Effect of azoxystrobin and kresoxim‐methyl on rice blast and rice grain yield in China

Sensitivity to azoxystrobin and kresoxim‐methyl of 80 single‐spore isolates of Magnaporthe oryzae was determined. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting mycelial growth of the 80 M. oryzae isolates were 0.006–0.056 and 0.024–0.287 µg mL^?1, respectively. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting conidial germination of the M. oryzae populations were 0.004–0.051 and 0.012–0.105 µg mL^?1, respectively. There was significant difference in sensitivity to azoxystrobin or kresoxim‐methyl between the tested isolates representing differential sensitivity to carbendazim (MBC) and kitazin P (IBP); however, there was no correlation between this difference in sensitivity to azoxystrobin or kresoxim‐methyl and sensitivity to MBC or IBP, indicating that there was no cross‐resistance between azoxystrobin or kresoxim‐methyl and MBC or IBP. In the protective and curative experiments, kresoxim‐methyl exhibited higher protective and curative activity than azoxystrobin when applied at 150 and 250 µg mL^?1 accordingly, while azoxystrobin exhibited stronger inhibitory activity against M. oryzae isolates than that of kresoxim‐methyl in the in vitro test. The results of field experiments also suggested that both azoxystrobin and kresoxim‐methyl at 187.5 g.a.i. ha^?1 gave over 73% control efficacy in both sites, exhibiting excellent activity against rice blast. Taken together, azoxystrobin and kresoxim‐methyl could be a good substitute for MBC or IBP for controlling rice blast in China, but should be carefully used as they were both at‐risk.     

Control of smoulder (Botrytis narcissicold) in narcissus with fungicides

Smoulder, caused by Botrytis narcissicola, is the most widespread foliar disease of narcissus (Narcissus cultivars) in the UK and causes significant losses in bulb and flower yield. A range of current and novel fungicide treatments was examined to determine if control of the disease could be improved and to measure the effect of treatments on bulb yield. In assays on pot-grown plants, carbendazim+flusilazole, epoxiconazole, iprodione + thiophanate-methyl, tebuconazole and vinclozolin reduced lesion size by more than 90%, compared with untreated plants, when applied 1 day before inoculation with the fungus; vinclozolin and tebuconazole were also effective when applied 2 days after inoculation. In field experiments in Cambridgeshire and Lincolnshire, significant reductions were observed in secondary smoulder symptoms (leaf lesions and stem rot) following fungicide sprays. Spray programmes of the novel fungicides azoxystrobin, cyprodinil, kresoxim-methyl, tebuconazole and pyrimethanil were as effective, or more so, than the standard treatments (chlorothalonil, vinclozolin) used by growers. Mixtures of carbendazim + tebuconazole and azoxystrobin + tebuconazole also gave effective control of smoulder. Programmes of four to six sprays, using two or three fungicides with different modes of action, applied alternately, reduced smoulder by 35–69% and increased bulb yields by 7–59%. Although treatment around and after flowering resulted in the greatest control of secondary smoulder, treatment before flowering was required for the highest bulb yields. The choice of fungicides for use in spray programmes to provide effective and reliable control of smoulder, and the possibility of control using fewer sprays, are discussed.     

Interactions between fungicide, plant growth regulator, nitrogen fertiliser applications, foliar disease and yield of winter barley

Leaf size and foliar disease in winter barley increased with increasing total amounts of nitrogen applied to the crop: flag leaf areas increased at an average of 10% per 35 kg N ha^-1 Nitrogen top dressing applied in mid-March (G.S. 31) resulted in larger leaves, more foliar disease, more straw, delayed ear emergence, fewer grains ear^-1 and less grain yield than nitrogen applied in mid-April (G.S. 31). Application of chlormequat at G.S. 30 gave a variable response, but overall it increased fertile stems m-² and crop yield and decreased crop height but had no significant effect on straw yield. Fungicide treatments suppressed foliar disease and improved yield. Yield responses were greater when plant growth regulator and mid-March nitrogen had been applied at sites where more disease prevailed than with April-applied nitrogen. In one of the field experiments, on cv. Sonja, delaying the main nitrogen application until April, without fungicide treatment, gave a similar yield to that provided by nitrogen in March with two or three fungicide sprays.     

