If you’re looking for a way to protect your alfalfa from weevils, you’ve come to the right place. This article will help you learn when it’s best to spray for alfalfa weevils, what products and techniques work best, and how to get your farm ready for treatment.

Alfalfa weevil infestations are usually caused by beetles that lay eggs on the plant’s leaves or buds. The larvae then feed on their host plant until they mature into adults and fly away in search of another host plant. Alfalfa weevils can decimate an entire crop if left untreated, so it’s important to keep an eye out for signs of an infestation and treat accordingly.

The simplest rule to follow is that you should spray when the alfalfa weevils are found. There are no good economic thresholds for a lot of these insects because alfalfa curculio, leafhoppers, or potato leafhoppers can come in and cause an enormous amount of damage in a very short period of time. It all depends on how much early growth there was and how rapidly the insects can destroy that early growth. Hopefully, everyone is out scouting their fields now so they don’t get hit with surprises like I did last year before I sprayed.

If you do have to spray, there are two options – insecticides and beneficial nematodes, if you aren’t worried about using chemicals on your crop. Insecticide use isn’t recommended unless it has been proven to be effective for controlling alfalfa weevils and does not kill the beneficial nematodes in the soil. When applying an insecticide, let it sit for at least 24 hours after application before turning cattle or horses back into a pasture containing treated hay – just to ensure they don’t have problems with insecticides either.

The alfalfa weevil hatch can be 10 days late this year.

In Minnesota, alfalfa weevils generally emerge between April and June depending on temperatures. Warmer temperatures cause insects to start emerging earlier in the spring. If early spring is warmer than normal, alfalfa weevils may emerge 10 days early.

The hatch can also be later than expected if spring is cool and wet. The alfalfa will be growing slowly and so will the weevils that are feeding on it. This means that you need to check your fields for damage before spraying for them or you may waste money!

How to Control Alfalfa Weevil

Alfalfa weevil larvae are a pest that can cause serious damage to alfalfa and other related crops. In fact, the larvae are capable of completely destroying an entire field of alfalfa within a matter of weeks. The best way to prevent this from happening is to spray for alfalfa weevils at the first sign of infestation.

  • Insecticide application is recommended when the first 50% of larvae are the size of the head of a pin (1/16 inch long), or when 50% of plants have shoot damage, or when the tips of plants are dead.
  • In addition to beneficial insects, planting an alfalfa variety resistant to alfalfa weevil can reduce problems. Consult your local extension office for more information on varieties available in your area.
  • Proper mowing and harvesting techniques can help prevent problems with alfalfa weevil by removing weevils from fields and reducing plant growth that would be susceptible to weevil feeding.

Alfalfa Weevil Life Cycle

The alfalfa weevil has four life stages: egg, larvae (the worm stage), pupae (or resting stage), and adult. The adults are small gray to black beetles with a white spot on their heads. Adults are active feeders and will damage the first growth of alfalfa in spring. However, the feeding of adults is not nearly as damaging as the feeding of larvae. Adult alfalfa weevils can be easily seen on the plants in early spring and lay small, pinhead-sized eggs at the edge of buds or into developing leaves.

After hatching from eggs, the tiny larvae feed for about two weeks before becoming 1/4 inch long and larval feeding peaks from bud to one-half bloom stage. Then larvae stop actively feeding and begin to drop to the ground, where they spin a cocoon and pupate for about one week before emerging as an adult beetle. Once emerged from its cocoon, an adult insect can live up to 40 days during late summer or fall if conditions remain favorable enough for them.

Alfalfa Weevil Damage

To determine when to spray for alfalfa weevils, it’s important to identify the damage they inflict. Alfalfa weevil is the most damaging insect pest of alfalfa in the United States. These tiny, light-brown beetles feed on all above-ground parts of the plant and are most damaging when found on immature plants during winter, spring, and fall. The alfalfa weevil can survive temperatures as low as 30 degrees Fahrenheit (1 degree Celsius) by entering a period of torpor to reduce its metabolic rate. They will begin to emerge from this state when temperatures reach 45 degrees Fahrenheit (7 degrees Celsius). The larvae are dark green with a tan or grey head capsule and white stripes along their backs. Larvae will also feed greedily on alfalfa plants before pupating into adult beetles after about three weeks.

Alfalfa Weevil Economic Impact

You’ll also want to control alfalfa weevil larvae because they can destroy large amounts of alfalfa. Indeed, if left unchecked, larval activity has the potential to cause a significant economic impact. For example, this damaging insect pest can reduce hay yields by up to 40% and lower forage quality by increasing the amount of fiber in the feed.

What to Spray for Weevils

The alfalfa weevil is a tiny brown insect with a dark stripe on its back. If allowed to get out of control, this pest can destroy an entire field of hay. The most efficient way to determine when to spray for alfalfa weevils is through the use of a sweep net. Sampling should start as soon as the first buds are noticed in the springtime and continue weekly until the alfalfa has started to bloom. At that time, the insects will have moved into other areas, and spraying will no longer be necessary.

Sweep sampling consists of making 50 sweeps with a 5-foot (1.5-meter) net in at least five locations throughout the field or pasture. Record how many insects you catch in each spot and average them together. If it looks like there are more than one or two insects per sweep, your crop is probably in danger and it’s time for treatment.

If you don’t have a sweep net or don’t want to bother with it, another method is to take note of when the first flowers appear on plants in your area—this is called “bloom.” Alfalfa can be sprayed up until right before this stage without damaging pollinators such as bees, so if you keep track of when bloom happens every year, you’ll know approximately what time spraying needs to stop later on down the road.

Final words,

Alfalfa weevils are a serious threat to alfalfa crops. They feed on the leaves of alfalfa plants, and can cause significant damage if left untreated. The most effective way to control alfalfa weevils is by spraying your crops with a biological insecticide. Here are some tips for when to spray for alfalfa weevils:

  • Spray during the early morning or late evening when the air is still and there isn’t much wind, because this will help keep the spray from drifting away from your target area.
  • If you’re spraying in areas where there’s heavy frost or snowfall, wait until spring to spray so that any larvae that have survived won’t have time to develop into adult beetles before they’re killed by the chemical treatment.

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