Pierstorff, A. L.

English

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No. ~39 BULLETIN MARCH, 1934 OF THE AGRlCULTURAL EXTENSION SERVJCE, THE 0HJO STATE UNIVERSITY Apple Scab and Its Control ScABBY BALDWINs-THE PENALTY FOR PooR SPRAYING By A. L. Pierstor:ff Extension Specialist in Plant Pathology The Ohio State University Ou10 STATE UNIVERSITY AND THE UNITED STATES DEPARTMENT OF AGRICULTURE, COOPERATING AGRICULTURAL ExTENSION SERVICE, H. C. RAMSOWER, Director, Columbus FREE-Cooperative Agricultural Extension Work-Acts of May 8 and June 30, 1914 Missing Pages Missing Pages Fig. 4.-Section through a scab fruiting body as seen through a high powered microscope. Latin name, inaequalis. average there are at least 5 these spore sacs, or asci, in fruiting body, and with 8 spor each ascus, there would be than 400 spores per fruiting b. As shown in Fig. 3, one-for. part of a leaf may have over IO these perithecia, so one leaf c contain more than 4,000 frui bodies or 1 ,600,000 scab spore Why should you as a fruit gr er be interested in these figu, Just follow along for a minute you will undei;stand the necessit thorough spraying. You will probably admit t there are at least Io scabby lea per tree in your orchard, whic not very many when you consi that an average apple tree has. least 30,000 leaves. On this b there would be produced roo more spores per square inch duri a normal spring. How thick would the spores be if there were I oo per square inch? Place I oo pencil dots in the I -inch square and you will be surprised to see how close they are to each other. This demonstrates how thoroughly a spray must be applied to kill all scab spores. It is easy to see that any portion of the foliage which is missed by the spray will surely get scab, because there is plenty of op-portunity for scab spores to be present and cause infection. Also, looking at it in this way, it becomes quite evident that raking and burning, or plowing down the scabby leaves, is of little value when ort or two leaves produce so many spores. Growers sometimes wonder why the have so much scabby fruit. To me, the wonder is "Why do they have an clean fruit?" SCAB IN SPRING Naturally you ask, when are all these spores produced and what type weather conditions promote spore production? As a rule some scab spores at mature by the time apple buds reach the delayed dormant stage, as illustrate in Fig. 5. Sometimes they mature earlier and we have frequently found the · ripe in some sections of Ohio as early as February. Most of the scab spor mature after green foliage is present on the tree, and are discharged onl during rainy periods. 4 Three things are necessary before scab infection can take place: First, re'must be green leaves on the trees; second, moisture (rain) must be pres-; third, the spores must be mature and ready to shoot. Spores Shoot from Sacs.-The method by which se spores are shot into the air is very interesting. efore maturity glycogen, a carbohydrate material ething like sugar, is formed in the base of the spore However, this material does not absorb water ,dily. After maturity the glycogen changes to sugar, ich takes up water rapidly, and as more and more ater is absorbed into the spore bearing sac, the pres-, e becomes greater and greater until finally the sac eaks and the spores are forcibly shot into the air. metimes the top one-third or one-half of the fruiting dy is blown off by this explosion. How high do these spores shoot? I have had any fruit growers guess on this point, and some have easoned that since scab is abundant in the tops of some r their apple trees, the scab spores must shoot that fgh. This would be a long shot for such a little spore, nd the best measurements indicate that }'j inch is out the maximum height. Spores Float in Air.-However, these seeds are so Fig. 5,-Delayed dor-ight that they are readily carried by air currents. They mant stage. oat about in the air until they settle on some object ust as dust settles on a table top. If this landing place is a littib or trunk rJf n apple tree, or any place other than a green apple leaf, or fruit, the spore dies nd cannot reproduce itself. If it settles on a green apple leaf and moisture is resent, it germinates just as any other seed and starts growing into the leaf. t grows right through the cuticle of the leaf and in four to five hours is nside, if the temperature is around 68° Fahrenheit. Spore Germination Depends on Temperature and Moisture.-Scientists ·ave determined that the rate of germination and penetration into the leaf epends upon the temperature. For example, at 43° Fahrenheit it takes 15 ours; at 48°, I I hours; at 59°, 7 hours; at 68°, 4 to 5 hours; 75°, 6 hours; nd 79°, 10 hours. It is evident, therefore, that the leaves must remain wet three times as long as 43° F. as at 68° F. in order to permit scab infection. Not all the perithecia mature at the same time. You will notice by re-erring again to Fig. 4 that the perithecia are of different sizes; the larger ones are more nearly mature and consequently will discharge their spores fir-;t. Spore discharge from the old leaves may begin before the delayed dormant stage is reached. It usually reaches its maximum somewhere near the pink period, and continues until after petal fall (Fig. 6). If we have several long rains before bloom most of the spores are discharged during that period. How-'ever, with continuous rains, such as occurred during 1933, spore discharge ··and development continued until the end of the rains on May 26. As a rule, ff the p'etal fall spray is thoroughly applied and the pre-blossom sprays preceding 'it-have been well timed and thorough, our fight against apple scab for: season is won. SCAB IN SUMMER If some parts of the orchard have been unprotected, as they usually . or rains have been too frequent during the spring, some scab spores may h penetrated into the green leaves. T about one week after petal fall oh green spots, as mentioned on page begin to show on the foliage. , these spots a second type of spor produced which may be termed "summer spore," or "second' spore." These summer spores :i produced in countless millions, a are not carried by the wind, but washed and !plashed over the lea and fruit below, during each r throughout the summer and fall. T spread of scab from secondary spot is extremely difficult to check, and this reason our contro} measures a directed most intensively at the p mary spores. The scab fungus is a cool weath~ organism, and is spread most readil Fig. 6.