Management of Insect Pests of Corn

In Western North Carolina

Management of Insect Pests of Corn

In Western North Carolina

John Van Duyn, EntomologistNCSU Cooperative Extension Service

John Van Duyn, EntomologistNCSU Cooperative Extension Service

Chapter I. Corn Insects in The NC Piedmont and Mountains

Chapter I. Corn Insects in The NC Piedmont and Mountains

In western NC, field corn is primarily grown with no-tillage, little rotation, and in small field.

Yield potential of corn is sensitive to plant stand and plant health; stands and health may be reduced in the seed / seedling stage by insects.

Mid-season rootworms may also reduce plant health and lower yields.

Many fields will not have damaging insect numbers; it is difficult to accurately predict which fields are at risk.

Field Corn IS: a plant population sensitive crop, very sensitive to insect damage when young, & more tolerant to insect feeding as plants grow.

Field Corn IS: a plant population sensitive crop, very sensitive to insect damage when young, & more tolerant to insect feeding as plants grow.

Corn, a population sensitive crop

Corn, a population sensitive crop

0

50

100

150

200

250

14000 19000 24000 29000 34000 39000

Plant Population, plants acre-1

Yie

ld,

bu

ac

re-1

Beaufort 2005

Perquimens 2005

R. Heiniger, NCSU

Early season insect pests that may reduce plant stands and seedling

quality

Early season insect pests that may reduce plant stands and seedling

quality

On the seed: wireworms, seed corn maggot, southern corn rootworm, seed-corn beetle, & others.

On small seedlings: wireworm, southern corn rootworm, cutworms, white grubs, root aphids, stink bug, & sugarcane beetle.

On large seedlings and whorl stage plants: western corn rootworm and stalk borer.

A. Insects on corn seedA. Insects on corn seed

Swelling / sprouting corn seed is very sensitive to insect feeding, especially if the germ is damaged.

Wireworms (small and large) are the most common seed feeding insects.

Wireworms can quickly detect and find planted seed in the soil.

A. Insects on corn seed

A. Insects on corn seed

Seed-corn beetle and other seed feeding ground beetles may also feed on kernels but usually do minimal damage.

In sites with decaying plant material or manure, seed corn maggot (shown)may be abundant and cause seed damage.

These pests tend to be more severe in no-til fields.

The most common seedling insects are wireworms and cutworms.

Seedlings can be easily killed, but larger plants are more tolerant and they are quite tolerant by the 8th leaf.

Southern corn rootworm, brown stink bug, corn root aphid, and others also attack seedlings.

These pests tend to be more severe in no-til fields.

Corn root aphid

Southern corn rootworm

B.Insects on small seedlings

Black cutworm, and other cutworms, can be very damaging. Small seedlings may recover from being cut-off. Larger seedlings may be seriously damaged.

Brown stinkbug can kill and disable small seedlings. Damage is confined to no-tillage fields. Brown stink bug also attacks developing ears.

B. Insects on small seedlings (cont.)B. Insects on small seedlings (cont.)

C. Insects on larger, whorl-stage plants

C. Insects on larger, whorl-stage plants

Western corn rootworm eggs start hatching by mid-to-late May.

Small larvae eat root-hairs and large larvae eat and tunnel roots.

Heavy feeding will reduce the root mass (right).

Western corn rootworm is confined to corn after corn.

Western corn rootwormWestern corn rootworm

C. Insects on larger, whorl-stage plant (cont.)

C. Insects on larger, whorl-stage plant (cont.)

Stalk borer over-winters on weeds and grasses, in and around fields. They generally are not abundant. Many grass and broadleaf crops are attacked, notably corn and tomato.

Chapter 2. Management of corn insect pests of seeds & small seedlings

Chapter 2. Management of corn insect pests of seeds & small seedlings

Rotation has little affect on seed / seedling feeding insect pests.

Conservation tillage increases the abundance of wireworms, cutworms, corn root aphid and others.

Sites that have been out of row-crop production (e.g. pastures) often harbor high populations of grubs, wireworms, and / or cutworms; consider avoiding these sites for corn planting.

At-planting insecticide can be cost-efficient ----if ---- pest populations are adequately high.

Chapter 2. Management of corn insect

pests of seeds & small seedlings

Chapter 2. Management of corn insect

pests of seeds & small seedlingsPractices that can reduce losses to seed /

seedling insects include: Favorable agronomic practices to

promote rapid seedling germination and growth.

Rapid sprouting & growing hybrids. Using hybrids least population

sensitive. Starter / pop-up fertilizer will help

seedlings grow-off rapidly. Avoid no-til to reduce pest risk. Use an at planting insecticides, if

warranted.

Field factors affecting the abundance of at-planting insect pests of corn

Field factors affecting the abundance of at-planting insect pests of corn

Less Likely If;– Soils are drier

natured– Conventional tillage– Low history of insects– Low manure – Little litter / mulch– Rotation– Previous broadleaf

crop

More Likely If;– More moist soils– No-tillage– Positive insect

history– Routine manure – Lots of litter / mulch– Corn after corn– Pasture or CRP

Is an insecticide needed to protect planted seed and seedlings?

