Field CORN BORER CONTRO. Corn. ~AR n. 'H;: t--- UNIVERSITY (,. Circular 637 UNIVERSITY OF -ILLINOIS C.OLLEGE OF AGRICULTURE

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1 CORN BORER CONTRO 'H;: t--- I - j I J tf 0;- ~AR n UNIVERSITY (,. Field Corn Circular 637 '" UNIVERSITY OF -ILLINOIS C.OLLEGE OF AGRICULTURE EXTENSION SERVICE IN AGRICULTURE AND HOME ECONOMICS In cooperation with IlliNOIS STATE NATURAL HISTORY SURVEY

2 3 DEFENSES AGAI NST CORN BORER DAMAGE IN FIELD CORN Before May 10 plow under all cornstalks and other plant refuse. Adiust planting time. On fertile soil plant about mid-may. Avoid very late planting - that is, after June 1. Use hybrids adapted to your locality. ALL 3 MEASURES are needed. They are practical and will do the job. Spraying may be worth while for some growers who cannot adjust their time of planting. Urbana, Illinois February, 1949 Cooperative Extension \Vork in Agriculture and Home Economics: University of Illinois, College of Agriculture, and the l:nited States Department of Agriculture cooperating. H. P. Rt;SK, Director. Acts approved by Congress :\lay 8 and June 30, 1914.

3 CORN BORER CONTROL IN FIELD CORN Prepared jointly by the ILLINOIS STATE NATURAL HISTORY SURVEY and the DEPARTMENTS of AGRONOMY and AGRICU LTURAL ENGINEERING of the ILLIKOIS A GRICULTU RAL EXPERIME~T STATION 1 ILLIN OIS farmers and research workers have now had nine years' experience with the European corn borer.2 Both have learned luany valuable lessons regarding its control. During this tin1e the borer has become well established in the northern half of the state. Borer populations of 10,000 to 40,000 an acre are common in the stalks at the end of the season. Any time that weather and growing conditions favor the insect, these numbers could cause very severe dan1age. During at least half this nine-year period, wet weather in the spring forced many farmers to delay corn planting. As a result of this forced delay, the insect has been partly checked. Even so this pest cost farmers more than $14 million in 1946, n10re than $31 million in 1947, and at least as much in The most favorable conditions for the insect and the greatest damage are most likely to occur in the northern half of the state and in an area around East St. Louis. Except in the East St. Louis area, the insect has not built up in numbers south of a line across the state at about Taylorville. Along the river borders of the state south of this line it may be expected to increase at any time. Both scientific research and farn1ers' experience have shown the value of three procedures in the borer fight. These are: (1) get rid of cornstalks in the proper way; (2) plant at the right time; (3) use adapted corn hybrids. Some farmers and 1 The following members of the research st a ffs a re participating in the investigations in Illinois: In t he Illinois Natural History Survey - J. H. BIGGER, Entomologist ; and J. M. WRIGHT, Assistant Entomologist. The drawings a re t he work of C. O. MOHR, formerly Associate Entomologist. In t he Illinois A gricultural E xperim ent Station - G. H. D UNGAN, Professor of Crop P roduction Research ; R. W. J U GEN H EIM ER, Professor of Plant Genetics Research; A. L. LANG, P rofessor of Soil Experiment Fields R esearch ; and A. L. Y OUN G, Associate Professor of Farm P ower, 2 P yrausta nubilalis (Hbn.). 3

4 4 CIRCULAR No. 637 many seed producers have found it impossible or impracticable to follow time-of-planting recomn1endations. For these men a program of insecticide treatment is being developed. This circular aims to bring Illinois farmers up-to-date on the best-known ways of controlling the borer. LIFE OF THE BORER During its lifetime, the borer goes thru four stages of development: egg, worm, cocoon, and moth. An understanding of this insect and its habits will show why clean plowing and time of planting are so important in preventing damage. Two strains in Illinois. The moths of one strain produce only one generation a year. Moths of the other produce two, and in southern Illinois a few try to produce three generations a year. Usually about half of all the early-season worms change into moths that lay eggs for the second generation. Of the two strains, the one which reproduces more than once a year is the more important. It may produce a very large number of borers late in the season even when conditions early are unfavorable to it. These late-season borers not only damage the crop that year but live thru the winter to threaten the next year's crops. It is impossible to tell the worms of the two strains apart by looking at them. Habits of the borer. Moths spend the daytime in fence rows, fields of small grain, and in like places. In the evening they fly into cornfields and lay most of their eggs just after sunset and just before sunrise. The eggs, deposited in masses of 15 to 25 on the underside of corn leaves, hatch in 5 to 7 days. The moths are very choosey about where they deposit these eggs. They select the tallest or most advanced corn in a neighborhood (Fig. 1). Worms from eggs laid by early-season moths survive better on taller, usually earlier, corn than on shorter, usually later, corn. This fact has been proved by research in Illinois and other states, especially Connecticut. 1 If the corn is small when the eggs hatch, most of the worms will die. To live 1 Beard, R. L. and Turner, Neely, Investigations on the Control of the European Corn Borer. Conn. Agr. Exp. Sta. Bul

