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TABLE 2. YIELDS AND LODGING OF SEVERAL FORAGE SORGHUMS WHEN CUT IN THE SOFT DOUGH be harvested at the bloom-to-milk stage STAGE OF MA~RI~.IMPERIAL VALLEY 1960 to avoid harvest problems created as the Tonst'acre at 70% moisture % Lodging increasing grain weight causes the stalks Varieties First Second First Second cutting cutting Tot01 cutting cutting to bend or break. Browley ....................... 37.3 17.6 44.9 1 3 Because the hybrid forage sorghums Lindsey lOlF ................... 21.6 29.7 51.3 0 8 and sudangrass-sorghum hybrids are NK 300' ....................... 16.9 30.9 47.8 0 0 often ensiled at high moisture content, DeKalb FSld .................. 17.0 29.3 46.3 0 0 DeKolb FS-22 ..................29.1 16.2 45.3 55 49 as in the case of harvest at bloom stage, Hegari* ....................... 17.9 26.7 44.6 0 0 a preservative may sometimes be neces- Silo King ...................... 28.5 13.8 42.3 47 55 sary to insure the production of high &kn .......................... 24.9 15.8 40.7 0 60 quality silage. Prussic acid, which at ' Duat purpose forage sorghums. times can be a problem when these crops are used for pasture or green chop, does and southern San Joaquin Valley, this are known to occur. Although the crop not present a problem when sorghums are temperature usually occurs between can stand periods of moisture stress, best used for silage. March 1 and April 1. In the Sacramento yields can be expected where water is John D. Prato is Extension Agronomy Valley this may not occur until April 15 adequately supplied. TeGhnolo~st,Vern ~arbleis Ext~ns~n to May 1. Hybrid forage sorghums of the dual Agronomist, Dale G. Smeltzer is Assist- purpose or intermediate types should be Fertilization ant Professor and Assistant Agronomist cut for silage at the mi~k-to-soft-dough in the Ex~r~men~ stat^^ U~i~ersityof Most California soils require high rates stage of kernel development. Tall-grow- California, Davis, and George F. Worker, of nitrogen fertilization to achieve maxi- ing types should be harvested at bloom- Jr., is Associate Specialist in Agronomy mum yields. Other fertilizers should be to-milk stages to avoid lodging, The and Supt., Imperia~Vall~ Fie& tion, on, added in areas where nutrient deficiencies sudangrass-sorghum hybrids should also El Centro. _- L. R. JEPPSON Climatic and weather conditions directly None of the six major mite pests of Joaquin Valley and the Yuma mite is re- affect the necessity for mite treatment in citrus in California are distributed stricted to the desert valleys. Factors citrus, the number of applications needed throughout all the citrus growing areas. limiting the distribution of the latter two per year, the type of application required Differences in average temperatures species are as yet unknown. and the effectiveness of acaricides used. among the different citrus districts do The property of acaricides to be trans- not appear to be sufficient to limit the Citrus red mite development of any of these mite species. located is less advantageous, even for Extreme weather conditions, however, Lemon trees are considered the most foliage applications, when made during may be a major factor in limiting the favorable variety for citrus red mite, fol- the cooler periods of the year. Seasonal damage caused by the pest-and perhaps lowed by oranges, whereas grapefruit is changes of the host and the direct or distribution. Citrus bud mite, citrus rust infested least frequently. One of the fac- indirect influence of weather on the mite mite, and the six-spotted mite, for exam- tors contributing to these favorability dif- and the host are essential factors deter- ple, are pests only in the coastal districts. ferences is that citrus red mites lay more mining mite control and treatment sched- Frequent occurrences of hot dry winds eggs on young than old citrus leaves. As uling under California conditions. in the interior areas prevent injurious a result, the most rapid development of populations of these pests from develop- citrus red mite populations occurs during these growth cycles. Green lemon fruits AILURE OBTAIN the expected con- ing, whereas, in coastal districts, longer TO are aIso more favorable for egg produc- trol of mite infestation from an intervals between such adverse conditions F a tion than the more mature lemon-colored application of an acaricide is often at- permit the development of injurious pop- tributed to application techniques, resist- ulations. fruit. As lemon trees produce new leaves ance or inferior batches of the acaricide. Although the citrus red mite popuIa. and fruit most of the year, they provide Acaricide treatments that are more effec- tions are influenced by such conditions, suitable conditions for mite population tive than was expected are perhaps as injurious infestations occur throughout increase whenever weather factors per- frequent, but often go unnoticed. These the intermediate citrus-growing districts mit. Therefore, favorable