Activity of fungicide mixtures against Botrytis cinerea isolates resistant to benzimidazoles,strobilurins and dicarboximides

Botrytis cinerea, the causal agent of grey mould in a broad range of crops, is considered a high‐risk plant pathogen for fungicide resistance development. The use of fungicide mixtures, particularly combinations with synergistic activity, can be a useful tactic to counteract resistance build‐up in pathogen populations. The present study aimed to investigate the effects of different ratios of two‐way mixtures of carbendazim, iprodione, kresoxim‐methyl, tebuconazole and penconazole on four B. cinerea isolates that were sensitive or resistant to benzimidazoles, dicarboximides and strobilurins. The isolates that were resistant to benzimidazoles and strobilurins had E198A and G143A mutations in β‐tubulin and cytochrome b genes, respectively. The mixtures had different effects on each of the isolates in vitro but, in 13 combinations, the synergistic effect was observed against all or three isolates. In greenhouse experiments, 11 fungicide combinations used in decreased (EC₇₅) concentrations showed the maximum control efficiency. The two follow‐up greenhouse experiments using six selected combinations revealed they were highly effective against additional isolates with various fungicide resistance profiles. The identified mixtures‐ratios have potential for use in grey mould management programs in the greenhouse.     

Fungicide sprays can injure the stigmatic surface during receptivity in almond flowers

Fungicides can be detrimental to flower development, pollen function and fruit set in a number of crops. Almond is a self-incompatible nut crop that has a fruit set of only approx. 30 % of the total number of flowers. Thus, interference of pollination and fertilization by fungicide sprays is of concern, and identification of chemicals having the least detrimental effects would be desirable. The objective of this study was to evaluate the effect of fungicide sprays on stigma morphology in almond using a laboratory spray apparatus that simulated field applications. Four fungicides (azoxystrobin, myclobutanil, iprodione and cyprodinil) were applied, and fresh, unfixed stigmatic surfaces were observed using a scanning electron microscope at 4 and 24 h after spraying. Increased exudate accumulation was induced by azoxystrobin at both time periods, and localized damage and collapse of stigmatic cells were observed after 24 h. Damaged stigmatic papillae exhibited wrinkling, surface distortion or collapse. Likewise, myclobutanil caused significant damage to and collapse of papillae; these were more extensive at later observations. Iprodione had no effect on exudate accumulation but caused marked and severe collapse of stigmatic papillae which was pronounced at 24 h. Cyprodinil promoted a copious increase in exudate secretion and caused the most severe collapse of stigmatic cells of all the fungicides evaluated. Damage was somewhat localized at 4 h but more global at 24 h. This study has verified that certain fungicide sprays have direct detrimental effects on stigma morphology and enhance exudate production in almond flowers.     

Green leaf area decline of wheat flag leaves: the influence of fungicides and relationships with mean grain weight and grain yield

A modified Gompertz model was derived to describe the fractional decline in green area of wheat flag leaves in field experiments where green leaf area at time t=100exp[‐exp(‐k(t‐m))]. Curves fitted over time to visual assessments of green leaf area (% of total leaf area) throughout flag leaf life accounted for more than 98% of variation in 45 of 48 wheat cultivar × fungicide treatment (+/?) comparisons. This data set spanned 17 yr and therefore included cultivars of contrasting parentage and age. In the absence of fungicide, green leaf area decline was associated with drought or infection with a number of foliar pathogens including Septoria tritici (sexual stage Mycospherella graminicola), Erysiphe graminis and Puccinia striiformis. Fungicides applied to the flag leaf included propiconazole, propiconazole plus tridemorph, flusilazole or azoxystrobin. Fungicide effects on m (i.e. time to 37% green area) were closely related to fungicide effects (% of untreated) on mean grain weight (variation accounted for (VAF) = 80%) and grain yield (VAF = 85%).     

Effects of fungicide treatments and variety on development, grain growth and yield of spring barley

