THE USE OF ENDRIN AND OTHER INSECTICIDES AGAINST LETTUCE ROOT APHID, PEMPHIGUS BURSARIUS L

Several insecticides have been used as protectants against lettuce root aphid, including, in 1955, lindane, schradan, aldrin and endrin; the last-named giving the most promising results. With a dressing of an equal weight of 50% endrin dust added to lettuce seed, 86% reduction in aphid numbers was obtained. In 1957, a seed dressing with endrin also gave a good control, which was superior to that obtained with thimet 44D. However, in 1956 and 1958 endrin seed dressing failed to control the aphid. When a seed dressing with endrin was supplemented by an endrin spray applied to the seedlings a consistently good control resulted.
A high level of aphid control was obtained in 1958 with two sprays of diazinon applied along the lettuce rows, the first applied after singling and the other at the early rosette stage. Diazinon or endrin, applied to the soil at 4 lb. actual insecticide/acre and rotavated into the top 3 in. before sowing, also gave high levels of control.
No recommendations for the use of endrin on lettuce can be made until levels and persistence of residues are known.     

FACTORS AFFECTING INFECTION GRADIENTS FROM A POINT SOURCE OF PUCCINIA POLYSORA IN A PLOT OF ZEA MAYS

Two plots of Zea mays were planted in April and September, respectively, at Ibadan, Nigeria during 1956. A point source of inoculum consisting of potted maize plants heavily infected with the American corn rust, Puccinia polysora Underw., was introduced at pre-arranged times before the plots became naturally infected. Disease gradients from these point sources of infection were assessed by the number of pustules subsequently appearing on plants along the circumferences of concentric circles around the source of infection. 'Control' plots were planted at the same time as the main trial and the pattern of natural infection was observed in an attempt to assess the degree of contamination in the main experiment.
In the centre of the main experiment a volumetric spore trap gave continuous records of the uredospore content of the atmosphere immediately above the crop during both plantings for periods of 2 weeks before planting until 2 weeks after the last assessment of infection.
The forms of the disease gradients were considerably altered by several factors—principally contamination by inoculum from outside sources, the method of assessment and the time at which the assessments were made.     

Seasonal variations in the activity in soil of Phytophthora cactorum, P. syringae and P. citricola in relation to collar rot disease of apple

Phytophthora species were isolated from infested orchard soils using apple fruit as bait at intervals during the periods July 1956 to August 1957, January 1957 to June 1958, and January 1969 to June 1970. When baited soils were kept out of doors P. cactorum and P. citricola were isolated only from April or May to October, when mean temperatures exceeded 8 and 10 °C respectively; P. syringae was isolated in all months except June, July and August.
The results did not suggest that the incidence of these species was particularly associated with apple as a host plant, but the periods of activity of P. cactorum and P. syringae in soils coincided closely with the periods when apple trees were susceptible to infection by either pathogen. With collar rot disease caused by P. cactorum it was considered that, the time of commencement of activity of the pathogen in the soil, together with the availability of water, might be critical in determining the severity of disease outbreaks.     

EXPERIMENTS ON THE CONTROL OF BOTRYTIS DISEASE OF LETTUCE

Experiments were made during 1955-57 on the fungicidal control of Botrytis attack on lettuce, cv. May Queen, matured in frames from November to April, and cv. Trocadero Improved, grown as seedlings in frames from November to March and then matured in the field from March to June. The frame lettuce were treated during their whole period of growth and the field lettuce in the seedling stage only.
On both types, 0.33% thiram sprays applied on up to five occasions gave the best control of disease: 5% tecnazene dust was effective on the frame crop, in 2 out of 3 years when applied to the plants and also when incorporated in the top soil at the rate of 15 g. per sq.yd. Tecnazene applications did not give a good control of the disease on the field crop. Sprays with 0.25% captan were almost as effective as the thiram treatments on the field lettuce but not on the frame crop.     

THE EFFECT OF CERTAIN PREDATORS ON THE NUMBERS OF CABBAGE ROOT FLY (ERIOISCHIA BRASSICAE (BOUCHÉ)) AND ON THE SUBSEQUENT DAMAGE CAUSED BY THE PEST

To determine the importance of beetle predators on the natural control of cabbage root fly, experiments were carried out in 1958 and 1959 using various types of barriers to obtain different levels of beetle populations on cauliflower plots. A barrier of DDT-treated straw, placed in the soil around some plots, decreased the numbers of beetles within them and allowed a greater number of eggs and larvae of cabbage root fly to survive than on the untreated plots, resulting in a greater crop damage. Another type of barrier allowed the beetles to enter plots but made it difficult for them to leave. On these, fewer cabbage root-fly eggs and larvae survived and the crop damage was much less than on the plots surrounded by straw barriers. Where plants were treated with insecticide the root-fly population was reduced to a minimum and crop yields were considerably increased. The insecticide, however, caused a reduction in the numbers of predatory beetles.     

