20 BULLETIN 784, V. S. DEPARTMENT OF AGRICULTURE. 



Class exercise. — The following topics are suggested as the basis of 

 the class-room discussion: 



A. Fundamentals of control : 



Thorougli spraying, clean cultivation, destruction of rubbish, and rotation of 

 crops. Since there is a similarity in general methods, control of insects and 

 diseases may be considered together. 



B. Insect pests: 



Insects damaging the potato crop may be classified as follows: (1) Insects 

 chewing the leaves; (2) insects sucking the leaves and tips; (3) stalk 

 borers; (4) insects affecting the tubers. 

 The following may be considered the chief insect pests of the potato plant : 

 Colorado potato beetle — Eats the leaves ; controlled by spraying with 



arsenate of lead or Paris green. 

 Blister beetles — Leaf eaters ; controlled same as Colorado beetles. 

 Potato flea-beetles — Leaf eaters ; harder to control ; spray with Bordeaux 



and arsenate of lead as probably the best means of control. 

 Leafhopper and plant-lice — Suck the leaves and tips; control by spray 



of nicotine sulphate or kerosene emulsion. 

 Potato-stalk weevil — Bores into the stalk ; burn all infested vines ; clear 



ground and burn all old stalks ; destroy all related weeds ; rotate crops. 

 White grubs (the larvse of May beetles or June bugs) — Commonly known 



as " grub worms ; " control by fall plowing and turn soil again in spring ; 



rotation of crops. 



C. Potato diseases : 



1. Common diseases affecting the skin of the tuber : 



{a) Common scab — Control; treat seed, rotation of crops. 



( & ) Russet scab — Control ; treat seed, change of soil, deep prepara- 

 tion and cultivation. 



(c) Powdery scab — Control; treat seed. 



{d) Late blight dry-rot — Control; Bordeaux for blight, careful sort- 

 ing and storing of the tubers. 



(e) Powdery dry-rot — Control; care in handling; sorting out of in- 

 jured potatoes. 



(/) Eelworm — Control; careful selection. 



2. Diseases of stem and leaves: 



(a) Blackleg — Control; selected seed, formaldehyde treatment. 



( h ) Fusarium wilt — Control ; rotation and sanitation. 



(c) Bacterial wilt — Control; clean seed, sanitation. 



((Z) Early blight — Control; Bordeaux spray. 



(e) Late blight — Control; Bordeaux spray. 



(/) Rhizoctoniose — Control ; clean seed, formaldehyde treatments, ro- 

 tation. 



{g) Tipburn — Control; in a measure, by Bordeaux, thorough cultiva- 

 tion. 



D. Summary of control measures: 



1. Results of seed selection ; results in eliminating wilts, blackleg, eelworm, 



and other diseases which show on vines. 



2. Results of seed treatment and rotation ; reduce injury from Rhizocto- 



niose, scab, and blackleg, give clean seed. 



3. Results of spraying ; prevents early and late blight, prevents the blight 



rot, reduces injury from tipburn, repels flea beetles, kills most of the 

 other insect pests, stimulates the vines to longer growth, gives in- 

 creased yields. 



