w. W. Yothers, Entomologist,* and M. R. Osbum, Assistant Entomologist

122 FLORDA STATE HORTCULTURAL SOCETY think it would be a good thing to let these sandsoaks go back. notice a large nunlber of groves, going over the state, sometimes out of a fortyacre tract, 35 acres may be doing well, and it goes for ten years without any injury. Then the owner gets it in his head that this land next door should be in grove, too. He may put in some soil aids, but be would be.better off and so would the citrus industry if he would quit planting. One thing did not mention and that is the type of tool, and feel everyone will use the tool be uses best. use long handled clippers with billhook and crosscut saw. THE EFFECT OF THE FREEZE OF DECEMBER 12 AND 13 ON CT- - TRUS /PESTS N FLORDA w. W. Yothers, Entomologist,* and M. R. Osbum, Assistant Entomologist Bureau of Entomology and Plant Quarantine U. S. Department of AgriCUlture, Orlando Fortunately for the citrus grower, it is not very often that an opportunity is available for determining the effect of freezes on citrus pests in this State. n 1917 we made extended observations on the effect of that freeze on citrus pests. T hese results were published in The Florida En 'tomologist, Vol 1, No.3. After the freeze of December 12 and 13, 1934, we undertook to deter.. mine just what effect the low temperatures had on the several important pests attacking citrus. CTRUS WHTEFLY Previous records and observations following the freeze of 1917 show that the citrus whitefly is not especially sensitive to freezing temperatures. Also, this insect is found as far north as North Carolina, and it was not expected that temperatures as low as 22 F. would kill the pupae. After the freeze of December, 1934, seedling orange leaves and tangerine leaves from the trees and from the ground under the trees were examined for the presence of whitefly pupae. The number of living whitefly pupae found on 200 each of orange and tangerine leaves is given in Table. t will be observed that there is a difference in the number of living pupae found on leaves on the trees and fallen leaves. This was no doubt due to adult whitefly preference for young and 0Retired May 31, 1936. vigorous leaves for oviposition. Old and partially non-functioning leaves would no doubt be less attractive to the adult whitefly,' but more liable to fall, especially under any abnormal condition such as drought and freeze. The presence of so many living pupae on leaves that had been injured by the freeze is most convincing evidence that the whitefly is much more resistant to cold than either orange or tangerine trees. The data contained in the table indicate that the direct effect of the freeze on the whitefly pupae has amounted to very little, and it is doubtful if the cold killed any pupae other than those deprived of normal food supply by defoliation. THE RED SCALE After the 1917 freeze observations on this scale were made on camphor trees, but following the recent freeze many examinations of this insect TABLE EFFECT OF DECEMBER, 1934, FREEZE ON CTRUS WHTEFLY Seedling orange 1 Tangerine. Living whitefly pupae on 100 leaves on tree 115 141 100 unwilted leaves on ground 58 102-

FLORDA STATE HORTCULTURAL SOCETY 123 were made on citrus trees in several localities THE PURPLE SCALE where the temperatures caused severe injury to Many adult female purple scales were examined fruit and foliage. in several localities to determine the effect of The number of dead and living red scales found the low temperatures. n making the counts only under various conditions which were subjected to recently-dead adult females were recorded as having been killed by the freeze. No actual record a temperature of 22 F. are given in Table. of living and dead purple scales were made in any On the severely injured grapefruit most of the particular grove immediately before the freeze limbs an inch or less in diameter had been killed. occurred, but some data have been secured since On the less injured tree very little of the bearing wood had been killed and some leaves still the freeze which may be of interest. n a grove where the temperature fell to 22 F., remained on the tree. The results from the red 200 tangerine leaves were examined and the number of living adult female scales found are given scale counts on grapefruit indicate that about 30 per cent. of the adult females survived the low in Table. temperatures. There appeared to be no difference in the percentage of living from the injured TABLE tree and from the less severely injured tree. The THE EFFECT OF THE DECEMBER, 1934, FREEZE ON THE PURPLE SCALE NFESTNG TANGERNE LEAVES counts on oranges from the same grove in identically the same location gave a slightly greater Living Living adult percentage of kill. Only 5.6 per cent. survived adult females Total on grapefruit foliage. These data agree exactly females with with the results obtained in 1917, when it was eggs found that nine per cent. of the red scales had 100 tangerine leaves on tree 91 47 138 been frozen on camphor foliage, when the tem- 100 tangerine leaves peratures were almost identical. on ground 46 51 97 TABLE THE EFFECT OF THE DECEMBER, 1934, FREEZE ON THE RED SCALE Adult fe~ale red scales Dead Number Number Per Cent. Grapefruit tree, severely injured Fruit on ground under tree 88 38 39.0 Fruit on tree 88 32 26.6 Grapefruit tree, less injured Fruit on ground under tree 88 34 27.8 Fruit on tree 142 42 29.6 Grapefruit, severely injured Location 2 Oranges, severely injured 100 53 34.6 200 45 22.5 Grapefruit foliage on tree 200 11 5.6

