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A complicating factor for soybean rust detection and control are the large number of legume hosts that can harbor soybean rust. In addition to soybean, there are 30 species in 17 genera of legumes reported to be hosts for soybean rust in nature, with 60 species in 26 genera that were successfully inoculated under laboratory conditions. One widespread host in the United States is kudzu, Pueraria montana var. lobata, that could serve as a reservoir for soybean rust. There are a variety of other important hosts that are leguminous crops or weeds that have shown varying degrees of susceptibility to both species of Soybean rust. Some other common hosts are yellow sweet clover (Melilotus officinalis), vetch (Vicia dasycarpa), medic (Medicago arborea), lupine (Lupinus hirsutus), green and kidney bean (Phaseolus vulgaris), lima and butter bean (Phaseolus lunatus), and cowpea or backeyed pea (Vigna unguiculata).

Soybean rust forms two types of lesions on leaves, tan and reddish brown. The tan lesions when mature, consist of small pustules with masses of tan colored spores on the surface. Reddish brown lesions appear different with reddish brown necrotic areas surrounding the pustules.

The most important element in managing soybean rust is staying ahead of the disease with well-timed, well-chosen preventive* fungicide applications. Soybean rust is so virulent that once the disease is established - especially in the mid- and upper-canopy - it can be extremely difficult to manage with a curative approach. (*Preventive is defined as 0-<2% incidence of rust in lower canopy; 0% in mid or upper canopy. A preventive application generally should be made at R1/R2.)

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Armyworms

Research shows that armyworm moths migrate from southern states in late spring and early summer. This helps explain the sporadic infestations that occur. When moths arrive, they prefer to lay their eggs in moist, shady areas, usually where grasses have lodged. Infestations that develop within soybean fields are often due to grassy weed problems. Armyworms are more of a problem in small grains and corn. However, damage to soybeans can occur when the armyworms usual host plants become exhausted due to feeding or dry conditions. When their food is depleted in the hatching site, the armyworms may move in large numbers, or "armies", eating and destroying plants or crops in their path.

Control of armyworms is recommended when 25 to 30% of the foliage is destroyed or if significant injury to pods is evident. Most often in soybeans, infestations are due to migrating armyworms. Under these circumstances, treatment of a couple of swaths ahead of the migrating armyworms to establish a barrier strip is suggested to prevent further migration and injury.

Armyworms are greenish-brown with longitudinal stripes. Full grown larvae are smooth, striped and almost hairless. Armyworms feed for three to four weeks. When full grown, larvae are 1½ to 2 inches in length. Armyworm larvae have six growth stages, or instars. The armyworms final instar lasts about 10 days and they consume large amounts of plant material during that time.

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Cutworms

Most damage by cutworms occurs when soybean plants are in the early stage of development. Damage consists of young plants being chewed off slightly below or at ground level. Some cutworm feeding injury may occur on foliage. Treatment guidelines used over the years include when one cutworm or more is found per 3 feet of row and the larvae are small (<3/4 inch long). Another guideline is when 20% of plants are cut or when gaps of 1 foot or more exist in the plant row.

Grasshoppers

In the northern plains, grasshopper egg hatch normally begins in late April to early May. Most grasshoppers emerge from eggs deposited in uncultivated ground. Soybean growers should expect to find grasshoppers feeding first along bean field margins adjacent to non-crop sites where the nymphs are hatching. Later infestations may develop when grasshopper adults migrate from harvested small grain fields. Grasshoppers will feed upon leaves and pods, chewing holes in them. A result of these migrations is soybean fields becoming sites for significant egg laying.

Many of the grasshopper infestations in soybeans will be the heaviest on the field margins. Treating these areas may lessen the total numbers of grasshoppers successfully entering a field.

Grasshopper control is advised whenever 50 or more small nymphs per square yard can be found in adjacent, non-crop areas, or when 30 or more nymphs per square yard can be found within the field. When 20 or more adults per square yard are found in field margins or 8 to 14 adults per square yard are occurring in the crop, treatment would be justified.

