Unit 1: Insect Pest Management for Field & Forage Crops

n Unit 1 Objectives: –Discussion of insect pest management for Illinois crops –Identification of proper pesticide choices for prevention and control –Understanding of control methods without the use of pesticides

Unit 1: Insect Pest Management for Field & Forage Crops n Integrated Pest Management (IPM) –comprehensive approach that uses combined methods to reduce pest densities to tolerable levels while maintaining a quality environment –uses several methods for pest control host-plant resistance cultural resistance mechanical control biological controls

Unit 1: Insect Pest Management for Field & Forage Crops –When should an insecticide be used? When insect population has reached/exceeded and economical threshold –damage > cost of control only after risks and benefits have been identified and evaluated –human –environmental

Unit 1: Insect Pest Management for Field & Forage Crops n Insecticides in this Chapter –Most common insecticides are included, however, label changes, generics, etc. may not be current –Insecticides cited will be of most common trade name and formulation –Refer to tables 2-8

Unit 1: Insect Pest Management for Field & Forage Crops n Managing Corn Rootworms –Pressure has been greatest in northern 2/3 of the state –Can have problems in corn after corn rotations –Control of rootworms needs to be a long- range plan that includes: Crop rotations Scouting Effective use of insecticides

Unit 1: Insect Pest Management for Field & Forage Crops –Soil applied insecticides at planting are usually very effective An aerial application may also be effective at preventing egg laying and have residual control –Only use in corn on corn situations –Long-range Corn Rootworm Mgmt. Strategies Proper crop rotation where avg. # of adults/plant exceeds.75 or more, or if insecticide didn’t control in previous yr.

Unit 1: Insect Pest Management for Field & Forage Crops If planting corn on corn, apply insecticide at planting time –Granular insecticides have provided the best control »Aztec »Counter »Force »Lorsban –Liquid insecticides have not been as effective –Environmental/pest conditions can still have an impact »Delayed larval hatch »Early planting

Unit 1: Insect Pest Management for Field & Forage Crops »Large #’s of larvae »Hot/dry conditions Two seed treatments are labeled for control of larvae –Force ST & Prescribe –Applied to corn seeds before bagging –Effective control when rootworm pressure is moderate, however, control is not as effective if high risk areas

Unit 1: Insect Pest Management for Field & Forage Crops Control egg laying adults –May take two applications –Caution should be taken: »Nebraska has observed the development of Corn Rootworms that are resistant to the insecticide »This mgmt. strategy should be used sparingly –Controlling egg laying and silk clipping is not the same thing »Silk clipping occurs much earlier than egg laying »Densities of 5+ adults/plant will reduce pollination

Unit 1: Insect Pest Management for Field & Forage Crops Scouting: –Mid-July through September in corn fields –Soybean fields planned for corn the following yr. »Rootworms have started laying eggs in soybean fields in anticipation of corn the following yr. »Has increased the number of first-yr. rootworm damage »Can set traps in soybeans to evaluate rootworm populations »Treatment should be considered if no. of adults >5/trap/day

Unit 1: Insect Pest Management for Field & Forage Crops Growers in western and southern IL are encouraged not to treat to prevent pest resistance Corn Rootworm damage has not been reported in our part of the state

Unit 1: Insect Pest Management for Field & Forage Crops n Managing European Corn Borers –Has caused yield losses in many parts of IL –Larger populations have been supported by the trend to plant longer season corn earlier Susceptible to both first and second generations Reduced-tillage systems increase overwintering of corn borers

Unit 1: Insect Pest Management for Field & Forage Crops –Planning is difficult because an economic infestation is hard to predict Densities of the population depend on: –Overwintering survival rate –Weather during egg-laying and the larval stage –Time of planting –Mgmt. w/ Bt Corn Gene taken from soil bacterium Bacillus thuringiensis –Produces a protein that is toxic to some caterpillars

Unit 1: Insect Pest Management for Field & Forage Crops Decision to plant Bt corn should be included in a long-term plan –Careful consideration should be given to the development of resistant corn borers to the Bt gene –Benefits of Bt corn will only be realized in yrs. where densities of corn borers will cause an economic yield loss –Decision to plant should be made when an economic yield loss is realized in 7 of 10 yrs. »Infrequent yield losses should not encourage growers to plant Bt corn due to increased cost and increased development of resistance

Unit 1: Insect Pest Management for Field & Forage Crops Bt corn should provide 100% control –If some survive, growers should ensure that they mate w/ adults from areas that didn’t have Bt corn –Bt corn planting strategies »Provide one entire field of non-Bt corn just to ensure a population of unexposed corn borers »Alternating strips of Bt and non-Bt corn in the same field »A block of non-Bt corn within a Bt planted field (should not be less than 20%) »Non-Bt areas can still be treated if levels of corn borers exceed economic levels

