Weed management in direct-seeded lowland rice under iron toxic sites in Nigeria

Field trials carried out during the wet season of 1987 at Edozhigi in the Southern Guinea Savanna and in 1988 at Bende in the Forest Zones of Nigeria indicate that the performance of rice varieties under iron toxic soils could be improved by delayed flooding due to the application of selective soil persistent herbicides. Yield increments of 33.3% and 76.9% were recorded at Edozhigi when the mixture of oxadiazon plus propanil at 0.5 + 2.4 kg a.i./ha was applied compared with bentazon alone at 3.0 kg a.i./ha under IR26 and Farox 306–3–6 (susceptible). Similarly at Bende, yield increments of 76.1% and 84.6% were obtained when the mixture of piperophos plus dimethametryn at 1.6 + 0.4 kg a.i./ha was applied compared with pre-emergence butachlor alone at 4.0 kg a.i./ha also under IR26 and Farox 306–3–6. Breeding resistance to iron toxicity will be desirable because of poor peristence of herbicides in warm flooded soils.     

Brassinosteroid analogues effects on the yield and quality parameters of greenhouse-grown pepper (Capsicum annuum L.)

The effects of spraying two brassinosteroid analogues, DI-31 and DI-100, were evaluated at concentrations of 4, 8 and 12?ppm together with a seaweed extract and amino acid mixture called Tomex Amin (2.5?l/ha) to enhance their activity. These were sprayed ten times to foliage of pepper var. Orlando grown under greenhouse conditions. Treatment with DI-31 at a dose of 12?ppm (30?mg/ha) resulted in the highest production increases, which were 13.55?% relative to the control with Tomex Amin (T02). Correlation between net photosynthesis increase and yield increase due to DI-31 treatment, which produced the maximum yield increase and also the highest net photosynthesis with significant differences with respect to the control, was observed. This increased yield was caused by an increase in pepper/plant number. The physic-chemical variables related to pepper quality, such as fresh weight, h/d ratio, lobe number/fruit, firmness, colour and ripening index, were similar in the control and treated peppers. Total antioxidant activity and phenolic content was higher in pepper treated over T02. The results showed that sprayed DI-31 may play an important role in increasing the yield of field grown pepper due to an increase in fruits number per plant without any undesirable effects on their nutritive and organoleptic properties.     

The effect of seed and stem base spray treatment with iprodione on white rot disease (Sclerotium cepivorum) in autumn-sown salad onions

Iprodione applied to seed at 250 g a.i./kg controlled white rot in autumn-sown salad onions until July the following year, and reduced losses during the winter caused by Botrytis spp. At 25–150 g a.i./kg seed, iprodione controlled autumn and spring infections but it was less effective later in the summer. Treatment of autumn-sown onions at 50 g a.i./kg seed followed in March by a single stem base spray at 0.031 g a.i./m row (total rate c. 2.4 kg a.i./ha) gave complete control; seed treatment at 25 g a.i./kg followed by a stem base spray at 0.125 g a.i./m row (c. 4.5 kg a.i./ha) was equally effective. Four stem base sprays of iprodione at 0.075 g a.i./m row/spray (9 kg a.i./ha) applied in spring to plants raised from untreated seed, controlled spring and summer infections but yields were low because of losses caused by infection in the previous autumn. A single stem base spray of iprodione at 0.125 g a.i./m row applied in spring to plants raised from thiophanate-methyl treated seed at 125 g a.i./kg gave complete control and high yields.     

Influence of formulation on chlorfenvinphos uptake and cabbage root fly control on radish

