May 21, 2021

Alfalfa is called the queen of forages. It is the perfect crop for those involved in livestock production. It produces great yields and is highly nutritious containing very digestible fiber and protein. Once planted, it can last for many years depending on how well the producer takes care of it. Harvested too many times a season and the stand will thin. This native of the “Cradle of Civilization” area of the world, which includes Turkey, Syria, Iraq, and Iran has a deep taproot that allows it to grow in low moisture areas.

Just like alfalfa being imported from Southwest Asia, its major pest, alfalfa weevil also came from that area of the world. This year, those insects’ numbers are up dramatically. The little green worms hatch from eggs laid last year and start feeding on the tips of alfalfa. This year the cold and dryness of spring slowed the alfalfa growth allowing these little larvae to do extensive damage. As they consume new growth on the plant they also reduce the amount of tissue that can photosensitize, slowing the plant growth even more.

My first introduction, as a boy, to this insect, was baling hay. Riding the hay wagon, stacking bales during the first cutting in June there would be thousands of brown bugs with a black stripe down its middle and a short snout. These are the adult weevil. They have pupated from the larva stage which is a small, light green worm with a wide, white stripe down the center of its back. The adult beetle also feeds on alfalfa but does not do near the damage as the larva.

There are almost 100,000 known species of weevils with adults the ones who have the elongated snout with chewing mouthparts. There are many species of weevil that consume grain by boring holes into seeds. Purdue has been involved in a project in Africa to help farmers protect stored cowpeas from weevil damage. They trained farmers on the use of a special bag that could store grain and seal out moisture, leading to the death of any infesting weevils. This resulted in about half a billion dollars per year in saved grain each year.

There is a type of weevil in fruit and nut production called a curculio. The plum curculio is a major insect in apples and cherries. The adult female cuts a crescent shape into a small developing apple and lays an egg. If the apple falls to the ground, the insect will develop. If the damage is not severe enough to cause the fruit to drop, then the growing apple will crush the bug and leave a tan scar on the fruit. Either way, the fruit is lost or damaged.

The weevil that has had the most publicity is the boll weevil. The Boll Weevil Song reach number 2 on the music charts in 1961. This insect severely damaged cotton crops and led to destitute farmers especially during the depression years of the 1930s. The eventual answer was to use insecticides like calcium arsenate and DDT as they become available.

Just like the alfalfa weevil, it is the boll weevil larva stage that does the most damage. The alfalfa weevil really only has one damaging generation per year while the boll weevil can have 10. Most farmers' solution to alfalfa weevil is to cut the crop early and reduce the weevil population. Some may survive and feed on the second cutting and have to be sprayed with insecticide.

When it comes to feeding the world there is a weevil somewhere bent on thwarting your efforts. Man has been successful in outsmarting the boll weevil by perfecting a synthetic attractant pheromone blend, creating a lure that is used to trap the boll weevils. Combining that with timed insecticide applications has almost eradicated the bug in the US. No such luck for us alfalfa farmers here in Indiana.

Mark Kepler, Extension Educator- Agriculture and Natural Resources 

Purdue Cooperative Extension Service-Fulton County 

1009 West Third Street, Rochester IN 46975

574 223 3397 http://www.ag.purdue.edu/counties/fulton/pages/default.aspx https://www.facebook.com/Purdue.Extension.Fulton