STUDIES ON SOIL POPULATION OF CONTARINIA PISI WINN. IN 1957 IN YORKSHIRE AND LANCASHIRE

For studying the population of pea-midge cocoons, larvae and pupae in the soil, a new method of examining the 'float' obtained from washing soil through the wet-extraction apparatus is described.
Examination of soil samples in the summer of 1957 from fields which carried heavily attacked pea crops in 1956 indicated that pupae were present at depths of 0–3, 3–6, 6–9 in., respectively, from 18 June onwards, and that the peak emergence of midges was in the period 28 June-2 July; observations on adult activity in pea fields confirmed this. Small numbers of pupae were recovered throughout July.
Similar studies on pea fields in 1957 showed the build-up of the cocoon population and the rate of pupation of this generation of larvae. The first flight of 1957 was composed of individuals from the 1956 generation and was far larger than the second flight, which was composed of some 1956 generation and part of the first 1957 generation.
There were indications that increases of temperature might accelerate pupation with a resulting earlier emergence of adults.
The size of midge populations recorded from soil from green pea and dry-harvesting pea fields tended to be similar and appeared to be related to sowing date.     

THE USE OF SOIL INSECTICIDES TO CONTROL POTATO APHIDS AND VIRUS DISEASES

A replicated trial was done to find whether the insecticides Thimet and Rogor applied in the soil affected the spread of aphid-transmitted viruses from infected to healthy plants with potato crops. The insecticides were applied at planting as activated carbon formulations at rates equal in cost to three sprays with DDT emulsion at 2 lb. DDT per acre. The infected plants were removed (rogued) in late June.
Thimet applied along the furrows with the fertilizer, and Rogor applied in individual doses beneath each tuber, kept the plants free from aphids from a week after the plants emerged until early August. Thimet in individual doses was less effective but greatly decreased the aphid infestation. All treatments prevented or greatly decreased the spread of leaf-roll virus, but they only slightly decreased the spread of virus Y. No treatment damaged the plants or depressed yields significantly.
Tubers harvested from the plots treated with insecticides contained only very small quantities of the insecticides, but shoots from them, when infested with adult Myzus persicae (Sulz.), carried fewer aphids a week after infestation than did shoots from control tubers. Shoots of tubers from treated plots also grew more slowly than those from the controls.
The aphicidal efficiency of Thimet applied as individual doses separated from the tubers by distances of up to 6 in., decreased as the distance increased, but the effect of distance became less as time passed.
Reasons for the differences in the behaviour of the insecticides are discussed, and the possibilities that the method offers to control virus diseases. The application of insecticides to soil promises to be a useful way of controlling the spread of viruses, provided the harvested crop is free from toxic residues.     

INVESTIGATION OF FIRE-BLIGHT OF PEAR IN ENGLAND

Outbreaks of fire-blight, caused by Erwinia amylovora , in Kentish orchards during 1957 constitute the first authenticated record of the disease in Europe. The origin of the disease is unknown, but evidence suggests that it was not present in the orchards prior to 1957.
The seasonal development and symptoms of the disease are described in detail. Fire-blight attacked trees only during the growing season; infection began in the blossoms, particularly summer blossoms, and spread into the branches forming cankers, in many of which the pathogen remained viable during the winter 1957–8. In the orchards examined there was a higher incidence of new infections by July 1958 on trees attacked the previous year than on those which were then healthy, and this is discussed in relation to overwintering sources of inoculum. The distribution of the disease in orchards during 1957 and 1958 was consistent with spread by pollinating insects rather than rain.
The outstanding susceptibility of the variety Laxton's Superb in all localities was attributed partly to its tendency to produce abundant secondary blossom. Inoculations of blossoms, fruits, shoots and branches showed it also to have less inherent resistance than the varieties Williams's Bon Chrétien and Conference, neither of which has been seriously affected in the field. The progress of symptoms following inoculation of pear and infection experiments with apple, Cotoneaster sp., Pyracantha sp., and other hosts, are described.
A comparison of climatic conditions favouring the disease in the U.S.A., i.e. high temperatures and high humidity, with meteorological records at East Malling, suggests that epidemic infection of spring blossom would be exceptional in this country.     