Border Treatment In most years, treating either the crop margin or the border area surrounding the crop is adequate for control. A border treatment of 150 feet beyond the crop edge should be adequate in most situations, depending on the size of the grasshopper source area, but season long control may require up to a 1/4 mile border treatment when the population source is large. Under extreme pressure, control may be difficult and multiple border treatments may be required. Using insecticides with the longest residual activity would be most effective. The residual activity of the treatments will vary with the chemical and environmental conditions. It is important to monitor the border areas and crop margins after treatment to make sure grasshoppers do not re-enter the field. See more information on our row crop grasshopper page.

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Bean Leaf Beetle

This beetle emerges from overwintering, moving into bean fields as the seedlings emerge. The white larvae develop in the soil, feeding on the roots and nodules. New adults emerging in August feed on foliage and pods. Feeding injury to leaves appears as small round holes between the leaf veins. Injury to pods appears as lesions similar in size and shape to leaf feeding holes. The injury to pods results in secondary infections by fungi and bacteria, causing rotting and discoloration. Treatment would be recommended when 3 to 7 beetles per sweep are found.

Soybean Aphid

Aphids suck fluid from plants. When infestations are large, infested leaves are wilted or curled. The aphids excrete honeydew, a sweet substance that accumulates on surfaces of lower leaves and promotes the growth of sooty mold. This aphid colonizes tender leaves and branches from seedling to blooming. Later, as the growing point slows, the aphids slow their reproductive rate, move down to the middle and lower part of the plant, and feed on the undersides of leaves. Towards the end of the season the colonies begin to rapidly increase in number, again. These increases are followed by a migration to the overwintering, alternate host, buckthorn.

The critical growth stage for making most soybean aphid treatment decisions appears to be the late vegetative to early reproductive stages (Vn to R3). Assessing aphid populations at this time is critical. Conclusions from 2001- 2003 management programs found that the best results from an aphid treatment occurred from mid-July to early-August. Treatment to manage soybean aphid would be recommended at growth stages R1 to R4 when aphids are abundant on most plants (guideline: aphids number 25 or more per sampled leaflet OR 250 total aphids per plant).

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Seedcorn Maggot

Seed corn maggots attack soybean seed, preventing sprouting or weakening the seedlings. The adult flies emerge in spring when soil temperatures reach 50o. When cool, wet conditions occur during planting, the slow emergence of the seedling extends the period of time it is vulnerable to feeding by the maggot.

Spider Mites

Feeding damage by mites in soybeans first appears as small yellow spots ("stipples"). As feeding activity increases, leaves become yellow, bronzed, brown, and eventually shed from the plant. Mites usually become a problem when hot, dry weather occurs. These environmental conditions stress the plant, whether mites are present or not. If conditions continue, treating for mites is no guarantee plants will recover.

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Aphids
Corn Leaf and Greenbug

The greenbug and corn leaf aphid are the most common species causing problems with corn and sorghum. The greenbug is the most injurious because it injects a toxin with its saliva during feeding. The critical period for injury by corn leaf aphid is during tassel emergence through pollination. Treatment is suggested only when 50% of the corn plants have 100+ aphids per plant during tassel emergence and plants are drought stressed.

Armyworms

Armyworm outbreaks occur when large migrations of moths from southern states occur in late spring and early summer. Moths prefer to lay eggs in moist, shady areas where small grains or grasses have lodged or been damaged by hail or wind. Treat when 25 to 30% of the plants have 2 or more worms or 75% of the plants have 1 worm. Treat migrating armyworms a couple of swaths ahead of the infestation in the direction of movement to form a barrier strip.

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Cutworms

Cutworm is known to lay eggs on sunflowers. Crops following sunflowers in rotation are at greatest risk of injury by this cutworm. Other harboring areas tend to be in surface crop residue from reduced or minimum tillage, bottom land or low spots in fields, poor drainage areas, and near shelterbelts with grassy ground cover.

