Insect pests provide a continual challenge in row crops.
By Angus Catchot
Mississippi State University Extension entomologist
Every year, insect pests cost producers millions of dollars in losses. Just when farmers figure out one pest, another one quickly fills the void. Many factors influence the status of a given pest over time or within a given year. One of the most common and troublesome is resistance.
Resistance commonly occurs with insecticides but it also can occur with transgenic traits. There also are cases where a pest has always been present, but some change in the production system may elevate their status. Sometimes things as simple as changing the crop mix to capitalize on market prices may be enough to cause major shifts in pest species we're accustomed to dealing with. And finally, environmental factors can play important roles in the overall economic importance of a pest on any given year.
We can cite numerous examples of insecticide resistance in most major crops, but the bigger question is why it occurs and what we can do about it. A few individuals within a population already contain the genetics to withstand insecticides.
With repeated use of an insecticide, we simply select for those individuals that are not susceptible. Insects are the perfect candidates for resistance because most have multiple generations each year, allowing resistant genes to multiply quickly throughout the population.
Many pests feed on multiple crops grown on the same farm. When farmers make huge changes in crop mixes from previous years, we sometimes see more problems with certain insect pests.
A great example is corn earworm in soybean. Producers in the South have taken advantage of very high corn prices in recent years, more than doubling the acres of corn they traditionally plant. Because corn is a preferred host, growers in the region have seen many more corn earworms cycle through corn in recent years. These pests then attack soybeans.
Sometimes weather itself is enough to influence pest outbreaks. An example is the drought that struck the Midwest in 2012. Hot and dry conditions are very conducive for spider mite outbreaks; as a result, record numbers of corn and soybeans required treatment to control this pest.
Environmental conditions also may prevent timely plantings, which may expose crops to late-season insects such as soybean looper. These pests migrate north every year, attacking soybeans. Early planting has been a relatively effective cultural control method for this pest.
What to do?
It's clear that many factors may influence pest population dynamics. Some can be controlled, others cannot. Producers can do their part to minimize risk from pest outbreaks and to delay resistance by scouting crops on regular intervals and making treatments based on thresholds rather than making automatic applications.
New active ingredients have been slow to reach the market in recent years. It will be critical to use a multi-tactical approach that incorporates all available tools to manage pests and delay the onset of resistance. This will protect the effectiveness of chemistries and transgenes we currently have available.