Scientists fighting plague of fire blight that has destroyed fruit tree orchards throughout much of US

Title "'Wonder drugs' come to aid of agriculture" superimposed over close panning shot of pieces of fruit / shot from moving vehicle of desolate farmland / sign on side of road saying "For sale by owner 560 acre ranch" / gate in fence of deserted farm / two shots of branches lying on ground of dead pear trees destroyed by fire blight / CU hand pulling brittle leaves of dead branch / CU dead pears on branch / close shot of hand of man sticking pencil into dead pear on branch / shot of exterior of USDA lab in Marysville, CA / words on door saying "Tree fruit disease laboratory" / plant pathologist John C. Dunegan looking through microscope at dead fruit tree branch / CU hand cutting diseased apple in half with knife next to healthy apple / pear tree orchard in Marysville / two shots of Dunegan pouring mixture of terramycin and streptomycin into spraying machine / three shots of farmer driving tractor pulling spraying machine spraying orchard with mixture / Dunegan looking at healthy pear tree branches / Dunegan looking at healthy pears on branch / CU healthy pears in bin / grocer handing healthy pear to boy at market / CU boy eating pear / Note: exact day not known