ON AVOCADOS AND MANGOS

Transcription

1 288 FLORIDA STATE HORTICULTURAL SOCIETY, 955 better shape, particularly with the Esmeralda Pineapple, to have whole crops produce pine apples on this basis of blooming naturally when they reached a size and maturity and degree of development that would enable them to bloom and bloom naturally and make a nice large pineapple. This will cut down the number of barren plants to the acre. How ever, this probably should be attained by the process of planting not more than 56 plants to the acre. Because of the larger fruit pro duced by the smaller number of plants the probability is that the same tonnage of pine apples will be produced on an acre for 56 plants as would be produced by more than, plants to the acre, by any other process. Then, there is the matter of having these plants in the nursery, probably % of their life. When these plants come from the nursery, they have attained a size and degree of development, so that, they can be set in the field and the time to the fruit from the time of setting out plants in fruiting formation in the field will be much shortened. Then there is the matter of care of these plants in the nursery. All phases of care from fertilization to protection from frost will be simplified, particularly during the time that the plants are in the boxes, which will prob ably be six or seven months. The boxes, of course, will be portable, in case of frost, they can be stacked and covered, and the plants kept safe from frost during that period. In the nursery, there will be a vast lot of plants in a concentrated territory. They can be regularly fertilized with liquid fertilizer with out too much cost. They can be covered with hay, or old sacks, or any other material, in case of frost. So that, while these plants are in the boxes and in the nursery they can be cared for through fertilization, protection from frost and protection from insect pests on a concentrated basis in a small area. There is another item that is going to be important over most of Florida. Actually, I think it is important over all of Florida. It will be possible to so arrange this nursery enterprise that the plants are in the nursery or in the boxes during the winter period when frost conditions are probable and that they go into the field in fruit formation early in the spring and produce their fruit during the fall and early winter. This will greatly lessen the hazards from cold, To summarize the accomplishments of the moment, we can now fertilize pineapples with ordinary fertilizer ingredients at ordinary costs. We can now harvest pineapples full color and serve the Northern market with ripe pineapples, and this has never been done before. The market has already demonstrated that it will pay from 2% to 4 times the going price of the market at the moment for ripe pineapples as opposed to pineapples harvested green and shipped to the Northern market. We can now produce planting stock in almost any quantity that is desirable and that will enable us to have planting stock for a new enterprise in pineapples all over the State of Florida wherever there is suitable land. It seems quite possible that all of these items added together will make a comeback of the pineapple industry in Florida a certainty, where before it has only been a conjecture. It is quite possible that all of the items in this paper are applicable to all varieties of pine apples. I wish to stress the fact, however, that up-to-the-moment these practices have only been tried with the variety known as Esmeralda from Mexico. BURROWING AND MEADOW NEMATODES ON AVOCADOS AND MANGOS T. W. Young and Geo. D. Ruehle Sub-Tropical Experiment Station Homestead AVOCADOS - The burrowing nematode, Radopholus similis (Cobb) Thorne, and the Florida Agricultural Experiment Station Journal Series, No meadow nematode, Pratylenchus brachyurus (Godfrey, 929) n. comb., are closely related endo-parasitic nematodes of great economic importance. Suit and DuCharme (4) found the burrowing nematode to be the cause of "spreading decline" disease of citrus in Flor ida. According to Steiner (3) meadow nema todes apparently are the most destructive and

2 YOUNG AND RUEHLE: AVOCADO AND MANGO NEMATODES 289 widely distributed of the endo-parasitie ne matodes. Both nematodes were reported on avocados by DuCharme and Suit (). In one grove they observed, mature trees infested with burrowing nematodes only were unthrifty and they concluded that this nematode was the cause of a decline in avocados. This evidence was circumstantial only. To obtain definite information on the role that either of these nematodes may play in avocado decline, in vestigations were started early in 954 by the Sub-Tropical Experiment Station. A prelim inary report (6) on this work was given be fore this Society in 954. Some additional information has been gathered since then and the more pertinent is presented here. Something of the distribution, number and possible soil preference of these nematodes on avocados was learned by examining roots from practically all the avocado-growing areas of the state. Burrowing and meadow nematodes