NDSU Crop and Pest Report

Entomology


ISSUE 9  June 27, 2002

 

PALESTRIPED FLEA BEETLES DAMAGING SUNFLOWER IN SOUTH DAKOTA

This insect has been reported feeding on sunflowers in some south central counties of North Dakota, but not at the same levels causing damage in central South Dakota. The following article is from Mike Catangui, Extension Entomologist, South Dakota State University. Further information can be found on the internet at:

http://www.abs.sdstate.edu/plantsci/ext/ent/entpubs/SEE_Mail.htm

Reports of damaging numbers of palestriped flea beetles have recently come from Hughes, Potter, and Sully counties, where most of sunflowers are grown in South Dakota.

Palestriped flea beetles are about one-eighth of an inch long, black in color with two white stripes on the back, and can both jump and fly -- hence the name "flea" beetle. Palestriped flea beetles chew on the true leaves, cotyledons, and hypocotyls causing the sunflower seedlings to wilt and die. Injured leaves become riddled with holes giving them a "lacey" appearance.

Plaestriped flea beetle image feeding injury to sunflower image
Palestriped flea beetle adult Feeding injury to sunflower
(Photos by Mike Catangui, SDSU Ext. Entomologist)

This is the third straight year that palestriped flea beetles have caused injuries on sunflower seedlings in north central South Dakota. Palestriped flea beetles can cause significant stand losses in sunflower seedlings. Spraying with an insecticide may be justified if 20 percent of the stand - one out of five seedlings - shows extensive feeding by the flea beetles.

No insecticides are currently labeled for use specifically against palestriped flea beetles on South Dakota sunflowers. However, our research has indicated that several insecticides, already labeled for use against common sunflower insects, would also control palestriped flea beetles.

Baythroid (2.8 fluid ounces per acre), Sevin XLR Plus (32 fluid ounces per acre), and Warrior (2.56 fluid ounces per acre) were effective in reducing palestriped flea beetles in our research near Onida last year (2001).

SDSU Extension Entomology is currently testing various seed treatments and insecticide sprays for potential use against palestriped flea beetles near Selby and Agar. Funding for these studies come from the National Sunflower Association and the SD Oilseeds Council.

Palestriped flea beetles overwinter as adults under the soil and plant residues on the field. They then resume feeding on weeds in the spring. For some unknown reason, they have recently started to feed on sunflower seedlings. Palestriped flea beetles did not use to be a pest of sunflowers in South Dakota. Its transformation into a pest of cultivated sunflowers is an example of the ability of insects to change hosts over time.

Scientific records do indicate that palestriped flea beetles have always been in South Dakota. Their known plant hosts in the United States include various weeds, potato, tomato, carrot, peanut, corn, oat, cotton, pea, beans, strawberry, watermelon, grape, and pumpkin. Palestriped flea beetles are considered an important pest of commercially grown vegetables in California and North Carolina.

Mike Catangui
SDSU Extension Entomologist
michael_catangui@sdstate.edu

 

CEREAL APHIDS DETECTED IN SOUTHEAST ND

Cereal aphids, particularly Bird Cherry Oat aphid, were found in wheat fields in Richland County late last week. Colonies were generally small, numbering only 2 to 5 aphids each. Percent of the stems infested was low, ranging from 2 to 20%.

The greatest risk of yield loss from aphids feeding on grains is in the vegetative to boot stages. Many of the fields scouted in Richland County were at early to fully headed stages and therefore past the point where aphids pose great risk to yield. Remember that significant yield reductions after the onset of flowering could not be demonstrated in research published from South Dakota in 1997 (Voss et al., 1997. J of Economic Entomology 90: 1346-1350). Reasons for these conclusions were that:

Other components of yield are determined earlier (number of spikelets - determined at jointing; number of seeds - determined at flowering).

To protect small grains from yield loss due to aphid feeding, the treatment threshold is 85% stems with at least one aphid present, prior to complete heading. Fields in the vegetative stages should be monitored for aphids from this point to determine if colonization and population increases occur.

Aphid Identification

There are four cereal aphids we expect to see each season. You can recognize these aphids by the follow traits:

Cereal Aphids image

 

SOYBEAN APHID INSECTICIDE OPTIONS

In the next few weeks, decisions to control soybean aphid infestations are going to be made. Several insecticide efficacy trials were conducted last season in states where aphids were abundant. The following table provides a summary of part of one trial conducted by University of Minnesota researchers. The rates correspond with the high label rate. With these rates, the objective is to achieve well over 85% control, minimizing the numbers of aphids surviving the treatment in order to delay the anticipated increase of the aphid population, and give the soybean plant a chance to progress to a growth stage where aphid feeding will have minimal impact on yield.

Though many will not like the idea of using the high label rate, the best results are expected to be achieved with treatments that are in the upper range of the label rates. Using low rates will increase the risk of leaving enough aphid survivors to result in a rapid increase in the population, especially in the absence of predators and parasites that will be killed by the insecticide treatments. A rapid recovery of the population could result in the need to reapply treatments for adequate protection.

