192 FLORIDA STATE HORTICULTURAL SOCIETY

OBSERVATIONS ON THE JANUARY 1940 COLD INJURY TO TROPICAL AND SUB TROPICAL PLANTS

S. J. LYNCH Sub-Tropical Experiment Station, Homestead, Florida

The effects of the cold on tropical and sub as windbreaks, buildings, water, etc., must al tropical plants in Florida from tfce January so be taken into consideration. 1940 freeze is becoming more apparent as Avocado plantings are sufficiently extensive the occasional rains and warming spring to permit the drawing of general conclusions weather are stimulating growth in the unin as to the relative cold resistance between rac jured tissues. On a good many plants I doubt es and among the more widely planted varie that the full extent of the injury can as yet ties. As stated before, a considerable varia be measured. However, from the plants ob tion in resistance to cold was noticed within served through South Florida shortly after a variety in any particular grove. This vari the freeze and in counties lying in the ex ation in a variety in different groves is some treme southern end of the state during the times more pronounced, butcan be account past several weeks, some notes of compara ed for in part by differences in cultural treat tive hardiness can be made. ment, tree conditions, and slight differences There are several points affecting cold in in temperature. Young trees under two years jury observation that made these notes at old were much more seriously damaged in best but generalities. Tropical and subtropical proportion to their size than older trees of fruits, with the exception of citrus, avocados, the same variety. The small trees kave much guavas and mangos, are in such smallplant more succulent wood in proportion to their ings in any one locality asto make coldin size than do the older trees; and also their jury counts unreliable. This 1940 freeze was root systems are not as well established as quite spotty in its effect, as were all of the those of older trees, thus appreciably reduc previous freezes reported in the Proceedings ing their vigor of growth. Old trees with of the Florida State Horticultural Society. grafted tops less than two years old are also For example, avocado trees of a given variety susceptible to cold injury due to the vigorous in the same condition of growth showed in succulent type of growth of the scion. jury on branches one inch in diameter in one The three races of avocado and their hy portion of a five-acre block, and in another brids, with minor exceptions in almost every portion with apparently no better cold pro group, ranged in hardiness during the 1940 tection they suffered the loss of but a few freeze in descending order, as follows: Mexi leaves. The condition of the treeas to its can, Mexican-Guatemalan hybrid, Guatemal vegetative activity, the age of the tree, and an, Guatemalan-West Indian hybrid, and West among young trees, the degree to which the Indian. Thisagrees with observations report roots are established, affect the resistance to ed before the Florida State Horticultural So cold. Disease and insect injury also make a ciety by Wilson Popenoe in 1919, W. F. Ward difference in cold resistance, as weakened in 1928, and H. S. Wolfe in 1935. Interest trees receive a greater injury from cold than ing exceptions to the aboverange of hardi do healthy trees of the same varietylocated ness include the Schmidt, which, although a near by. The location of the planting in re Guatemalan variety, is as tender as the West lation to physical protection from cold such Indians. The fruit itself is also tender. Tern- FLORIDA STATE HORTICULTURAL SOCIETY 193 peratures between 29 and 31 degrees F. for som injury. However, groves on Pine Island eight hours caused the fruit to show black and a few small plantings in the Palm Beach areas in the pulp from cold damage. This sus and Ft. Lauderdale area were unhurt. On in ceptibility to cold damage is quite general dividual trees the injury in most cases was among the West Indian varieties, as was re greatest on the top and on the south1 side of ported to the Florida State Horticultural So the trees. In the colder areas where the tem ciety last year after a cold storage study by perature dropped much below 29 degrees F., A. L. Stahl and the writer. The Winslowson, all of the bloom, practically all of the leaves, a West Indian-Guatemalan hybrid, is as ten and many of the smaller branches were lost. der to cold as the tenderest West Indian va In the coldest spots some large wood, four to riety observed. six inches in diameter, was killed. From the Among the principal varieties of avocado bloom that escaped injury during the freeze grown in Florida following this freeze, the some fruit is set, but the writer seriously Taylor and Lula again proved the hardiest. doubts if much of this fruit will reach matur On the lower east coast generally they suf ity, particularly on the Haden variety. Sev fered only minor leaf damage, and are now eral hundred small Haden fruits, pea size putting out a generous bloom. A little less and larger, gathered at random from trees in hardy but suffering somewhat more leaf in Dade County, have been dissected. All have jury were Itzamna and Nabal. These should failed to contain the normal sized seed which also have a normal bloom on the lower east seems to be necessary for the fruit to size coast this year. Next in hardiness was the up and mature normally. Normal seeds were group containing many of the Guatemalan- found in small fruits of the Brooks and Sai West Indian hybrids. They suffered from 20 to gon varieties. Since the last week of Febru 40 percent leaf damage and had many of the ary, a second bloom has appeared on the un tender outer twigs injured by cold. Collinson injured twigs of such varieties as the Haden, and Hickson belong with this group but suf Mulgoba, Brooks, Sandersha and Paheri. In fered slightly more leaf and twig damage contrast to this, little or no second bloom than the others in the group. All seven va has appeared on trees of the Saigon or Phil rieties are blooming on about three quarters ippine type. It is of interest that the first of the original twigs and will probably set a mango bloom was mostly of staminate flow satisfactory crop on the lower east coast. ers, with a very low percentage of perfect The varieties which proved least hardy and flowers. The second bloom contains a rela which suffered the loss of practically all their tively high percentage of perfect flowers. leaves, small twigs and a portion of their Very little difference in hardiness among small branches include Schmidt and Win mango varieties appeared. However, the slowson, and the West Indians such as Waldin, Brooks variety and the Saigon or Philippine Fuchsia, Trapp, Pollock, and Simmonds. Bloom type seemed to suffer slightly more damage is appearing on the uninjured small twigs to bloom and leaves than did adjacent trees and branches but in instances where cold in of the Haden and Mulgoba varieties and the jury extended to large limbs no bloom is ap Turpentine seedlings. Young mango trees un pearing. How much of the fruit will set and der two years old suffered much more cold mature will depend to a great extent on damage than older bearing trees, of course. whether the new foliage will develop soon In order that we could have a fair basis enough to offer protection and manufacture on which to judge the relative hardiness of food. some of the minor tropical and subtropical Mangos at the time of the freeze were in fruits, observations were based upon plants bloom throughout most of South Florida. The growing in the areas comparable in cold tem trees in general suffered leaf, twig, and blos perature to the Redlands section of Dade 194 FLORIDA STATE HORTICULTURAL SOCIETY

