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Atmospheric effects are another source of systematic error in surface displacement estimates from SAR interferometry because they change the refraction index , through which the radar signal passes , and thus corrupt the radar phase observable . Fertilize the soil every month during late spring and summer , but mix your fertilizer half-strength . North-facing slopes and sites that experience winter shade would both work well . Reapply the mulch every few years as it breaks down . 2.3 and 2.4 ) have both been identified in SAR interferometry images ( Massonnet and Feigl , 1995a ) . Although one will not know exactly what one is getting with a seedling rootstock — every single seed is a genetically different individual — hardiness , anchorage and adaptability to different soil types are generally excellent . Some common diseases include apple scab and fire blight . Control efforts with fungicides require reapplication every 7 to 14 days . Pear trees , as a rule , also require cross-pollination by another pear variety to produce a large crop . Symptoms of gray mold depend on both host and the environmental conditions . ‘ Liberty , ’ ‘ Redfree , ’ and ‘ William ’ s Pride ’ are all scab resistant . Southern blight can be confused with white mold ( Sclerotinia sclerotiorum ) , another fungus with a broad host range that produces white , cottony mycelia . By this we mean that , within a given pixel , the position of radar scatterers has not changed to any significant degree , but the ensemble of scatterers ( i.e ., the entire ground surface within that pixel , as well as some adjacent ones ) has moved up , down , or sideways in some correlated fashion . If some peony shoots wilt , yet the basal parts look perfectly sound , your plant may be suffering from Verticillium wilt . Varieties and Rootstocks : Apples Selecting Apple and Pear Varieties Apple flowers must receive pollen from another variety of apple to produce fruit . Pruning and destroying all dead or diseased canes in the spring will reduce the initial fungus population . The best solution of course is to choose varieties with some resistance to the disease . The main distinguishing feature between the two species is that the Japanese beetle has five tufts of white hair along both sides of the abdomen and two small dots of white hair on the tip of it . In order to be effective , they must be applied at the first sign of disease and repeated every 7-10 days . Apples are insect pollinated , with bees and flies transferring pollen from flowers on one tree to those on another . The quality of the fruit from these disease-resistant trees is acceptable , although it may not measure up to that of some other varieties recommended in Table 1 for zones 4a and 4b . Remove all soil within one foot of the infected plant , to a depth of one foot . In principle , all three compo-nents of surface displacement could be obtained from space ; in practice , we are only likely to obtain at most two , if data from both the ascending and descending passes of the satellite are available .