! ~.~~,..., 124 FLORDA STATE HORTCULTURAL SOCETY Further examinations of purple scales were made on fruit and foliage which varied in the degree of injury caused by the low temperatures. The results of some of these examinations are given in Table V. There seemed to be a slightly greater mortality on severely injured trees than on less injured ones. A great~r percentage of purple scales were killed when exposed to a low temperature of 19 F. than when exposed to a low of 22 F. At 19 0 F. there was a most striking difference in the mortality on the ieaves and on the fruit. This is perhaps due to the greater heat radiated by the fruit than by the foliage. Since the above counts were made numerous crawlers have been observed, which shows that many purple-scale eggs were not frozen. Following the freeze in 1917 it was found that the purple scale was more resistant to low.temperatures than the red scale, and extensive examinations of both insects after the recent freeze substantiate these findings. The purple scale is much more resistant to the low temperature of 22 F. than the red scale. Examination made of the respective species in the same grove showed " that 71.7 per cent. of the purple scales and only 28.5 per cent. of the red scales survived. This is about 40 per cent. more survivals of the purple than of the red scale. THE RUST MTE At the time of the cold wave there was an abundance of mites present. No doubt the low temperatures actually froze some rust mites, but great numbers were also left and were present on completely frozen fruit immediately after the freeze. On December 26, 1934, counts were made of rust mites present on foliage left on the tree and on unwilted leaves that had fallen to the ground; On 25 squares counted on leaves left on tangerine trees there was a total of six adults and 18 young on the upper surfaces and two adults on the lower surfaces. On 10 squares on the fruit there were 263 mites, or an average of 26, per square. Only five mites were found on 00 wilted leaves on the ground. No doubt these came from eggs deposited before the freeze. OTHER MTES After the freeze several living specimens of Tenuipalpus irritans and Tetranychus cit,.i were found. t is very doubtful if very many of these TABLE V THE EFFECT OF THE FREEZE OF DECEMBER, 1934, ON PURPLE SCALES Low Purple Scales-Adult Females Temp. Dead o F. Number Number Per cent. Grapefruit tree, severely injured Fruit on ground under tree 22 11 29 67.4 Fruit on tree 22 10 17 63.0 Grapefruit tree, less injured Fruit on ground under tree 22 11 38 77.5 Fruit on tree 22 11 41 78.8 Orange fruit, severely frozen 22 40 100 71.4 Grapefruit foliage on tree Location 3 19 200 96 32.4 Grapefrujt on tree severely frozen Location 3 19 7S 100 57.1

