considerable portion of the foliage. Up to the present time, the tendency- among users of sprinkler irrigation-has been to apply too little rather than too much water at each irrigation. Many problems dealing with the rate of appli- cation and the length of the sprinkling FIRST FOOT - SECOND FOOT THIRD FOOT FOURTH FOOT 15- 19 16 7 26 15 JUNE JULY AUG.<br><br> SEPT. OCT. Soil moisture contents in a mature Duarte plum orchard, showing an excellent irrigation program.<br><br> The available soil moisture, shown by the portion of solid bars above the dotted line, representing the wilting percentage-S%-indicate some moisture left from rain and previous irrigations, when water was applied. period remain to be worked out. Experi- mental results, however, indicate that the growth and fruiting of sprinkled trees are the same as those where surface ap- plications are used, provided the supply of readily available moisture is main- tained in the soil containing most roots.<br><br> Growth of fruit is a sensitive index of soil-moisture conditions because a de- crease in the rate of growth of the fruit coincides with the exhaustion of the readily available soil moisture. Experiments with Santa Rosa plums and Bartlett pears were carried out in sprinkled and in furrow irrigated or- chards. The soil, a Holland sandy loam, with a field capacity of 12% and a per- manent wilting percentage of five, was the same in all of the plots.<br><br> The interval between irrigation was 12 days which was short enough to maintain a supply of readily available moisture. Neither the furrow irrigated nor the sprinkled plots reached the permanent wilting per- centage before the fruit was picked. The results obtained with the Santa Rosa plums on peach root showed that increases in fruit size were essentially equal under both furrow and sprinkler irrigation.<br><br> The fruits in both plots grew rapidly from about the middle of April until the middle of May when they slowed down slightly during the pit-hardening period, and then resumed rapid growth until picked. The Bartlett pears in the furrow and sprinkler plots grew at the same rates from-late in May until picked shortly after the middle of July. The results from the tests with the Santa Rosa plums and the Bartlett pears show that the method of applying the water is without effect on the growth of the fruit-provided the soil moisture is not reduced to the permanent wilting per- centage during the growing period.<br><br> Ideal irrigation practice consists of the maintenance of readily available mois- ture in the root zone. The soil moisture record of a mature Duarte plum orchard, on a Holland sandy loam-represented by the bar graph on page 2 h o w s how this ideal program was approximated in 1951. The trees were about 15 years old at the time the record was obtained.<br><br> They are planted on 20-foot triangles and in Continued on page 12 CALIFORNIA AGRICULTURE, APRIL, 1953 3 SPRINKLER Continued from page 3 a healthy vigorous condition with the branches of adjoining trees coming to- gether in many cases. The orchard is in a permanent cover crop, principally grass which is mowed several times a year. The sprinklers are supplied from an under- ground pipe system and are moved in a regular rotation that provides each tree with a watering every 12 days.<br><br> The sprinklers are run about 12 hours and apply a little over 3 d of water at each setting. The soil holds about 1.25 d of available water per foot of depth. The bar graph shows the percentages of soil moisture around a recently irri- gated tree, and one just before the water was applied.<br><br> The open bar of each pair shows the average soil moisture content a few hours after sprinkling, and the solid bar, the moisture content a few hours before the end of the 12-day in- terval. The dry tree-solid bar-was brought up to about the same moisture content as the sprinkled one within the next 24 hours. The length of the solid bar indicates that, in the early part of the season, while there was some moisture left from the winter rains and the previous irrigations, the soil moisture could be maintained above the permanent wilting percentage easily.<br><br> Later in the season, however, the amounts of water applied were barely adequate to maintain readily available moisture during the 12-day interval. The last irrigation-October 15-wet down only about 2 9. The difference between the amount of moisture found at the end of each 12-day period and the amount applied at the be- ginning, indicates that the average daily use of a mature plum orchard in perma- nent cover crop in the foothills of central California is closer to 0.3 d per day than to 0.2 d-the amount sometimes used.<br><br> A study of the distribution of water by sprinkling was made in a pear orchard where many branches hung down and touched the ground. The orchard was left unirrigated for several weeks until the soil moisture was reduced to the perma- nent wilting percentage--5%-to a depth of 4 9. The orchard das then irri- gated.