptoms in the Pinot noir cultivar. However, enhancement of plant resistance can be affected by several factors, including plant genotype. In order to further extend the use of resistance inducers against downy mildew, the physiological and molecular properties of T39‐ and BTH‐activated resistance in different cultivars of table and wine grapes were characterized under greenhouse conditions. T39 treatment reduced downy mildew symptoms, but the degree of efficacy differed significantly among grapevine cultivars. However, efficacy of BTH‐activated resistance was consistently high in the different cultivars. Expression profiles of defence‐related genes differed among cultivars in response to resistance inducers and to pathogen inoculation. T39 treatment enhanced the expression of defence‐related genes in the responsive cultivars, before and after P. viticola inoculation. A positive correlation between the efficacy of T39 and the expression level of defence‐related genes was found in Primitivo and Pinot noir plants, while different genes or more complex processes were probably activated in Sugraone and Negroamaro. The data reported here suggest that the use of a responsive cultivar is particularly important to maximize the efficacy of resistance inducers and new natural inducers should be explored for the less responsive cultivars.     

小麦品种混种对白粉病的调控及其对部分产量性状及蛋白质含量的影响

对品种混合种植控制小麦白粉病的效果以及对小麦穗重、千粒重、蛋白质等指标的影响进行了研究,为混合种植控制白粉病提供理论依据和品种组合。在对37个小麦品种进行SSR多样性分析的基础上,选用8个生产品种（后备品种）,按品种数3、4、5、6、8进行组合,在田间以随机区组设计种植混播组合和单播小区,人工接种白粉菌,比较各小区中小麦白粉病的AUDPC值、穗重、千粒重和粗蛋白差异。结果表明,8个品种亲缘关系较远;4品种混种时AUDPC最小,穗重最重。26个品种混种组合中有防治效果的组合占到73.08%,相对防效为1.23%~56.65%;混种未对穗重和粗蛋白含量造成负面影响。品种多样性种植可以用做调控小麦白粉病的一项措施。     

Taxonomy,distribution and biology of lettuce powdery mildew (Golovinomyces cichoracearum sensu stricto)

This paper reviews the taxonomy, biology, importance, host–pathogen interactions and control of lettuce powdery mildew. The main causal agent of this disease, Golovinomyces cichoracearum s.s., is an important powdery mildew pathogen of many members of the family Asteraceae. The pathogen is distributed worldwide and occurs on Lactuca sativa as well as wild Lactuca spp. and related taxa (e.g. Cichorium spp.). Powdery mildew of lettuce can be a major problem in production areas with favourable environmental conditions for disease development (dry, hot weather). The fungus grows ectophytically and appears as white, powdery growth on both the upper and lower sides of leaves. There is rather limited information on the geographic distribution of powdery mildew on wild Lactuca spp. Most L. sativa cultivars have been found to be susceptible. Large variability in virulence was confirmed and existence of different races is supposed. Resistance in L. sativa and some related wild Lactuca spp. is characterized by race‐specificity, but the genetic background of resistance is poorly understood. Sources of resistance are known in L. saligna and L. virosa. Lettuce powdery mildew can be effectively controlled by common fungicides (e.g. sulphur, myclobutanil, quinoline, strobilurins, etc.) and protective compounds (e.g. extract of neem oil, Reynoutria sachaliensis extracts). However, fungicide resistance may arise. Non‐fungicidal activators of plant systemic acquired resistance (SAR) had no direct effect on the causal agent. Future issues regarding lettuce powdery mildew research are summarized.     

Integrated Control of Powdery Mildew on Field-grown Mango Trees by Foliar Sprays of Mono-potassium Phosphate Fertilizer, Sterol Inhibitor Fungicides and the Strobilurin Kresoxym-methyl

