New Pomegranate Mite russeting and cracking of peel characterize injury responsible for much culling

Walter Ebeling and Roy J. Pence

Pomegranate growers in a section Mites Appear in Summer A small percentage of the fruits will some five miles north of Porterville in have a cracked and discolored surface Tulare County began about six years ago The mites hibernate during the winter whether mites are present or not. An in- to notice a russeting and cracking of the in large colonies under loose flakes of experienced person might mistake this peel of pomegranate fruits in some or- bark on the larger branches of the pome- type of blemish for mite injury, but the chards. granate trees. In July or August, depend- two types of blemish can be distinguished The malady each year became more ing on the season, the mites may be seen readily. severe and widespread. The cause was on the fruit, at first near the stem end, In the accompanying illustration the not known, but was believed by some to then extending progressively further two upper fruits are mite-infested. The be due to thrips. By October 1947 about downward. They cause a brownish dis- checked area radiates out from the stem 75 acres of pomegranates were severely coloration which extends further from the end and will be found at varying distances affected. It was estimated at the time of stem end of the fruit as the season ad- from the stem, depending on the age of harvest that from 50% to 90% of the vances and may eventually envelop the the infestation. The light brown dis- fruit was culled because of its unsightly entire fruit. This is followed by a crack- colored area extends beyond the checked appearance. In 1948 it was found that the ing of the rind and the formation of scab area and grades off in severity without malady was also extensively distributed issue between the cracks. Continued on page 14 in Fresno County. The acreage of pomegranates in Cali- fornia is small, amounting to only 663 acres in 1947, confined almost entirely to Fresno and Tulare counties. Although many trees are grown in border rows for orchards of other fruit crops or for vine- yards, there are also some orchards planted entirely to pomegranates. One such orchard near Mendota, Fresno County, contains 200 acres.

Species Identified An examination of affected fruits on November 4,1947 showed that in all cases cast skins of an unfamiliar species of mite were found in the cracks that are so characteristic of the injury. It was too late in the year at the time of the first survey in November to find many live mites, but such specimens as were found were identified as a species of the genus Brevipalpus, later named lewisi, which was first discovered near Porterville in the fall of 1942. At that time they were causing injury to tender wood and fruit stems of lemons, as well as causing a darkened, scarred area on the surface of the fruit. Brevipalpns lewisi McGregor can hard- ly be seen without the aid of a magnifying glass, for it is only about 0.25 mm. long. It varies in color from a carrot to a salmon red. A dark area in about the center of the mite is characteristic of the species.

Above. lniury to pomegranates caused by the new mite Brevipalpus lewisi. Below. A checking and sharply delimited brownish discoloration occmsionolly found on pomegranates, but not caused by mites.