County. Temperature readings at the Sub- indica), custard-apple (Annona reticulata) Tropical Experiment Station, centrally locat and sugar-apple (Annona squamosa). ed in the Redlands, showed a low of between 29 and 30 degrees F. for six hours on the Some of the fruit trees withstood the morning of January 28. On the mornings of freeze without any apparent injury. The trees January 29 and 30 a minimum of 30 de proving this hardy at bearing age are: long- grees P. was recorded, but only for a few min an (Nephelium longana), Indian jujube (Zi- utes. zyphus mauritiana), lychee (Litchi chinen- The tenderest of the tropical fruits ob sis), woolly-leaf white-sapote (Casimiroa tet- served were the cashew nuts Anacardium oc- rameria), white-sapote (Casimiroa edulis), cidentale) and the malay-apple (Eugenia ma- governors-plum (Flacourtia ramontchi), lin- Iaccensis), small and medium sized specimens garo (Elaeagnus philippnesis), bael-fruit (Be- of which were frozen to the ground even un lou marmelos), Queensland nut (Macadamia der paper, burlap, and wooden coverings. The ternifolia), cattley guava (Psidium cattleia- largest specimens observed, 6 to 8 feet tall, num), sapodilla (Achras sapota), rose-apple Jost their leaves and branches, but will prob (Eugenia jambos) and Barbados-cherry ably sprout again from the main trunk. (Malpighia punicifolia). Trees of bearing age whrose leaves and The ceriman (Monstera deliciosa) in ex small branches were killed but are making new posed locations lost some leaves, but the fruit growth from the main branches and trunk in and climbing stems were unhurt. Some of clude: akee (Blighia sapida), sapote (Calo- the exposed fruits on loquat trees were dam carpum mammosum), Spanish-lime (Melicoc- aged but the foliage was unhurt. Peach trees ca bijuga), soursop (Anonna muricata), were in bloom and had set a few fruit. The mountain soursop (Annona m on tana), star- small fruits about Vz inch in diameter were apple (Chrysophyllum cainito), ambarella injured but the blossoms and the blossom buds (Spondias cytherea), red nombin (Spondias survived unharmed. They have since set a purpurea) and common guava (Psidium gua- good crop of peaches. Bananas lost their java). leaves, and in more exposed locations the A number of fruit trees of bearing age suf stems were frozen. In almost every clump fered the loss of a few leaves with some in either new shoots from the roots or sprout jury to the fruit but were apparently other ing hearts of uninjured stems are making wise unharmed. They include: carambola (Av- their appearance. errhoa carambola), muntingia (Muntingia The 1940 freeze has taught us, as have calabura), jackfruit (Artocarpus integrifo- previous freezes, that many of the tropical lia), mammee-apple Mammea americana), and subtropical fruits are decidedly not suited imbe (Garcinia Iivingstonei, Ceylon-goose to localities subject to low temperatures. But berry (Dovyalis hebecarpa), canistel (Lucu- many plants which are quite tender when ma nervosa), black-sapote (Diospyros eben- young attain a certain degree of hardiness aster), carissa (qarissa grandiflora), Ota- as they reach bearing age. This might war heite-gooseberry (Phyllanthus acidus), jam- rant their culture in colder areas provided bolan (Eugenia jambolana), Surinam-cherry they can be protected during the first few (Eugenia uniflora), tamarind (Tamarindus years of their existence.