Use of Trichoderma harzianum in combination or alternation with fungicides to control cucumber grey mould (Botrytis cinerea) under commercial greenhouse conditions

A preparation of Trichoderma harzianum was sprayed on cucumber plants in greenhouses in order to control fruit and stem grey mould. Up to 90% control was achieved by the biocontrol agent (0·5–1·0 g/l) which in most experiments under commercial conditions was as effective as the dicarboximide fungicides iprodione or vinclozolin (0·5 g/l each) alone or alternated with diethofencarb + carbendazim (0·25 g/l each). However, in one experiment disease incidence in Trichoderma -treated plots did not differ significantly from the control. A mixture of T. harzianum with a dicarboximide fungicide resulted in up to 96% control of grey mould. In this case control was always significant ( P =0·05) but improvement of control compared with each treatment alone was not significant ( P =0·05). The alternation of sprays with the biocontrol preparation and with a dicarboximide fungicide was tested in three out of the five experiments and was found to be effective, thus enabling a reduction in the use of chemical sprays. Populations of T. harzianum were on a level of 3 × 10⁵-8 × 10⁵ c.f.u. per leaf and ten times lower on one fruit. They remained high after the second and third sprays. Conditions favouring the ability of T. harzianum to control grey mould were temperatures above 20°C and relative humidity between 80 and 97%.     

Berry infection and the development of bunch rot in grapes caused by Aspergillus carbonarius

The effects of different levels of inoculum of Aspergillus carbonarius and time of inoculation on berry infection and the development of aspergillus bunch rot on grapevines (cv. Sultana) were studied under field conditions. Inflorescences at full bloom were inoculated with aqueous spore suspensions of A. carbonarius containing 0 or 1 × 10⁶ spores mL⁻¹ in 2004/05 and 0, 1 × 10² or 1 × 10⁵ spores mL⁻¹ in 2005/06. In both years, the incidence of infection in inoculated berries was significantly higher than in uninoculated berries. Incidence of infection in berries from veraison until harvest was higher than at earlier stages of bunch development (berry set to berries that were still hard and green). Inoculation of bunches at veraison did not significantly increase A. carbonarius infection prior to harvest, at harvest, 6 days after harvest or when berries were over-ripe. Bunches inoculated at harvest did not significantly increase infection 6 days after harvest or when berries were over-ripe. Aspergillus carbonarius was isolated more frequently from the pedicel end (53·1%) than from the middle section (37·5%) and distal end (35·0%) of berries that were inoculated with 10⁵ spores mL⁻¹.     

Visual and PCR assessment of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) cultivars

Methods to assess light leaf spot ( Pyrenopeziza brassicae ) on winter oilseed rape cultivars were compared in laboratory, controlled-environment and field experiments. In controlled-environment experiments with seedling leaves inoculated at GS 1,4, the greatest differences in percentage area affected by P. brassicae sporulation were observed with inoculum concentrations of 4 × 10³ or 4 × 10⁴ spores mL⁻¹, rather than 4 × 10² or 4 × 10⁵ spores mL⁻¹, but older leaves had begun to senesce before assessment, particularly where they were severely affected by P. brassicae . In winter oilseed rape field experiments, a severe light leaf spot epidemic developed in 2002/03 (inoculated, September/October rainfall 127·2 mm) but not in 2003/04 (uninoculated, September/October rainfall 40·7 mm). In-plot assessments discriminated between cultivars best in February/March in 2003 and June in 2004, but sometimes failed to detect plots with many infected plants (e.g. March/April 2004). Ranking of cultivar resistance differed between seedling experiments done under controlled-environment conditions and field experiments. The sensitivity of detection of P. brassicae DNA extracted from culture was greater using the PCR primer pair PbITSF/PbITSR than using primers Pb1/Pb2. P. brassicae was detected by PCR (PbITS primers) in leaves from controlled-environment experiments immediately and up to 14 days after inoculation, and in leaves sampled from field experiments 2 months before detection by visual assessment.     

