Damaged plants can scare farmers. Never before have they seen this type of damage, where the insect eats through so much of the leaves. Farmers know about stem borers, but because they aren’t often seen (hidden in the stems), they don’t often scare farmers like this new pest, the Fall Armyworm.
The spectacular-looking damage is very photogenic. The combination of farmers’ nervousness, media alarmism, and politicians’ quick reaction to do something has led to some bad decisions, including the use of Highly Hazardous Pesticides. Some older pesticides, which have long been banned in other parts of the world due to demonstrated human health impacts, are still available and used in some African countries. Some of the older pesticides don’t work, because FAW has developed resistance to them.
Such panicky responses are likely when the farmers and others don’t understand the potential impact of FAW damage. The quick response to sight of significant-looking damage is to assume that it will cause dramatic yield reduction. But that’s not necessarily true. In fact, we know that in most cases FAW does NOT cause “total destruction”. In most cases the leaf damage does cause some yield reduction, but it is probably far less than what farmers without experience with the pest believe.
Maize has been selected by humans for thousands of years to yield well, even in face of damage to insects, pathogens and other threats. These eons of selection have resulted in maize plants that have considerable capacity to compensate for foliar damage.
The response of maize yield to FAW infestation has been studied in the field a number of times in the Americas. A review of these studies shows that while of concern, FAW damage in maize is not devastating.While a few of the studies show yield reductions due to FAW of over 50 percent, the majority of the field trials show yield reductions of less than 20 percent, even with high FAW infestation (up to 100 percent plants infested). Maize plants are able to compensate for foliar damage, especially if there is good plant nutrition and moisture. While FAW needs to be managed sustainably by farmers, it is not cause for panic.
In FFS, we can examine our maize’s ability to compensate for defoliation by conducting a Special Topics experiment (see section B.6.7). The experiment will look at the impact of defoliation of maize plants at different growth stages on grain yield.