MISCELLANEOl'S NOTES ON ECONOMIC WORK 61 



experiments in co-operation with tlie Plant Patholot^y Division 

 liere at the Uni\-ersity Farm we have found that this dcirmant spray 

 is of no particular use against these diseases, the later sprayin_e;s 

 being the most effective. 



The three imjjortant and effective sprayings of the orchard 

 should be given as follows: 



1. As the flower buds begin to show color; in the apples when 

 the center bud of the fltnver cluster begins to show pink. 



2. Just after the blossom falls ; in the case of apples, and Avhen 

 the fruit is the size of very small peas, in the case of the plum. 



3. The third s]ira}ing should be given two itr three weeks 

 after the second in the apple, and in the case of plums, just as the 

 fruit begins to show color. 



The materials to use in the spray each time are, — three pounds 

 of arsenate of lead paste or one and one-half pounds of arsenate of 

 lead pow^der, one and one-fourth gallons of lime sul])hur, if the 

 specific gravitv reading is 2>2° on the Baume scale, in fifty gallons 

 of water. If plant lice are doing damage- at the time of any of these 

 spravings a half pint of a 407c nicotine sulphate solution may be 

 added to the mixture with excellent results. 



Orchard and Tree Insects. 



(3ne of the most important tree insects studied critically is the 

 oak twig girdler [A^rUus arcnatiis), an insect not previously re- 

 ported from the state. The life history of this insect has been care- 

 fullv studied, and all its damage w^orked out in detail. This pest is 

 a flat-headed borer, a very close relation to the oak bark borer, that 

 is killing so many oaks in the southern half of Minnesota. The 

 oak bark-borer works in the main trunk of the tree, killing from the 

 trunk up. This one works from the twigs down the limbs, often 

 meeting the work of the bark borer. The majority of the dead limbs 

 seen on the red oak is due to the work of this little twig girdler. 



The work of the insect is first noticed during August. At this 

 time the leaves on the twigs hang dried out as if by blight. Egg 

 shells will be found at the base of these leaves, and the hatched 

 grubs tunneling beneath the bark of the twng, cut off' the food supply 

 to the leaf. These grubs or larvae burrow on down the stem some- 

 times beneath the bark, sometimes in the center of the twig, and in 

 July of the second year have reached their full growth. Just be- 

 neath the bark in the wood of the limb, often six or eight feet from 

 its entrance burrow, it pupates. The last of July and the first of 



