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Category: Sorghum

Tips for managing armyworms

Posted on by Department of Entomology
Monitoring for armyworms is the first step to managing infestations.

By Madeline Drake, K-State Extension news service

MANHATTAN, Kan. — As recent harvests and scouting reports may indicate, armyworms and fall armyworms seem to become a more serious problem for Kansas farmers each year.

For those who may have experienced problems with the insects this year, Kansas State University crop entomologist Jeff Whitworth and agronomist Tina Sullivan say it’s a good idea to understand the issue and develop tactics for tackling future infestations.

Whitworth said the start of any good management program involves early scouting.

“Start by periodically monitoring whatever the vulnerable area you are worried about is to detect any infestation while the ‘worms’ are still small and have not yet caused much damage,” Whitworth said.

When scouting, it’s important to know the thresholds that signal when action should be taken.

“Generalized thresholds are four to five larvae per square foot,” Sullivan said.

Usually two to four generations of armyworms per growing season means monitoring should continue until temperatures turn cold, approximately mid-20 degrees Farenheit for two hours, Whitworth said.

While armyworm infestations cannot be totally prevented, Whitworth recommends traps available to deploy around target areas.

“These traps will not control or prevent an infestation, but they can catch the moths to indicate when these adults are actually flying and thus depositing eggs,” he said.

“Armyworms have chewing mouth parts, thus they bite and chew their food, most often a grass crop like sorghum, brome, wheat, fescue or other,” Whitworth said. “Armyworms eat off the above ground green portion of whatever grass the moth deposited the eggs on.”

Once a field is infested with armyworms, there are some options for eradicating them with insecticides.

“There are several insecticides labeled for armyworm control. Most work quite well if utilized according to the label,” Whitworth said.

Sullivan added that forage stands are especially vulnerable.

“Our forage stands tend to be the most damaged year after year. The cost of insecticide applications is often more economical compared to the seed and planting costs of re-establishing any of our forage fields – tame or native,” she said.

Maintaining a healthy forage stand, Sullivan noted, comes down to good fertility, timely grazing and cutting schedules, and awareness of weather conditions.

More information on crop production and other agriculture-related topics is available at local extension offices in Kansas.

See original posting on K-State Research and Extension News.

More information:
Jeff Whitworth, 785-532-5656, jwhitwor@ksu.edu
Tina Sullivan, tsullivan@ksu.edu

Related: Facts & Information on Crop Pests in Kansas | Armyworms

Armyworms in Crops

Posted on by Department of Entomology
Armyworm feeding on wheat head.

Listen to Agriculture Today’s Episode 2004 where crop entomologist, Jeff Whitworth shares recent concerns with armyworms across crops in Kansas.

Related: Armyworms: Kansas Crop Pests

Agriculture Today is a daily program from K-State Research and Extension and distributed to radio stations throughout the state and region. K-State agricultural specialists and other experts examine agricultural issues facing Kansas and the nation.

Fall Armyworm Active Across Kansas

Posted on by kansasbugs

Fall Armyworm, Spodoptera frugiperda, can damage several important Kansas crops as well as pasture, turf and home landscaping and is currently being reported across the state in various crops and pasture scenarios.  The first fall armyworm flight into Kansas occurred during the first week of July in south central parts of the state and trap counts of adult moths continued to increase in those areas through July while moths also started showing up in the central and northeast part of the state in notable numbers.  There were scattered and treatable infestations of caterpillars in these areas during that timeframe. During this first two weeks of August, fall armyworm moths are noticeable statewide. Trap counts of moths are increasing dramatically in south central areas and reports of significant infestations in the central and eastern parts of the state have been reported.

Given these recent trap observations and reports of caterpillar outbreaks, scouting should continue until the first frost of the season for at risk crops and pasture.  It is critical to scout often and treat, if needed, when the caterpillars are less than a half inch long.  Larger caterpillars are harder to control and do the most damage.  Recommended thresholds and products labeled for control of fall armyworm caterpillars (Table 1) can be found below.

 

Fall Armyworm Thresholds

Alfalfa:  1-2 caterpillars per square foot can destroy seedling alfalfa.  10-15 per square foot can destroy 12” tall plants.

Corn:  damage to whorl stage in early summer is typically not a concern and will not impact yield.  Bt corn may prevent ear damage.

Sorghum:  damage to whorl stage in early summer is typically not a concern. 1-2 larvae/head during flowering to soft dough reduces yield 5-10%.

Wheat:  Larval “window-paning” in early planted wheat can be a concern. Very late second generation fall armyworm will be the biggest concern for wheat.  If 25-30% of plants show damage, examine field frequently.  Treat at 2-3 active larvae/ft.

