Published on February 7, 2008
Slide 1: Management of Insect Pests of Corn In Western North Carolina John Van Duyn, Entomologist NCSU 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. Slide 3: 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 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 seed: A. 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. Slide 8: 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 Slide 9: 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.) 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 rootworm Slide 11: 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. Slide 13: Chapter 2. Management of corn insect pests of seeds & small seedlings Practices 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 Category Lower Moderate Higher Slide 17: At-planting insecticides in conventional tillage corn. Wilkes Co., NC. 2004* * Means followed by a same letter are not statistically different (p=.05) JVD Slide 18: At-planting insecticides in no-tillage corn. Iredell Co., NC. 2004 * * Means followed by a same letter are not statistically different (p=.05) JVD Slide 19: 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 * a ab abc ef JVD f Kernel Gard cd Plants Per/Acre *Means followed by a same letter are not statistically different (p=.05). Slide 20: 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; Counter 15G in lbs. / acre applied in-furrow. Grain Yield Under A High Wireworm Population. Pasquotank Co., NC. 09/15/03* a ab bcd ef f KERNEL GARD cd Bu/Ac *Means followed by a same letter are not statistically different (p=.05). JVD Slide 21: UTC 3717 plants per acre (14% of planted seed) Slide 22: Lorsban 6.5 lb IF 13626 plants per acre (51% of planted seed) Slide 23: 19939 plants per acre (75% of planted seed) Cruiser .25 mg/Ker Slide 24: Poncho .25 mg/ker 20239 plants per acre (76% of planted seed) Slide 25: Whorl stage pest 1 generation / year Adults and larvae eat corn eats roots, silks, & leaves Over-winters as eggs Corn after corn only At-plant chemicals or Bt corn Western corn rootworm Northern corn rootworm Southern corn rootworm Seed / seedling stage pest Many generations / year Eats seed, roots, and stems Adults and larvae eat corn Overwinters as adults Seed protection chemicals or Bt Chapter 3. Western corn rootworm Slide 26: WCR Larvae 1st occur at late seedling Eat root hairs & roots Reduce plant growth Reduce standability Reduce yield Slide 27: Corn rootworm damage Iowa 6 point scale 5 2 3 4 Slide 28: Lodging following root damage by WCR larvae Slide 29: WCR pupa Larva constructs a chamber in soil Larva changes to a pupa during June Slide 30: WCR adult Emerge in late June / July Eat silks Eat foliage Eat pollen Mate Lay eggs Die Slide 31: Leaf feeding by adult western corn rootworm Slide 32: WCR Eggs Laid in the soil Mainly laid in corn fields Pass the winter Hatch in late spring Larvae in last years corn Slide 33: 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. Slide 34: 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 Category Less Important More Important Slide 36: 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. Slide 38: Summary of YieldGard Rootworm® tests under light and moderate-to-heavy corn rootworm pressures. Iowa. 2003 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 Slide 39: At-planting insecticides in no-tillage corn. Iredell Co., NC. 2005 * * Means followed by a same letter are not statistically different (p=.05) JVD Questions ?: Questions ?