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Slide 1: Now available at www.ag.ndsu.edu/county/steele/ INSECT PEST OF CORN By Dr. Ayanava Majumdar P.O. Box – 316, Finley, ND 58230
Slide 2: Welcome to the Corn Workshop How are the topics organized? • Insect basics • Sucking insect pests - aphids • Chewing insect pests – armyworm, rootworm, European corn borer • For each major insect – diagnosis, scouting technique, injury, threshold, treatment • Minor insects – cutworm, grasshopper, white grub • “Smart Scout” techniques • “Things to do” list
Slide 3: Basic categories of corn insects Sucking insects: corn leaf aphids, greenbug Chewing insects: armyworms, cutworms, grasshoppers Feeding tube of aphids Strong jaws in caterpillars
Slide 4: Corn leaf aphid & greenbug Corn leaf aphid: Rhopalosiphum maidis Diagnostics: high numbers in 2007, look for black cornicles or “tail-pipes”, rapid breeding insect, nymphs pale in color, winged forms are migrant insects Greenbug: Schizaphis graminum
Slide 5: Corn leaf aphid & greenbug Scouting method: look in the plant whorl, sign of natural predators like syrphid flies may indicate concealed populations Injury: • sucking mouth-parts…inject toxin with saliva • Transmit some viruses (status in ND unknown) • May stress plants in a dry year • Critical period – tassel emergence to pollination Threshold: 50% corn plants with 100+ aphids, economics of treatment difficult to establish (contact a specialist!)
Slide 6: Corn leaf aphid & greenbug Natural control: • lady beetles, aphid lions, syrphid flies, parasitic wasps – common in this region • Powerful suppression…naturally Chemical treatment: • Treat only if popns are incredibly high (consult someone!) • Synthetic pyrethroids (e.g., bifenthrin products), Cobalt, chlorpyrifos products, etc.
Slide 7: Armyworms Armyworm larva & adult: Pseudaletia unipunctata Diagnostics: larva with horizontal markings, inverted Y on caterpillar head, moth has conspicuous white dots on front wings, larvae do not overwinter (migratory insect), feeding at spots at night
Slide 8: Armyworms Injury: • Late planted fields at greater risk • Patchy defoliation, esp. around field margins • Consume leaves, mid-rib intact (a diagnostic symptom) • Severe defoliation can cause yield losses 7 to 8 leaf stage…2 to 3% loss 9 to 10 leaf stage…4 to 6% loss
Slide 9: Armyworms Scouting method: • Remember…caterpillars of several insects may look similar • Scout soon after storms in midsummer • If you suspect plant injury occurring at night, look for fecal pellets under plants. • Dig around the plants (keep a trowel handy in summer) • Got no-till or strip-till? watch for armyworms in stubble! Threshold: treat if 25% plants have two or more caterpillars (contact a specialist for correct ID!) Treatment: syn. pyrethroids (permethrin, beta-cyfluthrin, bifenthrin), carbaryl, chlorpyrifos, Bt products
Slide 10: Corn rootworm (CRW) Western CRW, Diabrotica virgifera Southern CRW, D. undecimpunctata howardi Northern CRW, D. barberi Diagnostics: larvae pale, look much different from adults, larvae overwinter, female can lay eggs close to the roots up to 12 inches deep in dry years
Slide 11: Corn rootworms Injury: • Small larvae feed on fine root hairs • Large larvae feed on primary roots causing severe plant health problems • Adults may feed on leaves (by scraping) and also on silk (called “silk clipping”) • Severe problem in continuous corn (rotation is important in ND)
Slide 12: Corn rootworms Scouting method: • Look for randomly lodged plants (gooseneck symptom) • Uproot lodged plants and check the roots • Scout crops especially closer to the pollination period Threshold: record the number of beetles on the foliage & silk; if you find a beetle on every plant, it is time to rotate out of corn or apply an insecticide (slow pop. growth) Treatment: crop rotation, transgenic corn, syn. pyrethroids (lambda-cyhalothrin, bifenthrin), terbufos (Counter 15G), chlorpyrifos (Lorsban 15G)