<br><br> Soil samples were taken to a depth of 4. 9 at eight compass points about 8 9 from the trunk of a tree with low-hanging branches. The sprinkler position was on the east side of the tree. No water reached the northwest and the west sides of the tree in the top foot of soil.<br><br> Water pene- trated the second foot in four of the sampling places, the third foot in three, and the fourth foot in only one sample. The total amount of water at the eight sampling points is shown in the bottom unit of the diagram on this page. 12 FOURTH FOOT a$+EElq S 0 8 0 E Distribution of roil moisture from sprinklers in a pear orchard where low branches interfered with uniform delivery.<br><br> Observation throughout the orchard showed dry areas behind each tree when the position of the low-hanging branches interfered with the distribution of water. Moving the pipeline to change the rela- tive position of the sprinklers with regard to the trees would change the position of the unsprinkled area, so that the same area would not remain dry all season. These studies showed that whether irri- gation of deciduous orchards is by sprinklers or by surface methods, the growth of the fruit is the same-provided the supply of readily available soil mois- ture is maintained.<br><br> A. H. Hendrickson is Lecturer in Pomology, F.<br><br> J. Veihmeyer is Professor of Irrigation, The above progress report is based on Re- University of California, Davis. University of California, Davis.<br><br> search Project No. 6334. LEAFHOPPERS Continued from page 5 yards were killed after 43-hour exposure to DDT-treated leaves.<br><br> On leaves treated with malathon-dipped in a suspension one fifth as concentrated as the DDT- treated leaves-the leafhoppers from both vineyards were all dead in 24 hours. In this test the cages were cloth covered on opposite sides. This lessened the pos- sibility that malathon killed leafhoppers by fumigant action.<br><br> Malathon is a new organic phosphate insecticide of much lower toxicity to humans and animals than most of the other organic phosphates. It is less per- sistent than DDT-especially in warm weather-and part of its effectiveness ap- pears to result from its fumigant action. Probably the fumigant effect is less dur- ing the cooler weather of spring, so in the pre-bloom dust applications good cover- age is most important., As compounded during the 1952 sea- scn, malathon dusts possessed an un- pleasant odor which, however, could not be detected in the vineyard the day after treatment.<br><br> Taste tests conducted with grapes either sprayed or dusted with nor- mal dosages have shown no off-flavors. As presently licensed for use on grapes, malathon may be applied not later than two weeks before harvest. Although field tests and grower experi- ence during the 1952 season showed malathon to be outstanding for leafhop- Fer control where DDT resistance is present, some questions as to dosage and timing still await solution.<br><br> Further tests with malathon are planned for 1953. E. M.<br><br> Stafford is Associate Professor of En- tomology, University of California, Davis. Frederick L. Jensen is Farm Advisor, Tulare County, University of California.<br><br> The above progress report is based on Re- search Project No. 962. STRAWBERRY Continued from page 7 be high enough to prevent serious infesta- tions of cyclamen mite.<br><br> In most fields, however, TEPP applications against red spider destroy the predators and early- season or mid-season infestations of cyclamen mite are the natural result. Populations of these predators recover fairly soon from a single early spring treatment but applications of TEPP- where no real red-spider threat exists- are likely to do more harm than good. Three or more repeated applications over an interval of time may so reduce the ,predator population that it will not re- appear in sufficient numbers to regain control of the cyclamen mite until serious loss has resulted.<br><br> Pesticide applications to adjoining crops may drift into fields under natural predator control and destroy the preda- tors throughout a wide margin of a field and disrupt an achieved control. This has been observed where dust applications of adjacent crops by airplane were made. Research is in progress to develop methods of mass-rearing this predator or of harvesting it from clipped strawberry tops, cold-storing them, and distributing them in developing infestations of early- season 2nd-year, or late-season 1st-year fields.<br><br> C. B. Huffaker is Associate Entomologist in Biological Control, University of California, Berkeley.<br><br> C. E. Kennett is Principal Laboratory Techni- cian in Biological Control, University of Cali- fornia, Berkeley.<br><br> The above progress report is based on Re- search Project No. 1490. CALIFORNIA AGRICULTURE, APRIL, 1953<br><br>

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