The effects of four fungicide treatments for the control of mildew on spring barley were assessed in three field experiments, one in each of the years 1981, 1982, 1983. The fungicide treatments (+/ - triadimenol seed treatment and +/ - triadimefon foliar spray applied during early booting) were chosen to control mildew, and hence affect yield determining processes, at different times in the life of the crop. Two of the experiments also tested different nitrogen amounts and the third tested four varieties differing in their degree of mildew resistance. Mildew appeared too late to affect the production and survival of spikelets and shoots, but reduced average grain weight by reducing the rate of grain growth. Grains in the upper part of the ear had a considerably lower growth rate and final weight than grains in central and basal positions but there was no evidence that the effects of mildew on grain size depended upon grain position within the ear. Mildew incidence increased with increasing nitrogen and varietal susceptibility but there were few significant interactions between these factors and fungicide treatment for grain yield. The degree of mildew control achieved by the seed treatment varied with barley variety. Use of the two successive fungicide treatments did not yield more barley than use of either alone. Amongst varieties, grain positions within the ear and fungicide treatments there was a close correlation between rate of grain growth and final grain weight. Duration of grain growth was not related to rate of grain growth or final grain weight but was inversely correlated with mean temperature during the period of rapid grain growth. The temperature sums during the period of rapid grain growth were similar for the three years and it is suggested that a more precise knowledge of the relationships between mildew incidence, varietal susceptibility and rate of grain growth may enable more accurate predictions to be made about likely yield responses to fungicide treatments.     

Photosynthetic Gas Exchange in Common Bean Submitted to Foliar Sprays of Potassium Silicate,Sodium Molybdate and Fungicide and Infected with Colletotrichum lindemuthianum

This study investigated whether foliar sprays of potassium silicate (KSi), sodium molybdate (NaMo) or a combination of both (KSi + NaMo), with or without the fungicide azoxystrobin (Azox), could reduce anthracnose symptoms, improve photosynthesis and increase yield. Two 2 × 4 factorial experiments, consisting of untreated or fungicide‐treated plants sprayed with KSi, NaMo or KSi + NaMo were arranged in a randomized block design with three replications. The treatments were as follows: (i) KSi; (ii) NaMo; (iii) KSi + NaMo; (iv) Azox; (v) Azox + KSi; (vi) Azox + NaMo; (vii) Azox + KSi + NaMo; and (viii) control (no KSi, NaMo or Azox). The KSi, NaMo and Azox treatments were applied at the rates of 35 g/l, 90 g/ha and 120 g ai/ha, respectively. KSi was applied at 20, 27, 40 and 55 days after sowing (das). NaMo was applied only at 27 das, whereas the fungicide was applied at 27, 40 and 55 das. The plants were inoculated with Colletotrichum lindemuthianum at 23 das. The anthracnose severity was reduced by 64.25% and yield increase by 156.2% in plants sprayed with fungicide compared with non‐sprayed ones. The KSi, NaMo and NaMo + KSi applications reduced anthracnose severity by 31.8, 16.1 and 37.9%, respectively, while the yield increased by 16.8, 18.9 and 63.9%, respectively. There was no difference between treated and non‐treated plants with KSi with respect to the leaf gas exchange parameters C_i, E and g_s. However, A significantly increased by 16.9% in plants treated with Azox. The A was not affected by KSi or NaMo spray; however, it was significantly increased by 12.5% after spraying with NaMo + KSi. In conclusion, bean plants treated with Si and Mo were associated with a decrease in anthracnose as well as an enhancement in photosynthesis activity under field conditions.     

The effect of applied sulphur on the growth, grain yield and control of powdery mildew in spring wheat

During the years 1998 and 1999, two field experiments were conducted at the University of Wales, Aberystwyth, UK, to test the effects of soil‐ and foliar‐applied sulphur (S) in spring wheat. S was applied at 0, 20, 40, 60 kg ha^?1 in 1998 and at 60 kg ha^?1 in 1999, using CaSO₄ as a source for the soil application and micronised S (Thiovit, 80%), with and without an organosilicone adjuvant, as a source for the foliar application. Senescence was retarded and grain yield was increased in 1998, following application of foliar S in conjunction with the organosilicone adjuvant. Application of foliar S was associated with a reduction in the level of mildew (Erysiphe graminis) recorded on the upper leaves and ears of the canopy. In 1999, grain yield was unaffected by treatments. A low level of mildew in the crop, particularly on the ears, is thought to be the reason for the lack of response in spite of the fact that senescence was retarded with foliar S application. A combined application of foliar S and commercial fungicide (cyproconazole) to the crop appeared to be more effective at controlling mildew than either S or fungicide applied alone. The study shows that there may be a role for S in a low‐input/organic wheat production system, where there is a need to reduce artificial inputs.     