-Pink stage. during the spring and early fall. there is considerable scab on the fol' age, frequently the fruit is severely specked by harvest time. Sometimes in. fection is so late that it is scarcely visible at harvest time, and when such fru} is stored the scab continues to grow in storage, and app:es which appeared t be clean at harvest time are scabby when brought from the storage. There fore the late summer sprays should carry a sufficient amount of fungicide t insure against late infection. It has been definitely determined that scab spores spread during harvest ing operations do not cause infection, and that no further infection takes plac during storage. ' How TO PREVENT ScAB LossEs Calculations on page 4 show that ten scabby leaves per tree may produc I oo spores per square inch during the spring of the year. This emphasizes the necessity of very thorough and timely spraying every spring, especially in locations where scab is a problem. Regardless of previous control, scab may, be so serious during any one season as to ruin an entire crop, if p.roper control measures are not applied. The abundance or scarcity of scab one season has very little influence on its prevalence the following year. Spring rains are th~ deciding factor in respect to spore production and infection. , The most efficient control measures so far developed require the thorough, application of sprays (from delayed dormant to calyx), just preceding rainy 6 "ods w~ich are of sufficient duration to permit infection. A spray applied thin 24 hours after the beginning of a rain will kill out some recent infec-ns, but cannot be relied upon to give control. Some years one pre-blossom ay is sufficient, but generally in central and northern Ohio two pre-ossom sprays are necessary in addition to the delayed dormant spray. During ~ 1933 season some growers applied many as five pre-blossom sprays, a as later events proved were high-repaid. If the pink spray has been plied too far ahead of bloom or the ason is exceptionally rainy, a spray bloom is advised. This will not njure the set nor the bees if arsenate f lead is omitted. Spaying Suggestions.-General rocedure would be about as follows: A delayed dormant and one or ore pre-blossom sprays, using either pounds of dry or 2 gallons of liquid 1me-sulfur to 100 gallons of spray. A calyx spray of either 5 pounds 'f dry or l 0 gallons of liquid lime-. rilfur. Another application lo to l 4 aays after petal fall if one-fifth <Jr ore of the leaves show scab spots. se dry lime-sulfur 4 pounds, or l 0 Fig. 7.-Calyx cue,, stage. allons of liquid for this and the two ubsequent sprays, which should be timed 3 to 4 weeks and 9 to lo weeks after petal fall. Eight pounds of lime should be added to each loo gallons of spray if burning of foliage occurred in previous years. Insects and other diseases may also be controlled while spraying for scab if other materials are added. For the complete spray schedule get a copy of Extension Bulletin l 28 from your county agricultural agent. Each fruit grower should study his location in respect to general condi-.tions, and careful observation over a number of years will reveal whether or not he needs to apply more or fewer sprays than those recommended. Control Secured of Apple Scab in Ohio Orchards, 1928-1933 Year 1928' ' ' 1929 ' ' . ' ' . ' 1930.' '.' ' . . .. ' ' . '' ''' 1931' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' 1932' 1933' Number of Orchards 22 23 98 94 80 45 7 NoofS'q Percentage of Applied ~ Scabby Fruit 5.7 ' 5.9 7.3 10.04 6.o 2.37 5.5 2.0 5.2 7.54 6.o 5.3 ~hat scab can be controlled in Ohio in all locations is evident when the preceding table is studied. The growers' orchards used in these tests were not selected from the standpoint of scab freedom, but scattered throughout the state. Many of them are located in areas where scab is an annual problem. Every detail of the spray equipment should be in the best working order ~o wage a successful fight against s~ab. Providi.ng an adequate water supply m the orchard at one or more locat10ns, or haulmg water to the sprayer in a supplementary tank, will frequently double the number of gallons applied in one day. Our records show, that where poor control has been secured, the one general shortcoming, present in more orchards than any other, is the failure to spray thoroughly. It would help many growers if they would study the spny methods of a neighbor who is successful in scab control. Thoroughness, time-liness, and proper materials are the big three in spraying. If they are practiceJ, clean fruit instead of alibis will be the result. Remember that "nature waits for no man." Summary for Control of Scab.-In brief, if poor control of scab has been obtained, permit me to suggest the following procedure: Make sure that your spray equipment is in excellent condition and r,f sufficient capacity to cover your orchard in not longer than two days. See your county agricultural agent and ask that your name be placed on his spray service mailing list. Tune in on the radio broadcasts, which are usually given about noon over WL W, Cincinnati, and WT AM, Cleveland, and an hour earlier over WOSU, the Ohio State University Station, from the last of March, until the middle of May. Spray thoroughly and on time. Use standard materials in correct dilutions. THE REWARD OF THOROUGH SrRAYING 

Apple Scab and Its Control

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Apple Scab and Its Control

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