Is an insecticide needed to protect planted seed and seedlings?

Not all corn fields need at-planting insecticide. A scoring system is used to determine the

need for at-planting insecticide: the system is a general guide based on field factors that increase the odds of high pest insect numbers; it is not infallible.

Apply the scoring system to single fields or groups of similar fields in close proximity.

If needed, use a seed treatment (e.g. Poncho or Cruiser at 0.25 mg/kernel) or an in-furrow applied granule or spray insecticide.

Scoring field need for insecticide for protect from seed & seedling Insects

of corn Treat at minimum of 66 total points

Scoring field need for insecticide for protect from seed & seedling Insects

of corn Treat at minimum of 66 total points

Soil Dryer – 3 Mod. - 6 Springy -10

Tillage Full – 6 Strip - 25 None –35

Mulch Little – 6 Mod. - 15 Heavy –25

History Rare – 3 Mod. - 6 Often – 10

Manure Low – 3 Some - 6 Heavy – 10

Rotation

Yearly – 3 2nd year - 6 Never – 10

Prior crop

Broadleaf-10 Grain,Corn-20 Pasture - 42

Category Lower Moderate Higher

At-planting insecticides in conventional

tillage corn. Wilkes Co., NC. 2004*

At-planting insecticides in conventional

tillage corn. Wilkes Co., NC. 2004*

Treatment

Plant

Height (in)

5/26/04

Damaged

Plants/

200 RF

5/26/04

Plants

Per Acre

5/26/04

Plants

Per Acre

9/9/04

Silage

Tons / Ac

8/11/04

($ / AC +)

Untreated 18.7 a 21.7 a 20531 c 19529 c

29.0 b

($0)

Force 3 G 18.5 a 6.7 a 22941 b 22264 abc

32.0 a

($84)

Poncho

1.25/mg/ker 19.0 a 8.3 a 23522 ab 24127 ab

31.5 a

($70)

Cruiser

1.25/mg/ker 18.4 a 6.0 a 25433 a 24756 a

32.9 a

($109)

YG RW +

Poncho

0.25 mg/ker

19.0 a 17.7 a 21867 bc 21610 bc

32.9 a

($109)

* Means followed by a same letter are not statistically different (p=.05) JVD

At-planting insecticides in no-tillage corn. Iredell Co., NC. 2004 *

At-planting insecticides in no-tillage corn. Iredell Co., NC. 2004 *

Treatment

Plant

Height (in)

5/26/04

Damaged

Plants/

200 RF

5/26/04

Plants

Per Acre

5/26/04

Plants

Per Acre

9/9/04

Silage

Tons / Ac

8/11/04

($ / AC +)

Untreated 14.8 a 23.7 a 22071 a 25414 a 22.8 b

($0)

Poncho

1.25 mg/ker 16.3 a 3.7 b 25362 a 22731 a

23.5 ab ($19.6)

Cruiser

1.25 mg/ker 15.5 a 16.3 ab 24781 a 22045 a

24.3 a

($39.2)

YG RW

0.25 mg/ker 17.1 a 8.7 b 23135 a 23861 a

24.2 a

($42)

* Means followed by a same letter are not statistically different (p=.05)JVD

0

5000

10000

15000

20000

25000

UTC

Poncho 250

Gaucho

Cruiser

Lorsban 15G

.25 .25 .16 3.75 oz 6.5

Seed treatments in milligrams / kernel; Kernel Gard in oz / 100 lb seed; Lorsban 15G in lbs. / acre, applied in-furrow.

Corn Plant Stand Under A High Wireworm Population. Pasquotank Co., NC. 7/25/03 *Corn Plant Stand Under A High Wireworm Population. Pasquotank Co., NC. 7/25/03 *

a ab abc

efJVDf

Kernel Gard

cd

PlantsPer/Acre

*Means followed bya same letter are not statisticallydifferent (p=.05).

0

20

40

60

80

100

120

140

160

180

UTC

Poncho250

Gaucho

Cruiser

Lorsban 15G

.25 .25 .16 3.75 oz 6.5 Seed treatments in milligrams / kernel; Kernel Gard in oz / 100 lb seed; Counter 15G in lbs. / acre applied in-furrow.

Grain Yield Under A High Wireworm Population. Pasquotank Co., NC.

09/15/03*

Grain Yield Under A High Wireworm Population. Pasquotank Co., NC.

09/15/03*

a ab bcd

ef

f

KERNEL GARD

cdBu/Ac

*Means followed bya same letter are not statisticallydifferent (p=.05).

