Robert Pore's Ag Blog

LINCOLN — Producers across the state might not recognize another factor behind poor alfalfa growth -- potato leafhoppers and alfalfa weevils, a University of Nebraska-Lincoln forage specialist said. "The severity of their impact is just greater during dry years," said Bruce Anderson, forage specialist in the university's Institute of Agriculture and Natural Resources.

Potato leafhoppers are tiny, yellowish-green, wedge-shaped insects that turn alfalfa yellow and stunt plant growth. Early symptoms appear as discoloration on the tip of alfalfa leaves, but as leafhoppers continue to feed the entire plant may stop growing, Anderson said."Right now, we don't know how severe the damage is going to be," he said.

Because leafhoppers are migratory, their arrival is dependent on winds from the southeast, Anderson said. Some have already arrived, but early summer is a typical time of year for producers to begin seeing leafhopper damage, he said.

Alfalfa weevils also are preventing regrowth in a number of fields, said Keith Jarvi, integrated pest management specialist at UNL's Northeast Research and Extension Center at Norfolk. Not only has the lack of rainfall stressed alfalfa, but so has the reduced presence of a fungal disease that reduces weevil populations, he said.

"We've already seen some damage on regrowth from the adults," Anderson added. "Growers just aren't recognizing it because conditions have been so dry."

After the first alfalfa harvest, adult weevils feed on emerging shoots preventing fields from becoming green shortly thereafter, Anderson said.If fields begin to look poor, producers should scout fields for individual insects, Jarvi said. Adult weevils are approximately three-eighths of an inch long and light brown with a dark brown stripe halfway down the back. If fields don't green up three to five days following harvest, there is a good chance insects are involved, he said.

"It takes close examination because weevils are so small. Adult weevils like to hide under plant litter and dead material, especially during the heat of the day," Anderson said.
Both leafhoppers and weevils can be controlled with insecticides if the situation permits, Anderson said. The key is to scout fields regularly to detect pests early and spray while they are still present and before irreversible damage has been done, he said.

If leafhoppers have stunted growth, first remove poisoned plant tissue that can ultimately reduce yields to stimulate new growth before applying insecticide, Anderson said. Mow new seedlings and then spray insecticide if necessary, he said.

As with any chemical, be sure to follow instructions, restrictions and precautions, Jarvi added. Remember to examine new growth following treatment because factors including weather, non-uniform or inadequate chemical application and poor choice of insecticide may adversely affect chemical control, he said.

Besides insects, the big problem facing alfalfa producers this season is lack of moisture, Anderson said.“Producers have to realize there isn't a whole lot they can do. If yields aren't going to reach expected levels, they should begin thinking about other sources for hay," Anderson said.