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UNITED STATES DEPARTMENT OF AGRICULTURE

BULLETIN No. 703

Contribution from the Bureau of Entomology

WASHINGTON, D. C.

L. O. HOWARD, Chief

November 20, 1918

MISCELLANEOUS TRUCK-CROP INSECTS IN

LOUISIANA.

L-INSECTS INJURIOUS TO THE GLOBE ARTICHOKE IN LOUISIANA.

By THOS. H. JONES,

Entomological Assistant, Truck-Crop Insect Investigations.

INTRODUCTION.

Insect injury to the globe or burr artichoke (Cynara scolymus) apparently has received little attention from American economic entomologists. While the artichoke has not as yet attained the rank of an important food plant in the United States, the demand for the edible heads is increasing in the markets. The crop is grown in Louisiana, and since the fall of 1914, when the writer was assigned for work on truck-crop insects, in cooperation with the Louisiana Experiment Stations, many growers have complained of insect injury to the plants.

The most serious damage to the globe artichoke in Louisiana is caused by two species of plant-lice, or aphids, Myzus braggi Gillette and Aphis rumicis Linnaeus, both usually occurring in the same field and being most numerous during the late winter and in the spring.

INJURY CAUSED BY THE ARTICHOKE APHIS, MYZUS BRAGGII.

The artichoke aphis is the most common and, generally speaking, the most injurious insect enemy of the globe artichoke in Louisiana. It occurs in great abundance on the under sides of the leaves and

its

green color harmonizes with that of the leaf. In cases of severe

infestation its presence brings about a condition such as that described in the following letter sent in by a correspondent in Rapides Parish: "Please let me know what to do for burr artichoke plants attacked by a dark smut which attracts large flies and bees. I had

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the same disease attack my plants last year about the same time. Most of the plants recovered, but seem to have lost vitality and did not bear fruit as early or as plentifully as in former years.' The presence of the "dark smut," the flies, and the bees referred to is accounted for by the "honeydew" from the aphids, and in fields where the Argentine ant (Iridomyrmex humilis Mayr) is present, this obnoxious pest attends the aphids. Besides this complaint from Rapides Parish, there are also at hand records of Myzus braggi injuring globe artichoke in East Baton Rouge, Ascension, Iberville, Terrebonne, and Plaquemines Parishes.1

Myzus braggii also infests the yellow thistle (Cirsium horridulum) which is a common weed in Louisiana. (See Pl. I, fig. 1.) This plant is closely related, botanically, to the globe artichoke, so that the presence of the same species of insects on the two plants is to be expected. Prof. C. P. Gillette, who described Myzus braggii' from Colorado in 1908, and who has determined material sent to him from Louisiana, states that at Fort Collins, Colo., it is found on Canada thistle (Cirsium arvense) during the latter part of the summer and early fall, and that "the winter hosts are the Russian olive, Hippohaes rhamnoides, and Shepherdia arvensis." 3

ENEMIES OF THE ARTICHOKE APHIS.

While no internal parasite has been found attacking this aphis, a number of predacious insect enemies have been observed. These include the larvæ of the syrphid flies Allograpta obliqua Say and Syrphus americanus Weidemann, the larvæ and adults of the coccinellid or ladybird beetles Scymnus puncticollis LeConte, Scymnus terminatus Say, Hippodamia convergens Guérin, and Cycloneda sanguinea Linnaeus, as well as the larvæ of a chrysopid and a hemerobiid, both undetermined. The coccinellid beetle Megilla maculata DeGeer and the predacious bug Triphleps insidiosus Say have been taken on globe artichoke infested with Myzus braggii and probably feed upon this aphis. The aphid is attacked by a fungus, which Dr. A. T. Speare, Bureau of Entomology, has determined as Entomophthora fresenii Nowakowski. At Baton Rouge Scymnus puncticollis appears to be its most efficient enemy.

INJURY CAUSED BY THE BEAN APHIS, APHIS RUMICIS.

While not as common on globe artichoke in Louisiana as Myzus braggii, this aphis is more difficult to control by spraying than is the latter species, largely because of the fact that infested leaves

1 Dr. F. H. Chittenden states that he has collected the species on globe artichoke at Washington, D. C.

2 GILLETTE, C. P. NEW SPECIES OF COLORADO APHIDIDAE, WITH NOTES UPON THEIR LIFE HABITS. In Can. Ent., v. 40, no. 1, p. 17-20, pl. 1. 1908.

GILLETTE, C. P. CONFUSION OF RHOPALOSIPHUM HIPPOHAES KOCH, AND MYZUS BRAGGII GILLETTE. In Jour. Econ. Ent., v. 8, no. 3, p. 375-379, pl. 17, 18. 1915.

become distorted in such a manner that the aphids can be reached only with difficulty with a contact insecticide. (See Pl. II, figs. 1 and 2.)

CONTROL OF THE APHIDS ATTACKING ARTICHOKE.