Effect on carrot root yield and size distribution of the growth-retardants chlormequat chloride and aminozide

In two experiments, foliar sprays of either chlormequat chloride or aminozide depressed top growth, increased root yield and enhanced leaf and root colour in six carrot cultivars. In the first experiment, a direct correlation between concentration of the two retardants and root yield was apparent within the range 0–2000 mg/1 a.i. applied as run-off sprays to two cultivars. In the second experiment, increases in total root and canning-size yield and root/shoot ratio were obtained with four cultivars, but the magnitude of these effects was dependent on the time at which the retardants were applied and the time of harvest of the crop. The effects of aminozide on root yield were less persistent than those of chlormequat chloride, the yield differences between untreated and aminozide-treated plots decreasing with time after application.     

Take-all and grain yields in sequences of winter wheat crops testing fluquinconazole seed treatment applied in different combinations of years

A seed treatment containing fluquinconazole as the only active ingredient was tested in sequences of up to six consecutive crops of winter wheat. It was applied or not applied in each year, and was tested in all possible combinations with treatments applied in previous years. Take‐all was controlled effectively, and grain yield usually increased, when the disease intensity was moderate or severe in non‐treated crops, but control of the most severe take‐all did not result in acceptable yields or grain quality. Treatment of a first wheat or second wheat with little take‐all did not usually benefit the subsequent crop. Non‐treatment of a crop grown after a treated, diseased crop usually resulted in a marked increase in disease, indicating that treatment had delayed progress of the epidemic. Take‐all was controlled by treatment of a crop grown after a treated, diseased crop but the amount of control and of increased yield was often less than that in a treated crop grown after a non‐treated crop in the same crop sequence. Similar effects of seed treatment were apparent in crops grown on a site with take‐all decline. The alternative fungicide, silthiofam, applied as a seed treatment in the later years of some experiments, was usually as effective as fluquinconazole. From these experiments, it is recommended that: a) fluquinconazole seed treatment should be applied to a second or third wheat crop, grown after a first wheat crop that was managed to avoid rapid take‐all development (e.g. by avoiding very early sowing); b) a break crop should follow the treated crop; c) the seed treatment should not normally be used in longer sequences of wheat or on take‐all decline soil unless it is planned to follow the treated crop with a non‐cereal break.     

Individual and combined effects of dosages of azoxystrobin and epoxiconazole in wheat

The effects of single fungicide applications on Mycosphaerella graminicola (septoria leaf blotch) control and winter wheat yield were evaluated in field trials conducted in central Belgium between 2000 and 2004. Individual applications of 25, 50, 75 and 100% of the manufacturer's recommended dose rates of azoxystrobin and epoxiconazole, and all the combinations of these treatments, were made at GS 39 in 2001 to 2004 and at GS 59 in 2000. Disease assessments were made at growth stage 75, some 7-8 weeks after the last applications. Between 2000 and 2003, no significant difference was observed for disease control between the products when applied alone. With regard to the dose responses, the differences between the recommended dose rates and the 50% reduced dosages were not important. In 2004, azoxystrobin was less effective than epoxiconazole. This was probably the result of strobilurin-resistant isolates of M. graminicola reaching an occurrence of 32% before fungicide application. The combination of different dosages of azoxystrobin and epoxiconazole revealed that there was very little synergy between these products when applied in a single application. The combinations of these products were better than individual applications only when high dosages of both compounds were used.     

The importance of weather and agronomic factors for the overwinter survival of yellow rust (Puccinia striiformis) and subsequent disease risk in commercial wheat crops in England

Disease survey data from 4475 randomly selected crops of wheat from England and Wales during 1985–2000 showed that yellow rust was most prevalent in 1988, 1989, 1990, 1998 and 1999. Disease severity on the upper two leaves was low as >95% crops had received foliar fungicides. Factors affecting the presence or absence (incidence) of yellow rust were investigated using random effects logistic regression (general linear mixed model). This enabled crop management (risk) variables for individual crops to be combined with meteorological variables measured at the county level. Two models are presented that analysed the effect of host genotype on incidence either solely through yellow rust resistance rating (Model 1) or by including both resistance rating (fixed effect) and cultivar (fitted as a random term) (Model 2). In both models, the percentage of crops with yellow rust decreased with cultivar disease resistance ratings ≥3, the occurrence of severe frosts (P < 0.05) of timing of fungicide sprays, previous cropping or summer weather. The use of risk variables associated with overwintering survival may help adjust fungicide inputs to seasonal risk.     