Factors influencing infection of eucalypts by Cylindrocladium pteridis

The pattern of Cylindrocladium pteridis adhesion, germination and penetration in eucalypt leaves was assessed using scanning electron microscopy. The effects of inoculum concentration, leaf wetness period, plant age and branch position of cylindrocladium leaf blight and defoliation severity were assessed in greenhouse studies using two Eucalyptus grandis × E. urophylla hybrid clones. Penetration occurred through stomata, and there was no difference in the number of penetrations between young and old leaves. Percentage leaf area with lesions and defoliation increased with the increase in inoculum concentration (1 × 10² to 10⁵ conidia mL⁻¹), duration of leaf wetness period (6 to 48 h) and plant age (60 to 180 days). Branch position in plants also significantly affected the percentage leaf area with lesions and defoliation, the latter variable being significantly higher at the stem base. The highest values of lesion area were also observed on leaves at the stem base in both clones. The Pearson correlation between defoliation and leaf area with lesions was significant in all experiments ( r  > 0·9) indicating a high association between these two variables.     

Virulence for faba bean and production of ascochitine by Ascochyta fabae

The production of ascochitine by seven isolates of Ascochyta fabae accounted for the toxicity of culture filtrates of the fungus to cells isolated from leaves of Vicia faba. The LD₅₀ value for cells from cultivars that were susceptible, tolerant or resistant to the fungus was similar i.e. 3·0 × 10⁻⁵ m , 3·8 × 10⁻⁵ m and 2·9 × 10⁻⁵ M, respectively. Ascochitine affected neither the germination of seeds nor the growth of mature plants at 5·17 × 10⁻⁴ m but caused necrosis and wilting of plant cuttings at 2·5 × 10⁻⁴ m and 5·10⁻⁴ m . There was no association between virulence of 16 isolates of A. fabae for three cultivars of V.faba and the production of ascochitine in vitro. One isolate produced no ascochitine in vitro and yet was the most virulent for two of three cultivars. The toxin could not be extracted from infected plants.     

Effects of avirulent bacteriocin-producing strains of Pseudomonas solanacearum on the control of bacterial wilt of tobacco

Root systems of tobacco dipped in suspensions containing 2 × 10⁹ colony forming units (CFU)/ml of avirulent bacteriocin-producing strains (ABPS) of Pseudomonas solanacearum and assayed immediately after planting in steam-sterilized soil had 8 × 10⁶ CFU/root system of ABPS. The bacterial population declined to an average of 5·3 × 10⁵ CFU/root system after 30 days. Roots of seedlings dipped in bacterial suspensions of ABPS were more effectively protected against wilt caused by P. solanacearum than those dipped in suspensions of an avirulent nonbacteriocin-producing strain (ANBPS). Lipopolysaccharide (LPS) isolated from one ABPS (121) inhibited the attachment of bacteria on roots by 70% but had no effect on the reduction of wilt, whereas bacterial cells significantly reduced the disease severity as compared to LPS or water treatment. In steam-sterilized soil containing a 1:1 mixture (5 × 10⁵ CFU/g of oven-dried soil) of ABPS 121 or 237 and the virulent strain K-60, ABPS 121 reduced multiplication of the virulent strain in soil and in the rhizosphere of seedlings. When roots of seedlings were dipped in a suspension of 2 × 10⁹ CFU/ml of ABPS before planting, root colonization by the virulent strain added to steam-sterilized soil at 2 × 10⁶ CFU/g of oven-dried soil was significantly reduced. When roots were dipped in a suspension of ABPS and assayed 20 days after planting, 98% of the bacterial population was found in the original zone of inoculation and only 2% was detected in new growths of the root system. Plants which were grown in soil infested with ABPS 121 or K-60 had both strains present at variable populations along all sections of roots.     

Factors influencing infection of mechanical wounds by Fusarium circinatum on Monterey pines (Pinus radiata)

Pitch canker, caused by the fungus Fusarium circinatum , is a disease affecting many pine tree species. In California, Pinus radiata (Monterey pine) is the principal pine host affected by pitch canker. This investigation into factors affecting infection frequency by F. circinatum of P. radiata examined the influence of: (i) wound size; (ii) relative humidity; (iii) time of inoculation; (iv) inoculum density; and (v) wound age. Wounded branches sustained significantly more infections when large-diameter (1·6 mm) rather than small-diameter (0·5 mm) wounds were made. Infection frequencies tended to be higher at 100% RH than at ambient humidity, although these differences were not statistically significant. Infection frequencies were significantly higher on branches inoculated after 17·00 h than on branches inoculated before noon. Infection frequencies were significantly higher for wounded branches spray-inoculated with 5 × 10⁷ rather than 1 × 10⁷ spores mL⁻¹. Infection frequencies of pruning wounds declined as wounds aged.     

