Even Harley Davidson Can't Resist the Tug of Overseas Factories The New York Times CalPhotos: Rhododendron calendulaceum; Flame Azalea Building a Forest Floor in Five Steps with the Esoteric Science of Throwingthingsonthegroundology The Survival Gardener Genetically modified (GM) crops may have some harmful effects if not managed properly. . There are also concerns about possible health effects and environmental impact, such as gene transfer to non GM plants.