weather rather differences can sometimes be attributed as well as coastal areas. This species, how- than growth cycles generally governs pop- to the presence or lack of predators. An- ever, has not been found in the desert ulation trends and the necessity for chem- other important factor considered was the valleys (Coachella and Imperial). The ical control. Mite populations usually de- effect of weather on the need for or efE- citrus flat mite is distributed throughout velop rapidly on grapefruit and Valencia ciency of control applications. these warmer valleys as well as the San orange trees only during the fall and CALIFORNIA AGRICULTURE, OCTOBER, 1963 11 spring growth cycles. Therefore adverse Sulfur and the dinitroeyclohexyl phenol weather conditions during these cycles acaricides are known to be more effec- may prevent the normal seasonal develop- tive when applied under warm rather ment of injurious mite populations. than cool weather conditions. Neotran ap- Acaricide applications sufficiently effec- plications resulted in relatively ineffective tive to protect the new growth may also control when hot weather conditions oc- prevent the development of injurious pop- curred during and for a few days after TANOAK ulations until the next growth cycle. the application. Neotran residues are Mature (yellow) navel orange fruit is short lived under these hot weather con- more favorable for development of citrus ditions and therefore are not of sufficient AND SHRINKAGE red mite populations than the immature persistency to be toxic to the mites which (green) navel fruit. As a result, mite pop- hatch from eggs present at time of treat- ulations frequently increase during the ment. Aramite has notably resulted in winter as well as the spring and fall. poor mite control when applied during Therefore, in contrast to Valencia oranges rainy or damp weather conditions. Either and grapefruit it is more frequently high humidities or heavy morning dews necessary to apply mite control treatments result in loss of residual toxicity. Ovex H. RESCH B. A. ECKLUND to navel oranges during the winter and Tedion were influenced very little by months. Chemical control measures at weather extremes including rains. Kel- this time are often ineffective because it thane applications in winter result in ef- is more difficult to obtain spray coverage fectively reducing mite populations on BOUT TWO BILLIONboard feet of tan- or adequate spray deposits of the acari- the leaves but are frequently ineffective oak (Lithocarpus densiflorus) saw cides on the mature fruit. Because mites on the fruit. Bioassay and chemical timberA is available in California. The are less active during the cooler weather, studies on residue persistence indicate wood of California’s tanoak exhibits out- they are also less likely to contact toxic that the Kelthane is readily absorbed into ;tanding strength properties and pleasant acaricide residues. the oil of the citrus peel and is therefore nppearance. However, its commercial use In obtaining green lemon fruit for use not available to the mites. depends on the proper approach to sea- in laboratory rearing, it was found that As previously indicated, the adult and soning. The general interest of the State’s fruit taken from the interior districts dur- nymphal stages of citrus red mite popula- [umber industry as well as specific pro- ing the summer was less favorable for tions are reduced by hot dry winds leav- duction problems in the manufacture of mite egg production than similar fruit ing the remaining population largely in heavy industrial flooring made desirable from coastal orchards. This occurs espe- the egg stage. Acaricidal application these investigations of shrinkage and dry- cially during and following periods of hot, properly timed following these adverse ing methods for green or partially air- dry, windy weather. Field data indicate weather conditions results in more effec- seasoned 5/4-inch lumber-as well as in- that not only the fruit, but also the fully tive control of this mite than is normally vestigating the merits of predrying as a developed younger leaves, were less sus- obtained. When such extreme conditions means of accelerating the evaporation of ceptible to rapid increase in mite popula- occur over an extended period or con- free water from wood. tions after such weather conditions have secutive periods of such unfavorable Previous studies have indicated that occurred. It appears, therefore, that these weather occur, mite populations may be air seasoning of tanoak lumber to below weather extremes not only adversely af- reduced to below economic levels for a 20% moisture content, followed by kiln fect mite populations directly but alter period of several months. drying, will give optimum results. How- the host favorability. The citrus bud mite remains confined ever, observations made on the drying The citrus bud mite Aceria sheldoni is under bud bracts except during its mi.

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