Plan for pests this growing season
Changes in weather conditions and chemical use has impacted field crop pest outbreaks throughout the United States. Kevin Rice, University of Missouri (MU) Rice gave Missouri farmers an overview of what to expect this year at a field day hosted by MU last week.
Last year, the United States saw the biggest fall armyworm outbreak in 30 years. While fall armyworm outbreaks tend to happen in boom/bust cycles, experts expect outbreaks to occur more often.
“That’s because of our milder winters,” Rice said. “Fall armyworms only overwinter in the tip of Florida and in Texas, and each year they reinvade the whole North American continent. Now, because of our milder winters, they’re overwintering in higher latitudes, but their natural enemies are not. They are able to get a jump start and get a higher population higher overwinter population, so we might see more fall armyworm outbreaks on a more regular basis than every 30 years.”
Though many integrated pest management tools exist for fall armyworms, others have recently proven ineffective.
“We found that fall armyworm is resistant to pyrethroids (insecticides) in our neighboring states,” Rice said. “We are not tracking that at the University of Missouri because those females fly over thousands of miles. We can assume if they found resistant populations in five neighboring states, that those genes are being passed and mixing throughout the population.”
While many other options exist to manage fall armyworms, supply can be an issue.
“We’ve been using pyrethroids, and last year there was a scramble in competition among growers to get that supply,” Rice said. “I’m hoping that maybe the chemical companies have adjusted and might have more supplies.”
Working with a knowledgeable chemical representative when making fall armyworm decisions is crucial.
“They’re called armyworms because they move in and devastate a field like an army,” Rice said. “Personally, I would go for something that you know works on fall armyworms, because they are so devastating so fast.”
Drought conditions in 2018 decimated Japanese beetle populations over the past three years, but populations are expected to rebound soon.
“The larvae of Japanese beetles will only feed on grassroots. They can't feed on anything else,” Rice said. “When we experience a drought that shrivels up the roots, they don't have a food source and you get this massive population crash.”
Japanese beetles can greatly damage soybeans without impacting yields.
“Your thresholds are 20% defoliation in the reproductive stage, and that's the entire plant,” Rice said. “You can see a lot of damage on the top. It’s almost cosmetic. You have to look at the whole plant to really determine if you're at that threshold, because it looks a lot worse than it usually is.”
Native stink bugs have emerged as a key pest across the United States. Several theories why exist. One is that fewer broad-spectrum pesticides that used to target lepidopteran insects like European corn borer before the advent of Bt transgenic corn. This may have opened up access for stick bugs, Rice says.
Brown marmorated stink bugs, an invasive species in Missouri, have also seen a large population increase.
“Brown marmorated stink bugs prefer late-season beans,” Rice said. “It likes to be on carbohydrates at the beginning of this season. Then at the end of the season, before it overwinters, it likes to go stock up on proteins [such as late-season soybeans]. That creates a problem for scouting, and no one really likes to scout late season beans, especially when they’re really tall.”
MU researchers are working on a new stink bug management threshold system that hopes to eliminate the need for field sweeps. In early trials, clear sticky traps infused with pheromones to attract multiple species of stink bugs were placed 5 meters from each corner of soybean fields.
“Then we went out and surveyed the fields with sweep nets,” Rice said. “We looked at the number of bugs on [the sticky traps], and for three years, we found that it’s strongly correlatedWhen you sweep the field and get higher number of bugs, you get higher number of bugs on these traps.”
Additional trials are expected to be held across 15 states in the next two years, with a goal to determine new thresholds for spraying.