Unit 1: Insect Pest Management for Field & Forage Crops –Managing Corn Borers w/ Insecticides Scout for first-generation corn borers and injury in June –Unroll the whorl to find the borers –Examine at least 50 plants (10 plants from each of 5 areas in the field) –Avoid sampling only damaged plants Scout for second-generation July through mid- August –Counting egg masses

Unit 1: Insect Pest Management for Field & Forage Crops –Signal to begin checking is when you observe moth flight –Most eggs laid in the ear zone (middle 7 leaves) –Mgmt. worksheets are provided to aid in decision- making »If eggs are examined on leaves, must calculate to account for eggs in other parts of the plant »Level of infestation, expected yield, value of the grain, cost of control are all included in the worksheet –Insecticide must be applied soon after egg hatch »Begin to tunnel into stalk ~10d after hatch

Leaf damage and damage near stalk

Hatching Larvae

Unit 1: Insect Pest Management for Field & Forage Crops n Other Insect Problems –White Grubs Reports of damage to seedlings are increasing –Mild fall and winter weather likely aiding in their survival “True” White Grub (3 yr. life cycle) –Trees are hosts for the adult –Infestations usually not widespread, but close to a food source

Unit 1: Insect Pest Management for Field & Forage Crops Annual White Grub –Most problems attributed to the Japanese Beetle –No consistent pattern for infestation is established Mode of Action –Devour roots and root hairs –Symptoms include: »Irregular emergence »Reduced stands »Stunting or wilting »Purple coloring due to reduced P uptake »Spotty areas of injury Must be controlled w/ soil applied insecticides, rescue treatments not effective

Japanese Beetle Larvae

Unit 1: Insect Pest Management for Field & Forage Crops –Southwestern Corn Borer Significant damage in southern IL from ’98-’02 –Most economic losses occurred south of I-64, but much south of I-70 Can overwinter during mild winters 2 generations/yr. Eggs laid in June 1 st generation –Younger larvae feeds on whorls, cause little to no economic loss –Older larvae bore into stalks

Unit 1: Insect Pest Management for Field & Forage Crops 2 nd generation –Eggs laid in July –Tunnel into stalks and cause much more economic damage –Full-grown larvae tunnel to bottom of stalk and prepare to overwinter –Can cause severe lodging Populations can be decreased by disking or shredding cornstalks after harvest Infestations also decreased w/ early planting

Unit 1: Insect Pest Management for Field & Forage Crops Insecticide treatment: –Should begin when 20-25% of crop infested from 2 nd generation Bt corn also provides good control

Unit 1: Insect Pest Management for Field & Forage Crops n Bean Leaf Beetle –High densities in last few yrs. –Problems associated w/ BLB Clipped pods Pod feeding Disease introduction –BLB lifecycle Adults can overwinter in debris and wooded areas Feed on alfalfa & clover in the spring

Unit 1: Insect Pest Management for Field & Forage Crops Colonize soybeans when they emerge –Lay eggs in soil –Feed on cotyledons, leaves, stems Eggs hatch quickly –Larvae feed on roots and nodules Peak adult populations occur in late July Severe infestation will have leaves riddles w/ holes 2 nd generation emerges in September and can continue the infestation –This generation overwinters

Unit 1: Insect Pest Management for Field & Forage Crops Scouting should occur: –At emergence –When 1 st generation adults begin to feed –Pod-filling time is most critical Economic damage: –Begins when beetles are >16/ft. of row –5-10% injured pods Control may be needed during pod-filling if defoliation >20%

Unit 1: Insect Pest Management for Field & Forage Crops –Soybean Aphids Found for the 1 st time in the U.S. in 2000 Little is known about them Eggs overwinter on buckthorn plants Can have 18 generations/yr. As colonies increase, they will spread Usually found on leaves and stems Feed by sucking fluid from the soybean leaves Caused crinkled/cupped leaves

Unit 1: Insect Pest Management for Field & Forage Crops Have reduced yields by as much as 28% in China Very difficult to treat –Weather can cause a population crash quickly –Predatory control –Infestation can increase 10x in a week »Insecticide may only control for small period of time »May take 2 applications for control

Not treated Insecticide applied

Unit 1: Insect Pest Management for Field & Forage Crops –Wireworms Have typically been a problem restricted to grass/sod Becoming more of a problem in corn/soybeans Feed on the seed and roots Cause problems w/ germination, reduced stand, etc. Usually localized infestation Larvae will spend 2-6 yrs. in the soil developing Adults are called “Click Beetles” and will live mos. before laying eggs in grass

Unit 1: Insect Pest Management for Field & Forage Crops Rescue treatment is not effective for control Insecticide is recommended for high risk fields at planting time for good control Highest risk fields are those that are coming out of pasture/CRP, or fields that might be adjacent to these