Granular and liquid formulations of chlorfenvinphos were applied to a sandy-loam as continuous logarithmically-changing doses of approximately 0.2 to 4.0 kg a.i./ha and radish were sown immediately and 23 days after treatment. After 62 days, insecticide concentrations in the soil had not diminished detectably in the granule treatment but had declined by about 20% in the liquid treatment. In both sowings, residues in the harvested radish were higher, dose-for-dose, from the granule than from the liquid treatment and with both formulations were lower in the second than in the first sowing. Within treatments there were log-log relationships between the dose of insecticide and residue concentrations in the soil and radish. In both sowings the residues were most variable between replicate soil and crop samples from the granule treatment. In the first sowing, cabbage root fly damage was reduced most by the liquid treatment but in the second sowing equivalent doses of the two formulations gave similar protection. At 2.0, 2.24 or 3.0 kg a.i./ha, chlorfenvinphos incorporated before sowing protected radish better than pre-sowing or pre-emergence applications to the soil surface. When applied before sowing, the liquid formulation gave better protection and lower residue concentrations in the radish than the granules. As a post-emergence spray, chlorfenvinphos was much more effective than fonofos, diazinon or triazophos but it was often phytotoxic, decreased yield significantly, left large residues in the radish in two of the four experiments and, in common with other surface treatments, substantially decreased the Z:E chlorfenvinphos isomer ratio. Although a single application of granules protected two successive radish crops, it was concluded that third and subsequent sowings on the same land should probably be treated with smaller doses to limit terminal residues.     

Investigations into the movement of glyphosate from treated to adjacent untreated plants

Transfer of glyphosate from treated to adjacent untreated plants was investigated under glasshouse conditions using wheat and Agropyron repens. When glyphosate was used at concentrations characteristic of conventional field application rates, and where shoot contact was prevented, no symptoms were observed on untreated plants. When there was shoot contact, and when glyphosate was used at 2 kg a. i./ha (10 g a. i./litre), phytotoxic effects were observed on untreated plants. At higher concentrations of glyphosate (90 or 180 g a. i./litre), typical of selective applications with ropewick or roller applicators, evidence of root transfer of herbicide was found. In pot experiments these phytotoxic effects were variable, due, perhaps, to variable amounts of root contact. Confining the roots, by growing the plants in tubes, increased the level of phytotoxicity.     

Chemical control of wheat bulb fly (Delia coarctata) attacking winter wheat in Eastern England, 1969–1981

Dry powder, liquid and microencapsulated formulations of organophosphate and synthetic pyrethroid insecticidal seed treatments were tested as possible alternatives to the standard organochlorine seed treatments for autumn-sown wheat in mineral and organic soils heavily infested with wheat bulb fly eggs and (subsequently) larvae. Retention of insecticides on the seed coat varied from 40% to 120% of the target dose; it was usually good when microencapsulated formulations were used. Chlorfenvinphos, fonofos, isofenphos and triazophos, each applied at 2-0 g a.i./kg seed, were phytotoxic, the symptoms varying from a slight delaying effect upon germination to an adverse effect upon grain yield. Chlorfenvinphos at 0–2 to 2-0 g a.i./kg seed was consistently effective against wheat bulb fly larvae in both mineral and organic soils. Athidathion 0–8 g a.i./kg, carbophenothion 1–2 g a.i./kg, ethion 1–7 g a.i./kg and fonofos (microencapsulated formulations) at 1-0 or 2-0 g a.i./kg were also effective in mineral and organic soils. Of the synthetic pyrethroids tested as seed treatments, permethrin gave excellent results in mineral soils at 1-0 g a.i./kg or in synergised formulations at 0–12 or 0–24 g a.i./kg but was disappointing in organic soils. In a single comparison of seed treatments applied to wheat sown early (14 October) and late (20 November), chlorfenvinphos was effective at both sowing dates whereas athidathion, ethion and pirimiphos-ethyl gave better results in late-sown wheat. A single trial compared deep with shallow sowing of treated seed. Most insecticides performed better on shallow-sown wheat, but chlorfenvinphos was equally effective against the pest at both sowing depths. Most insecticides restricted the numbers of larvae entering host plants but had little or no subsequent effect upon larval survival within attacked shoots. Fonofos and isofenphos, and to a lesser extent chlorfenvinphos, seed treatments additionally killed many larvae within plant shoots.     