CALIFORNIA AGRICULTURE, JUNE, 1949 11 STORAGE In a single storage test of Valencia SULFUR Continued from page 7 oranges dipped in 2,4-D solutions, it was found that, as with the lemons, they de- Continued from page 4 to storage the grapefruit were washed veloped fewer black buttons than the non- yses of the lemon peel. Thus it was proved with 1/2"/0soap solution, then treated with treated fruit. ground sulfur can enter citrus fruits as 11/4%of Exchange Wax No. 22. sulfur vapor or gas. Compared to nonsprayed fruit, those Wm. S. Stewart is Associate Plant Physiolo- gist in the Experiment Station, Riverside. Sulfur vapor alone in a glass bottle sprayed with either eight or 16 pprn 2,4-D heated to the melting point of sulfur will had a reduced amount of surface decay, The above progress report is based upon Re- search Project No. 1346. combine with hydrogen to produce hy- aging and black buttons throughout the drogen sulfide. Oxygen is needed for this storage. There was also a decrease in in- The study initiated in January 1947 was a cooperative project between the Research De- reaction and sulfur dioxide is produced ternal Alternaria decay as shown by cut- partment of the California Fruit Growers Ex- in the process. ting the black button fruit after storage. change, Ontario, and the Division of Plant Glass tubes having the same surface as After 15 weeks of storage, the fruit Physiology of the University of California Citrus the lemons used in the experiments were Experiment Station, Riverside. from trees sprayed with 16 pprn 2,4-D sulfur dusted and placed in a bottle which was rated the best with regard to firm- was kept at 105" F. At the end of two ness, color and general appearance. The days time, no hydrogen sulfide nor sulfur eight ppm 2,4-D fruit rated next best, and POMEGRANATES dioxide gas had been formed. This, it is the nonsprayed fruit was the poorest of Continued from page 11 believed, shows that elemental sulfur the three lots. must get into citrus fruit to make hydro- being sharply delimited. The lower two gen sulfide and sulfur dioxide gases at 2,4-D Treatment After Harvest fruits have the blemish occasionally found atmospheric temperatures. On May 17, 1948, after washing and on pomegranates, but not associated with Plants need sulfur to build proteins. waxing, both light green and green lem- the mites. The checked and dark brown Sulfur, usually in the form of sulfate, is ons from non-2,4-D-sprayed trees were discolored areas coincide and are sharply supplied to plants through the soil. The dipped for two minutes in a lanolin emul- defined. There is no tendency for the sulfate may be put on the soil as a neutral sion containing either 500 or 1,000 pprn blemished area to be concentrated at the salt or as a weak solution of sulfuric acid. acid equivalent of the butyl ester of 2,4-D. stem end of the fruit. The roots absorb sulfate, but must be able Another sample of green lemons was to change the sulfate into other forms in exposed for 69 hours to the vapor of the Control order to build the sulfur into protein. isopropyl ester of 2,4-D. After exposure, In experiments made in 1948 it was the treated lemons were placed in the stor- Enzymic Action Suggested age chamber with the nontreated fruit. shown that all the commonly used mite treatments will control the Brevipalpus Inspection showed that after 115 days Another experiment was conducted to mit?, but since sulfur dust is highly ef- of storage at 58" F to 60" F and 88% observe what would happen if citrus fruit relative humidity, the nondipped light fective as well as being inexpensive, it is were dipped in weak radioactive sulfuric green lemons had 1.88% surface decay recommended as a control measure. Ex- acid and kept at about 115" F for several and 51.3% black buttons. perimental and commercial control treat- hours. The fruit yielded slightly radio- In contrast, after 162 days of storage, ments made in June and July 1948 with active sulfur dioxide and hydrogen sul- the light green 2,4-D-dipped lemons had one half pound of sulfur dust per tree, fide gases, very radioactive sulfate and only 376 with black buttons and none resulted in excellent control, while un- protein. The sap in the peel had become with Alternaria decay. At this time no treated check trees were severely infested, more acid. surface decay had developed on the with a high percentage of blemished fruit. It might be said in passing that the fruit dipped fruit compared to 3.85% on the Walter Ebeling is Associate Professor of En- resembled sulfur-burned fruit as did the nondipped. tomology and Associate Entomologist in the fruit kept at 105" F in hydrogen sulfide The green lemons dipped in either 500 Experiment Station, Los Angeles. or sulfur dioxide gas for a few hours. Roy J. Pence is Laboratory Technician in the This experiment suggests that enzymes or 1,000 pprn 2,4-D solutions had failed Division of Entomology, Los Angeles. to develop a single fruit with a black are present in the fruit peel which can The above progress report is based on Re- change sulfate to other forms of sulfur. button or Alternaria decay after 162 days search Project No. 1339. of storage. Surface decay was 0.60% for But the rate of change of sulfur to sulfate the dipped fruit compared to 12.25% for is a more rapid process than the one the nondipped. changing sulfate back to other forms of The 2,4-D vapor treatment of green ALMOND sulfur. lemons for 69 hours at the beginning of Continued from page 10 Experiments are under way to deter- storage also reduced black buttons and mine the effect of temperature on the rela- Alternaria decay as well as surface decay There is a great variation in the type tive rates of changing sulfur to sulfate or compared to nontreated fruit. The re- of hulls obtained in harvesting different vice versa. duction was much less than for the dip varieties of almonds. Certain hulls, such Other experiments in which lemons treatment. as the IXL which were used in this test, are being treated with radioactive hydro- are thick and meaty, while those from gen sulfide and sulfur dioxide are being some other varieties are thin and papery. run. This and other work probably will Wax Preparations The nutritive value of the hulls undoubt- bear out the evidence already found on In addition to the dip and vapor 2,4-D edly varies accordingly. It is planned to how ordinary elemental sulfur is changed treatments, 500 ppm 2,4-D as the butyl do further work on almond hull feeding to sulfuric acid. ester was added to the Exchange Water- this fall. Wax preparations. In comparison to non- ~ F. M. Turrell is Associate Plant Physiologist Robert F. Miller is Professor of Animal Hus- in the Citrus Experiment Station, Riverside. treated lemons in all color groups there bandry and Animal Husbandman in the Experi- M. B. Chervenak is Senior Laboratory Assist- was a remarkable reduction in percentage ment Station, Davis. ant, Citrus Experiment Station, Riverside. of fruit with black buttons, internal Alter- The above progress report is based on Re- The above progress report is based on Re- naria decay and surface decay. search Project No. 700. search Project No. 1200.

14 CALIFORNIA AGRICULTURE, JUNE, 1949