HORTICULTURAL DIVISION 



697 



upper leaf surface, which increase in size until leaf tissue 

 bulges out, the convex side usually on upper surface. 

 Curling of leaves may result. Control: Spray with 

 Bordeaux (4-4-50) after leaves fall and before buds 

 swell. Rake up and burn fallen leaves. 



POPLAR. Canker (Dothichiza populea). Occurs in 

 Eastern and Central States. Depressed cankers form 

 on bark of twigs and branches. Small gray-black pus- 

 tules appear on affected areas. Control: Control is 

 difficult. Disease often can be checked by pruning out 

 all diseased twigs and branches. Protect all cut sur- 

 faces by painting. Spray trees when dormant with 

 Bordeaux (4-4-50). 



SYCAMORE. Anthracnose (Gnomonia veneta). Symp- 

 toms and control same as for oak. 



CHESTNUT. Blight (Endothia parasitica). Present in 

 all Eastern States that have extensive chestnut growth. 

 Cankers on limbs and trunk which enlarge until girdle 

 is completed. Leaves on girdled parts turn brown. 

 Control: No control of this disease in native chestnut. 

 Ornamental Japanese and hairy Chinese chestnuts usu- 

 ally can be saved if affected limbs and trunk cankers 

 are removed as soon as noted and all wounds painted. 



WHITE PINE. Blister rust (Cronartium ribicola). 

 Occurs in the New England States, New Jersey, Penn- 

 sylvania, Michigan, Wisconsin, Minnesota, Washington 

 and Oregon. In Canada it occurs in the Provinces of 

 British Columbia, Ontario, Quebec, Prince Edward 

 Island, New Brunswick and Nova Scotia. Disease was 

 introduced into this country from Europe and appar- 

 ently is of Asiatic origin. On currant and gooseberry 

 bushes, from Jun to October, the disease appears as 

 an orange-yellow rust on the under side of the leaves. 

 Spores from diseased bushes infect white pines through 

 their needles, and the fungus grows into the bark, pro- 

 ducing cankers on the branches and trunk. The can- 

 kers are not readily recognized until about three years 

 after infection. They then usually appear as spindle- 

 shaped swellings on the branches or the trunk. The 

 edges of the cankers are marked with a yellowish green 

 or orange discoloration. From April to June blisters 

 about the size of a navy bean burst through the dis- 

 eased bark. These blisters are full of orange-yellow 

 spores. The blisters break open and the spores infect 

 the leaves of currant and gooseberry plants. The rup- 

 tured bark dies after the spores are discharged. The 

 fungus continues to grow into the live ba-k and each 

 year new blisters are produced until the branch or tree 

 is killed. The bark of old cankers is irregularly cracked, 

 rough and scaly in appearance. Sometimes rodents eat 

 the diseased bark, leaving barkless patches of white 

 wood. These patches turn dark gray in color, and the 

 canker becomes more or less covered with white streaks 

 of dry pitch. Many diseased trees under ten years of 

 age have a stunted, bushy growth and a yellowish color. 

 On older trees the first indication of damage appears 

 as scattered dead and dying branches. The damage 



becomes more apparent with the continued develop- 

 ment of the disease until the tree dies. Control: Blister 

 rust spreads from one currant or gooseberry bush to 

 another, but cannot spread from one pine to another. 

 It can infect pines only through the medium of currants 

 and gooseberries. The rust can be controlled effectively 

 in pine stands by systematic eradication of all species 

 of currant and gooseberry bushes within a short radius 

 of the trees. The exact distance varies with local con- 

 ditions, but ordinarily a distance of nine hundred feet 

 will be sufficient to protect the pines. Cultivated black 

 currants (Ribes nigrum) should be eradicated within a 

 radius of one mile. The black currant is more suscep- 

 tible to the disease than other species of currants and 

 gooseberries and is an important factor in its spread 

 over long distances and its local establishment. The 

 Department of Agriculture is opposed to its growth in 

 the United States and recommends its elimination from 

 the Pacific, Rocky Mountain, Atlantic, Appalachian, 

 Ohio Valley, upper Mississippi and Lake States. 



ORNAMENTAL SMALL CONIFERS. Blight (Phomopsis 

 juniperoi'ora) . Occurs in Eastern and Middle Western 

 States and extends throughout the South to the Gulf 

 coast. Fungus blights the tender growth of young 

 stock, producing a canker on the stems of junipers, 

 arborvitae, cypress, Retinospora, Cryptomeria and 

 Taxus. Control: Spray systematically with Bordeaux 

 (5-5-50), beginning early in season. Add one pound 

 resin fish oil soap to every twenty-five gallons as an 

 adhesive. Destroy badly blighted stock. 



HYDRANGEA. Leaf spot (Phyllosticta hydrangea:). 

 Common. Rusty brown spots on leaves, or blighting of 

 entire tops. Control: Spray with Bordeaux or lime- 

 sulphur. 



LILAC. Mildew (Microsphfera alni). Common 

 wherever lilac is grown. Whitish, cobwebby growth on 

 surface of leaves, which gives them a dusty appearance. 

 Control: Dust with mixture of nine parts finely ground 

 sulphur and one part arsenate of lead at intervals of 

 about two weeks during the summer. Spray with Bor- 

 deaux (4-4-50) when leaves fall in autumn and again 

 in the spring before growth commences. 



ROSE. Black spot (Diplocarpon rosee). Found wher- 

 ever rose is grown. Purplish black spots that have irreg- 

 ular ringed margins appear on upper leaf surface. 

 Leaves turn yellow and fall early. Control: Dust with 

 mixture of nine parts finely ground sulphur and one 

 part arsenate of lead at intervals of two weeks during 

 the growing season. Spray with Bordeaux (4-4-50) 

 when plants are dormant. Rake up and burn infected 

 leaves. Grow more resistant varieties and keep plants 

 healthy by cultivation and by winter protection if nec- 

 essary. 



Mildew (Spheerothfca pannosa). Occurs wherever 

 rose is grown. Whitish or grayish patches on leaves 

 give them a powdery appearance. Leaves curl, die and 

 fall. Thorns, shoots and even buds may be affected. 



