Blister Rust on White Pine 



457 



tare), whose roots are often so tangled 

 with those of other plants that hand- 

 pulling is difficult and costly. A com- 

 plete kill was had with one application 

 of the spray to foliage and stems ; about 

 a pound of chemical was used in a gal- 

 lon of water. Equally good results were 

 obtained on this species with ammoni- 

 um sulfamate and with dichlorophen- 

 oxyacetic acid, commonly called 2,4-D. 



Ribes with roots extending under 

 logs, between rocks, or in places where 

 it is hard to dig are cut off at the 

 crown; the freshly exposed surface is 

 treated with equal parts of salt and 

 borax, saturated ammonium sulfamate, 

 or with concentrates of aqueous amine 

 or ester in oil formulations of 2,4-D. 

 When so applied, small amounts of the 

 chemicals kill the crowns and roots of 

 several species of ribes. 



Intensive forest management is im- 

 portant in blister rust control areas as 

 an aid in the suppression of ribes. Also, 

 it helps keep the stands in vigorous 

 condition and will result in the highest 

 possible returns from the timber crop. 



After the white pine crop is har- 

 vested, the viable ribes seed stored in 

 the forest-floor mantle germinate. This 

 exhausts the old seed, and removal of 

 the new ribes before they produce seed 

 prevents formation of another seed- 

 storage problem and leaves the area 

 essentially free of ribes. Thus, in the 

 next crop cycle the suppression of ribes 

 and management of pine stands for 

 blister rust protection will be greatly 

 simplified. 



PROGRESS is being made in the work. 

 The blister rust control area totals 

 about 28 million acres. The rust is un- 

 der control on nearly 12 million acres, 

 or 42 percent of the area. In the future 

 only a low-cost maintenance program 

 is needed to keep this acreage safe for 

 the production of white pine. The ini- 

 tial phases of control have been applied 

 to an additional 1 1 million acres, or 40 

 percent, of the control area. The acre- 

 age comprising this part of the control 

 area is still in a critical condition with 

 respect to the disease. The follow-up 



phases of suppression work must be 

 properly timed and applied to bring 

 control to where future needs can be 

 met by a small maintenance program. 



On the remaining 5 million acres, 

 there is great need for initial removal 

 of ribes. The disease is well distributed 

 and ready to intensify and cause 

 severe damage to pine when favor- 

 able infection conditions occur. In 

 many areas the pine already has been 

 abandoned to the rust because most 

 of the trees are fatally infected. How- 

 ever, only a small amount of this 

 untreated acreage can be worked an- 

 nually with present facilities because 

 first priority must be given to the neces- 

 sary follow-up work on areas where 

 the initial phases of control have been 

 completed. 



Control operations began in 1922 

 in cooperation with the Northeastern 

 States. They were extended to the 

 North Central, Southern Appalachian, 

 Northwestern, and Pacific coast re- 

 gions as they were invaded by the 

 disease, but 11 years elapsed before 

 control work was well under way in all 

 commercial white pine regions. One of 

 the first steps in controlling the rust in 

 each region was to delay its natural 

 spread as much as possible by removing 

 the cultivated European black currant 

 (Ribes nigrum). This plant is highly 

 susceptible and one of the chief agents 

 in the long-distance spread and estab- 

 lishment of the disease in new localities. 

 Its early removal was an important 

 factor in retarding the advance of the 

 disease. 



Extensive acreages were cleared of 

 ribes between 1933 and 1941, first with 

 members of the Civilian Conservation 

 Corps and later with workers paid from 

 unemployment-relief funds. When the 

 Second World War began, it was im- 

 possible to maintain control of the 

 disease in all protected areas because of 

 labor shortages, increased costs, and 

 other war-made conditions. Only a 

 holding program on the better white 

 pine areas was practicable then. Some 

 of the progress already made was lost 

 because partly protected areas could 