JVD

UTC

3717 plants per acre (14% of planted seed)

Lorsban6.5 lb IF

13626 plants per acre (51% of planted seed)

19939 plants per acre (75% of planted seed)

Cruiser.25

mg/Ker

Poncho.25 mg/ker

20239 plants per acre (76% of planted seed)

Whorl stage pest1 generation / yearAdults and larvae eat corn eats roots, silks, & leavesOver-winters as eggsCorn after corn onlyAt-plant chemicals or Bt corn

Western corn rootworm

Northern corn rootworm

Southern corn rootworm

Seed / seedling stage pestMany generations / yearEats seed, roots, and stemsAdults and larvae eat cornOverwinters as adultsSeed protection chemicals or Bt

Chapter 3. Western corn rootworm

WCR Larvae

1st occur at late seedling Eat root hairs & roots Reduce plant growth Reduce standability Reduce yield

Corn rootworm damageCorn rootworm damage

Iowa 6 point scale

52 3 4

Lodging following root damage by WCR larvae

WCR pupa

Larva constructs a chamber in soil Larva changes to a pupa during June

WCR adult

Emerge in late June / July

Eat silks Eat foliage Eat pollen Mate Lay eggs Die

Leaf feeding by adult western corn rootworm

Leaf feeding by adult western corn rootworm

WCR Eggs

Laid in the soil Mainly laid in corn fields Pass the winter Hatch in late spring Larvae in last years corn

Cultural tactics for managing western corn rootworm

Rotation is the first line of defense.

Can rotate with sorghum, Sudan grass, small grains, alfalfa, or any other crop.

Early planting helps plants gain size before larval and adult feeding.

Practices that improve rapid corn seedling growth are beneficial.

Insecticidal management of western corn rootworm

Use an at-planting insecticide or Bt biotech seed in corn after corn, if the scoring system measures 60 points or greater.

See Agricultural Chemicals Manual for recommended insecticides and follow label.

Some granular and seed treatment insecticides may not work well in very early plantings.

Guide for selecting insecticide or Bt corn for western corn rootworm management

Treat when 60 points or higher

Guide for selecting insecticide or Bt corn for western corn rootworm management

Treat when 60 points or higher

Soil Dryer - 3 Mod. To Springy - 8

Tillage Conventional - 3

Conservation - 8

Mulch Low - 3 Mod. To High - 8

History Low - 3 High - 6

Manure Low - 3 Mod. to High - 6

Follows Corn

No - 0 Yes - 40

Category Less Important More Important

Western corn rootworm management with biotech corn

Western corn rootworm management with biotech corn

Monsanto and Dow Agrosciences have labeled Yieldgard Rootworm® and Herculex RW® biotech Bt corns.

These biotech corns have done well in university trials and should be considered by growers needing rootworm protection.

Both brands have no effect on seed / seedling insect pests and seed treatment or at-planting soil insecticide is suggested when these pests are a threat.

Do you expect both seed & seedling insect pests and corn rootworm?

Do you expect both seed & seedling insect pests and corn rootworm?

If a granular at-planting insecticide is used for rootworm, it also will satisfy the need for seed / seedling protection.

For rootworms, seed treatments must be used at the high rate (1.25 mg / kernel) for Cruiser ® and Poncho 1250 ® and even then damage may occur.

If Bt biotech corn is used and seed / seedling insects are expected, a treatment of a low rate (0.25 mg/ kernel) of Cruiser ® or Poncho 250®, or an in-furrow granule is suggested.

Summary of YieldGard Rootworm® tests under light and moderate-to-heavy corn rootworm pressures.

Iowa. 2003

Summary of YieldGard Rootworm® tests under light and moderate-to-heavy corn rootworm pressures.

Iowa. 2003

Treatment

Low CRW (3 Tests) High CRW (3 Tests) Node- Yield Node- Yield Injury1,2 (bu/a)2

Injury1,2 (bu/a)2

Yieldgard Rootworm

0.003 a 146.2 a 0.03 a 159.3 a

Insecticide3 0.074 b 145.8 a 0.33 b 137.5 b

Untreated 0.563 c 145.7 a 2.02 c 130.1 b

1 Iowa State Node-Injury Scale (0-3). Number of full or partial nodes completely eaten.2Means sharing a common letter do not differ significantly (Ryan’s Q Test (P< 0.05)).3Averages of Aztec 2.1G and Force 3G insecticide treatments applied T-band at planting.

M. Rice, ISU

At-planting insecticides in no-tillage corn. Iredell Co., NC. 2005 *

At-planting insecticides in no-tillage corn. Iredell Co., NC. 2005 *

Treatment

Plants

Per Acre 5/17/05

Damaged

Plants/200’

5/17/05

Silage

Tons / Ac

8/16/05

$ Increase

VS

UTC

@$28 / ton

Untreated 23011 b 5.7 a 16.97 b 0

Force 3 G 23905 ab 0.7 a 16.50 b - $13 / Ac

Poncho

1.25/mg/ker 23905 ab 0.7 a 18.07 ab $31 / Ac

Cruiser

1.25/mg/ker 25979 a 0.0 a 19.20 ab $ 63 / Ac

YG RW +

Poncho

0.25 mg/ker

24549 ab 1.0 a 22.07 ab $143 / Ac

* Means followed by a same letter are not statistically different (p=.05) JVD

Questions ?Questions ?