Slide 13: European corn borer (ECB) ECB male moth ECB, Ostrinia nubilalis Note the female & egg mass A very hungry caterpillar! Cause over $1 billion of crop losses in all corn production areas, many host plants (cotton, fruits, and vegetables) Diagnostics: moths have wavy lines on wings, first two larval instars are small and feed on leaves, third instar larva starts to bore into the stalk, multiple generations
Slide 14: European corn borer (ECB) Injury: • Physiological stress • Early instars scrape leaf surface (“window-pane symptom”) • Mid instar that bore through the whorl causing series of holes (“shotholing”) • Later instars make home inside the corn stalk (overwinter), total loss • Multiple generations-second generation could feed on corn ears (ear drop), high losses
Slide 15: European corn borer (ECB) Scouting method: • Lengthy emergence interval create difficulties in monitoring • Two generation per year in southern ND • Start scouting in June (first generation) - look for egg masses • Corn in sixth-leaf stage? Scout weekly for several weeks • Walk around the grassy edges of field (moths mate here) Threshold: refer to worksheets available from NDSU Entomology, whorl stage – pull 10 plants from 5 location and tassel stage – study seven leaves for egg masses from 20 plants Treatments: Bt corn (several products), syn. pyrethroids (permethrin, bifenthrin, beta-cyfluthrin), chlorpyrifos (Lorsban 4E), biorational insecticides (spinosad)
Slide 16: Minor insect pests of corn May become major concerns under special circumstances, e.g., lack of natural control, plant stress due to drought, etc. Monitoring is very important for these pests! Black & Dingy cutworms Dingy cutworm (Feltia jaculifera) overwinters and then becomes active in early to mid-May (ET: 3 to 6% cut plants)
Slide 17: Minor insect pests of corn Grasshoppers: migratory insect, infestations begin from field margins, scout in July for late attacks (silk clipping, damage to ear leaf), dry summers may aggravate population build-up Treatment: natural pathogens, several pyrethroid insecticides give quick control, spot treatment may be needed Wireworms: C-shaped larva, three-year lifecycle, assoc. with willow and cottonwood trees or weedy areas, damage main roots
Slide 18: “Smart scout” your crops • Be motivated to scout, work in small groups if time permits, call your Extension office • General Scouting supplies: insect net, cutting tool, magnifying lens, plenty of Ziploc bags, gather good field books and use them in field • Scout by going inside the canopy!! • Scout randomly in the field, beginning from field margins! • Small plants: look under crop debris, or the top few inches of soil!! • Uproot whole plants when scouting, study soil around plants for concealed insects
Slide 19: “Smart scout” your crops • If you suspect an insect, mark the perimeter of heavy infestation with tall flags; come back in a few days & observe the perimeter • Think about investing in monitoring tools (sticky traps, pheromone traps…investment under $10 per trap) • Larger the sample size better the accuracy of scouting! Randomly choose plants throughout the field. • Maintain record of your scouting for reference ECB trap from Trece Which is the armyworm? Consult a field guide!!
Slide 20: “Smart scout” your crops Remember…insect traps will only indicate pest presence, NOT crop injury Remember…scout for natural predator populations, natural control works Things to do today… • Provide us your email, fill the workshop registration form • Signup to receive Steele County Ag Alert 2008 • Signup to receive the Crop Production Guide 2008 ($10 per copy) • Purchase a copy of the Corn & Soybean Field Guide from Purdue Univ. ($8 per copy, limited availability) • Sign up to receive a copy of Corn & Soybean Field Guide
Slide 21: References • Picture sources: Iowa SU, University of Illinois, Univ. of Nebraska, NDSU • Crop production Guide 2008: insect chapter by Dr. Janet Knodel of NDSU, pages 231-252 • Other NDSU Extension pubs. E493 on aphid management, E631 on corn insects, E830 on armywom and cutworm management, E188 on wireworm management Please make sure you rate individual presentation on the feedback sheet! Write any additional comment anywhere on the sheet. Thank you very much. QUESTIONS?