were widespread and frequently numerous in the light sandy soils of the Ridge and West Coast. Meadow nematodes were always as sociated with burrowing nematodes. Meadow nematodes alone, usually in relatively small numbers, were found in many groves on sandy loam and sandy muck soils along the East Coast and in the rocky (Rockdale) soils of south Dade County. Neither nematode was found in 2 of the 6 groves examined. The general distribution of these nematodes and soil types involved are shown in the following table: Location Indian River Area Davie Area South Dade County Polk & Highlands Counties HUlsborough County Pinellas County TOTAL Soil Type to Loary Muck Rocky Total No. Inspected u 2 6 Orovoa No. Groves Found With: Burrow Kaadov A survey covering 5 avocado or mixed avocado and citrus groves in Dade County also was made by the U.S.D.A. cooperating with the Florida State Plant Board. No bur rowing nematodes were found, but meadow nematodes were present in a majority of the groves inspected. 5 h 33 h 2 k9 The relative numbers of the two nematodes in typical infestations were approximated by counting the adults of both species that emerg ed upon incubation (5) from weighed field collections of roots. Some samples contained but few nematodes. The largest number of adult burrowing nematodes recorded was 65 per gram wet weight of root and of meadow nematodes, 39. The larger populations of both species often were from trees showing no decline. This may be accounted for by their habit of migrating to healthy roots of adjoining plants as roots are destroyed by their feeding. On the average, meadow nema todes appeared to be the more numerous, al though there were a few notable exceptions where the converse was true. There was no good correlation between the observable incidence of these nematodes and tree condition. Decline symptoms in the top may have been slightly more prevalent in a few groves infested with both species than in those where only meadow nematodes or no nematodes were found. However, these symp toms were not peculiar to nematode infested trees only. There was little to indicate a systematic spread of decline, as in citrus, in any case. Furthermore, in several groves re ceiving normal care where the indications were that infestation by both nematodes was of long-standing the trees had remained pro ductive. At most, only a few scattered trees had declined to the point of unprofitableness. Without question, the damage to avocado feeder roots by these nematodes is detrimental to the tree, but it may be an insidious sort of thing not readily detected in the tops. As well as could be determined by field observa tions and population studies, damage to the root system of avocados by the two species was comparable when the infestations were equally heavy. The probable economic dis tinction between the two species was establish ed through inoculation studies. Healthy avo cado seedlings were grown in nematode-free sandy soil in individual containers under con trolled conditions. The soil in one series was inoculated with practically pure collections from avocado roots of several hundred living burrowing nematodes and a similar series with an equal number of living meadow nema todes. Another series in uninoculated soii served as controls.

3 29 FLORIDA STATE HORTICULTURAL SOCIETY, 955 Examination of the roots in situ several months after inoculation showed numerous characteristic lesions on the feeder roots of the burrowing nematode series. Feeder roots in the meadow nematode series had somewhat fewer lesions. Feeder roots were relatively few in the burrowing nematode series, but were almost equal to the controls in the meadow nematodes series. The control trees had good root systems, free of lesions which characterize attack by these nematodes. Root samples were taken from each plant for nematode counts, using the incubation tech nique. All specimens (adults and larvae) were counted that definitely could be identi fied as burrowing and meadow nematodes under a stereomicroscope at 2X. The num ber found in the burrowing nematode treat ments ranged from to 469 (avg. 292) per gram wet weight of root and from 4 to 38 (avg. 5) per gram in the meadow nema tode series. Thus, from the same initial num ber, burrowing nematodes had increased ap proximately 9 times more than meadow nema todes. Control trees were free of these nema todes. Trees in the burrowing nematode series grew less in height than those in the meadow nematode or control series. At the time of inoculation the average height of trees in the burrowing nematode series was.3 inches. About a year later it was 42.3 inches, an in crease of 274 percent. Trees in the meadow nematode series grew from an average of.5 inches to 58.8 inches, an increase of 4 percent. Control trees increased from. inches to 5.3 inches, or 43 percent. The more vigorous, as well as the larger, plants were selected for inoculation; otherwise the differences probably would have been more striking. In a general way, the population of burrowing nematodes was reflected in seedling height as an inverse relationship the smaller plants having