The relationship between the entry of isoproturon into Alopecurus myosuroides and its effect on growth and CO2 fixation

Alopecurus myosuroides (blackgrass) was grown in nutrient and with isoproturon added to the solution when plants had three leaves. The transpiration stream coefficient factor was calculated over a period of 96h after treatment to be approximately 1. On this basis isoproturon entry into A. myosuroides was estimated using data for water loss through plants and there was a linear relationship between herbicide entry and plant weight 14 days after treatment. Treatment for at least 7 days with isoproturon at a dose of 1 μg a.i./15 ml nutrient solution (≡ 0.32 × 10^-6M) before returning plants to fresh nutrient was necessary for damage to be still evident after 14 days. This time period corresponded with the reduction of CO₂ exchange to zero as measured by infra-red gas analysis. Some recovery occurred from 6 h treatment with 120 μg a.i. isoproturon/15 ml nutrient solution when assessed after returning plants to untreated nutrient for 14 days. A quicker depletion in CO₂ uptake by blackgrass occurred when both the primary and secondary roots were treated compared with secondary alone but eventually the levels reached were similar. The ‘CALF’ model predicted much higher concentrations of isoproturon than appeared necessary to damage A. myosuroides. This suggests a major influence of climate on the plant and this and other interactions are discussed.     

Control of pea cyst-nematode, Heterodera goettingiana, by small amounts of aldicarb, Du Pont 1410, Ciba-Geigy 10576 or Dowco 275 applied to the soil at planting time

Aldicarb, or Du Pont 1410 (S-methyl-I-(dimethylcarbamoyl)-N-[(methyl-carbamoyl)oxy]thioformimidate), at 2.8–22.4 kg a.i./ha incorporated in the seed-bed before sowing greatly increased the yield of peas in a clay loam and two sandy clay soils infested with pea cyst-nematode, Heterodera goettingiana, and lessened or prevented increase in the number of nematodes. CibaGeigy 10576 (an organophosphorus compound) at 5.6–22.4 kg a.i./ha was similarly effective in a sandy clay soil. Dowco 275 (O, O-diethylO-(6-fluoro-2 pyridyl) phosphorothioate) at 5.6 or 11.2 kg a.i./ha also controlled the nematode well in the clay loam and in a sandy clay soil but although it greatly increased the yield of peas in the clay loam, it did not increase yield in the sandy clay.     

Control of stem nematode, Ditylenchus dipsaci, in onions, by granular nematicides applied to the soil

Aldicarb at 1.4–5.6 kg a.i. ha^-l or oxamyl at 1.3–5.2 kg a.i. ha^-1 applied over the seed furrows during sowing prevented much of the damage resulting from stem nematode attack in spring-sown onions. Rotting of bulbs in store due to stem nematode infestation was sometimes lessened by these treatments. Neither sowing onion seeds on soil ridges, nor applying aldicarb in two equal doses, one over the seed furrows during sowing, the other over the plants mid-season, controlled the nematode better or increased onion yields more than a single equivalent dose over the seed furrows. Applied as two doses in this way, aldicarb was sometimes more effective against the nematode in summer-sown onions than was an equivalent amount applied over the seed furrows during sowing. Only 2.5 kg or less aldicarb ha^-1 can be applied to onions without leaving unacceptable residues (>0.15 μg g^-1) in the harvested bulbs.     

Exogenously-sourced ethylene increases stomatal conductance, photosynthesis, and growth under optimal and deficient nitrogen fertilization in mustard

In order to ascertain the stomatal and photosynthetic responses of mustard to ethylene under varying N availability, photosynthetic characteristics of mustard grown with optimal (80 mg N kg(-1) soil) or low (40 mg N kg(-1) soil) N were studied after the application of an ethylene-releasing compound, ethephon (2-chloroethyl phosphonic acid) at 40 days after sowing (DAS). The availability of N influenced ethylene evolution and affected stomatal conductance and photosynthesis. The effect of ethylene was smaller under deficient N where plants contained higher glucose (Glc) sensitivity, despite high ethylene evolution even in the absence of ethephon, potentially because the plants were less sensitive to ethylene per se. Ethephon application at each level of N increased ethylene and decreased Glc sensitivity, which increased photosynthesis via its effect on the photosynthetic machinery and effects on stomatal conductance. Plants grown with sufficient-N and treated with 200 μl l(-1) ethephon exhibited optimal ethylene, the greatest stomatal conductance and photosynthesis, and growth. These plants made maximum use of available N and exhibited the highest nitrogen-use efficiency (NUE).     

