The turnip maggot, seed-corn maggot and
onion maggot are the root maggots of economic
importance in Alaska. They feed on crucifers,
crucifers and other crops, and onions, respectively.
The damage they cause can be materially lessened
by properly timed applications of insecticide and
certain cultural practices.Cooperating with the United States Department of Agriculture, Agricultural Research Administratio

Washburn, Richard H.

English

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LIBRARYCircular 19 February, 1953^GrcuJlar ( Alasba, A ^ ri u lto Jl-H * per i merit SVcct-'i 0 05Root Maggots in AlaskaBy Richard H. Washburn Department of EntomologyeoMASVCJKS3 3EZZno.University of Alaska Alaska Agricultural Experiment StationDON L. IRWIN, D ir e c to rPALMER, ALASKACOOPERATING WITH THEUNITED STATES DEPARTMENT OF AGRICULTURE AGRICULTURAL RESEARCH ADMINISTRATION1ASMUSON '2SUMMARYThe turnip maggot, seed-corn maggot and onion maggot are the root maggots of economic importance in Alaska. They feed on crucifers, crucifers and other crops, and onions, respectively. The damage they cause can be materially lessened by properly timed applications of insecticide and certain cultural practices.ROOT MAGGOTS IN ALASKAByR ic h a r d  H. W a s h b u r n *SPECIES OF ROOT MAGGOTS IN ALASKARoot maggots are the immature stages of a group of small flies of the genus Hylemya, family Anthomyiidae. The 3 species which are injurious to crops in Alaska at the present time are the turnip maggot H. florialis (Fall.), seed-corn mag­got H. cilicrura (Rond.), and the onion maggot,H. antiqua Meigen. The well known cabbage mag­got, H. brassicae (Bouche), has not been identi­fied from Alaska.TURNIP MAGGOTThe turnip maggot is the most widely dis­tributed of the 3 species and is found wherever plants of the cabbage family are grown in the Ter­ritory. It is probably a native species. Infested crucifers (plants of the mustard family) are often found in the first planting on newly cleared land, possibly because a number of species of wild mus­tards may serve as wild hosts.There is usually 1 generation a year. The adult flies emerge from overwintering pupae during the period of mid-May to late June, depending upon weather conditions and other factors. The females commence laying eggs a few days after mating. The small, whitish eggs, about 1/8 by 1/16 inch, are often fastened to the leaf petiole or crown of the plant at, or slightly above, the surface of the ground. If the soil is very loose, the eggs may be placed slightly below the ground sur­face on the tap root. Each female lays a number of eggs, usually depositing 1 per plant. A  partial decomposition of plant tissues appears to make a more attractive egg laying site. For this reason several females may lay eggs on the same plant.•Entomologist, Alaska Agricultural Experiment Station, Palmer,4Thus larvae of varying sizes often are found in 1 plant. The eggs hatch in 7 to 10 days, and larvae begin to penetrate the stem or root surface of the plant. The larvae feed and molt several times during growth, and usually leave the root to pupate in the surrounding soil when mature. Occasionally pupae are found in cabbage heads.SEED-CORN MAGGOTAlthough this species mainly attacks crucifers in Alaska, it injures many other crops in the States including potato seed pieces, gladioli, nur­sery stock, germinating beans and corn. The only other injuries besides crucifers observed in Al­aska have been in potato seed pieces and leaf mining of chard and spinach. In Alaskan crucifers it appears to attack plants already infested by turnip maggots. As far as is known it is restricted in distribution to the Matanuska Valley area. The life cycle appears to be similar to that of the turnip maggot in Alaska.ONION MAGGOT The onion maggot was thought to be of little potential importance until the last 2 years. It is periodically introduced in onion sets grown in infested areas of the States. In 1951 it was found in onions from seed in the Matanuska Val­ley, and again in 1952, indicating it has become established in this area. The life history of this insect under Alaskan conditions has not been worked out as yet.MAGGOT INJURY IN CRUCIFERSMaggot susceptibility or resistance varies con­siderably among different types of crucifers. Cauliflower, broccoli and cabbage are usually the only types killed by maggot injury. The root types, namely radishes, rutabagas and turnips, are sel­dom killed but usually rendered inedible. Kale and kohlrabi are seldom, attacked. Cauliflower appears to be considerably more susceptible to maggot in­jury than either broccoli or cabbage. An inter­planting of the 3 will often show a complete kill of cauliflower and only an occasionally wilted cabbage or broccoli plant. Maggot burrows are a good invasion route for fungi and bacterial rots.ROOT MAGGOT CONTROLCultural control is the most desirable, but though helpful it cannot be completely relied upon to produce a maggot-free crop.The elimination of the yellow-blossomed mus­tards would be desirable, as this group is a wild host plant, and a continuing reservoir of maggots. Three infested species have been collected thus far, and it is possible that any mustard with a tap root of 1/4 inch or larger may be a wild host plant.Crop rotation, whereby the most susceptible crops are planted as far as possible from the previous year’s planting, helps cut down on the degree of infestation. Although this may help the truck gardener, it is of little use to the home gardener.Experiments in maggot resistance of radishes, turnips and rutabagas- show that turnips which are flattened in shape are the only type with any degree of resistance to maggot attack.Those varieties whose leaves have an upright growth habit are easier to cover with insecticide than the types whose leaves lay on the ground.The following equipment may be used in the application of materials for the chemical control of root maggots:For DuslsCheesecloth or sugar sackHand dusterKnapsack dusterPower duster DuslsDue to the costs involved, dusts are generally impractical for all