ENVIRONMENT AND WHITE PINE BLISTER RUST INFECTION 487 



COMBINED EFFECTS 



In the southern part of the Lake States, these vegetative radiation 

 and topographic air-drainage influences reinforce each other and add to 

 the incidence of rust where small openings are in valleys. A formula 

 constructed by adding together these features for a site gave a guide 

 that permitted prediction of rust presence or absence with an 89% accuracy 

 in southwestern Wisconsin. Absence of rust where it was predicted 

 occurred 10% of the time. Infections occurred where not predicted only 

 1% of the time (Van Arsdel, et al. 3 1961). 



NIGHT BREEZES —LAKE DRAINAGE WINDS 



A more difficult concept to understand is the distribution of rust 

 in specific patterns because of the paths taken by certain nocturnal 

 breezes. The night breeze distribution control is noted only in the 

 coolest and wettest areas of the Lake States where the climate is most 

 favorable to the rust fungus. Near the Great Lakes, night breezes have 

 been implicated as carriers of the pine-infecting spores. These 2-mph 

 breezes develop as a result of the differences between the water tempera- 

 tures of Lakes Michigan and Superior and the land temperature on the 

 40-mile-wide strip of land between them. The study area was a part of 

 Michigan's Upper Peninsula. 



As the land gets cold at night, adjacent cooled air moves in a low, 

 cold flow out over the warmer lake. Spores released from currant bushes 

 less than 5 miles from the lake are usually carried out over the water 

 by this breeze. Thus, pines near the lakes are seldom infected. Above 

 this cold flow a reverse flow carries the warmer lake air over the land. 

 Updrafts over smaller local spots of warm air, such as occur over 

 swamps, forests, and small lakes, loft some spores to this backflow 

 level. The backflow carries these spores to a strip approximately 

 7 miles wide and 10 to 17 miles from the lake, where they are carried 

 down by a downdraft . These spores infect pines as much as 5 miles from 

 the nearest currant bushes and even infect them high in the crowns . The 

 map in Fig. 6 shows the rust distribution on pines; the chart shows a 

 diagram of the flow. 



Although we have not traced the spores all the way along this path, 

 we have watched the lake breeze carry smoke and balloons along the way. 

 We know the spores have 5 hours to move (before light kills them) in a 

 breeze of 2 mph, so they can go 10 miles. This movement just fits the 

 pattern of rust infections in the past 20 years (Van Arsdel, 1963). 

 Breezes around smaller lakes carry spores in similar patterns. 



Other night winds that affect local rust distributions are down- 

 valley winds and reverse flows from down-slope winds on valley slopes. 

 The larger scale backflow spore impact areas can be seen in the map in 

 Fig. 2. Slope winds into swamps and their reverse flows located 15 to 

 25 ft above the ground are also important in placing rust infections 

 (Van Arsdel, 1958). Fig. 7 shows a typical swamp-slope air movement. 