FLORDA STATE HORTCULTURAL SOCETY 125 were frozen. Eggs and newly hatched young of the latter species were present. THE EFFECT OF THE FREEZE OF DECEMBER 12 AND 13 ON THE PAPAYA FRUT FLY Papaya plants in central Florida were killed to the level of the ground by the freeze. n one planting consisting of about 50 plants all the fruit fell to the ground and most of it had not rotted on January 1 when the examinations to determine the effect of the freeze on the papaya fruit fly were made. One hundred fruits were cut, and 16 living and seven dead larvae were found. The living larvae were about mature and in a few days would have left the fruit to pupate in the ground. There was considerable evidence that several fruits had been infested with larvae, which had left the fruit and gone into the ground to pupate snce the cold wave. EFFECT OF SULPHUR ON RUST MTES DURNG A PEROD OF LOW TEMPERATURES t has been known for a long time that when citrus trees are dusted with sulfur when the temperature is about 90 F. complete mortality takes place in less than 30 minutes. n fact, the greatest percentage of kill takes place in the first 10 minutes. n practical grove work, however, examinations are made 24 hours after the dusting when the bodies of the dead mites have dried up or when most of them have fallen from the fruit. t has also been known for a long time that when citrus trees are dusted in winter when the temperatures do not reach a maximum of more than 75 F. living mites may be found on the trees after as long as four or five days, even though the greatest mortality takes place within a few hours after the dust has been applied. Fortunately, from the standpoint of experimental work, we had an opportunity to determine the effect of dusting when much lower temperatures prevailed while the dust was being applied and for many days thereafter. n a seedling orange grove where experimental work is being conducted it was noticed on December 6, 1934, that there were great numbers of mites present, and the grove was dusted with sulfur on December 7. While the sulfur dust was being supplied theweather was cool and cloudy and the atmospherewas very humid. During the day the temperature was only 67 F. and toward evening it fell. Since this is the only experiment that we haveever known to be conducted under such temperature conditions, the rust mites were counted in the grove almost every day. The number of mites per square and the minimum and maximum temperatures are given in Table V. TABLE V RUST MTE COUNT AND TEMPERATURES, GROm. DUSTED DEC. 7, 1934 Aver. No. No. Temperatu-res Date days Mites after per dusting square Min. Max. Dec., 19341 Number Number 7 53. 48 70 8 1 7.3 35 53 9 2 No count 30 60 10 3 5.3 38 65 11 4 4.1 36 40 12 5 5.3 23 51 13 6 4.1 21 ro 14 7 72 38 65 15 8 No count 38 7(} 16 9 No count 42 75 17 10 3. 43 75 18 11.9 58 70 19 12.17 60 70 20 13.65 43 50 21 14.52 45 67 22 15.4 45 71 23 16 No count 42 72 24 17.25 50 75 25 18 No count 55 76 26 19.08 58 77 Z7 20 No count 56 76 28 21.02 t will be seen there was a high percentage of mortality immediately after the sulfur was applied, but there was little or no mortality duringthe low temperatures. n a good commercial control it should be impossible to find a single rust mite for two to three weeks after treatment. This is the only time we have ever observed livingrust mites in the midst of sulfur. Even thougb this experiment is largely the result of accident~ '1 i

126 FLORDA STATE HORTCULTURAL SOCETY we consider it one of t~e most importan~ pieces of work we ha.ve ever done at this station. Orlando, Florida, March 8 t 1935., Mr. Yothers: would like to say a few words on the control of scale, which did not get to this morning. Mr. Taylor: We will be glad to have you do that. Mr. Yothers: One of the things we must remember, as growers, is that it is very difficult to get a spray program here in the state, because of the fact that when you get a program for the control of a fungus disease it works against the control of the insects, flies, etc., so many, many years ago we built up a spray program with the entomogenous fungi as the center of the program. believe now that the presence of these fungi in Florida is one of the main reasons that we can grow oranges here so inexpensively compared with other places. t is because our scale and whitefly and other insects are all attacked by these fungi. When fungicides are used for the control of these diseases such as the gentleman mentioned this morning, they are used, as you know, in the spring of the year, practically always, and that is the time of the year when the entomogenous fungi are not very active. So since the use of these fungicides throws the natural balance out ()f line, the thing for us to do is to get a program to follow up after the applications of these fungicides, just as soon as possible. We find that. if any fungicides have been applied, the best time to apply any scalicide is around the last few days in june or the first week in July, as that is the time when the greatest numbers of scales are present in the crawler stages, and a dollar spent during this period brings many times the results that a dollar spent at practically any other time during the year. We agree with Mr. Thompson and others that scales can be very easily controlled at this period if lime sulphate solution, 1 to 50, to which is added five pounds of wettable sulphur, is used. This wettable sulphur sort of peps up the lime sulphur solution and does not increase in any way the liability to damage. believe a combination like this, applied most thoroughly and during this period, brings almost perfect results for scale control. Then, after this application, the rains come and~ the fungi take care of the scales and a good many insects during the balance of the year. do not have much else to say, excepting that a year ago-you will be glad to hear this, guess-dr. Phillips had an airplane dusting and they dusted forty of fifty acres in less than half an hour. mention this because it was a much better demonstration than what we saw yesterday. The mad didn't have a fair show yesterday, because he could not put the sulphur on the east side where the main grove was, because it woutd dust the people in the cars. believe that's all have to say about control of scale. Question: With reference to the fungi which begin to operate in the wet part of the year, if you used Bordeaux after the first spraying, wouldn't you do away with those fungi? Mr. Yothers: Theoretically, yes, but as a matter of fact it is almost impossible to rid the grove of these entomogenous fungi. don't believe have ever seen a grove completely rid of them.