Foliar sprays of solutions of di-potassium hydrogen orthophosphate, K2HPO4 (DKP) and potassium di-hydrogen orthophosphate, KH2PO4 (MKP), commercial systemic fungicides, and an alternating treatment with phosphate fertilizer and systemic fungicides inhibited development of the powdery mildew fungus, Oidium mangiferae, on flowers and bloom clusters of field-grown mango trees. The effectiveness of the alternation treatments with an appropriate systemic fungicide and 1% solution of mono-potassium phosphate (MKP) in controlling powdery mildew on bloom clusters was similar to that of the commercial treatment with the systemic fungicides. However, application of the systemic fungicides alone, on the same dates on which they were applied in the alternation treatment, without application of the phosphate treatment was significantly less effective in controlling the disease than either the phosphate or the alternation treatment. This indicates that the use of phosphate fertilizer has a significant role in disease control and that it can reduce the number of fungicide treatments necessary against powdery mildew by up to 50%. These results were confirmed in large-scale demonstration trials conducted in commercial orchards in 1994 and 1995. Our 1997 findings also revealed that tank-mix treatments of 1% MKP solution with half the recommended quantity of sterol inhibitor fungicide applied at 14-day intervals provided a protection against powdery mildew comparable with or superior to that given by the standard fungicides-based treatment applied at 7-day intervals. Tank-mix treatments of MKP (1%) with sterol inhibitor at the recommended rate or with the new strobilurin Kresoxym-methyl (BAS 490F, strobi), or the BAS 490F alone, were the most effective, and provided >95% protection against O. mangiferae, compared with the control. Phosphate solutions were found not to be phytotoxic to plant tissue. These treatments affected the yield of mango trees: a significantly lower yield was observed on control untreated trees, probably because of powdery mildew infection on flowers. The inhibitory effectiveness of phosphate salts makes them a potential major component of an integrated pest management program.     

An Ulva armoricana extract protects plants against three powdery mildew pathogens

The protective activity of a crude extract prepared from the green macroalga, Ulva armoricana, previously shown to induce plant defence responses, was evaluated on three plant species, common bean, grapevine and cucumber, cultivated in the greenhouse and inoculated with three powdery mildew pathogens Erysiphe polygoni, E. necator and Sphareotheca fuliginea respectively. Chemical analyses showed that the extract was enriched in ulvans, which are green algae polysaccharides essentially composed of uronic acid and sulphated rhamnose. Weekly applications were performed by spraying of the green algal extract at various dilutions on bean, grapevine and cucumber leaves. A significant effect (50% protection) was observed using a dilution corresponding to about 3 g l⁻¹ dry matter and up to 90% reduction of symptom severity was obtained for the highest concentration (1/9 dilution, 6 g l⁻¹ dry matter) for the three plant species. To study the natural variability of the protective activity, five extracts prepared from algae batches harvested at different year periods were evaluated. Although polysaccharide composition varied among batches, all extracts elicit a reporter gene regulated by a defence-gene promoter in a transgenic tobacco line, and protect cucumber plants against powdery mildew infection. Together, these data demonstrate that U. armoricana is a reproducible source of active compounds which can be used to efficiently protect crop plants against powdery mildew diseases.     

Leaf scald (Xanthomonas albilineans) incidence and its effect on yield in seven sugarcane cultivars in Guadeloupe

Seven 5—month-old sugarcane cultivars difTering in resistance to leaf scald disease were inoculated by the decapitation technique with Xanthomonas albilineans. The effects of disease progress and incidence on yields were studied for the plant (first harvest) and two ratoon crops (second and third harvest). The percentage of diseased stalks and disease severity at first harvest 5 months after inoculation were 0·7 and 0·4, respectively, for the most resistant cultivar and 71·0% and 63·3, respectively, for the most susceptible cultivar. They decreased in all cultivars in both ratoon crops, but were still important in one cultivar (B69379). Significant ( P = 0·05) yield reductions of 12% and 21% occurred in two of the seven cultivars (B69566 and B69379, respectively). The number of symptomatic sugarcane stalks in the first ratoon crop (second harvest) was lower than the number of stalks colonized by the pathogen. Symptoms and yield losses of cultivars R570 and B69566 varied with the crop. Yield losses occurred in cultivar R570 only in the plant crop when this cultivar displayed numerous symptoms. Cultivar B69566 appeared to recover from the disease to a certain extent from the plant to the second ratoon crop (third harvest), as did the resistant cultivars in the first ratoon crop. In contrast, severe leaf scald symptoms were observed in the case of cultivar B69379 regardless of the crop, and significant yield losses occurred in the two ratoon crops. These results support the recommendation that cultivar B69379 should not be replanted in Guadeloupe.     

Effect of defoliation by livestock on stem canker caused by Leptosphaeria maculans in Brassica napus