the greater number of nema todes. There was no such relationship in the meadow nematode series. Although individuals of the two species appear to be equally patho genic to avocados, under favorable conditions burrowing nematodes may increase tremend ously in number, as compared to meadow nematodes, and become noticeably deleterious through sheer numbers. The field and laboratory studies suggest that in general avocados are more tolerant to attack by burrowing nematodes than is citrus. DuCharme (2) reported from 5 to 75, and occasionally as many as 5, burrowing nema todes per gram of root in declining citrus. Counts on field collections of roots from several groves indicated that the population of these nematodes on avocados was frequently equal to the average on declining citrus with out the avocados showing decline. Besides, growth of inoculated seedlings was not re tarded until about a year after inoculation although the number of burrowing nematodes in the roots was approximately twice the maximum found in citrus. Within six weeks after citrus seedlings were planted experi mentally in burrowing nematode infested soil (4), it was apparent none were making normal growth. A part of this tolerance of avocados may be due to their ability to re generate new feeder roots rapidly above nema tode damage. It is barely possible that some cases of tolerance may be accounted for through root stocks. A large variety of stocks have been used, but cannot be identified other than through records. Trees on these miscellaneous stocks have been planted pro miscuously in individual groves. Some may be more tolerant to nematode attack than others; this would explain why healthy and unthrifty trees, growing side-by-side, are sometimes about equally infested with burrowing nema todes. It remains, however, to establish the degree of tolerance in avocados. In the mean time, growers should take reasonable precau tions against infestation by burrowing nema todes. This applies especially to the Rockdale soils in Dade County where about 85 percent of the industry is located and the burrowing nematode has not been found yet in groves. It would be valuable to know why the bur rowing nematode has not become established in groves on Rockdale soil, or if so, why it is not widespread. To date there is no satis factory answer. Some have theorized that the generally shallow, rocky soils are not suit able in texture or that soil temperature around the shallow roots is not favorable. The fact that the meadow nematode is fairly wide spread in these soils, although not in large numbers, disputes these. Moreover, in inocula-

4 YOUNG AND RUEHLE: AVOCADO AND MANGO NEMATODES 29 tion tests with avocados in coarsely screened Rockdale soil, an average of 52 burrowing nematodes per gram of root was recovered several months after inoculation. This was under more favorable temperature conditions than would prevail in the field. However, in avocados on the Ridge burrowing nematodes repeatedly have been found active in roots at a depth of two inches in unshaded soil where the mid-afternoon summer temperature of the sandy soil at two inches surrounding the roots ranged from 5 to F. Tem peratures in Rockdale soils probably do not vary greatly from those in Ridge soils. Finally, there is a limited number of trees on the deeper phases of Rockdale soil where soil conditions certainly would be favorable for burrowing nematodes if they were introduced. The best answer at present seems to be that they simply have not been introduced; or if so, that the shallow soils actually are un favorable to their wide distribution and that they were missed by the surveys. Extensive and thorough inspection for root parasitic nematodes requires a large number of samples taken at least a few inches below the surface in moist soil. Further inspections will be made, devoting primary attention to what seems to be the more favorable soil areas. Although morphologically the same, there has been some question as to whether the burrowing nematodes found on various plants in Florida were of the same physiological strain. To answer this question for avocados, citrus and bananas, cross-inoculations between these plants have been made. With respect to avocados and citrus, recently such tests have shown that burrowing nematodes go readily from infested avocado seedlings to healthy citrus seedlings planted alongside in the same container to permit preferential feed ing. Healthy avocado seedlings growing in nematode-free soil were inoculated with col lections of burrowing nematodes from citrus. The results of these inoculations are still some what in doubt. To be conclusive, adults and larvae should be dissected from the inoculated roots. No specimens were found by dissect ing a number of roots, but if the infestation is light this can be expected. As an alternative, a quantity of roots were thoroughly dried with cloth and exposed to the air for about an hour until no trace of moisture remained on the root surfaces when examined under a stereomicroscope. This treatment should kill any chance nematodes on the roots. The roots were then moistened and incubated in the conventional manner*. Nine living specimens were thus recovered from about grams of roots. Similar results were obtained on avocados inoculated with burrowing nematodes from banana. Crossinoculation tests are being continued in the manner mentioned, with two or more test plants present, to determine the degree of pre ference by burrowing nematodes for each. MANGO No decline of mangos suggest ing the trouble to be from parasitic nema todes has been observed. Mango roots were examined from 4 groves on the East Coast, Ridge and West Coast by the Sub-Tropical Station and 2 groves in Dade County by the U.S.D.A.