but the home gardener where costs are of less importance than ease of applica­tion. The material should be applied to the base of the plant at ground level.SpraysMost farmers have water available and many have boom-type sprayers for weed control al­ready on hand. By the use of nozzles which may be adiusted to give a fan-type spray at the base of plant or using spray shoes,* effective coverage♦May be seen at Horticulture Department at Matanuska Experi­ment Station.5-For SpraysCupSprinkling can Knapsack sprayer Low pressure boom type weed control sprayer.may be obtained. S^ray shoes are the most desir­able, since the guards will raise the foliage so the spray covers the base of the plant and isn’t wasted on the upper portion. This is especially impor­tant if plants are treated late in the season.The following are recommended materials for root maggot control:Mercuric chloride1 Chlordan Aldrin HeptachlorAny of the above materials may have a place in maggot control. The weakest point in the life cycle is the egg or newly hatched maggot. The material used should be applied as soon as eggs are found and application repeated at 10-day intervals as long as egg laying continues. Four applications are usually sufficient. In order to avoid objectionable insecticide residues the last application should be applied at least 20 days prior to harvest.Corrosive sublimate, which is primarily effective against the eggs, has several disadvantages when compared to other materials. It is very difficult to suspend in water, thus making an even dis­tribution of toxic materials hard to obtain. It attacks metal and badly corrodes any metal equip­ment.The other materials may be formulated in any way desired and used as dusts or sprays. Due to high shipping costs it is not economical to use the low concentration dusts. It is very difficult to mix a dust of the newer insecticides on the farm be­cause of the fine particle size and low concentra­tion of insecticide needed for effective control. The emulsions are generally the most satisfactory as they may be mixed easily with water to give the desired concentration. They may be applied with hand sprayer, knapsack sprayer, tractor- mounted equipment or even a sprinkling can.Due to the fact that materials may be purchased in a range of concentrations, recommendations given are based on the actual amount of active in­gredient. For example, dusts may vary from 1 to 50 percent active ingredient. Wettable powders may range from 15 to 75 percent. Emulsion con­centrates may range from 15 to 75 percent.tAnother name for corrosive sublimate or bichloride Of mercury.7TREATMENT OF RADISHES1. Furrow treatment with seed:A  convenient method for the home gardener is the application of a 1 percent dust of aldrin, chlordan or heptachlor at the rate of 2 ounces per foot of row with the seed before the seed is covered.2. Pest emergence treatment:Under certain conditions maggot-free radishes may be raised without chemical treatment. Ex­clusion of adult flies by screening is effective but may be too expensive to warrant it. If a grower can make daily observations it may be possible to get a crop before egg laying begins. Chemical treatment should begin as soon as eggs are observ­ed.If the use of insecticides is necessary, any 1 of the following may be used advantageously: Material Active ingredient asCorrosive sublimate 1 oz. to 10 gal. water to 35 foot of row Last treatment should be 20 days prior to harvest.TREATMENT OF TURNIPS — RUTABAGAS The same materials and rates of application as applied to radishes should be used for turnips and rutabagas. Due to the long season of growth of these crops, chemical treatment is usually re­quired. Two to 4 applications are usually neces­sary. Coverage is difficult as the plants mature, so weeds should be at a minimum and some device used to raise the foliage where possible during late season application.TREATMENT OF CABBAGE — CAULIFLOWERThe control program may vary with the cul­tural practices of the grower. If plants are set out, the first application may be applied in the transplant water, and following treatments ap­plied at 10-day intervals as long as egg laying persists.If plants are grown from seed the more de­sirable practice is to wait for egg laying to begin before treatment.dust or sprayHeptachlorChlordanAldrin % - 1 pound to the acre % - 1 pound to the acre 1 pound to the acreBROCCOLICONTROL SUMMARYCrop Treatment Number and timingof application'(Use any 1 of the following materials)Pre emergence Radish In furrow w/seed 1 treatment2 oz. 1% dust/5 ft. row Post emergence% -l lb/acre aldrin, heptachlor 1 treatment 1 lb/acre chlordan usually1 oz/10 gal water of corrosive sufficient* sublimate 35/ft of row Post emergence% -l lb/acre aldrin, heptachlot 2 - 4 at 10-day 1 lb/acre chlordan intervals.*1 oz/10 gal water o f corrosive sublimate 35/ft of row Post emergenceVz-1 lb/acre aldrin, heptachlor 2 - 4 at 10-day 1 lb/acre chlordan intervals.*1 lb/50 gal transplant waterTurnip,rutabagaCabbage,cauli­flower,broccoliGreenonionsY2-I lb/acre aldrin, heptachlor 1 lb/acre chlordan2 - 4 at 10-day intervals.*Onion sets No effective control for infested sets is known. Use only sets from a reputable dealer.EXAMPLE OF CALCULATIONThe recommendation for root maggot control calls for 1 pound of chlordan per acre per appli­cation. How many pounds of the 5 percent dust are needed for ^  acre of turnips ? For 1 acre it will take 20 pounds of 5 percent dust to give an amount equal to 1 pound per acre. For % acre it will take 10 pounds.For cutworms there is available a 72 percent emulsion concentrate which contains 8. pounds of chlordan per gallon. The recommendation calls for the application of 2 pounds per acre. Since there are 4 quarts in the gallon, 1 quart mixed with 50 to 100 gallons of water and distributed over the acre wilf give an application rate of 2 pounds per acrerDosages for small areas can be calculated in a similar manner.

Circular 19

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Circular 19

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