Insect responses to plant water deficits. I. Effect of water deficits in soybean plants on the feeding preference of Mexican bean beetle larvae

Abstract. 1. We examined the preference of larvae of the Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera: Coccinellidae), for foliage of soybean ( Glycine max [L.] Merr.) grown under several levels of water deficit. Third instar larvae were exposed simultaneously to excised foliage from plants that were either well-watered (control) or had experienced water deficits (treatment).
2. Water-deficient plants were re-watered 12 h prior to initiating feeding trials to eliminate physical differences between control and treatment foliage such as leaf water potential, diffusive resistance, relative water content, and foliage toughness.
3. Examination of the free amino acid contents of re-watered and excised foliage indicated that amino acid concentrations increased markedly in foliage grown under water deficits, and that this increase persisted during the preference tests.
4. Larvae preferred control foliage, but shifted preference to treatment foliage under mild water deficits. When the leaf water potential of water-deficient treatment foliage was lower than – 1.13 MPa or when it was more than 0.5 MPa lower than that of control foliage, larvae preferred to feed on foliage from well-watered control plants.
5. The expression of preference for well-watered control foliage was coincident with increases in the concentrations of total free amino acids and individual free amino acids in the water-deficient treatment foliage.
6. These results are inconsistent with White's (1974) hypothesis because Mexican bean beetle larvae avoid plants grown under water deficits that have increased concentrations of free amino acids.     

The interaction of protectants with EPTC on field bean, and tri-allate on wheat

Protectants (antidotes) were tested for their potential to protect field beans (Vicia faba L.) from EPTC damage, or wheat (Triticum aestivum L.) from triallate damage. For both crops there was considerable variation in the degree of protection shown from similar treatments in different experiments. For field bean, a seed treatment of 1,8-naphthalic anhydride (NA) at 5 mg/g seed gave some protection from EPTC applied pre-planting at 4–8 kg a.i./ha but not in all experiments. NA also caused marked chlorosis of the foliage. N, N-diallyl-2, 2-dichloroacetamide (R25788) at 20 mg/g seed severely damaged field bean in the absence of herbicide but 5 mg/g gave comparable protection from EPTC to that given by NA and did not cause chlorosis. Mixing R25788 with EPTC in the spray tank gave reduced protection. In a single experiment R4115 (chemistry undisclosed) gave some protection against EPTC damage. For wheat, a seed treatment of 5–20 mg/g NA sometimes countered damage from tri-allate applied pre-planting at 1 kg a.i./ha but not generally from higher doses. R25788 sometimes protected from weight loss due to tri-allate at 1 kg a.i./ha but not from damage symptoms, whereas R4115 at 20 mg/g seed alleviated these symptoms but did not prevent weight loss. R25788 at 4 kg a.i./ha mixed in the spray tank with the herbicide partially reduced weight loss and damage symptoms from a dose of 2 kg a.i./ha. Some treatments of R29148 gave complete protection from tri-allate at 1 kg a.i./ha. The results are discussed in the context of the full data from the two series of experiments.     

Barrier spraying to control the malaria vector Anopheles albimanus: laboratory and field evaluation in the Dominican Republic

Abstract. To develop a new strategy for control of exophilic/exophagic malaria vectors which rest on peridomestic foliage, Anopheles albimanus was used for laboratory bioassays of mosquito adulticides applied to various vegetation types. Of the three classes of insecticide tested, the pyrethroid (permethrin at 112 g/ha) showed greater foliar persistence than either the carbamate (bendiocarb at 340g/ha) or the organophosphorus compound (malathion at 277g/ha). Field evaluation of barrier spraying against An.albimanus was evaluated in rural villages of southwest Dominican Republic during 1989. The pyrethroid deltamethrin was sprayed aerially for ultra-low volume application at treatment rates of 17-19ga.i./ha in a radius of 500m around two villages. An.albimanus were monitored by light-traps and human bait collections at both treated villages, compared with two similar untreated villages, up to 9 nights post-treatment. Densities of female An.albimanus were significantly reduced in the sprayed villages for at least 8 or 9 nights. Further evaluation of barrier spraying is recommended to determine optimal pyrethroid formulations and applications rates, their impact on non-target fauna and efficacy against malaria transmission.     