STUDIES ON THE IMPORTANCE OF WILD BEET AS A SOURCE OF PATHOGENS FOR THE SUGAR-BEET CROP

Beet yellows virus, beet mosaic virus, rust ( Uromyces betae (Pers) Lév.), and downy mildew ( Peronospora schachtii Fuckel.) were found to be common in wild beet ( Beta vulgaris s.-sp. maritima L.) growing on the foreshores of south Wales and southern England. The virus diseases were more prevalent in southeast England than in the west, rust more in the west than in the east, and downy mildew is equally prevalent in all regions.
Beet yellows is the most commercially important disease and is more common in sugar-beet crops in East Anglia than elsewhere in Great Britain. There was no evidence that beet yellows spread in East Anglia from wild beet to nearby sugar-beet crops during the springs of 1958 or 1959, and Myzus persicae Sulz., the principal vector of yellows, was rarely found on wild beet growing on the foreshore.
In glasshouse experiments aphids colonized sugar-beet plants watered with tap water in preference to those watered with sea water. Daily watering with sea water made plants unpalatable to aphids within 14 days. Aphids also preferred leaves sprayed with distilled water to those that had been sprayed with sea water. Salt solutions gave results similar to those obtained with sea water.     

STUDIES ON SYSTEMIC FUNGICIDES. I. FUNGICIDAL PROPERTIES OF THE ARYLOXYALKYLCARBOXYLIC ACIDS

A method is described for assessing the systemic activity of compounds in checking the infection of broad bean ( Vicia faba ) by the fungi Botrytis cinerea or B. fabae. Treatment consisted in allowing the roots of young seedlings to stand in a solution containing 10 p.p.m. of the chemical for 2–3 weeks. The plants, together with controls, were then inoculated and when symptoms had had time to develop, the degree of chocolate spot infection was assessed. Several methods of disease assessment were examined and are critically discussed.
Certain phenoxyalkylcarboxylic acids tested by this method consistently gave a reduction in the mean size of fungus lesions on the bean leaves, clearly indicating systemic fungicidal action. The most promising substances were 2:4:6-trichlorophenoxyacetic, pentachlorophenoxyacetic and pentachlorophenoxy iso butyric acids. Further experiments with these compounds involving soil treatment, stem injection and spray application are described, and in most cases systemic fungicidal activity was clearly demonstrated. Certain compounds caused visible damage to the plants or resulted in a reduction in growth.
The results presented indicate that phenoxy acids can be fairly readily translocated in bean plants and that they tend to accumulate in actively growing tissues. It is considered unlikely, however, that they persist for long periods in plant tissue.
In the soil, the compounds appeared to remain effective for a considerable time, particularly the less soluble pentachloro acids, suggesting that soil application might provide a safe and useful method of treatment.     

EXPERIMENTS IN THE SUDAN GEZIRA ON CONTROL OF WILT OF DOLICHOS BEAN (DOLICHOS LABLAB) ASSOCIATED WITH ATTACK BY COCKCHAFER GRUBS (SCHIZONYCHA SP.)

Wilt of dolichos bean ( Dolichos lablab ) in the Sudan Gezira appeared to be due primarily to cockchafer grubs ( Schizonycha sp.) in the soil attacking the hypocotyls or roots of plants up to about 6 weeks after sowing. Many wilted plants also showed symptoms of ashy stem blight ( Macrophomina phaseoli ), but in these the fungus was probably a secondary invader rotting roots weakened or damaged by unfavourable soil conditions or insects. Wilt was often severe in dolichos sown on land cropped to sorghum ( Sorghum vulgare ) in the preceding season, sorghum roots in the soil harbouring the grubs. Under moderate grub attack seed dressings containing organomercurial and γ-benzene hexachloride (BHC) gave satisfactory-protection at 0.089%γ-BHC/seed but were inadequate when wilt was severe. Dieldrin and aldrin at 0.044 or 0.089%/seed gave excellent protection in all experiments, but their performance under exceptionally severe wilt conditions has yet to be tested, as also the relative efficiencies of seed treatment and soil treatment under such conditions. Fungicide-insecticide seed treatment also reduced preemergence rotting of germinating seeds due to grub attack.
Wilt rarely occurred in dolichos planted on land fallow in the preceding season, but, even in the apparent absence of wilt, seed treatment often appreciably improved emergence, plant populations, growth and yields. These effects possibly resulted from control of root damage by soil insects, such damage reducing growth and yields but not sufficiently severely to cause wilting. Pending further investigation a powder seed dressing containing organomercurial plus 20% dieldrin, and applied at 1:450 by weight to seed (about 5–6 g./acre of dieldrin), is recommended for dolichos bean in the Gezira.     