Brassica napus (canola, oilseed rape), an important break crop for cereals across the Australian wheat belt, is being rapidly adopted as a dual‐purpose (forage and grain) crop in mixed farming systems. Stem canker caused by the fungus Leptosphaeria maculans is the most important disease of B. napus in Australia. The primary source of inoculum is airborne ascospores released during autumn/winter which coincides with the grazing of dual‐purpose crops. Field experiments were defoliated by sheep to determine the effect of grazing on blackleg stem canker severity at plant maturity in B. napus cultivars differing in their resistance level and grazed at different times. One cultivar was sown on different dates to investigate the impact of grazing at the same time, but at different growth stages. Defoliation by mowing was compared to defoliation by livestock. Similar amounts of dry matter remained after defoliation by machinery (0·66 t ha^?1) or livestock (0·52 t ha^?1). However, stem canker severity was higher in the grazed (40% of crown cross‐section diseased) compared with the mown (25%) treatment, which was higher than the ungrazed control (9%). Stem canker severity generally increased with grazing, but the increase was eliminated or reduced in cultivars with good resistance. Grazing during vegetative plant growth minimized the increase in stem canker severity compared with grazing during reproductive growth. Currently, cultivars with good L. maculans resistance are recommended in high disease situations. To avoid excessive yield loss in dual‐purpose B. napus crops due to L. maculans it is recommended that such cultivars are grown even in low‐moderate disease situations.     

Comparison of three biological control agents against cucumber powdery mildew (Sphaerotheca fuliginea) in semi-commercial-scale glasshouse trials

The effect of three reported biological control agents, Ampelomyces quisqualis, Verticillium lecanii and Sporothrix flocculosa, was tested against cucumber powdery mildew (Sphaerotheca fuliginea). Two glasshouse experiments, one in the summer and one in winter/spring were conducted on a semi-commercial scale. In both experiments, a susceptible and a partially resistant cultivar were used. In the second experiment, the additional effect of integration of biological control and silicon amendments to the nutrient solution was also assessed. In both experiments, A. quisqualis did not control the disease. V. lecanii had a small effect on powdery mildew in the first experiment but not in the second. S. flocculosa gave the best control of powdery mildew in both experiments. In the first experiment, weekly application of S. flocculosa reduced disease in the partially resistant cultivar to the same level as a treatment in which the fungicides bupirimate and imazalil were each applied once. Addition of silicon in the nutrient solution in a concentration of 0.75 mM reduced disease by 10–16%, averaged over all treatments. There was no interaction between silicon and the biocontrol agents. Yield was recorded in the second experiment and was significantly increased by the fungicide treatment compared to the control in the partially resistant cultivar. Yield in the treatment with S. flocculosa was not significantly different from the fungicide treatment in this cultivar. Silicon had no effect on yield in either cultivar.     

Ontogenic resistance to powdery mildew in grape berries

ABSTRACT Berries of Vitis vinifera are reported to be susceptible to infection by Uncinula necator until soluble solids levels (brix) reach 8%, and established colonies are reported to sporulate until brix reach 15%. However, our analysis of disease progress on fruit of selected V. vinifera cultivars indicated that severity became asymptotic several weeks earlier in fruit development. When mildew-free fruit clusters of V. vinifera 'Chardonnay', 'Riesling', 'Gewürztraminer', and 'Pinot Noir' were inoculated at stages ranging from prebloom to 6 weeks postbloom, only fruit inoculated within 2 weeks of bloom developed severe powdery mildew. Substantial ontogenic resistance to infection was expressed in fruit nearly 6 weeks before fruit brix reached 8% and over 2 months before they reached 15%. Rachises of 'Chardonnay' and 'Riesling' fruit clusters developed severe powdery mildew when inoculated at bloom, and disease increased steadily over the next 60 days. The rachis of fruit clusters inoculated 31 days after bloom developed only trace levels of powdery mildew. Berry weight of all four cultivars at harvest was reduced when fruit clusters were inoculated at bloom or 16 days postbloom, primarily by splitting, rotting, and dehydration of mildewed berries, but the weight of later-inoculated berries was not reduced. Inoculation of berries just as ontogenic resistance increased markedly, approximately 3 to 4 weeks postbloom, resulted in the development of inconspicuous, diffuse, non-sporulating mildew colonies on berries, sometimes associated with a network of necrotic epidermal cells. Rather than a protracted and relatively static period of berry susceptibility lasting 3 months, fruit of V. vinifera appear to acquire ontogenic resistance rapidly after fruit set. A refocusing of disease management on this critical period of high fruit susceptibility should greatly improve the efficacy of fungicides directed against powdery mildew.     