Chemical control of onion fly, Delia antiqua

In nine trials done in 1972-4 seed treatments reduced attacks of onion fly larvae very effectively and most of the organophosphorus formulations gave protection up to harvest, 12–17 wk after sowing. Pirimiphos-ethyl and isofen-phos each at 10 or 20 g a.i./kg seed controlled onion fly larvae well and they were not seriously phytotoxic in any of the trials. Chlorpyrifos, trichloronate, ethion, iodofenphos, chlorfenvinphos wettable powder or triazophos all at iog a.i./kg seed were also effective, but they were tested in fewer trials. Diazinon at 10 or 20 g a.i./kg seed, carbophenothion and chlorfenvinphos liquid seed dressing at 10 g a.i./kg seed controlled onion fly well, but in some trials they were phytotoxic; methiocarb, mecarphon and oxamyl were much less effective. At 1–12 kg a.i./ha chlorfenvinphos granules applied over the rows shortly before the attack was expected was the best granular formulation, but it was not as effective as the better seed treatments.     

Chemical control of the cabbage stem flea beetle, Psy Modes chrysocephala, on winter oil-seed rape

In East Anglia, from 1974 to 1976, field experiments were carried out on the chemical control of the cabbage stem flea beetle (PsyModes chrysocephala). Carbofuran, 5% granules, proved an outstanding autumn preventive and mid-winter eradicant treatment under both wet and dry conditions, with 1–5-2-24 kg a.i./ha giving virtually 100% control of larvae. Fonofos and phorate granules at 2–24 kg a.i./ha were also effective. AC 92 100 and thiofanox granules were less extensively tested but both gave good control of P. chrysocephala. Several materials showed little or no activity against the pest. The effective preventive granule treatments were all superior to a standard spray of gamma-HCH.     

Effects of dalapon and TCA on the growth and yield of oilseed rape (Brassica napus)

The tolerance of oilseed rape (Brassica napus cv. Jet Neuf) to the herbicides dalapon and TCA was studied in two series of 10 experiments over four years. TCA (7.6–30.4 kg a.i./ha) was applied pre-emergence and dalapon (2.9–11.6 kg a.i./ha) was sprayed post-emergence between September and November at two growth stages (2–5, 4–7 leaves). Dalapon at all doses caused the leaves to appear yellow-green in colour and at the higher rates (5.8–11.6 kg a.i./ha), especially when applied at the later of the two growth stages, scorched the leaf margins and stunted the plants. TCA also caused the leaves to appear yellow-green and was noted to affect the retention of water by the leaf surfaces. In general the visible effects of treatment with dalapon were more severe than those of TCA. The effects of these two herbicides on rape seed yields were variable, with some trials showing statistically significant reductions and others none. However by combining the results of trials with similar treatments some underlying trends were identified. In the overall analyses dalapon at 11.6 kg a.i./ha, applied at both growth stages and at 5.8 kg a.i./ha, applied at the later one, reduced yields significantly. TCA at 15.2, 22.8 and 30.4 kg a.i./ha also caused significant yield reductions in the combined analyses. Further statistical analysis questioned the safety of the lower rates of both herbicides, which were similar to those recommended by the manufacturers. The severity of the foliar damage caused by dalapon was well correlated with the risk of significant yield reductions but not with the actual percentage loss of yield. No such correlations were possible with TCA as the visual symptoms were similar on all sites and were unaffected by dose. Recent changes in agricultural practices and in crop cultivar do not appear to have altered the sensitivity of rape to dalapon and TCA appreciably.     