Production and prevention of frenching of tobacco grown in the greenhouse

Summary The induction and elimination of frenching capacity in soils was studied in the greenhouse. It was found possible to induce this physiological disease in tobacco plants grown in normal soils following partial steam sterilization. High counts ofBacillus cereus Frankland and Frankland, the assumed causal agent, also resulted. Lime was added to soil neutrality, together with high dicalcium phosphate and a moderate quantity of cellulose. Growing plants with bottom heat (35°C) was of great aid in shortening duration of tests. Use of a method of successive plantings progressively depleted the soil of nitrogen and was necessary to obtain uniform and reproduceable results. Results with fertilizer ingredients were inconclusive except that low soil nitrogen, low acidity and high phosphate tended to increase frenching. Nitrogen deficiency and frenching symptoms were distinctly different and appeared independently of each other.The converse experiments at three levels of soil acidity and four of potassium nitrate gave coordinating results. Acidity and abundant nitrate diminished or prevented frenching of the plants, without however eliminating frenching capacity of the soil.     

THE CONTROL OF DISEASES OF LETTUCE BY THE USE OF ANTAGONISTIC ORGANISMS II. THE CONTROL OF RHIZOCTONIA SOLANI KUHN.

The antagonism of a number of bacteria, actinomycetes and fungi in pure culture on soil extract agar has been investigated. A considerable number of each of the three groups were highly antagonistic at 25° C., fewer were active at 15° C. and only a very limited number were effective at 5° C.
In greenhouse experiments damping-off of lettuce seedlings was substantially controlled by selected antagonists in sterile sand, soil or in sand/soil mixtures. Under similar conditions in unsterile soil, forms highly antagonistic in pure culture were generally ineffective in controlling disease. In one experiment control of disease in natural soil was obtained by the use of soil amendments, the effect being enhanced by the inoculation of one of these amendments with suspensions of antagonists.
Attempts to control disease in the field by the use of soil amendments are described. In one year a substantial increase in the stand of healthy seedlings was obtained with certain treatments.     

THE EFFECTS OF SPRAY TREATMENTS ON INFESTATION OF THE OAT CROP BY THE FRIT FLY (OSCINELLA FRIT L.)

Criteria are given for the timing and assessment of the effect of sprays on experimental plots, based on biological observations at Silwood Park from 1950 to 1955 and on previous work.
A preliminary experiment on small plots in 1952 indicated that 'blanket spraying' with DDT and parathion throughout the life of the crop gave protection against both tiller and grain attack. A more detailed replicated plot trial in 1953 showed that for oats planted on 22 April two carefully timed tiller sprays with parathion reduced tiller infestation from 31 to 3%. Six panicle sprays at weekly intervals reduced a heavy grain attack of 60% to 13%. Dieldrin was also effective but significantly less so than parathion. Much of the damage to the crop was caused by weed growth following initial loss of the primary oat shoots.
In 1954 and 1955 two and three parathion sprays were applied to 2-acre fields in order to study recolonization. Despite almost complete control of the tiller generation, a normal evenly distributed infestation of the panicles was found.
It is concluded that good control of the tiller generation may best be achieved by a spray programme based on knowledge of the phenology of the fly combined with that of the crop. The first general emergence in early May is likely to be critical.
Reinvasion of a sprayed crop may take place within 4–5 days and panicle infestation may not be causally related to tiller infestation in the same field.     

WILT OF LUCERNE CAUSED BY SPECIES OF VERTICILLIUM

A wilt disease of lucerne caused by species of Verticillium is described: at twenty-eight disease areas in England and Wales the pathogen was V. albo-atrum , while at one site it was V. dahliae . Both pathogens form superficial conidia on the basal regions of infected stems. It is shown that V. albo-atrum is introduced into a new area in contaminated plant material harvested with the seed from an infected crop. Rapid secondary spread of the disease follows the dissemination of spores from infected stems, and by contact of these and transported fragments of diseased tissues with the wounded surfaces of recently cut lucerne plants. It is recommended that seed should be collected only from healthy crops and that machinery, footwear, etc. should be disinfected before leaving a site of infection.
Manurial trials showed that the incidence of wilt induced by V. albo-atrum was very severe under all soil conditions tested, whereas V. dahliae is a virulent pathogen only to plants in soil rich in superphosphate. Generally the more vigorous the growth of the lucerne–in soils rich in potash and hoof and horn–the more rapid is both the onset of wilt and the resulting secondary spread of the disease throughout the crop.     