Plant age and ambient temperature: significant drivers for powdery mildew (Erysiphe cruciferarum) epidemics on oilseed rape (Brassica napus)

Powdery mildew (Erysiphe cruciferarum) is an important disease in oilseed rape crops worldwide, but of sporadic importance in most southern Australian crops. Six Brassica napus cultivars were exposed to E. cruciferarum simultaneously in four plant age cohorts. First symptoms of powdery mildew appeared 9 days after inoculation (dai) on the oldest plants [42 days after seeding (das)], but 44 dai in the youngest plants that were exposed to inoculum from sowing, although final disease severity did not differ with the plant age at exposure. The maximum level of pod peduncle infestation was unaffected by plant age (P = 0.37) or cultivar (P = 0.28). The effect of temperature was also investigated. The development of disease on plants was slower and final severity reduced at a day/night temperature 14/10 °C compared with 22/17 °C. In vitro, maximum growth of germ tubes from conidia of E. cruciferarum was at 15–20 °C and survival of conidia reduced by temperatures >30 °C. The results explain the sporadic nature of powdery mildew outbreaks in winter‐grown oilseed rape in Australia, where slow rates of infection occur when seasonal colder prevailing winter conditions coincide with the presence of younger plants, together curtailing rapid disease development until temperatures increase in late winter/early spring. These results explain why epidemics are most severe in the two warmer cropping regions, viz. the northern agricultural region of Western Australia and New South Wales. This study suggests that with increases in winter temperatures under future climate scenarios, earlier and more severe powdery mildew outbreaks in Australia will be favoured.     

Nitrogen-induced changes in colony density and spore production of Erysiphe graminis f.sp. hordei on seedlings of six spring barley cultivars

The influence of increasing nitrogen supply (30, 60, 120 and 240 mg N per pot) on susceptibility was studied on seedlings of six cultivars of spring barley inoculated with virulent isolates of powdery mildew. The colony density (CD) measured as colonies per cm² was significantly increased with increasing application of nitrogen on all cultivars, and a significant interaction was found between N and cultivar. The different reactions of the cultivars could not be ascribed to lack of N uptake. In general, increasing N application enhanced the sporulation capacity of colonies (CSC) irrespective of increased CD and the cumulative production of spores per cm² leaf (CSCM) increased strongly with N application in all cultivars. No interaction between N and cultivar was found for the latter component. The increase in CSCM closely corresponded with the increase in N content and fresh weight of uninoculated leaves. No interaction between N treatment and powdery mildew isolates was found for infection efficiency and spore production per colony, when tested on one cultivar. The N-induced changes in infection and sporulation can explain the main part of the increasing effect of N fertilization on powdery mildew development in the field. The results indicate that it may be possible to breed for or select barley cultivars with low N impact on powdery mildew development.     

铁春1号"小麦耐白粉病机制研究

 铁春1号小麦耐小麦白粉病的机制是:①光合补偿作用:"铁春1号"小麦旗叶的表现光合速率下降较小,而真正光合速率比健康植株高,表明侵染点间的绿色组织具有光合补偿作用,一定程度上弥补病原菌的破坏与消耗。②超氧化物歧化酶活性增强,能及时清除因病害胁迫产生的超氧自由基(O₂·),避免了O₂对细胞膜的伤害。"铁春1号"膜磷脂种类在染病后没有变化,而感病品种膜磷脂在染病后增加了2个组份。③贮存物质运转的补偿作用:"铁春1号"在病害胁迫下,叶、茎、叶鞘中的干物质,以及氮、磷等养分的运出率增大,通过充分利用贮存物质部分的补偿光合产物低之不足。最终使籽粒中氮、磷及碳水化合物不减少。     

Magnaporthe oryzae conidia on basal wheat leaves as a potential source of wheat blast inoculum

Wheat blast caused by Magnaporthe oryzae Triticum causes significant losses on wheat during outbreak years in several South American countries. Despite reports of wheat blast leaf lesions on some wheat cultivars, the importance of inoculum originating from leaves in severely affected commercial fields is disputed. It is generally considered that leaf lesions and/or sporulation on leaves do not usually appear before the occurrence of spike blast in wheat. The purpose of this study was to (i) determine the occurrence of wheat blast on basal leaves, (ii) estimate the number of conidia produced on these leaves, and (iii) determine the impact of current fungicide application practices on inoculum produced from sporulating lesions on basal wheat leaves. Inoculations at the three‐leaf stage showed that certain cultivar and isolate combinations caused more disease on old wheat leaves than young expanding leaves. Under optimum conditions, M. oryzae had the potential to produce tens to hundreds of thousands of conidia on small amounts of wheat basal leaves. A mean of 1 669 000 conidia were produced on 1 g dry basal leaves of a highly susceptible cultivar under optimum conditions for sporulation. Conidia production on leaves coincided with spike emergence under both greenhouse and field conditions. When field studies were conducted under natural epidemic conditions, foliar fungicide applications reduced the amount of M. oryzae conidia on basal leaves by 62–77% compared to non‐sprayed controls. An earlier application of foliar fungicides might reduce inoculum if conidia from basal leaves contribute to wheat spike blast development.