Effect of formulation on the rhizosphere competence and biocontrol ability of Trichoderma atroviride C52

The rhizosphere competence of the biological control agent Trichoderma atroviride isolate C52 was studied on onion roots both in the glasshouse and in the field when introduced into soil in a range of formulations. Proliferation of T. atroviride in the rhizosphere was formulation-dependent. A pellet formulation maintained the fungal concentration at 10⁵ cfu per g soil, whereas solid-substrate and seed-coating formulations gave concentrations of 10⁴ and 10¹ cfu per g soil, respectively. To facilitate rhizosphere-competence studies, a UP-PCR band profile generated with primer L45 for isolate C52 was used to enable conclusive identification of T. atroviride C52 when recovered from soil. When isolate C52 was introduced into Sclerotium cepivorum -infested soil as both pellet and solid-substrate formulations, there was no statistically significant difference in the disease control between these treatments, but the pellet treatment doubled the percentage of healthy plants compared with the control treatment.     

Effects of the mycoparasite Verticillium biguttatum on barley stunt disease caused by Rhizoctonia solani anastomosis group 8 in a model system

The height of barley stunted by Rhizoctonia solani anastomosis group 8 was significantly increased by up to 72·8% after incubation for 8 days at 20°C in seedling tray tests following application of the mycoparasite Verticillium biguttatum. The pathogen and mycoparasite were applied at the rate of 1% Perlite maizemeal inoculum (w/w potting mixture) resulting in propagule densities of approximately 24·0 and 6·6 × 10⁵ colony-forming units (cfu) per g potting mixture, respectively. Sieving (2 mm) R. solani inoculum prior to dilution in potting mixture increased the recovery of propagules from 1·2 × 2·1 × 10³ cfu per g inoculum compared with recovery when inoculum was sieved after dilution. Applications of a V. biguttatum isolate from the UK (vbl) and a Dutch isolate (M73) reduced stunting to a similar extent but did not stimulate the growth of healthy plants. The height of stunted plants was significantly increased after application of V. biguttatum inoculum after 6 days if inoculated trays were preincubated for 1 day prior to planting but a similar increase was only detected after 7 days if seeds were planted immediately. The number of stunted plants which emerged after 4 days was significantly increased by treatment with V. biguttatum but preincubation had no additional effect. These results suggested that control of R. solani was effected both before and after the initiation of disease.     

PCR-based specific and sensitive detection of Pectobacterium carotovorum ssp. carotovorum by primers generated from a URP-PCR fingerprinting-derived polymorphic band

A 24-mer primer pair was generated by sequencing a URP-PCR fingerprinting-derived polymorphic band that is uniquely shared in Pectobacterium carotovorum ssp . carotovorum strains (Pcc). The primer set (EXPCCF/EXPCCR) amplified a single band of expected size (0·55 kb) from genomic DNA obtained from 29 Pcc strains and three Pectobacterium carotovorum ssp. wasabiae (Pcw) strains, but not from other P. carotovorum subspecies atrosepticum , betavasculorum or odoriferum , or from other Erwinia spp. or bacterial genera. The Rsa I digestion profile of the amplified bands divided Pcc strains into five groups with a unique profile from Pcw strains. First-round PCR detected between 5 × 10² and 1 × 10³ colony forming units (CFU) mL⁻¹ and detection sensitivity was increased to as few as 2–4 CFU mL⁻¹ after second-round (nested) PCR. This PCR protocol was used directly to detect Pcc strains in infected plant tissues.     

Some properties of a virus-like agent found in Brachypodium sylvaticum in the United Kingdom

A spherical virus–like agent ($$32 nm in diameter) was isolated from a plant of Brachypodium sylvaticum (Huds.) Beauv. growing in a botanic garden in England and showing yellow streaks in the leaves. The agent was readily purified and sedimented as a single component in sucrose density rate gradients. The particles had a sedimentation coefficient at infinite dilution of $$122S and a buoyant density of 1.35 g/cm³ in CsCl and 1·33 in CS₂SO₄. The particles were stable at acid pH but above pH 7·0 in the presence of EDTA dissociated. A protein having a major polypeptide with a molecular weight of $$3·76 × 10⁴ and a species of single stranded RN A with a MW of 1·67 × 10⁶ were detected in the particles. The agent was not transmitted by manual inoculation, by the insects Myzus persicae Sulzer, Rhopalosiphum padi L. or Nephotettix virescens Distant, through soil by leakage from roots or by seed. The particles had physicochemical properties in common with tombus– and sobemoviruses but were not serologically related to 10 members of these groups or to 57 other small spherical RNA plant viruses.     