During 1917 Myzus braggii and Aphis rumicis were controlled satisfactorily at Baton Rouge by spraying with 1 part, by weight, of nicotine solution (containing 40 per cent of nicotine as sulphate) to 1,000 parts of water, with laundry soap (standard, noncaustic type) added at the rate of 1 pound to 25 gallons of water. (See Pl. I, fig. 2, and Pl. III.) Because the plants in some rows in the field where the experiments were conducted were never sprayed, these plants served as a constant source of infestation for the sprayed plants, especially those near the untreated plants. The Argentine ant apparently was responsible in part for the spread of the aphids. More frequent sprayings were necessary, therefore, than would have been the case had all the plants in the field been sprayed. The plants were sprayed seven times, January 31, March 2, March 14, March 29, April 19, April 26, and May 26, respectively. The material was applied with a compressed-air sprayer holding about 3 gallons. The first picking of edible heads from the sprayed and unsprayed rows was made on May 11 and at frequent intervals thereafter until June 29. From 65 plants in the sprayed rows 310 heads or burrs were obtained and from 39 plants in the unsprayed rows 39 heads, an average of nearly 5 heads from each sprayed plant and an average of 1 from each unsprayed plant. The difference in growth made by the sprayed and unsprayed plants was very noticeable and if the weather had not been dry there is little doubt that the increase in the crop from the sprayed plants would have been still greater than that from the unsprayed plants.

It is especially advisable to begin spraying globe artichokes when the aphids first appear on the plants, which is usually when they are small. One reason for this is that after Aphis rumicis has become abundant the leaves are so badly distorted as a result of feeding that it is very difficult to reach them with the spray. Another reason for timely spraying is that if delayed until the aphids have reached their maximum abundance, much of the injury for which they are responsible already has been done, and as the period of maximum abundance under such conditions often comes when the plants have developed a heavy growth of leaves, a larger amount of spray material and more time for its application are required than when the spraying is done early. Some growers who spray for the control of the aphids, but who do not begin until the plants are large and heavily infested, find it advisable first to cut off and destroy the older and badly distorted leaves.

It is interesting to note that a company which grows each year from 10 to 15 acres of globe artichokes in Plaquemines Parish, Louisiana, has found that the aphids can be killed successfully by a nicotine-sulphate spray. Mr. E. P. Barrios, county agent of the parish, at whose suggestion the spraying was begun, has furnished the writer with the following information regarding the methods followed. The spray mixture, which is applied with knapsack sprayers equipped with angled nozzles, is made up as follows:

Tobacco extract containing 40 per cent nicotine as sulphate-ounces__
Fish-oil soap-----

Water

8

--pounds__ 3

--gallons__ 50

This mixture contains 1 part of nicotine sulphate to 800 parts of water. As an additional aid in controlling the aphids, the method of planting followed makes it possible to utilize the same ground for artichokes during successive years. The young shoots are transplanted each fall in rows between the rows of old plants. Since the old rows are placed 8 feet apart there is ample space between rows to make this practical. When the young sets have taken root the old plants are plowed under and, as they are well covered with dirt, the aphids present on them are killed. The aphids on the young plants now may be more readily controlled by spraying, because of the smaller amount of foliage they present.

It is possible that aphids on globe artichokes could be economically killed by fumigation, especially when only a few are. grown, and for this purpose nicotine paper might be utilized, a cover to confine the fumes being placed over each plant as it is fumigated.

OTHER INSECTS ATTACKING THE GLOBE ARTICHOKE IN
LOUISIANA.

The banded leaf-footed plant-bug, Leptoglossus phyllopus Linnaeus, feeds on the globe artichoke. Its normal food plant, as has been noted by Chittenden,' is the yellow thistle, Carduus spinosissimus (=Cirsium horridulum). The adults and nymphs are often numerous upon both plants, the adults being especially common on the thistle during late winter and early spring.

Larvæ of the corn earworm (Chloridea obsoleta Fabricius) have been found boring into the edible heads, and a plant-bug, Thyreocoris pulicarius Germar, has been observed clustered upon them. Nymphs of Nezara viridula Linneaus have been found on the heads, and a scarabaeid beetle, Euphoria sepulchralis Fabricius, has been captured under conditions indicating that it was injuring them.

1 CHITTENDEN, F. H. SOME INSECTS INJURIOUS TO GARDEN AND ORCHARD CROPS. U. S. Dept. Agr. Bur. Ent. Bul. 19, n. s., 1899. See p. 47.

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FIG. 1.-YELLOW THISTLE (CIRSIUM HORRIDULUM), A COMMON WEED IN UNCULTIVATED FIELDS IN LOUISIANA.

It is closely related to the globe artichoke, and some of the aphids which attack the latter feed on the thistle.

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FIG. 2.-GLOBE ARTICHOKES ON WHICH APHIDS, MYZUS BRAGGII, HAVE BEEN CON

TROLLED BY SPRAYING.

WILD AND CULTIVATED FOOD PLANTS OF MYZUS BRAGGII.

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