26 JorRNAL OF Ti£i«: Department of AcRicrLTURE. — July, 1922. 



healthy feeder root system will be developed, leading- to the recovery 

 of weakened trees. 



Early and deep fall ploug-hing- shears off the p^reater part of the 

 older feeder roots, and encourages the growth of a new set which 

 will g-reatly benefit the tree. 



Referring- to the last cause of citrus-tree decline noted, namely, 

 absorption of ])oisons freed by trunk and root diseases, it is apparent 

 that citrus will not stand the attack of decay-producing- org-anisnis 

 without suffering- characteristic symptoms of poisoning- as evidenced 

 by exudation of g-um and yellowing- and dying- of the foliage. 



All wounds caused either by pruning-, ploug'bing", or insect attack 

 should be covered with asphaltum, wax, or bordeaux paste as soon 

 as possible to prevent entry of wood-decay org-anisms. Scaly bark, 

 foot-rot, brown rot gum disease, gray mould gum disease, and shell 

 bark are all apt to follow if wounds are not treated. To keep the 

 tree free from disease-causing fungi have the bud union well above 

 the ground ; do not allow the soil to accumulate about the bud union ; 

 irrigation water should be prevented from standing about the trunks 

 of the trees. 



The two main factors, therefore, in the cure of deteriorated 

 trees are: (1) Furrow manuring; (2) guarding against disease-causing 

 fungi. Throughout this State it has been found that citrus trees 

 on heavy and shallow soils with poor drainage are the first to show 

 decadence, while severe infestations of scale attack and overbearing 

 will bring about the decline sooner. These, however, as has been 

 mentioned, are only minor factors in orchard decline. 



The Psylla Pesti — With regard to severe infestations of Psylla 

 very little is known, mainly because it is not important in California, 

 where Psyllids do not attack citrus fruits; in fact, there is no 

 injurious species attacking orchards in California. Mr. Essig, one 

 of the greatest entomologists in California, recommends for their 

 control a miscible oil, or a light distillate emulsion or a crude carbolic 

 acid emulsion. 



Devastating Frosts. — California has just experienced one of the 

 worst frosts since the beginning of the citrus industry; in fact it 

 was almost as bad as the 1918 freeze, when more than 60 per cent, 

 of the crop was lost, when there was a heavy frost for five days, and 

 the farmers were not so well equipped with frost-fighting equipment, 

 consequently the crop was almost lost. This year, notwithstanding 

 the advancement made in orchard heating equipment, about 50 per 

 cent, of the crop was lost, the temperature dropped to 20° F. in many 

 places, while the average temperature was around 24° F. Usually 

 ii farmer will apply artificial heat to an orchard if the temperature 

 drops below 28° F. It is evident that 28° F. is dangerous for citrus. 

 Oranges, if fairly dormant, will stand a temperature of 25° or 26° F. 

 for an hour or so witliout injury. Below 25° F. the fruit begins to 

 freeze; first that on the outside near the ground, and later the 

 inside fruit. At 20° to 22° F. the twigs begin to die back, and the 

 leaves fall, while 17 or 18 degrees for four or five hours, unless the 

 tree is quite dormant, will kill them back to branches two or three 

 inches in diameter. Lemons are more tender, and the fruit will be 

 injured at 26° or 28° F. Limes are killed back considerably at 

 28° or 80° F. 