Reduction of Winter Wheat Yield Losses Caused by Stripe Rust through Fungicide Management

Stripe rust of winter bread wheat (Triticum aestivum L.) causes substantial grain yield loss in Central Asia. This study involved two replicated field experiments undertaken in 2009–2010 and 2010–2011 winter wheat crop seasons. The first experiment was conducted to determine grain yield reductions on susceptible winter wheat cultivars using single and two sprays of fungicide at Zadoks growth stages Z61–Z69 in two farmers’ fields in Tajikistan and one farmer's field in Uzbekistan. In the second experiment, four different fungicides at two concentrations were evaluated at Zadoks growth stage Z69. These included three products from BASF – Opus (0.5 l/ha and 1.0 l/ha), Platoon (0.5 l/ha and 1.0 l/ha) and Opera (0.75 l/ha and 1.5 l/ha) – and locally used fungicide Titul 390 (0.5 l/ha and 1.0 l/ha). One and two sprays of fungicides did not differ significantly (P > 0.05) in increasing grain yield. Stripe rust reduced grain yield and 1000‐kernel weight (TKW) from 24 to 39% and from 16 to 24%, respectively. The benefits from the two concentrations of the same fungicide did not consistently resulted in significantly higher grain yield, suggesting that the lower concentrations could be more cost effective. Our study provides important information about the selection of fungicides, spray concentrations and number of spray to control stripe rust and increase grain yield. The findings could play an important role in developing stripe rust management approaches such as fungicide rotation and strategic fungicide applications in Central Asian countries.     

Experiments with foliar sprays of thiabendazole and captafol for control of potato gangrene

In an experiment designed to measure the effect of foliar sprays of fungicides on gangrene in stored tubers thiabendazole but not captafol reduced yield by 30%. Although both fungicides reduced disease incidence in stems and tubers the extent of the reduction was so small that foliar sprays were considered unimportant as a method of control. Sprays of thiabendazole and captafol applied to the haulm 1 wk or 1 wk and 2 wk after desiccation did not reduce the incidence of gangrene in storage.     

Physiological and biochemical response of potato (Solanum tuberosum L. cv. Kara) to O3 and antioxidant chemicals: possible roles of antioxidant enzymes

An Egyptian cultivar of potato (Solanum tuberosum L. cv. Kara) was grown in the field at two locations in northern Egypt: a ‘rural’ and a ‘suburban’ site, from October 2000 and November 2002. The antiozonant ethylenediurea (EDU) and the fungicide chlorothalonil (1,3‐benzenedicarbonitrile‐2,4,5,6 tetrachloroisophthalnitrile) were applied as a foliar spray to plants at both sites. It was found that foliar injury symptoms were reduced greatly in plants treated with EDU and/or chlorothalonil, and the yield of treated plants was higher than that of the untreated ones, with the EDU having a greater protection than chlorothalonil. Antiozonant (EDU) and fungicide (chlorothalonil) combination sprays were even more effective in reducing O₃ injury. Moreover, the percentage of protection was higher in the rural area than in the suburban one, and this was associated with higher levels of O₃ recorded in the rural area. The response to O₃, EDU, and chlorothalonil of the leaf antioxidant scavenger system was examined. Antiozonant‐treated plants had the highest reduced glutathione/oxidised glutathione ratio. The results suggest that EDU and chlorothalonil do not act directly as antiozonant to inhibit O₃ injury but act through maintaining some antioxidant enzymes during O₃ exposure. To the best of knowledge, this is the first report demonstrating the marked enhancement of yield and plant oxidative enzymes by fungicides as a mechanism of protecting plants against noxious oxidative stress from the environment in the developing world.     

Strobilurins Seed Treatment Enhances Resistance of Common Bean Against Bean common mosaic virus

Commercial formulations of strobilurins (azoxystrobin, kresoxim‐methyl, trifloxystrobin and pyraclostrobin) were evaluated for their efficacy against Bean common mosaic virus (BCMV) in screenhouse and field conditions. Highest seed germination and seedling vigour were recorded with 20 μg/ml pyraclostrobin seed treatment in comparison with the control. In screenhouse studies, 76% protection against BCMV was recorded with pyraclostrobin seed treatment at 10 μg/ml. Under field conditions with natural BCMV inoculum, pyraclostrobin seed treatment resulted in 65% protection against BCMV. The protection offered by strobilurins against BCMV was evaluated by ELISA, with lowest immunoreactive values recorded in common bean seedlings raised from seeds treated with pyraclostrobin and kresoxim‐methyl. Strobilurins in addition to exerting a direct positive physiological effect on common bean plants also protect bean plants against BCMV infection in screen house and field conditions. Thus, it is proposed that these reduced‐risk pesticides are potential inducers against BCMV and growth enhancers and could be a beneficial component of integrated disease management of common bean.     

