Page io 



BETTER FRUIT 



October, 1920 



Red Spider in Prune Orchards and Methods of Control 



THE attention of fruit growers is 

 again called to the fact that 

 there are two species of Red 

 Spider, common throughout the state, 

 which are found in more or less num- 

 bers on various kinds of fruit trees, 

 small fruit, gardens, and other forms 

 of vegetation. Some prune orchards 

 in southern Idaho are at present being 

 severely damaged. The species which 

 is doing the most damage is the true 

 Red Spider (Tetranychus bimaculatus) 

 and the other species commonly found 

 is known as the Brown, or clover, 

 Mite (Bryobia pratensis). The Red 

 Spider spins a web and winters as 

 an adult, while the Brown Mite does 

 not spin a web and winters in the 

 egg stage. 



Some prune orchards in the Payette 

 district are so severely damaged at 

 the present time by the Red Spider 

 that practically all the leaves and fruit 

 have fallen, causing an entire loss of 

 this year's crop. This condition also 

 devitalizes the tree for the future. 

 There are all degrees of injury ap- 

 parent from an occasional limb, just 

 beginning to show, to an occasional 

 tree seriously affected in an orchard 

 otherwise in full vigor. In some orch- 

 ards only one or two rows are de- 

 cidedly discolored and showing the 

 gradual spread of the damage. Many 

 orchards are showing no apparent 

 damage. 



At Lewiston last year, apple orch- 

 ards were injured by the mites and 

 apple growers as well as prune grow- 

 ers should be constantly on the watch 

 for the presence of these pests and 

 control them by .spraying before the 

 damage is done. 



Nature of Injury. 

 The first symptom, usually, of the 

 presence of the Red Spider in an 

 orchard is the discoloration of the 

 foliage, which loses its vigorous, 

 healthy, green color and begins to 

 turn a light dusty to brown color. In 

 many cases the leaves begin to curl, 

 but often curling leaves on individual 

 limbs, or the entire tree, curl from 

 other causes. Upon close examination, 

 preferably with a magnifying glass, 

 small, finely spun webs are readily de- 

 tected which are present on the foli- 

 age and twigs and collect dust which 

 soon causes the tree to appear heavily 

 covered with road dust. In these webs 

 the Red Spider exists, but does not 

 confine itself to the protection of the 

 web constantly, as it works about 

 freely over the fruit, foliage and 

 branches in feeding. Its effect on the 

 foliage is such as to completely de- 

 foliate a prune tree during one sea- 

 son and causes the prunes to shrivel, 

 loosen from the stem and drop to the 

 ground. 



Due to the fact that these mites de- 

 velop rapidly and do serious damage 

 to the prune and apple orchards when 

 conditions are favorable, the fruit 



By W. H. Wicks, Director of Plant Industry, Idaho State Department of Agriculture 



growers should prepare to control tion, found the second formula effi- 

 them during the summer when the cient. The last formula has been used 

 mites appear and before damage is successfully by some growers in the 



done. 



When to Apply Spray. 

 Tests made by growers of the Pay- 

 ette district, State Experiment Station 

 and State Department of Agriculture 

 show for this year that these insects 

 have been controlled by applying the 

 spray as late as August 5th, but the 

 best way to be sure of the correct 

 time is to examine the orchard at 

 least twice a week for the presence 

 of the insects and apply the spray be- 

 fore they have an opportunity to cause 

 damage to the trees and fruit. A spray 

 applied this season from June 15th to 

 July 15th, and even as late as the first 

 week in August, would have given suf- 

 ficient control of the Red Spider in 

 tHose orchards which are now suffer- 

 ing severely. It is highly important 

 that growers acquaint themselves with 

 this insect and plan to combat it 

 whenever its ravages are apparent. 



Spray Material. 

 Efficient control of the Red Spider 

 can be secured by the use of one of 

 the following solutions, if applied at 

 the right time and used thoroughly: 



Lime sulphur, 33° Baume 6 gallons 



Flour, made into paste 8 pounds 



Water 194 gallons 



or 



Powdered sulphur 40 pounds 



Soap 5 pounds 



Water 200 gallons 



Payette section. 



Other Injuries. 



In ascertaining the presence and 

 damage of the Red Spider, growers 

 should bear in mind various other 

 blemishes and defects of the fruit and 

 tree which are not caused by these 

 mites. The blue, waterlogged areas of 

 the prune, the issuing of gum, and 

 the brown tissue in the flesh, which 

 is commonly noticed in the prune, is 

 due to a temperature and moisture 

 factor and is associated closely with 

 the vitality and vigor of the tree. 



Devitalized trees may be often due 

 to a number of cultural and environ- 

 mental factors and any cause which 

 will devitalize trees must be ascer- 

 tained and corrected insofar as pos- 

 sible by the grower. In the matter 

 of damage by unusual temperatures 

 the grower is usually helpless, but 

 problems of the soil, fertility, irri- 

 gation, cultivation, insect and disease 

 control, and pruning are controllable 

 factors. 



The first formula has given success 

 in California and other states, and 

 Mr. Longley, Idaho Experiment Sta- 



Number of Trees Per Acre. 

 There are 43,560 square feet in an 

 acre of ground. If the trees are set 

 square and planted 20 feet apart there 

 will be 108 trees to the acre. If 30 

 feet apart, 48 trees to the acre; 40 

 feet apart, 27 trees to the acre, and 

 when 50 feet apart, which is the 

 usual planting for walnuts, there will 

 be 17 trees to the acre. 



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