How to Get Rid of Worms in Alfalfa Plant: A Complete Guide

Alfalfa, also known as lucerne, is a popular forage crop grown around the world for feeding livestock. However, various species of worms can infest and damage alfalfa plants If left uncontrolled, worms can significantly reduce the yield and quality of your alfalfa hay or silage.

In this comprehensive guide we will discuss the most common worms that attack alfalfa how to identify them, and effective strategies to get rid of worms in your alfalfa plantings.

Types of Worms that Infest Alfalfa

There are several worm species that can be problematic in alfalfa fields

• Alfalfa caterpillar – The larvae of the alfalfa caterpillar moth. They are green worms with a white stripe down the back. They feed on leaves and can completely defoliate plants.

• Armyworms – The larvae of various moth species. Armyworms are smooth, greenish-brown worms with faint stripes. They are voracious leaf feeders.

• Cutworms – The larvae of several moth species, like armyworms. Named for their habit of chewing through plant stems at ground level.

• Webworms – Caterpillars that feed inside protective silken webs. Alfalfa webworms have a dark stripe bordered by a white line on their backs.

• Loopers – Inchworm caterpillars named for their looping movement. Alfalfa loopers are light green with faint white lines along the back and sides.

• Rootworms – Such as the alfalfa snout beetle, with C-shaped grubs that feed on roots.

How to Identify Worms in Alfalfa

Regularly scouting your alfalfa fields is key to identifying worm infestations before they cause major damage. Here are signs of their presence:

• Chewed or skeletonized foliage with leaf veins remaining. Armyworms, loopers, and webworms feed this way.

• Large, irregular holes in leaves. Cutworm and alfalfa caterpillar feeding damage.

• Plants severed at the stem base. Indicative of cutworms.

• Presence of silken webs with worms inside. A sign of webworm infestation.

• Patches of stunted or dying alfalfa. Can be caused by rootworm larvae feeding on roots.

• Frass (worm droppings) on leaves and ground. Shows caterpillars are actively feeding.

• Seeing the worms themselves is definitive evidence. Compare to pictures to identify the species.

Cultural Control of Worms in Alfalfa

Cultural control methods create an environment less favorable for worms while enhancing growing conditions for the crop itself. Here are some useful practices:

• Crop rotation – Rotating alfalfa with non-host plants like corn or wheat helps break pest cycles.

• Harvest timing – Timely cutting and removal of hay deprives worms of food and shelter.

• Irrigation – Avoid overwatering as excess moisture encourages worm issues.

• Weed control – Eliminate weeds around fields that can harbor worm pests.

• Field sanitation – Promptly remove hay stubble and destroy crop debris after harvest.

• Fertilization – Foster healthy, vigorous alfalfa stands, which are less susceptible to worms.

• Plant resistant varieties – Some alfalfa cultivars have enhanced worm resistance.

Biological Control Options

Biological control uses natural predators and pathogens to suppress pest populations. Here are biologically-based worm management options:

• Predatory insects – Encourage beneficial predators like lady beetles, ground beetles, parasitic wasps, and lacewing larvae which will feed on worms.

• Parasitic nematodes – Microscopic roundworms that parasitize and kill worms but not plants.

• Bacillus thuringiensis (Bt) – A bacterial insecticide that is effective against caterpillars but harmless to other organisms.

• Entomopathogenic fungi – Fungal insecticides can control worms while preserving beneficial insects.

• Nosema locustae – A protozoan pathogen used to control grasshoppers but also infects caterpillars.

• Viruses – Certain viruses are worm-specific and can be applied as bioinsecticides.

Mechanical Control Methods

Mechanical techniques physically remove worms from plants:

• Handpicking – Labor intensive but useful for small infestations. Drop picked worms in soapy water.

• Resistant varieties – Some alfalfa varieties tolerate worm feeding better than others.

• Vacuuming – Specialized vacuums can suck worms off foliage.

• Tilling – Tilling exposes and kills overwintering pupae in the soil.

• Mowing – Well-timed cutting and removing hay before worms can reinfest new growth.

• Flaming – Using propane flames to burn worms off plant surfaces.

• Sticky traps – Yellow traps lure adult moths to monitor populations.

• Pheromone traps – Traps baited with sex attractants capture male moths.

Chemical Control Measures

When other methods fail to control heavy worm infestations, insecticide application may be warranted. Follow these guidelines:

• Use selective insecticides that target worms but not beneficial insects. Products containing Bacillus thuringiensis (Bt) are a good option.

• Rotate chemical classes to prevent resistance developing in worms.

• Follow all label directions carefully regarding rates, timing, protective gear, grazing/harvest intervals, etc.

• Target young worms as insecticides are most effective against early larval stages before extensive damage occurs.

• Repeat applications if needed according to label instructions as new generations hatch.

• Avoid broad-spectrum insecticides like organophosphates that kill natural enemies leading to secondary pest outbreaks.

Integrated Worm Management in Alfalfa

The best approach combines multiple tactics into an integrated pest management (IPM) strategy:

• Start with preventive cultural practices to promote plant health and disrupt pest cycles.

• Scout regularly to detect worms early before populations explode.

• Use forecasting models to time monitoring and management actions.

• Employ biological control options first to conserve beneficial insects.

• Apply mechanical control methods where feasible to reduce reliance on pesticides.

• Use selective insecticides as a last resort if required to prevent economic loss.

• Keep detailed records of pest pressure and management outcomes to refine future IPM plans.

Worm pests can significantly hamper alfalfa growth, vigour, and productivity if left unchecked. But implementing a well-planned integrated pest management strategy can effectively protect your alfalfa plantings. The key is diligent monitoring to detect infestations early, starting with preventive cultural practices, incorporating biological control agents, and using selective insecticide applications only when absolutely necessary. By proactively managing worms with IPM, you can successfully safeguard your alfalfa yields and quality.