Interaction of post harvest disease control treatments and gamma irradiation on mangoes

The effects of gamma irradiation and disease control treatments on disease severity and post harvest quality of several mango cultivars were investigated.
In mangoes cv. Kensington Pride, irradiation doses ranging from 300–1200 Gy reduced disease, but the level of control was not commercially acceptable. Hot benomyl immediately followed by irradiation provided effective control of anthracnose (Colletotrichum gloeosporioides) and stem end rot (Dothiorella dominicana) during short-term storage (15 days at 20°C). The effects of the two treatments were additive.
Satisfactory disease control was achieved during long term controlled atmosphere storage when mangoes were treated with hot benomyl followed by prochloraz and then irradiated. Effects of fungicide treatment and irradiation were additive. Fungicide, or irradiation treatments alone, were unsatisfactory.
Irradiation of cv. Kensington Pride at doses in excess of 600 Gy caused unacceptable surface damage (i.e. lenticel spotting, surface discolouration and retardation of degreening) which was particularly severe after long-term controlled atmosphere storage.
In a separate short-term storage trial, several other mango cultivars were assessed. Hot benomyl followed by prochloraz controlled anthracnose on all cultivars and stem end rot on some. Irradiation at 600 Gy contributed only minor improvements to disease control. The severity of surface damage that developed following irradiation and fungicide treatment varied with cultivars.     

粉剂防治粘虫Pseudaletia separata (Walker)研究

粘虫Pseudaletia separata(Walker)是粮食作物的毁灭性害虫,也是全国农业发展纲要(修正草案)所规定要消灭的八大害虫之一。粘虫在大发生时为害面积很广,虫体发育迅速,食量很大,过去多采用人工器械捕打办法,但不能澈底解决问题,尤其在作物密植的情况下,捕打也发生了困难,常因捕打时将作物践踏而引起损失,因此要求在发生时应用化学防治方法,以达到迅速消灭为害之目的。     

Spraying bananas in Fiji to control black leaf streak disease

Three sprays, maneb in water applied by hydraulic knapsack sprayer and maneb in an oil/water emulsion or an oil/water emulsion alone applied by mistblower were compared for the control of black leaf streak disease of banana caused by Mycosphaerella sp.
Although there were no differences in yield in the 'plant' crop, maneb, especially as a water-based spray, resulted in much better disease control and leaf survival. Oil seemed to have an adverse effect on fruit quality but not on plant growth.
Since it is unlikely that oil alone will adequately control the disease in ratoon crops fungicides may be necessary.     

Integrated control of white rot disease on beans caused by Sclerotinia sclerotiorum using Contans® and reduced fungicides application

This study was conducted to determine the compatibility of Contans® (Coniothyrium minitans) with fungicides against Sclerotinia sclerotiorum. Results showed that both Contans® and Topsin® significantly reduced the disease incidence caused by S. sclerotiorum by 90% and 95% survival plants, respectively when they were individually applied and compared to control. While, soil application of Contans® and Sumisclex mixture was the most effective in suppressing the white rot disease incidence that produced 100% survival plants, application of C. minitans combined with the reduced doses of fungicides would be advantageous in saving labor cost, thus increasing production efficiency of bean.     

The Toxic Action of Molybdenum in Relation to Soils and Crops

The harmful effect of molybdenum on animals is well established, but there is comparatively little knowledge of the conditions in which molybdenum is poisonous to plants. Obvious differences in response to molybdenum poisoning in different soils have been previously noted, but no adequate explanation has been put forward.
Tomatoes grown in ordinary loam showed little outward sign of poisoning with heavy doses of sodium molybdate, but some depression of crop occasionally occurred, especially when the dose was divided into early and late treatments. The response varied with season and variety. On certain light and fen soils the plants were killed at an early stage with the heavier dressing of molybdate, and seriously injured with the lighter dose, the leaves showing the golden colour characteristic of molybdenum poisoning in various plants.
The reaction of different crops varied considerably in the same soil with similar treatments. On old cucumber soil tomatoes showed no sign of toxicity even with the heavy dressing, flax was progressively damaged with increasing doses, while Solanum nodiflorum was most seriously affected even with the lighter dressing of molybdate. It was impossible to predict the reaction between soil, poison and crop without actual experiment.
The growth of flax was greatly impeded on a manganese-deficient fen soil, and the molybdenum toxicity was masked in consequence. When the deficiency was corrected the poisonous effect of molybdenum on this soil was very marked, even with the lower dressing.
The composting of loam with peat usually, but not invariably, resulted in a reduction of the toxicity of molybdenum. The different results obtained with several crops on a variety of soils still yield no definite clue to the factors which determine the relative toxicity of molybdenum to plant growth and such points as soil acidity, response to climatic conditions and nutritive deficiencies are among those which need further investigation.