Heavy rainfall over parts of southwestern and south central Missouri may do more than replenish soil moisture needed by crops, say Extension specialists, at the University of Missouri.
Moisture also helps control insect pests, such as alfalfa weevil and armyworms.
Fungus and other natural controls need moisture to thrive and control the worm-like larvae that damage forages, said Wayne Bailey, MU Extension entomologist.
Vance Hambelton, Extension agronomist, at Gainesville, said he emptied 3.4 inches of rain out of his gauge during the weekend. "We're finally getting the rain that we have lacked the last couple of years."
Stacy L. Hambelton, specialist, at Alton, said he's getting calls about potential armyworm damage. Farmers are concerned after the devastation caused by a heavy infestation in 2001.
The Extension specialists were part of a weekly crop protection teleconference, from the MU campus, in Columbia.
Bailey said armyworms in particular are more likely to build up in dry weather than in wet. "Armyworms are very susceptible to moisture, as the fungal pathogens build up quickly.
"Typically, if we see a big buildup and damage one year, the next year the armyworms will start to build up, but die out. A big population builds reserves of parasites and pathogens that carry over."
Bailey is staying in contact with Extension entomologists, in Arkansas, to get an early warning of outbreaks to the south.
Alfalfa weevil populations reached threatening levels--until the rains hit. "Rain drowns recently hatched larvae as they move up the stem from the hatching sites to the plant terminal," Bailey said. "The larger death loss will come as moisture encourages a fungal infection."
Infected weevil larvae turn yellow and become lethargic. Once the fungus is established, the larvae die in a few days.
Weevil larvae, the worm-like immature stage, have a large appetite for alfalfa leaves, especially those in the growing tips.
Alfalfa weevil will continue to be a threat to be watched, as there was heavy egg laying much later than normal last fall, Bailey said.
Before the rain, the weevil population had built up to a treatment threshold, at Mount Vernon, Bailey said. "If the weather turns dry again, insecticides will likely be needed."
Alfalfa weevil populations are reported as far north as Interstate 70. Bailey found alfalfa weevil Wednesday, April 10, in plots at the University South Farm, Columbia.
Pat Guinan, Extension climatologist with the Commercial Agriculture Program, said much of the state received moderate rainfall, with heavier rains south of a line from Joplin to Springfield to Ste. Genevieve. "The heaviest rains fell from Branson, West Plains to Ellington," Guinan said.
Little rain fell on Poplar Bluff and Cape Girardeau. "The Bootheel is drying, which they need," Guinan said. "They had been too wet."
Dry weather continues in extreme northwest Missouri. Atchison, Nodaway and Worth counties are in near-drought condition. "Much of western Iowa is already in moderate drought," Guinan said. "They need rain."
The forecast for the state is for unsettled weather systems passing through the state in the coming week, with possibilities of rain in northwest Missouri.
The long-range outlook is for above-normal temperatures, which reduces the possibilities of killing frosts. "Northeast Missouri is in the center of a large, multi-state, area forecast for above-normal temperatures and above-normal precipitation," Guinan said.