5 CORN BORER CON TROL 5 they must hatch out on fairly tall corn. They are most likely to live when they hatch on corn that is almost ready to tassel. Worms that hatch from eggs laid by early-season moths move to the curl of the plant and feed there. As the plant grows, they burrow into the stalk. At this time they often also feed in the midribs of the leaves. Their feeding on the leaves causes a good many leaves to break (page 16). Broken leaves stunt the plant and cut down yields, sometimes as much as 12 to 15 percent. Boring also opens the way for the entrance of plant diseases. The borers do not stay in one place but often crawl out of one burrow and make themselves another. During their lifetime as worms many borers make two burrows. Early-season worms when full grown are most often found near the base of the plant. Moths laying eggs for the late-season worms look for plants that are still tender and juicy and that have fresh tassels. Corn planted very late will not be sturdy enough to withstand the attack of this generation as well as corn planted early or only moderately late. The hot, dry winds common during August are likely to destroy a good many of the eggs and young worms of 50 (/) ~40 u z ~ ~ 30 o U t... o l ts 20 W I 1-10 ocr! I, 1 I I I :J o EGG MASSES PER 100 PLANTS When given a choice, the moths of the corn borer select the tallest or the most advanced corn in a neighborhood to lay their eggs on. This test was made at Rochelle in (Fig. 1)

6 tv1ay JUNE JULY OVERWINTERING- LAST OVERWINTERING SOME FIRST-BROOD BORERS CHANGE TO BORERS PUPATE.PUPAE BORERS PUPATE ~D RESTING- STAGE (PUPAE) CHANGE TO MOTHS. CHANGE TO rv!o/.h5. IN OLD CORN ANDWEED MOTHS LAY EGGS MOTHS t AY STALKS AND SIM ILAR AND F='IRST _ BROOD 5ECOND-BROoD.cu~r<.J.,,j SHELTER BORERS BEGIN TO BEGIN TO H -, _il.(.,.1.'.--", HATCH.HE BO~ER RESTING STAG ORPUPA NATUR.AL- SI~E -=-~:/ ~':~~,-~- "~ ~?>:;..- ~- ~- ~~' '-".-e;::-. SEPTEMBER IWINTER MONTH LA5TOF FIRST-8ROOD SECOND- BROOD OCTOBER THRU APRIL BORERS PUPATE AND BORERS COMPLETE FULL-GROWN BORERS CHANGE TO MOTHS. THEIR GROWTH l:'ntea. IN CORN SECOND-BROOD BORERS " 5,' itub~ AND STALKS OF CONTINUE TO HATCH ~OR~\~D WEEDS '11 ~\i~ l ~\I /"/~~"\I ;.( I J.~_'...: :

7 CORN BORER CO~TROL 7 this generation. Late-season worms usually feed in the upper part of the stein and in cobs and in the shanks of the ears. Borer calendar. The history of the borer thru the year is shown on page 6 and described below. N ovember-aptil. Full-grown worms ovenyinter in cornstalks in the field and in the cobs of stored corn. Some will live thru in largestalked weeds..11ay. Many overwintering worms change to the cocoon (pupal) stage. Early moths begin to hatch. June. The cocoon (pupal) stage is fini hed and early moths come out of the cocoons and lay eggs. Late June and early July is usually the time of greatest egg laying. This time, however, depends on the weather and may come as early as mid-june or as late as mid-july. Moths choose the tallest or most mature corn on which to lay their eggs. During June, borers will be found in all stages - eggs, worms, cocoons, and moths. July. Moths finish laying eggs; early-season moths die. Worms from the eggs laid by the early-season moths are becoming full-grown. During the last of the month, full-grown worms of the strain that produces two or more generations a year go into the cocoon stage. In early seasons, the moths that come from these cocoons will appear and tart laying eggs. Single-generation worms do not go into the cocoon stage but remain worms the rest of the season and during the winter. August-October. lvloths of the two-generation strain are plentiful during August and continue in fewer and fewer numbers thru September and into October. Worms that they produce feed in the stalks the re t of the season, most of them becoming full-grown before winter. If moth flight is late and winter begins early, some borers may not become full-grown and will be killed during the winter. Effect of weather on the borer. More than anything else weather and the influence of weather on plant growth affect the entire life of the borer. The time when early-season moths will COlne out of their cocoons and the time they will lay their eggs may be detern1ined by the weather as early as March or April. These months were warm in 1946, and peak egg laying occurred about June 20. In 1947 these same n10nths were cold, and peak egg laying did not come until about July 1. May and June were much alike during both seasons.

