Carrot Fly Damage Research Articles

Mulching with Grass and Bark and Intercropping withMedicago litoralisagainst Carrot Fly (Psila rosae(F.))

ABSTRACT Over a 3-year period, intercropping and two mulching (ley clipping, bark) treatments in carrots were evaluated in three areas in Sweden in an effort to establish a reliable method for reducing damage by carrot fly (Psila rosae (F.)) without decreasing yield. The only treatment that clearly and consistently reduced carrot fly damage was intercropping with Medicago litoralis; however, this treatment also led to a reduction in yield.

Further studies relating chlorogenic acid concentration in carrots to carrot fly damage

SUMMARYThe effects of first generation carrot fly larval damage on chlorogenic acid concentration in carrots was investigated in a field experiment at Wellesbourne in 1985. In a separate experiment carrots grown in the absence of a resident population of carrot fly were also analysed for chlorogenic acid; these carrots maintained low concentrations of chlorogenic acid through the summer and autumn until low ground temperatures occurred from November to January. The relationship between chlorogenic acid concentration and damage by the first generation of carrot fly was described by a similar model to the one derived previously for late‐generation damage but without the cultivar dependence. This may have been because first generation damage takes place in mid‐summer when soil temperature is not sufficiently low for differential chlorogenic acid production by carrot cultivars. The model supports the hypothesis that carrot fly damage increases chlorogenic acid production which subsequently encourages further attack. The increase in acid production due to the low winter temperature may be the mechanism which, in turn, induced a differential cultivar response in carrots harvested during the winter.

A rapid non‐destructive technique for screening carrot seedlings for resistance to carrot fly damage

SUMMARYA technique based on fluorescence of carrot root tissues has been devised to enable large numbers of accessions to be screened for resistance to carrot fly using an epi‐fluorescence microscope. The technique is non‐destructive, and has been partly automated to assess at least 400 seedlings/hour. A data‐capture and handling package provides prompt summarising and print‐out of the results.

The effects of time of sowing and harvest on carrot biochemistry and the resistance of carrots to carrot fly

SUMMARYTwo carrot cultivars which represented contrasting levels of resistance to carrot fly, Psila rosae, were grown in a replicated field experiment at Wellesbourne in 1984–85. Seed was sown on five occasions between April and August 1984 and the crop harvested after a minimum growth in the field of 16 wk on seven occasions between August 1984 and February 1985. A highly significant correlation (r = ‐0.78; P > 0.001) between the levels of carrot fly damage and the concentration of chlorogenic acid in the roots enabled a model to be formulated to predict the relative predisposition to carrot fly larval damage; high levels of chlorogenic acid early in the season predisposed roots to severe attack when they were older.

The fate, distribution and biological performance of insecticide residues in vegetable crops following seedling treatment

SUMMARYCarrot, cauliflower and radish seedlings raised in sand culture and treated with aqueous suspensions containing chlorfenvinphos, diazinon, iodofenphos or triazophos were planted into the field in 1982 and 1983 to compare the performance against cabbage root fly and carrot fly of these treatments with that of bow‐wave applications of granular formulations at sowing.Initial residue concentrations were up to 4100 mg kg‐1 in the seedlings at planting. Thereafter the amounts of insecticides per root system declined. Residue concentrations in mature carrot and radish roots were smaller when plants had been treated as seedlings rather than by bow‐wave application. Chlorfenvinphos was the most effective insecticide against both pests. Amounts of insecticide applied in transplanted seedlings were < 5% of the amounts applied by the bow‐wave method but short‐term control of cabbage root fly on radish was similar. Carrot fly damage was reduced by 60% by some of the seedling treatments after 16 wk in 1982 but in 1983 they were less effective.Pot experiments with chlorfenvinphos showed that most of the insecticide in the seedlings was transferred rapidly into the surrounding soil and it was concluded that the bioactivity resulted mainly from uniform distribution of the released insecticide between and around individual plants.

Relationship between the concentration of chlorogenic acid in carrot roots and the incidence of carrot fly larval damage

SUMMARYChlorogenic acid (1·24‐3·36 mg/g) was identified as the main phenolic component in the peel of carrots by hplc analysis. The higher the concentration of chlorogenic acid in different cultivars the greater the susceptibility to carrot fly larval damage. Increases in concentration were found both after carrot fly damage and after carrots had overwintered in the field. The presence and location of chlorogenic acid was confirmed in sections of carrot tissues, mounted in 0·05 M ammonia solution by viewing them using a u.v.‐epifluorescent microscope. The importance of phenolic compounds and their function in the production of insect cuticle is discussed in relation to the different concentrations of chlorogenic acid and resistance to carrot fly in carrots.

Problems in field selection for resistance to carrot fly (Psila rosae) in carrot cv. Long Chantenay

SUMMARYIn field trials between 1973 and 1982 families of carrots of cv. Long Chantenay were assessed for their resistance to carrot fly (Psila rosae). In some but not all years, families selected for their observed resistance in earlier trials seemed more resistant than the parent line. In more than half the trials there was an association between carrot fly damage and root density, there being less damage on those families from which more roots were harvested. Thus, family selection within cv. Long Chantenay did not lead to a consistent improvement in resistance to carrot fly. Alternative strategies for achieving plant resistance to this pest are discussed.

