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K-State Agronomy eUpdates

Department of Agronomy

Kansas State University

1712 Claflin Rd.

2004 Throckmorton PSC

Manhatan, KS 66506

785-532-6101

agronomy@ksu.edu

Extension Agronomy

Insects common in alfalfa in late summer to early fall in southwest Kansas

This year there has been a noticeable abundance of insect pests on alfalfa in southwest Kansas, in particular alfalfa butterfly.

The following insects are common in late summer to early fall on alfalfa in southwest Kansas.

I. Insect pests

Alfalfa butterfly

Figure 1. Alfalfa butterfly lifecycle. Photos by Sarah Zukoff, K-State Research and Extension.

The alfalfa butterfly is commonly found in southwest Kansas throughout August and September. They can be found feeding on the nectar of just about anything blooming in the region by the hundreds or thousands. Although these butterflies are beautiful, they can be damaging to alfalfa. The entire lifecycle of this butterfly is completed in about three to four weeks, and they will have multiple generations per year. Their lifecycle is closely related to the cutting cycle of alfalfa. Pictured above is the complete lifecycle of the alfalfa butterfly. Note that these butterflies can be yellow, white, or orange.

Parasitic wasps can help keep these pests in check. However, if 10 caterpillars are found per sweep in established alfalfa, control may be necessary unless the alfalfa will be cut within a few days. In newly seeded alfalfa, the alfalfa caterpillar can quickly consume the whole plant. The threshold for this stage is relatively unestablished, however if one larvae per two plants are found, control may be necessary if no parasitized larvae are found. To check for parasitized larvae, cut the head off the caterpillar and gently roll it from the tail to the head. The wasp larvae should be pushed out and can be seen. Spraying insecticide onto parasitized caterpillars will greatly lower the number of beneficials later in the season.

Alfalfa Caterpillar Management Options

Insecticide

Rate

Beta-cyfluthrin (Baythroid XL)*

0.0125 to 0.022 lb. a.i./acre (1.6 to 2.8 fl. oz)

Carbaryl (Sevin)*

1 lb. a.i./acre

Chlorpyrifos (numerous products)*

Check label, but generally 1 to 2 pints/acre

Chlorpyrifos plus gamma -cyhalothrin (Cobalt)*

13 to 26 fl. oz. of product/acre

Chlorpyrifos plus zeta-cypermethrin (Stallion)*

5.0 to 11.75 fl oz/acre

Cyfluthrin (Tombstone)*

0.025 to 0.044 lb. a.i./a (1.6 to 2.8 fl. oz.)

Gamma-cyhalothrin (Proaxis)*

0.0075 to 0.0125 lb. a.i./acre (1.92 to 3.20 fl. oz.)

Lambda-cyhalothrin (numerous products)*

0.015 to 0.025 lb. a.i./acre

Lambda-cyhalothrin plus chlorantraniliprole (Voliam Xpress)*

5.0 to 8.0 fl oz/acre

Methomyl (Lannate)*

0.45 lb. a.i./acre

Zeta-cypermethrin (Mustang MAX EC)*

0.014 to 0.025 lb. a.i./acre (2.24 to 4.0 fl. oz.)

*Extremely hazardous to bees. Do not apply to alfalfa in bloom. Check label for additional info.

To check the relative toxicity of an insecticide to bees, see here: http://pubs.ext.vt.edu/456/456-016/Section-1_Protecting_Honeybees.pdf

 

 

Blister beetle

Figure 2. Spotted (top) and black blister beetles on alfalfa. Photos by Sarah Zukoff, K-State Research and Extension.

Blister beetles can be prevalent throughout the growing season in alfalfa. The first cutting will usually occur early enough to escape invasion of these beetles, however caution should be taken to ensure none are present if feeding to horses. The amount of toxin can be variable between species with some being far more toxic than others. The spotted and the black blister beetle pictured above are common in alfalfa in late summer and fall. Contact with adult beetles can cause blisters to human skin and can cause serious adverse health effects in horses. Interestingly, the larvae of these beetles feed on grasshopper eggs. Outbreaks of blister beetles are related to earlier outbreaks of grasshoppers.

 

 

Grasshoppers

Figure 3. Grasshopper on alfalfa. Photo by Sarah Zukoff, K-State Research and Extension.

Grasshoppers will feed on the tender new growth, flowers and seed pods of alfalfa. Often controlling grasshopper nymphs is easier than trying to control adults as the adults will readily fly away during insecticide application.

Beet armyworm

Figure 4. Beet armyworm. Photo by Sarah Zukoff, K-State Research and Extension.

Beet armyworms are common in southwest Kansas in a variety of crops including cotton and alfalfa. The beet armyworm can be differentiated from the alfalfa caterpillar by the presence of a black spot just behind the head on either side of the beet armyworm’s body.

 

 

Alfalfa leaf miner

Figure 5. Tunnels made by the alfalfa leaf miner larvae. Photo by Sarah Zukoff, K-State Research and Extension.

Tunnels made by the fly larvae of the alfalfa leaf miner, can be seen in this alfalfa leaf. The dark trail is frass left behind as the larvae tunnel in-between the leaves upper and lower layers. Damage made by this pest is usually minor and insecticide control is usually not recommended.

II. Beneficial insects

Ladybugs

Figure 6. Ladybug on alfalfa. Photo by Sarah Zukoff, K-State Research and Extension.

 

Ladybugs are excellent predators that eat a variety of eggs, aphids, and other small soft bodied creatures. The photo above shows the ladybug feasting on another predator, the Syrphid fly, as it pupates inside its cocoon.

Parasitic wasps

Figure 7. Cocoons indicating the presence of parasitic wasps on alfalfa. Photo by Sarah Zukoff, K-State Research and Extension.

If you spot the cocoons in the photo above, be assured that parasitic wasps are hard at work in your alfalfa. These wasps will lay eggs inside caterpillars and the larval wasps eat the caterpillar from the inside out. The larvae burrow out of the dead caterpillar and soon after, spin silken cocoons. Later they hatch and will fly off to lay eggs into another unsuspecting caterpillar.

 

 

Broconid wasps

Figure 8. Broconid wasp adult, a beneficial insect. Photo by Sarah Zukoff, K-State Research and Extension.

Broconid wasp larvae are beneficial, internal parasites of insect eggs and larvae and are excellent to have around in any garden or crop. The adults are commonly seen feeding on nectar of a variety of weeds species and alfalfa flowers in and around the alfalfa fields throughout the year.

For additional information on management and control options for insects in Kansas alfalfa see:
http://entomology.k-state.edu/extension/insect-information/crop-pests/alfalfa/

Alfalfa Pest management guide can be found at:
http://www.ksre.ksu.edu/bookstore/pubs/MF809.pdf

 

Sarah Zukoff, Extension Entomologist, K-State Southwest Research-Extension Center
snzukoff@ksu.edu

Doo-Hong Min, Southwest Area Crops and Soils Specialist
dmin@ksu.edu