The mixture of kresoxim‐methyl and boscalid,an excellent alternative controlling grey mould caused by Botrytis cinerea

Grey mould, caused by the fungus Botrytis cinerea, is one of the most destructive diseases in greenhouses for which serious fungicide resistance has developed. Between 2003 and 2005, 213 isolates of B. cinerea from two geographical regions were characterised for baseline sensitivity to kresoxim‐methyl. In the absence of salicylhydroxamic acid (SHAM), the mean 50% effective concentration (EC₅₀) values were 6.67 ± 0.61 (mean ± SD) and 0.37 ± 0.10 mg L^?1 during growth and germination, respectively. In the presence of 100 mg L^?1 SHAM, baseline sensitivities were distributed as unimodal curves with mean EC₅₀ values of 2.38 ± 0.21 and 0.28 ± 0.09 mg L^?1 for inhibiting growth and inhibiting germination, respectively. The mixture of kresoxim‐methyl and boscalid showed good control efficacy against strawberry grey mould disease. After the mixture was extensively used on strawberry for 2 years, 50 isolates were collected and determined for their sensitivity to kresoxim‐methyl and boscalid, respectively. The mean EC₅₀ of germination inhibition by boscalid was 0.39 ± 0.08 mg L^?1. The mean EC₅₀ of germination inhibition by kresoxim‐methyl was 0.26 ± 0.07 mg L^?1 in the presence of 100 mg L^?1 SHAM. Sensitivities of B. cinerea to both kresoxim‐methyl and boscalid did not show any significant decrease. These results suggest that their mixture is a satisfactory alternative candidate for management of grey mould disease in greenhouses.     

Possible explanations of synergism in fungicide mixtures against Phytophthom infestans

Single foliar sprays of oxadixyl, mancozeb or cymoxanil alone or the mixtures oxadixyl/mancozeb and oxadixyl/cymoxanil were applied to tomato plants (cv. Baby) one day before inoculating with a sensitive or a phenylamide-resistant strain of Phytophthora infestans. Fungicide mixtures were far more effective in controlling both sensitive and resistant strains compared to the individual components alone, representing significant levels of synergistic interactions. When analysed by the Abbott method, synergy ratios continuously decreased with increasing amounts of fungicides in the mixture. All fungicide mixtures showed higher synergy ratios against resistant strains when using the Abbott method, whereas only mixtures containing cymoxanil showed this phenomenon when using the Wadley method for interpretation of interactions. Synergism significantly decreased when the components were used as foliar split applications with intervals of 48 and 72 h. A combination of a drench application of oxadixyl and a single spray application of mancozeb or cymoxanil resulted in a high level of synergism. The explanation of synergism may be that the exposure of sporangia to sublethal concentrations of one fungicide affects them to an extent that sublethal doses of the other fungicide becomes detrimental.     

Effects of kelp (Macrocystis integrifolia andEcklonia maxima) foliar applications on bean crop growth and nitrogen nutrition under varying soil moisture regimes

A greenhouse experiment was designed to test the effects of two kelp(Macrocystis integrifolia andEcklonia maxima) concentrates, when prepared as foliar sprays, upon bean (Phaseolus vulgaris) growth and N nutrition under three soil moisture regimes. Plant growth and developmental responses in this greenhouse experiment have demonstrated the effectiveness of the two kelp foliar sprays as plant growth regulating substances. Bean growth and developmental responses to the kelp foliar spray treatments were dependent upon the soil moisture regime to which they have been subjected. Although the two kelp foliar sprays had varying and sometimes contrasting effects on bean growth and N nutrition, which were dependent on the soil moisture treatment, their developmental effects upon the number of nodes, shoot/root ratio, leaf area ratio and specific leaf area were quite similar. A soybean callus bioassay demonstrated the presence of cytokinin-like substances and a callus growth antagonist in the kelp concentrate. Increasing dilution of the kelp concentrate disproportionately reduced the callus growth antagonist relative to the growth promoting or cytokinin-like activity.