All About Corn: Pesky Problems and Beyond. Erik R. Echegaray and Silvia I. Rondon Hermiston Agricultural Research and Extension Center (HAREC)

Transcription

1 All About Corn: Pesky Problems and Beyond Erik R. Echegaray and Silvia I. Rondon Hermiston Agricultural Research and Extension Center (HAREC)

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3 Corn insect pests Corn aphid Armyworm Cutworm Seed corn maggot Wireworm Corn mite Earworm Corn rootworm

4 Corn aphids Aphids sucking mouth feed on the plant sap Recognized by the presence of tailpipes (cornicles)

5 Bird cherry-oat aphid Rhopalosiphum padi Corn leaf aphid Rhopalosiphum maidis Dark cornicles, short antennae

6 Damage during whorl stage. During and after flowering on corn tassels and silks. Honeydew and black mold may result in poor corn pollination; can reduce grain development. Virus vectors (maize dwarf mosaic virus, barley yellow dwarf virus)

7 Usually good biological control including pedators: lacewings, ladybirds, minute pirate bugs, syrphid fly larvae, damsel bugs, etc.

8 and parasitoids

9 Scouting is important: five locations, examine 20 plants per location. Economic threshold: 100+/plant in 50% of the plants sampled. Management: pyrethroids and reduced risk pesticides.

10 Armyworms Chewing mouthparts, feed on the leaves, defoliation

11 MOST IMPORTANT SPECIES IN THE PNW Armyworm Mythimna unipuncta Beet armyworm Spodoptera exigua

12 Damage on leaf whorls Armyworms often cause problems in corn when grassy areas of fields are destroyed by cultivation or by herbicides, also in no-till corn. Control: Bacillus thuringiensis, pyrethroids, spinetoram. Light and pheromone traps to monitor the adults.

13 Cutworm Adult Larva Common species in the PNW, The black cutworm Agrotis ipsilon The variegated cutworm Peridroma saucia

14 Adults migrate and emerge in April and start laying eggs. Migration and egg laying continue into June. Two generations per year Second generation in late August and September. Management: early monitoring in the seedling stage. Baits, soil insecticides at planting, seed treatments. Economic threshold: two or three cut plants or leaves in 10 ft row at several sites throughout a field.

15 Seed corn maggot adult fly Females deposit eggs around the base of plant Several generations per year larva (maggot)

16 Maggots can attack seed, small plants and cause loss of stand. Secondary problem: diseases. Gaps and skips may occur in the emerging stand as a result of maggot damage Yellow sticky traps to monitor the adults

17 Wireworms Larva Adult Life Cycle Click beetles ; Ctenicera and Limonius spp. Adults overwinter in the soil and emerge in early spring, late April to early May. ~ 200 to 400 eggs/female between late May and early June.

18 Larvae attack seed and cause stand loss during the seedling stage. Management: scouting, crop rotation, insecticides: pyrethroids, seed treatment, altered planting dates.

19 False wireworm Eleodes spp. Family: Tenebrionidae

20 Corn mites Several species including the Twospotted spider mite Tetranychus urticae Most important under dry conditions Overwinter as adults in debris, multiple generations per year. Control: systemic miticides

21 Drought stress conditions in late July and August make corn more susceptible to spider mites Insecticides may increase spider mite populations.

22 Efficacy trial using two miticides: Zeal wp (two rates) and Oberon. Overall good control. especially with Zeal at high rate and SC formulation.

23 Corn earworm (CEW) The CEW Heliothis zea is a major pest of sweet corn occurring at high levels every year. Damages corn by consuming leaves, tassels, silks and kernels. Prefer to attack the ears. Present throughout the year but most abundant during August and September.

24 One to three generations per year Eggs are laid on a silk strand. The larva hatches and crawls down into the ear.

25 MONITORING TRAPS

26 mean CEW moths per week Population dynamics of the CEW, Hermiston, OR /8 7/15 7/22 7/29 8/5 8/12 8/19 8/26 9/2 9/ Management: early plantings, plow or dig up plants in the fall to prevent overwintering. Biological control: Trichogramma spp. Insecticides: before silking. Degree day model

27 Corn rootworms Western corn rootworm Diabrotica virgifera Spotted cucumber beetle Diabrotica undecimpunctata The larva is the stage that cause the most damage to corn. The larvae feed on the roots, weakening the plant and decreasing yield.

28 Adult beetles may feed on the silk (called silk clipping) and interfere with pollination of the corn kernels, which reduces yield. Beetles can also feed on the foliage. Rootworms can be controlled using crop rotation in combination with soil applied insecticides or seed treatments at planting.

29 For pesticide recommendations and a list of registered insecticides please refer to: The Pacific Northwest Insect Control Handbook QUESTIONS..??