Effect of Gliocladium and Trichoderma on damping-off and blight of snapbean caused by Sclerotium rolfsii in the greenhouse

Aqueous suspensions of conidia of 285 wild-type strains and mutants of Gliocladium virens, Trichoderma hamatum, T. harzianum and T. viride were tested against Sclerotium rolfsii in the greenhouse. Ten strains of G. virens and four strains of T. harzianum suppressed damping-off of snapbean by 30-50% and blight by 36-74%. All strains of T. hamatum and T. viride tested as conidia were ineffective. In general, strains of G. virens were more effective in suppressing disease in the greenhouse than strains of T. harzianum. Several strains of G. virens and T. harzianum used alone were equal to or more effective than double and triple mixtures of such strains in disease suppression. Of four formulations of G. virens tested, germlings, alginate-bran-fermenter biomass pellets, and Pyrax-fermenter biomass mixtures reduced disease considerably and all three formulations were more effective than conidia in aqueous suspension. Strain G1-3 of G. virens added to soil as Pyrax-fermenter biomass mixtures in amounts to provide colony-forming units ranging from 1 -5 × 10³ to 1 -2 × 10⁴ per g soil provided statistically significant protection of the host at all concentrations. The extent of biological control with strains G1-3 and G1-21 of G. virens also depended on the strain of the pathogen used. Both strains effectively suppressed disease caused by strain Sr-1 (small sclerotia) of S. rolfsii. They were partially effective against strain Sr-116 (medium size sclerotia) and ineffective against strain Sr-3 (large sclerotia). Although strains G1-3 and G1-21 colonized the sclerotia of all three strains of S. rolfsii in soil effectively, they only reduced germinability of sclerotia of strain Sr-1.     

Variability in the reaction of squash (Cucurbita pepo) to inoculation with Sphaerotheca fuliginea and methodology of breeding for resistance

Reaction to inoculation with powdery mildew caused by Sphaerotheca fuliginea was observed on leaf discs and young plants of eleven representatives of seven edible cultivar groups of Cucurbita pepo. Disease intensity (i.e. number of infections per leaf) was highly correlated ( r ²=0·863, P <0·0001) with spore yield per leaf. Spore yield per leaf and frequency of sporulation on leaf disks were moderately ( r ²=0·505), but significantly correlated ( P <0·01), suggesting that frequency of sporulation can be used for initial screening against susceptibility in a breeding programme. Spore yield per leaf and spore yield per artificially inoculated leaf disc were highly correlated ( r ²=0·87, P <0·0001); this suggests that counting of spores on leaf discs, a laborious but accurate procedure, could be used on the remaining plants as a second step in selection for resistance of the variation in the response of edible C. pepo to the pathogen, 85·8% was attributed to differences between the edible groups and only 14·2% to individual cultivars within a group. Cultivars of the cocozelle and vegetable marrow groups were the most susceptible, whereas relatively resistant cultivars were found in the scallop and straightneck groups.     

Controlled environment studies on the infection of Emex australis by Phomopsis emicis

The effect of temperature, dew period, inoculum concentration and host maturity on the growth and development of Emex australis after inoculation with Phomopsis emicis was studied in controlled environments. Disease was assessed by recording changes in the length of stems, number of fully expanded leaves, dry weights, number of fruits and disease severity index. Disease was as severe at 18°C as it was at 28°C. There was a trend of increased disease with longer dew period. Inoculum concentrations of 1·10⁶ and 1·10⁷ conidia per ml resulted in a significant net reduction in stem growth compared with lower concentrations. Progressively higher disease ratings occurred as the inoculum concentration increased to 1·10⁷ conidia per ml. There were no significant effects of inoculation with P. emicis on either seedlings, rosettes or flowering rosettes, but 10-week-old plants were highly susceptible to infection and stem collapse. The implications of these results for the potential development of P. emicis as a mycoherbicide are discussed.     