8 8 CIRCULAR No. 637 EFFECT OF TIME OF PLANTING On naturally fertile or on well-fertilized soil in central and northern Illinois, corn planted from May 15 to May 25 will, in most seasons, escape much of the early-season infestation of corn borers. Corn planted at this time will still have time to rnature a normal crop in normal seasons. Just as it is a big risk to plant early, it is also a big risk to plant after June 1. Early planting on fertile soil helps build up borer numbers. Very late planting may do the same. In fact it may be even worse than early planting, as it may build up a lot of late-season borers. The late-season worms may not cause severe crop losses during the current season, because their attack comes too late, but they do build up the numbers that live thru the winter to cause trouble the next season. In tests on the Station farm at Urbana, in central Illinois, corn planted as late as the fourth week in May still gave good yields (Fig. 2). But when planted in June, yields fell off sharply. The later it was planted, the lower the yield. These tests were carried on during the last four years. Borer numbers were very light on the test field. On soils of low fertility there is no need to hold up planting in order to get away from borer damage. Borers are not usually attracted to corn on these soils in large enough numbers to cause serious damage. 100 o...j W ~ 95 ~ ::J ~ x 90 4: ~ u. 85 o 80 How time of planting affects acre yields of corn. Urbana (Fig. 2) DATE OF PLANTING

9 CORN BORER CONTROL 9 What happens when all farmers delay planting? Three times in the last eight years, rain during early May has forced farmers in eastern Illinois to delay planting. Each time the number of borers in the area fell off, as the autumn survey showed. EFFECT OF FERTILIZERS Whether corn can be fertilized without increasing too much the danger of damage by corn borers depends partly on when it is planted. One thing that is clear from the Illinois tests is that early-planted corn should not be fertilized where the corn borer is a threat. In tests on a naturally fertile field at Milford early-planted corn that was fertilized suffered more damage than early corn not fertilized (as measured by the amount of stalk breakage below the ear and the amount of leaf breakage). Corn planted in the middle of the planting season and fertilized also suffered more damage than that not fertilized but not so much damage as the early-planted corn that was not fertilized. (The yield of this fertilized corn planted in the middle of the planting season was on a par with that of the unfertilized corn planted early.) Even tho fertilized to hurry its development, corn planted late showed more second-generation borers and more breakage above the ear than any corn planted earlier. Table 1. - Effect of Fertilizers and Time of Planting on Corn Borer Infestation and Damage to Commercial Hybrids (Five-year average at Milford, Illinois, and 1947) Measures Early planting Medium planting Late planting Fertilized fer~li~ ed Fertilized fertili~ed Not Fertilized fertilized First-generation borers Plant height in inches..... Egg masses per plant... Larvae per plant.... Leaf-damage rating Percent plants broken Below ear Above ear Second-generation borers Larvae per plant Percent plants broken Below ear Above ear

10 10 CIRCULAR Ko. 637.t:6 t:\. I/) I Z ~IOO <...J Cl. I/) 60 Jao 0...J 0 W ~ 551 ~60 ex: => [J) 751 w ex: u 70 <( '-- BUSHELS OF CORN 501 l.v or f :\:::-iiiimber OF BORERS o M ML MLP o R RL RLP RLPK FERTILITY LEVEL w Cl (/) ex: w -120 ~ Effect of varying soil fertility on yields of corn and on borer numbers. Minonk, (0 = no fertilizer applied, M = manure, L = limestone, P = phosphorus, R = residues, K,= potassium) (Fig. 3) [J) The Minonk soil experiment field has been run since 1910 in such a way as to establish different soil fertility levels on separate parts of the field. In 1944 counts were made of the number of borers in the corn on the different parts of the field. Borer counts were highest on the highest-yielding parts of the field and lowest on the low-yielding parts (Fig. 3). This was true Fertilized corn is taller in June than unfertilized corn. Where the corn borer threatens, do not fertilize early corn. (Fig. 4)

