32 MISSOURI AGRICULTURAL EXPERIMENT STATION BULLETIN 176 



lead as soon as the foliage is well out and no damage will be done by this pest. 

 Too often one waits until the worms show up and by that time usually con- 

 siderable damage has already been done. 



Currant Louse (Myzus ribis). This louse in recent years has done 

 considerable injury to foliage especially of currant in this state. Its presence 

 is easily detected by the appearance of reddish blotching on the surface 'of in- 

 fested leaves. Where the lice are feeding on the lower surface of the leaves 

 they cause an upward projection of the surface of the leaves or a pocket-like 

 formation. Except in severe cases the leaves do not crumple up or develop 

 knot-like formations. On currants the lice appear shortly before the fruits 

 begin to ripen in this state. 



CONTROL. As with other plant lice one or two thorough applications of 

 nicotine sulphate will give relief. If a sprayer is not at hand double the strength 

 of the nicotine solution and apply it to the lower surface of the leaves with a 

 wisp of grass or dip the infested shoots where they are not bearing fruit. 



Here again much of the gooseberry and currant stock used in Missouri is 

 propagated in the east and north. The Federal regulations affect the move- 

 ment of currants from state to state, since it may carry the white pine blister- 

 rust. These regulations are given in full in Missouri Agricultural Experiment 

 Station Circular No. 99. 



INSECT PESTS OF BLACKBERRIES AND RASPBERRIES 



In Missouri the red spiders, which are not true insects, and the snowy tree- 

 cricket are the only pests that attract special attention on blackberries and 

 raspberries. The rose scale may at times do some injury. The nurserymen, 

 however, are also interested in the two important plant diseases, namely, anth- 

 rachnose and blackberry rust, since both these can be spread on nursery-grown 

 plants and both are classed as dangerously injurious diseases by the various 

 state nursery inspection departments. 



Red Spiders. The common red spiders are very small mites related 

 to common spiders and to the scab or mange mites of live stock. When they 

 cause trouble on blackberries or raspberries, it is due to favorable, dry, hot, 

 climatic conditions. In a normal summer in this state no injury results but 

 in dry summers these crops often suffer severely. The red spider spins some 

 silk as protection and usually feeds on the lower surface of the leaf. The 

 epidermis is broken and the liquid content of the leaf cells is consumed re- 

 sulting in a yellowing of the leaf in spots and eventually its complete drying up. 



CONTROL,. Where mites cause trouble and a liberal supply of water can 

 not be applied to the affected patch, dust with powdered sulphur when the dew 

 is on. 



Snowy Tree-cricket (Oecanthus nigricornis). This small active white 

 cricket is common in the state and at times may do considerable damage to 

 the young raspberry canes that are to produce fruit the following summer. 

 However, it is of much less importance with us than various reports show it 

 to be in other parts of the country. Where injury results it is due to the 

 work of the female in placing her eggs in the canes. This results in a splitting 

 and dying of many canes where extensive oviposition occurs. The eggs are 

 deposited in the fall, they hatch the following spring and the nymphs feed all 



