Iowa State University researchers said Monarch butterfly caterpillars were seven times more likely to die when they ate milkweed plants carrying pollen from Bt corn, which contain a pest-fighting gene, compared with conventional varieties. Bt is short for bacillus thuringiensis, a naturally occurring soil bacterium that acts as a pesticide. This gene is used to repel bollworms, European corn borer and other pests. Greenpeace stated that the findings indicated further testing of GM crops were needed. Drought during flowering decreases flower and then seed number per unit area.
Corn reacts by a delay in silk emergence relative to pollen shed and an increase in seed abortion.
Soybeans will increase pod abortion. In corn, the shorter filling period is caused by premature water loss from the seed. Drought stresses in later pod-filling stages in soybean result in a decrease in maximum seed volume. Temperatures at 95F with low humidity and the onset of droughty soil conditions can limit yields in fields. Soybeans grown in dry soils can reduce nodule formation, development and later nitrogen-fixation early in plant growth and these symptoms can also appear later when soil temperatures reach greater than 90F for several days.