Differences in the relative resistance of two carrot cultivars to carrot fly attack over five seasons

SUMMARYA comparison was made over five seasons of carrot fly (Psila rosae) damage on two carrot cultivars, Sytan and Danvers, which represented the extremes of resistance discovered in screening trials at Wellesbourne. Plants were harvested regularly during the seasons and at each harvest the number and weight of roots was recorded and carrot fly damage was assessed using various techniques; in 1979‐80 the numbers of carrot fly larvae and pupae in and around root samples were counted. The experiments confirmed repeatedly the relative resistance of cv. Sytan compared with Danvers. The estimated reduction in carrot fly larvae on Sytan relative to Danvers in early November in four seasons ranged from 40% to 67%. When tested against first generation carrot fly attack the reduction in larvae on Sytan was 54%. There were 45% fewer mines per root on Sytan resulting in less damage at each harvest in all seasons. Larvae took longer to develop on Sytan than Danvers and 18% more plants of Sytan survived carrot fly attack. Differences in seedstock, season, sowing time, generation of carrot fly, plant size and density did not account for observed differences in damage between the two cultivars. The studies indicated satisfactory practical techniques for assessing carrot fly damage in cultivar screening trials.

A method of using the proportions of undamaged carrots or parsnips to estimate the relative population densities of carrot fly (Psila rosae) larvae, and its practical applications

SUMMARYThe plant‐to‐plant distribution of carrot fly damage was studied on carrots and parsnips in field and microplot experiments. The observed data were well‐fitted by the relationship In (–In q) = In L+ constant, where q is the proportion of undamaged roots and L is the number of larval mines in a sample and is proportional to the number of associated larvae, N. Hence, if N1 and N2 are the numbers of larvae at two levels of infestation on one occasion, the relative numbers present, N2:N1 are estimated by In q2: In q1 In this way the relative efficiencies of insecticide treatments can be determined within an experiment from only q1 and q2 and compared between occasions. A nomogram relating q1, q2 and treatment efficiency is provided. The method can also probably be used to compare the relative susceptibilities of host‐plant cultivars to carrot fly attack.Guidance is given on the sample sizes needed to estimate q within 95% confidence limits and constraints on the application of the method are stated. An appropriate statistical procedure for analysing data sets on carrot fly infestations is by analysis of deviance and an example is given in an Appendix. The principles described can probably be adapted to other crop/pest problems.

The consistency of the resistance of eight carrot cultivars to carrot fly attack at several centres in Europe

SUMMARYEight carrot cultivars representing the range of resistance to carrot fly damage as assessed in England were grown at 12 sites in five European countries in 1977 and in 1978. The trials provided evidence of agreement with the findings in England for both years in the ranking of cultivars with respect to their resistance to carrot fly damage. The Nantes cultivar Clause's Sytan Original was the most resistant cultivar tested. Consistent results were obtained from sites where carrots were assessed at harvest and carrot fly attack was severe. A significant interaction between sites and cultivars was largely due to sites where carrots were stored prior to assessment.

Carrot Fly Maggot Damage to Different Carrot Cultivars in Relation to Root Length

SummaryThe amount of carrot fly damage at different positions on carrot roots was assessed in relation to root length, in microplots over nine years using a range of cultivars and two soil types, mineral and fen. The incidence and severity of damage were linearly related to root length, longer roots having more damage than shorter ones. However, the relationships differed for the various years, cultivars and soil types so that for roots of a given length some cultivars were more susceptible to attack than others. Roots with less damage tended to have more of the mines nearer the tip of the swollen root, apparently the preferred position for maggot feeding activity, but the proportion of damage at the tip tended to decrease during the season as the number and size of carrot fly maggots increased.

Attempts at Cultural Control of Carrot Fly Damage to Carrots in East Anglia

SUMMARYAt sites in Norfolk in 1970, 1971 and 1972, growing carrots were covered in situ with soil or straw for varying periods in attempts to prevent egg laying and subsequent late‐season damage by larvae of the carrot fly (Psila rosae) (F.))‐ Neither soil nor straw was sufficiently effective in this respect. Carrots chemically defoliated and/or covered during the main egg‐laying period in August and September were adversely affected in size and quality.

The Control of the Carrot Fly (Psila rosae, Fab.) (Diptera) with DDT.

(1) The proprietary emulsion “Guesapon ”, containing 5 per cent. DDT, gave an unsatisfactory control of carrot fly damage on a plot scale.(2) Treatment of the carrot foliage with this emulsion was more effective than treatment of the soil.(3) A I per cent. emulsion of DDT applied to carrot foliage in the field gave 100 per cent. mortality of carrot flies in the laboratory for 26 days after treatment and showed marked toxicity after a further 38 days.(4) The DDT spray deposits were very, resistant to treatment with water and remained active after death of the foliage. They were also very toxic and lasting on potato foliage.(5) Deposits given by ½ per cent. and I per cent. DDT emulsion were similar in toxicity and persistence. The ½ per cent. is, however, slower in action.(6) From a treated surface the carrot fly is able to acquire a lethal dose of DDT in a very short time, probably by absorption through the feet.(7) Emulsions containing ½ per cent. and I per cent. DDT applied to carrot foliage under cages in the field both gave 95 per cent. kill of carrot flies for a month after application. The treatments also gave a high kill of other insects.(8) Soil samples showed that the larval population and the damage was much lower in the treated than in untreated cages.(9) In a field trial 2⅓ acres of carrots were treated with ½ per cent. DDT emulsion at about 50 gals. an acre.(10) Sweeping showed a rapid decline in abundance of flies after treatment and high mortalities were observed. These features did not occur on neighbouring untreated carrots.(11) These effects lasted for some 21 days after treatment and a marked reduction of larval population and damage resulted.