11 CORi'< BORER CONTROL 11 even tho the field had been planted too late for the early-season worms to do much damage. When this field was planted, some of it was fertilized with a 111ixture which hurried the growth of the crop and so offset the dangers of the corn not l11aturing before frost. The fertilizer also helped to keep the crop from being damaged by the late-season worms because the corn nlatured rather early. Borers need to get at the corn when it is fairly tall but while the stalks are still tender and juicy. vvhen they got at this corn, it was too far along for thenl. USE HYBRIDS BEST ADAPTED TO LOCAL CONDITIONS Besides possessing resistance to borer attack or tolerance of it, a good hybrid must produce a high yield of top-quality corn on standing plants. Hybrids which have best met these qualifications for three years on test fields are given in the summary tables of the latest Illinois Hybrid Corn Tests, a bulletin published each year by the Agricultural Experiment Station, University of Illinois. A copy of this bulletin will be sent on request. R esistance to borer attack means that the plant is able to prevent or to avoid danlage. The plants of some inbreds and some hybrids seem to be unattractive to the moths. Tho the plants are in physical condition to invite attack, the moths will lay few eggs on thenl. The worms are not able to get into or to burrow into the plants of certain other hybrids and inbreds. Tolerance is the ability of the plant to grow and produce a good crop even tho the wontis may be in the plant in some numbers. These plants just have the strength and sturdiness necessary to take it. Corn breeders and entomologists are constantly trying to find corn that is better able to resist or to tolerate the corn borer. Each year since 1941 a rather large number of inbred lines have been tested. Results show the most satisfactory lines to be those now commonly used by Illinois seed producers, the lines most susceptible to borer attack and those least tolerant of it having being discarded. The Illinois hybrid corn tests have demonstrated this fact. In these tests nlost of the hybrids that Illinois farmers

12 12 CIRCULAR No. 637 use are compared each year. At harvest, hybrids are rated for grain yield, erect plants, maturity, grain quality, and ear height. The 1947 tests showed that in stalk breakage due to corn borer no real difference between three-year-tested hybrids existed. CLEANUP METHODS ESSENTIAL Proper handling of all crop remnants in which borers may be wintering is the most effective and efficient way to keep them from producing an infestation the next season. Dead borers cannot reproduce. Plowing is cheap and effective. Plowing is the cheapest and most effective way to destroy overwintering corn borers. All crop and weed residue must be turned under before mid-may and buried so deep that it will not be brought to the surface by later work in the field. If the plow is in good condition, has the necessary attachments, and is properly operated, few borers will live to produce a new generation. A moldboard plow with a bottom measuring at least 14 inches must be used to get good trash coverage. The moldboard must scour readily and be shaped to suit the soil and the speed at which it is pulled. The colter must be large enough and sharp enough to cut completely thru all trash. Plowing with properly equipped and adjusted plows, to cover stalks, destroys overwintering borers. Careless plowing will not control the borer. (Fig. 5)

13 CORN BORER CONTROL 13 Table 2. - Stalk Coverage and Borer Reduction in Plowing Experiments at Hoopeston, Illinois, in 1944 Plow attachments Linear feet of stalk N umber of borers per square rod Percent per square of field of rod Borer stalks reduction Before After covered Before After plowing plowing plowing plowing Jointers, colters, wires and It. It. perc/. perct. trash guides l Jointers, colters, and wires Jointers and colters Colters and wiresa l Plowed with the equipment of the farm operator. Rest of area was plowed with equipment furnished by and adjusted by an Experiment Station worker. Covering attachments needed. Jointers, either the moldboard or disk type, are essential. The moldboard type must be kept properly adjusted and repaired or replaced when wear prevents its doing satisfactory work. Wires or metal shields can be used to hold the trash down while it is being turned under. Wire should be passed thru the colter yoke and twisted tightly around the shank. Ten feet of Ko. 9 or of No. 7 wire per bottom is usually enough. In the spring of 1944 a plowing experiment was run in a n1achine-picked field near Hoopeston on which corn moderately infested with borers had grown the previous season. Before the field was plowed, an average of 113 borers per square rod (equal to 18,000 an acre) were in the stalks (Table 2). After good plowing that buried 98 to 99 percent of the stalks, only 1.7 to 2 borers per square rod (the equal of 275 to 300 an acre) could be found. In another part of the same field, only colters and wires were used and only 91 percent of the stalks buried. Almost 13 borers per square rod (the equal of 2,000 an acre) were left on top of the ground. For four years, Survey entomologists have checked farmers' plowing. The results show that the average farmer's handling of cornstalks for borer control can be much improved (Table 3). Thoro disking a help in machine-picked fields. In most fields where corn has been hand picked, the stalks can usually be turned under satisfactorily without a previous disking. The field can also be plowed in either direction. In machine-picked fields, however, the plow must follow the direction of the picker if