Host–parasite relationships of Meloidogyne incognita on spinach

Host–parasite relationships in root-knot disease of spinach caused by Meloidogyne incognita race 1 were studied under glasshouse conditions. Nematode-induced mature galls were large and usually contained one or more females and egg masses with eggs. Feeding sites were characterized by the development of giant cells containing granular cytoplasm and many hypertrophied nuclei. The cytoplasm in these giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density ( P _i) in a series from 0–128 eggs and second-stage juveniles per cm³ soil and growth of spinach cv. Symphony F₁ seedlings was tested under glasshouse conditions. A Seinhorst model [ y = m  + (1 −  m ) z ^P–T ] was fitted to fresh top- and total plant-weight data for inoculated and control plants. Tolerance limits ( T ) of spinach cv. Symphony F₁ to M. incognita race 1 for fresh top and total plant weights were 0·25 and 0·5 eggs and second-stage juveniles per cm³ soil, respectively. The minimum relative values for fresh top and total plant weights were zero in both cases at P _i ≥ 32 eggs and second-stage juveniles per cm³ soil. Root galling was least at low initial population densities and greatest at 16 eggs and second-stage juveniles per cm³ soil. Maximum nematode reproduction rate was 33·1-fold at the lowest P _i.     

The process of antagonism of Sclerotium cepivorum in white rot affected onion roots by Trichoderma koningii

Trichoderma koningii (strain Tr5) grew in the epidermal mucilage of onion roots without entering healthy epidermal tissue. When placed on the epidermis of Sclerotium cepivorum -infected roots, T. koningii colonized epidermal passage cells, with little colonization of other epidermal tissues, then branched and spread throughout the root cortical tissues damaged by enzymes and toxins which diffused ahead of S. cepivorum hyphae, and impeded the path of the infection. When T. koningii colonized infected tissue, many S. cepivorum hyphae became detached at septa, cell walls dissolved and many hyphal apices burst. Contact between hyphae was not necessary for lysis to occur. T. koningii produced two endochitinases ( R _f 0·15 and 0·24) and two exo-acting chitinolytic enzymes ( R _f 0·46 and 0·62) during degradation of crabshell chitin and S. cepivorum cell walls. The R f 0·24 and 0·46 proteins were detected when T. koningii colonized S. cepivorum -infected roots and are likely to be a component of the antagonism process.     

Pathogenicity of the root-knot nematode Meloidogyne javanica on potato

Host–parasite relationships and pathogenicity of Meloidogyne javanica on potatoes (newly recorded from Malta) were studied under glasshouse and natural conditions. Potato cvs Cara and Spunta showed a typical susceptible reaction to M. javanica under natural and artificial infections, respectively. In potato tubers, M. javanica induced feeding sites that consisted of three to four hypertrophied giant cells per adult female. Infection of feeder roots by the nematode resulted in mature large galls which usually contained at least one mature female and egg mass. In both tubers and roots, feeding sites were characterized by giant cells containing granular cytoplasm and many hypertrophied nuclei. Cytoplasm in giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density ( P ) [0–64 eggs + second-stage juveniles (J2s) per cm³ soil] and growth of cv. Spunta potato seedlings was tested under glasshouse conditions. A Seinhorst model [ y = m  + (1 −  m ) z ^{( P − T )}] was fitted to fresh shoot weight and shoot height data of nematode-inoculated and control plants. Tolerance limits ( T ) for fresh shoot weight and shoot height of cv. Spunta plants infected with M. javanica were 0·50 and 0·64 eggs + J2s per cm³ soil, respectively. The m parameter in that model (i.e. the minimum possible y -values) for fresh shoot weight and shoot height were 0·60 and 0·20, respectively, at P  = 64 eggs + J2s per cm³ soil. Root galling was proportional to the initial nematode population density. Maximum nematode reproduction rate was 51·2 at a moderate initial population density ( P  = 4 eggs + J2s per cm³ soil).     

