Controlling pests in Texas alfalfa fields challenges growers

By MANDY SPIKES | Central Texas Edition

Dale Mott holds a book about Managing Insect Pests of Texas Forage Crops during an alfalfa production workshop, held Mar. 6 in Temple. -Staff photo by Spikes

March 18, 2004 -- Insect control is a key factor in producing good quality alfalfa. Knowing the best way to control those pests on their fields, as well as knowing the difference between a pest and a beneficial insect remains a challenge for producers.

At the Intensive Alfalfa Production Workshop, which took place March 6 in Temple, Dale Mott discussed insect control for alfalfa growers.

"There are many definitions for integrated pest management (IPM), but they all have the same meaning," Mott said. "The economic aspect is that you minimize input and maximize profits. The ecological aspect is that you are trying to protect the environment."

Two components of IPM is knowing the difference between a pest and a beneficial insect. This can be done by knowing what the various insects look like and their biology. Another component is monitoring.

"Monitoring must be done on a regular basis. Without it, you don't know what's out there," he said.

Taking an accurate sample size and the location of the sample are important factors to remember. "You should do ten sweeps in four locations. You might ask why so many samples and locations. This is because of pest distribution, both with spacing and through time. "

Two types of alfalfa pests that Mott described are the chewing pests and the sucking pests. "Chewing pests are the alfalfa weevil, blister beetles, grasshoppers, and caterpillars.

"The first and second cutting are heavily damaged by the alfalfa weevil. The damage usually increases as the insects get larger. Blister beetles love alfalfa blooms and become abundant from June to September. You should scout your fields at least two weeks prior to bloom to see what the infestation is."

Grasshoppers are mostly damaging in the dry years, he continued. The best way to control them is to get them when they are small.

Sucking pests are the pea aphid, spotted alfalfa aphid, blue alfalfa aphid, cowpea aphid, leafhoppers, and thrips." The most commonly seen aphids in Texas alfalfa is the pea aphids. All aphids are pests and can reproduce very fast, he said.

Leafhopper population tends to be highest from late summer and thereafter. Several species of leafhoppers feed on alfalfa. "They are smaller and since they are also faster, it makes them harder to scout."

Thrips feed on alfalfa blooms, buds and leaves. Thrip damage to alfalfa grown for hay or forage is generally minimal. "Treatment is not needed for Thrips," Mott explained.

Beneficial insects that he listed are lady beetles, lacewing larva, spiders, pirate bugs, big-eyed bugs, and assassin bugs.

"The main thing you should do is monitor your crop and know what's out there. A sweep net is a good tool for monitoring many pests. Get to know your insects because identification is key."