Insecticide efficacy against soybean aphid based on mean # of aphids per plant, 4 days following treatment (Source: Ostlie, Ragsdale, and Hodgson.  University of Minnesota, 2001)

Treatment

Rate (oz /acre)

Mean # Aphids/Plant

% Control

Untreated control

-----

393.2 A

-----

Dimethoate 4 EC

16 (1 pint)

58.2 B

85.1

Pounce 3.2 EC

8.0 ( pint)

40.1 B

89.8

Fulfill 2 50 WG *

2.75

13.3 BC

96.6

Asana 0.66 EC

9.6

3.7 CD

99.1

Warrior T 1EC

3.2

2.0 D

99.5

Provado 1.6F *

3.75

1.6 D

99.6

Actara 25 WG *

3.0

1.2 D

99.7

Leverage 2.7 L *

3.75

1.1 D

99.7

Furadan 4F

8.0 ( pint)

0.03 D

99.9

Penncap-M 2FM

48 (3 pints)

0.03 D

99.9

Lorsban 4EC

32 (2 pints)

0.00 D

100.0

Means followed by the same letter are not significantly different
* Insecticide not labeled on soybean

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu

 

ALFALFA WEEVIL DAMAGE REPORTS

Numerous reports of alfalfa weevil larval feeding in alfalfa are coming in from southern ND counties, particularly those in south central and southwest. Many fields are being cut at this time. It is important to check fields after cutting to determine if larvae have survived at great enough numbers to cause problems with the regrowth.

If larval counts after cutting are 8 or more larvae per square foot, or larvae are suppressing regrowth, treatment with an approved insecticide would be recommended.

Diagnosis & Management Options

Alfalfa Weevil Larvae

Alfalfa Weevil Larva

Alfalfa weevil larvae range from yellow to light green in color. They are legless and, when mature, larvae are plump-bodied, green with a white stripe down the back, have a black head capsule, and are about 3/8 inch long. Typically, they feed for about 14 to 21 days to pass through their larval stage. Mature larvae usually move down near the base of the plant or into plant debris on the soil surface where they form silken cocoons and turn in to pupae. Adult weevils will usually emerge after they have spent between one and two weeks in the pupal stage.

Larvae injure the plant by feeding on foliage with chewing mouthparts. Injury first appears as small holes in leaves at or near the growing tip. Leaves take on a shredded, skeletonized appearance as feeding continues, and eventually entire growing tips can be eaten off. Damage becomes progressively more apparent in fields as weevil larvae continue to grow and mature. Leaves of severely damaged plants will take on a bleached, grayish, or frost-injured appearance. Impact is most severe to the first crop/cutting; however, populations are occasionally sufficient to inflict significant damage to the second crop. Adult weevils usually incite most of their plant damage to the second crop by feeding on developing buds and inhibiting regrowth.

Generally, the first line of defense against losses from alfalfa weevil larvae involves promptly cutting the crop. Immediate harvest is simple inexpensive, and considered to be the most efficient tactic for managing alfalfa weevil infestations, especially those affecting the first crop of the season. Harvesting alfalfa exposes them to sunlight and high temperatures that can be especially detrimental to survival of young larvae. Additionally, fresh green buds and foliage will be scarce for several days after cutting and many larvae will likely die of starvation.

If conditions warrant chemical control several products are currently registered in alfalfa for controlling alfalfa weevil larvae. Two important considerations regarding insecticide use in alfalfa are: 1) hazards to pollinators, especially honeybees; and 2) preharvest interval. Insecticides are extremely toxic to bees. They should never be applied if alfalfa is in bloom or if high numbers of flowering weeds are present. Also, notify beekeepers maintaining hives within a three-mile radius of the field so hives can be temporarily covered or moved out of the radius during the insecticide application. Additionally, the insecticide should be applied when most of the bees are away from the field and in the hive (between 8:00 p.m. and 8:00 a.m.).

The following table lists preharvest intervals for insecticides registered for alfalfa weevil control in North Dakota during the 2002 growing season. Please consult the North Dakota Field Crop Insect Management Guide for more information regarding chemical control of this insect pest. This publication is located online at:

http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

INSECTICIDE

DOSAGE
(# AI/acre)

PRODUCT PER ACRE

PREHARVEST
INTERVAL

permethrin    
   Ambush 2E   
   Pounce 3.2EC
                                   RUP

0.1 - 0.2


6.4 - 12.8 fl oz
4 - 8 fl oz

14 days if above 0.1 lb ai/ac

Baythroid
                                   RUP

0.025 - 0.044

1.6 - 2.8 fl oz

7 days

carbaryl

1.5

rate varies by formulation

7 days

Furadan 4F
                                   RUP

0.25 - 0.5

0.5 - 1 pt

7 days at 0.25 lb
14 days at 0.5 lb

Imidan 50 WP

0.75

2 lbs

7 days

Lannate
                                   RUP

0.9

3 pts

0 days (cutting)
7 days (feed/graze)

Lorsban 4E
                                   RUP

0.5 - 1

1 - 2 pts

14 days at 0.5 lb
21 days if above 0.5 lb/acre

Malathion 57EC

0.9 - 1.25

1.5 - 2 pts

None

Methyl parathion 7.5EC
                                   RUP

0.5 1

0.5 - 1 pt

15 days

Methoxychlor 2EC

1 - 1.5

2 - 3 qts

7 days

Mustang
                                   RUP

0.028 - 0.05

2.4 - 4.3 fl oz

3 days (cutting/grazing)
7 days (seed harvest)

Penncap-M
                                  RUP

0.5 - 0.75

2 - 3 pts

15 days

Warrior
                                  RUP

0.02 - 0.03

2.56 - 3.84 fl oz

1 day for forage
7 days for hay

RUP = Restricted Use Pesticide

Mark Boetel
Research & Extension Entomologist
mboetel@ndsuext.nodak.edu


NDSU Crop and Pest ReportTop of PageTable of ContentsPrevious PageNext Page