Pasture/Brome: If damage is notable or there is window-paning, treatment may be warranted with 4 to 5 caterpillars per square foot.

You can read more about fall armyworm in turfgrass here.

Chemical Name Trade Name Mode of Action Class Alfalfa Corn Sorghum Wheat Grass Forage/Hay
alpha-cypermethrin Fastac CS 3A yes yes yes yes yes
beta-cyfluthrin Baythroid XL 3A yes yes yes yes yes
bifenthrin numerous products 3A yes yes
biological insecticide Fawligen – yes
carbaryl Sevin 1A yes yes
chlorantraniliprole Vantacore 28 yes yes yes yes
cyfluthrin Tombstone 3A yes yes yes
deltamethrin Delta Gold 3A yes yes
gamma-cyhalothrin Proaxis 3A yes yes yes yes
indoxacarb Steward EC 22A yes
lambda-cyhalothrin+chlorantraniliprole Besiege 3A+28 yes yes yes
lambda-cyhalothrin numerous products 3A yes yes yes yes yes
methomyl Lannate 1A yes yes yes yes*
methoxyfenozide Intrepid 2F 18 yes
permethrin numerous products 3A yes
spinosad Blackhawk 5 yes yes yes yes
zeta-cypermethrin Mustang MAXX 3A yes yes yes yes
zeta-cypermethrin+bifenthrin Hero 3A yes

Table 1. Registered products for the control of fall armyworm in Kansas crops.  For more specific information relative to any insecticide, always refer to the actual label on the product. *for use only in bermudagrass pasture

 

By Anthony Zukoff

 

 

Fall Armyworm Season Approaches

Posted on by Department of Entomology

Fall Armyworm, Spodoptera frugiperda, can damage several important Kansas crops as well as pasture, turf and home landscaping.  This insect does not overwinter in Kansas.  Rather, it is native to the tropical regions of the western hemisphere and is active year-round along the gulf coast and southern Florida, migrating in from these locations each year.  Two full generations are possible in Kansas with defoliation and grain damage being the biggest concerns.  Each generation’s abundance and distribution across the landscape are usually different; the first generation does not necessarily impact the abundance of the second generation.  Feeding damage from fall armyworm during the vegetative stage in corn and sorghum causes chewed up and ragged looking leaves.  In fact, one of the common names used for fall armyworm during this stage is “ragworm”.  Sorghum is particularly at-risk during grain fill as fall armyworm will completely consume berries as they develop.  This caterpillar has been causing increased concern in eastern Kansas brome fields the last couple of seasons.  Brome fields can rapidly decline from fall armyworm feeding (Figure 1) as large numbers of caterpillars can be present consuming leaf material; often larger caterpillars are found along with younger ones.

Figure 1. Brome field damaged by caterpillars (Tina Sullivan).

Fall armyworm tends to begin arriving in Kansas towards the end of June, so scouting should start for this pest in at risk crops and on a weekly basis for the remainder of the growing season.  Caterpillars increase in size at an exponential rate and most of the feeding occurs during the later stage of development.  It is critical to scout early and treat, if needed, when the caterpillars are less than an inch long.  Larger caterpillars are harder to control and do the most damage.  Often, infestations are discovered after it is too late to treat. Recommended thresholds can be found below.

Fall Armyworm Thresholds

  • Alfalfa:  1-2 caterpillars per square foot can destroy seedling alfalfa.  10-15 per square foot can destroy 12” tall plants.
  • Corn:  damage to whorl stage in early summer is typically not a concern and will not impact yield.  Bt corn may prevent ear damage.
  • Sorghum:  damage to whorl stage in early summer is typically not a concern. 1-2 larvae/head during flowering to soft dough reduces yield 5-10%.
  • Wheat:  Larval “window-paning” in early planted wheat can be a concern. Very late second generation fall armyworm will be the biggest concern for wheat.  If 25-30% of plants show damage, examine field frequently.  Treat at 2-3 active larvae/ft.

Pasture/Brome: If damage is notable or there is window-paning, treatment may be warranted with 4 to 5 caterpillars per square foot.

Figure 2.  Caterpillars found damaging a brome field. Infestations can often include multiple species and multiple life stages (Tina Sullivan).

Since fall armyworm is present for several months of the growing season, it is possible that sometimes mixed infestations of different caterpillar species can occur (Figure 2).  As with any pest, proper identification is important to ensure that the right control recommendations are followed.  A species often confused with fall armyworm is true armyworm, Pseudaletia unipuncta.  The two species can be told apart with a couple of easily seen characteristics.  Fall armyworm has a noticeable inverted “Y” on its head (Figure 3), while true armyworm does not.  Additionally, the thickest stripe on the side of the fall armyworm caterpillar will be dark, while on true armyworm the thickest stripe is tan to orange (Figure 4).