Effect of temperature on head blight of wheat caused by Fusarium culmorum and F. graminearum

The effect of small temperature differentials (16 vs. 20°C) on the pathogenicity of deoxynivalenol producing single isolates of Fusarium culmorum and F. graminearum and on the fusarium head blight (FHB) response of eight wheat cultivars was examined. Fusarium culmorum inoculation caused greater visual disease symptoms at 20°C than at 16°C, both overall and on an individual cultivar basis (overall AUDPC = 13·5 and 9·6, respectively) ( P  < 0·05). In contrast, F. graminearum inoculation caused greater overall visual disease symptoms at 16°C than at 20°C, both overall and at the individual cultivar level (overall AUDPC = 12·8 and 10·9, respectively) ( P  < 0·05). Results showed both F. culmorum and F. graminearum inoculations caused a greater loss in yield at 20°C (54·3 and 46·9% relative 1000-grain weight, respectively) compared with 16°C (73·3 and 66·9% relative 1000-grain weight, respectively) ( P  < 0·05). Fusarium culmorum -inoculated heads contained similar amounts of fungal DNA at both 16 and 20°C (1·9 and 1·7 ng mg⁻¹ of plant material, respectively) (not significant), while for F. graminearum inoculation, plants contained higher amounts of fungal DNA at 20°C (2·0 and 1·0 ng mg⁻¹ of plant material, respectively) ( P  < 0·05). Overall, there was a significant negative correlation between AUDPC and percentage relative 1000-grain weight at both 16 and 20°C ( r  =−0·693 and −0·794, respectively, P  < 0·01).     

Reduced sensitivity of Cercospora beticola isolates to sterol-demethylation-inhibiting fungicides

In a survey conducted during October 1995, single-lesion isolates of the sugar beet leaf-spot fungus, Cercospora beticola , were tested for sensitivity to the sterol demethylation inhibiting fungicides (DMIs) flutriafol and bitertanol. The isolates were collected from fields in three different areas of northern Greece. Fields at Serres and Imathia had been sprayed with DMIs for about 15 years to control sugar beet leaf-spot. At the third site, Amyndeon, DMI fungicides had not been used. From each area 150 isolates were tested. ED₅₀ values were calculated for individual isolates by regressing the relative inhibition of colony growth against the natural logarithm of the fungicide concentration. The mean ED₅₀ values for flutriafol for the Serres, Imathia and Amyndeon populations were 1·07, 0·73 and 0·5 µg mL⁻¹, respectively (significantly different at P  = 0·05). For bitertanol the mean ED₅₀ values for the Serres and Imathia populations were 0·72 and 0·81 µg mL⁻¹, respectively, which were not significantly different at P  = 0·05. The mean ED₅₀ value of the Amyndeon population was 0·48 µg mL⁻¹, which was significantly lower than those of the other two populations ( P  < 0·05). A cross-resistance relationship was found to exist between the two triazole fungicides tested when log transformed ED₅₀ values of 60 isolates were subjected to a linear regression analysis ( r  = 0·81).     

Sensitivity of Sclerotinia homoeocarpa to demethylation-inhibiting fungicides in Ontario, Canada, after a decade of use

In late 2003, nine populations of Sclerotinia homoeocarpa in Ontario Canada (seven of which had been previously sampled in early 1994, prior to the registration of sterol demethylation-inhibiting (DMI) fungicides for turf disease control in Canada) were sampled and tested for sensitivity to propiconazole. Four of the nine populations had not been treated with DMI fungicides during the intervening years, and isolates from these locations were sensitive to propiconazole (geometric mean EC₅₀ values of 0·005–0·012 µ g mL⁻¹, compared with 0·005–0·008 µ g mL⁻¹ for the original 1994 populations). Among the five populations from 2003 that had been exposed to DMI fungicides, mean EC₅₀ values were significantly greater, ranging from 0·020 to 0·048 µ g mL⁻¹. A significant correlation of determination was found between estimated number of fungicide applications and log EC₅₀ ( R ² = 0·832, P  = 0·0001), and the equation predicted that 42·3 applications of propiconazole would be needed to bring a sensitive population (EC₅₀ < 0·01  µ g mL⁻¹) to a resistant level (EC₅₀ > 0·10  µ g mL⁻¹). Fungicide sensitivity vs. duration of fungicide efficacy was also tested, and it was found that isolates with decreased sensitivity were able to more quickly overcome the inhibitory effects of fungicide application, reducing the duration of control from 3 weeks to 2 weeks.