-State Plant Board cooperative sur vey. No burrowing nematodes were found. A few meadow nematodes were present in most samples and occasional specimens of other parasitic nematodes in some. In three groves a spiral nematode, Rotylenchus sp., was associated with mango roots in sufficient number to justify further investigation. In two groves on the Ridge, mango and avocado root samples were taken from the same holes under adjacent trees where the roots inter mingled. Only spiral and meadow nematodes were found in the mango roots. The avocado roots were heavily infested with burrowing and meadow nematodes. A series of inoculations on healthy mango seedlings growing in nematode-free sandy soil were made, using burrowing and meadow nematode from avocado and spiral nematodes from banana, in a manner identical to thos on avocados. All plants appeared healthy about a year after inoculation. Incubation of roots from the respective treatments failed to recover any burrowing nematodes. Meadow nematodes were recovered in medium numbers and spiral nematodes in large numbers. From field observations and inoculation tests, it ap pears that mango may be a preferred but strongly tolerant host for the spiral nematode. Meadow nematodes probably attack mangos rather generally, but do not build up to ap- * Note on technique: Immersing: roots in water at 3-4 F. for a moment is equally effective in killing chance nematodes on the root surface. With either method, only active specimens should be considered after incubation.

5 292 FLORIDA STATE HORTICULTURAL SOCIETY, 955 preciable numbers, apparently, if other hosts are available. Mangos appear to be resistant to attack by burrowing nematodes. LITERATURE CITED. DuCharme, E. P. and R. F. Suit. Nematodes as sociated with avocado roots in citrus spreading decline areas. Plant Dis. Reptr. 37: DuCharme, E. P. Private communication Steiner, G. Plant nematodes the grower should know. Fla. State Dept. Agr. Bui. 3 (New series) Suit, R. F. and E. P. DuCharme. The burrowing nematode and other parasitic nematodes in relation to spreading decline of citrus. Plant Dis. Reptr. 37: : Young, T. W. An incubation method for Collect ing migratory endo-parasitic nematodes. Plant Dis. Reptr. 38: Young, T. W. and Geo. D. Ruehle. Parasitic nematodes on avocados A preliminary report. Proc. Fla. State Hort. Soc. 67: SOME INSECT PROBLEMS ON GUAVAS F. Gray Butcher Division of Research and Industry University of Miami Coral Gables Various insect pests have been encountered in guava plantings at our Experimental Farm of recent years. These include the common forms previously reported on guavas, of which a few species justify further comments. The guava white fly, Trialeurodes floridensis (Quaint), and the green shield scale, Pulvinaria psidii Mask., are regularly encounter ed, and frequently require control. Parathion wettable powder has usually been used against them satisfactorily. Each spring a small curculionid weevil at tacks the developing fruit. This weevil, identi fied as Anthonomus irroratus Dtz. by R. E. Warner of the U. S. National Museum, begins attacks on the enlarged fruit ovule shortly af ter pollination of the blossom. The injury, somewhat similar to that of the plum curculio on plums, occurs where the adult female gouges out a small hole in the side of the young fruit and deposits one or more eggs within the injured area. The larvae develop ing within the fruit may consume most of the contents. An egg hatching in a young fruit on March 9 was observed in the pupal stage on March 27, and the new adult emerged on April, thus giving a period of about two weeks duration for the larval and pupal stages. Infested fruit soon drops from the tree, and extensive fruit loss can occur. In 953, over 5% of fruits on unsprayed trees were infested by this weevil early in April. These trees were then sprayed with a combination of BHC and parathion, and a few days later the in festation was less than 3%. Two weeks after spraying, infested fruit could not be found. In another instance, a spray of BHC alone, using 2 lbs. wettable powder per gallons of water, applied as soon as infestations were observed, prevented fruit loss satisfactorily. In this case, infestations of approximately 5% of the young fruit were reduced to less than % five days after spraying, and further in festations failed to develop. Fig. shows typical injury to the young fruit from this insect. Fig.. Typical injury to young guava fruit by the weevil Anthonomus irroratus Dtz.