The fall armyworm is depicted in a c-shape, with one thick black strip on its lateral sides.
Figure 3. Fall armyworm. Notice the thickest stripe is black (K-State Entomology).
Figure 4. True armyworm. Notice the thickest stripe is a light color (K-State Entomology).

For more information regarding fall armyworm management, take a look at the following Insect Pest Management Guides:

Anthony Zukoff – Extension Entomology, Western Kansas Research and Extension
Tina Sullivan – Northeast Region Extension Agronomist

 

Identifying Chinch Bugs and False Chinch Bugs

Posted on by Department of Entomology

Chinch bug activity has been elevated in Kansas the last couple of seasons. Now would be a good time to discuss the differences between chinch bugs (Blissus leucopterus) and false chinch bugs (Nysius sp.).  To make proper management decisions, knowing how to correctly identify these insects is critical.

Adults

Adult chinch bugs are 3-4mm long bugs with black bodies and white wings that are kept folded over their backs. Two dark, triangular markings are present near the center of the wings creating a distinctive “X” mark (Figure 1).

Adult false chinch bugs are very similar in appearance, but smaller.  Instead of having black bodies, false chinch bugs are brownish-gray with clear wings that lack a distinct “X” mark (Figure 2).

Figure 1. Adult chinch bug
Figure 1. Adult chinch bug
Figure 2. Adult false chinch bug. Note the lack of a dark “X”.
Figure 2. Adult false chinch bug. Note the lack of a dark “X”.
Immature Bugs

Immature chinch bugs are bright red after hatching, darkening to black as they go through a series of 5 molts.  A distinct white band will be visible across the nymphs’ bodies until the wing buds become large enough to obscure it (Figure 3).

Figure 3. Immature chinch bugs.
Figure 3. Immature chinch bugs.

Immature false chinch bugs are grayish-brown, never bright red, and lack the white band across their bodies (Figure 4).

Figure 4. Immature false chinch bugs.
Figure 4. Immature false chinch bugs.
Damage

Chinch bugs and false chinch bugs are true bugs in the order Hemiptera which means they both have piercing-sucking mouthparts that they use to puncture plant tissue to feed on plant juices.  However, the symptoms of feeding appear differently for these two bugs.  When chinch bugs feed, digestive enzymes are injected into the plant tissue causing it to break down and discolor (Figure 5).  Reddish spots often are present at chinch bug feeding sites.  Heavy chinch bug feeding can also cause stunting, wilting and necrotic lesions on plants.  False chinch bug feeding, on the other hand, usually has little effect on plants, but extreme numbers of the bugs on a plant can cause wilting and death (Figure 6).

Figure 5. Discoloration caused by chinch bug feeding (Photo Jeff Whitworth).
Figure 5. Discoloration caused by chinch bug feeding (Photo Jeff Whitworth).
Figure 6. False chinch bug feeding damage to sorghum.
Figure 6. False chinch bug feeding damage to sorghum.
Be proactive about chinch bug management

Think about chinch bug management before wheat is harvested.  Simply relying on rescue treatments for young sorghum fields is not recommended. If possible, avoid planting sorghum adjacent to wheat, particularly if the wheat stand is thin and stressed out.  Wheat fields should be scouted for the presence of chinch bugs before harvest to provide an estimate of risk to newly planted sorghum fields.  One adult chinch bug or 5 nymphs per foot of row will be a hazard to the borders of sorghum planted nearby.  If chinch bug problems are expected, an early planted trap crop of sorghum can be utilized between the wheat and sorghum fields and this trap crop can be sprayed if migrating chinch bugs become numerous.  Follow-up sprays will likely be needed if the local chinch bug population is high; 5 chinch bugs per seedling would warrant action.  Planting time insecticides and seed treatments can provide some early protection for young sorghum, but their effectiveness deteriorates beyond a few weeks.  Additionally, scouting should be done weekly during the growing season.  Plants a foot tall through flowering can be damaged by 50 chinch bugs per plant.

Additional details on life history and management recommendations for these two pests can be found in the following Kansas Crop Pest publications.

Chinch Bug:  https://bookstore.ksre.ksu.edu/pubs/MF3107.pdf

False Chinch bug: https://bookstore.ksre.ksu.edu/pubs/MF3047.pdf

By Anthony Zukoff, Extension Entomology, Southwest Research and Extension Center