14 14 CIRCULAR X o. 637 Table 3. - Borers Remaining in Farmers' Fields After Fields Had Been Prepared for Planting, and (Number of borers per acre) Spring 1943 Spring 1944 Spring 1946 Spring 1947 Ave rage of four years Reduction perct. Disked fields ,060 2,400 4,080 2, 510 3, 263 Plowed fields , ) 30':; stalks are to be well covered. If the plow is not to follow the direction of the picker, the field will need to be double disked before it is plowed. Early disking is best, because a rain between the time the field is disked and the tin1e it is plowed helps put the trash in condition to cover. Mechanical killers. Corn-picker attachn1ents for killing borers by shredding or chopping the stalks have been used experin1entally. One such machine, reported to give good results in experilnental tests, is being produced commercially. Shredded or chopped stalks are 1110re easily turned under than whole stalks. Moreover, if left on the ground, they prevent erosion better than the unchopped stalks. Chopping the stalks should also do away with the need of plowing for oats. But to kill borers by chopping the stalks after stock have been turned onto the field does not Seelll to be practicable. Burning not recommended. Burning cornstalks destroys organic 111atter needed by the soil and leaves many borers alive. It is not good control practice. Cleanup must be community effort. Since moths fiy long distances, all farmers in a con11llunity 111USt do a thoro job of cleaning up their fields. Only by the cooperation of all involved can any great a1110unt of control be obtained. ROTATION Seeding oats on disked cornstalk ground is a usual cropping practice in Illinois. In spite of the fact that higher yields of oats can be expected on plowed ground, farmers object to plowing for oats. Added cost and the difficulty of getting plowing done

15 CORX BORER CONTROL 15 in tin1e for oat seeding are understandable objections. A rearrangement of the rotation would renlove their objections. Use beans after corn. In areas infested with corn borers, sowing soybeans after corn is a good practice. There is then plenty of time to plow under the cornstalks. Soybean ground can be prepared for sn1all grain simply by disking. A suggested four-year rotation is corn, soybeans, sn1all grain, and clover. US E O F IN SEC TICIDES J\lany seed corn producers find it impossible or impracticable to delay corn planting to avoid early-season borer. For them, or for any grower who finds a heayy infestation threatening his field, a program of treating,,-itb insecticides may prove advisable. In unusual cases some treating for late-season \\'orms may also be advisable. Four years ago entomologists of the X atural History Survey began work on a program for treating field corn \\'ith insecticides. In this time it has not been feasible to develop all the possibilities of such a program. It is e timated, however, that 65,000 acres were treated in Illinois in 1947 and about 100,000 acres in Of all the materials tested, DDT and Ryania have been the most effective. DDT is more \\'idely used than Ryania and may at present be considered a standard treatment. The insecticide program which the entomologists are developing is another step directed to'ward helping growers produce a corn crop,,-ith the least loss and the least number of chaffy ears. Experiments are continuing, but growers \\'ho are interested can get current recommendations by \\Titing the OFFICE OF THE ENTO:\WLOGIST, NATURAL HISTORY S-cRVEY, Urbana, Illinois. USE OF PARAS ITES Several species of in ~ ects that are the natural enemies of the corn borer have been introduced into Illinois cornfields as possible aids to borer control. These parasitic insects have been released in thirty-six localities in twenty-three counties in the northern half of the state. Some of these insects appear to have become well established in many areas and are multiplying and spreading rapidly. Parasites, however, cannot be expected to control the borer completely, and other conttol measures will have to be continued.

16 16 CIRCULAR No. 637, Broken leaves and castings show that corn borers have been at work here. Stalk boring and leaf breakage lead to heavy losses in corn yields. This damage was done by first-generation borers on corn planted too early. (Fig. 6) 25M