Control of Globodera rostochiensis in Relation to Method of Applying Nematodes

Soaking potato tuber pieces for 15 min in 8,000 μg/ml of oxamyl just before planting reduced the number of Globodera rostochiensis cysts that developed on potato roots, but this treatment was phytotoxic. Five foliar applications of 1.12 kg a.i./ha of oxamyl or carbofuran at 10-day intervals beginning when 90% of the plants had emerged suppressed increase in G. rostochiensis densities. Similar foliar applications of phenamiphos were ineffective in controlling G. rostochiensis. Soil applications (in the row at planting) of aldicarb, carbofuran, phenamiphos, ethoprop, and oxamyl at 5.6 kg a.i./ha reduced the numbers of white females that developed on potato roots, but only those treatments involving aldicarb and oxamyl suppressed G. rostochiensis population increase. Combined soil and foliar treatments did not provide any advantage over soil treatment alone, as soil applications of 5.6 kg a.i./ha alone were equal to, or better than, combined soil (3.4 kg a.i./ha) and foliar (2.2 kg a.i./ha) applications in controlling G. rostochiensis.     

Elevated CO2 alleviates the impact of drought on barley improving water status by lowering stomatal conductance and delaying its effects on photosynthesis

We analysed the impact of elevated CO₂ on water relations, water use efficiency and photosynthetic gas exchange in barley (Hordeum vulgare L.) under wet and drying soil conditions. Soil moisture was less depleted under elevated compared to ambient [CO₂]. Elevated CO₂ had no significant effect on the water relations of irrigated plants, except on whole plant hydraulic conductance, which was markedly decreased at elevated compared to ambient CO₂ concentrations. The values of relative water content, water potential and osmotic potential were higher under elevated CO₂ during the entire drought period. The better water status of water-limited plants grown at elevated CO₂ was the result of stomatal control rather than of osmotic adjustment. Despite the low stomatal conductance produced by elevated CO₂, net photosynthesis was higher under elevated than ambient CO₂ concentrations. With water shortage, photosynthesis was maintained for longer at higher rates under elevated CO₂. The reduction of stomatal conductance and therefore transpiration, and the enhancement of carbon assimilation by elevated CO₂, increased instantaneous and whole plant water use efficiency in both irrigated and droughted plants. Thus, the metabolism of barley plants grown under elevated CO₂ and moderate or mild water deficit conditions is benefited by increased photosynthesis and lower transpiration. The reduction in plant water use results in a marked increase in soil water content which delays the onset and severity of water deficit.     

Bahiagrass,Corn, Cotton Rotations,and Pesticides for Managing Nematodes,Diseases, and Insects on Peanut

Florunner peanut was grown after 1 and 2 years of Tifton 9 bahiagrass, corn, cotton, and continuous peanut as whole-plots. Pesticide treatments aldicarb (3.4 kg a.i./ha), flutolanil (1.7 kg a.i./ha), aldicarb + flutolanil, and untreated (control) were sub-plots. Numbers of Meloidogyne arenaria second-stage juveniles in the soil and root-gall indices of peanut at harvest were consistently lower in plots treated with aldicarb and aldicarb + flutolanil than in flutolanil-treated and untreated plots. Percentages of peanut leaflets damaged by thrips and leafhoppers were consistently greater in flutolaniltreated and untreated plots than in plots treated with aldicarb or aldicarb + flutolanil but not affected by cropping sequences. Incidence of southern stem rot was moderate to high for all chemical treatments except those that included flutolanil. Stem rot loci were low in peanut following 2 years of bahiagrass, intermediate following 2 years of corn or cotton, and highest in continuous peanut. Rhizoctonia limb rot was more severe in the peanut monoculture than in peanut following 2 years of bahiagrass, corn, or cotton. Flutolanil alone or combined with aldicarb suppressed limb rot compared with aldicarb-treated and untreated plots. Peanut pod yields were 4,186 kg/ha from aldicarb + flutolanil-treated plots, 3,627 kg/ha from aldicarb-treated plots, 3,426 kg/ha from flutolanil-treated plots, and 3,056 kg/ha from untreated plots. Yields of peanut following 2 years of bahiagrass, corn, and cotton were 29% to 33% higher than yield of monocultured peanut.