Corn Rootworm

Rootworm beetles feed on the leaves, silk, and pollen of corn. Occasionally, the beetles congregate and feed on silks during early pollen shed. If silks are chewed back to the tips of ears (less than 1/2 inch of silks protruding) during the period of maximum pollen shed, poor pollination and grain set can occur. When an average of 5 or more beetles per silk mass are found during the first week of pollen shed, control may be necessary.

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White Grubs

White grubs have a three year life cycle. The most common white grub pest occurs in continuous cropping situations at sites where willow and cottonwood trees are present. White grubs are most likely to be found when rotation from grassland, pasture, or grassy weed sites occur. Most root feeding occurs in the second year of the life cycle. In most cases, the number of second year grubs will only be great enough to justify control once every three years. Treatment is recommended when sampling indicates an average of one or more white grubs per square foot are found. Begin taking samples 45 yards from shelterbelts. A total of 30 samples per field, randomly spaced along the shelterbelts are necessary. If at least a single grub is found in less than 40% of the samples, treatment may be required only out 20 yards from the tree line. If 40 to 60% of the samples are infested, treatment is needed to this distance and maybe as far as 65 yards. If greater than 60% of the samples are infested, treatment may be needed out to 90 yards from the tree line.

Wireworms

Wireworms are most likely to be problems when corn follows pasture or grassland. Continuous corn has developed problems in the past, also. Infestations often are found in coarse textured soils (sandy loam) where moisture is abundant, perhaps in low spots of fields. Sample 20, well spaced, one square foot sites to a depth of 4 to 6 inches for every 40 acres being planted. If an average of 1 wireworm per square foot is found, treatment would be justified.

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European Corn Borer
Field corn, Popcorn and Sweet corn

Most regions have the potential for one or two generations during the season. The two generation borers are present in the southern region of the state. Corn should be monitored weekly for at least five weeks once plants exceed an extended leaf height of 17 inches. At this point, corn borer larvae will be able to survive on the plant. Observing moth activity around field margins or within the field may alert you to developing infestations.

Grasshoppers

In the northern plains, grasshopper egg hatch normally begins in late April to early May. Peak hatch occurs about mid-June. Heavy infestations typically occur in areas of low rainfall or during drought years. Outbreaks are usually preceded by several years of hot, dry summers and warm autumns. Cool, wet weather increases disease occurrence and delays development of grasshoppers, reducing the overall population.

Border Treatment In most years, treating either the crop margin or the border area surrounding the crop is adequate for control. A border treatment of 150 feet beyond the crop edge should be adequate in most situations, depending on the size of the grasshopper source area, but season long control may require up to a 1/4 mile border treatment when the population source is large. Under extreme pressure, control may be difficult and multiple border treatments may be required. Using insecticides with the longest residual activity would be most effective. The residual activity of the treatments will vary with the chemical and environmental conditions. It is important to monitor the border areas and crop margins after treatment to make sure grasshoppers do not re-enter the field. See more information on our row crop grasshopper page.

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Cotton Insects

Boll Weevil

Boll weevils have caused an estimated $14 billion in yield losses and control costs to the U.S. cotton industry since arriving in the United States from Mexico in 1892.

Boll weevils damage cotton by feeding on squares and bolls. Adults puncture the fruit by use of chewing mouth parts at the end of the snouts. Females place eggs in some punctures and may cover the eggs with a glue-like substance. Eggs hatch into larvae that feed, develop and pupate within the square or boll. After emergence from the pupal stage, the adult chews its way out and, in a few days, begins to lay eggs for the next generation. Punctured squares in which eggs are laid usually fall off the plant with the resulting loss of that fruiting position. Boll damage may range from one damaged lock to loss of the entire boll. A common occurrence is boll rot because of weevil damage.

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Foliar Feeding - Foliar feeding is used when insufficient fertilizer was used before planting, when a quick growth response is wanted, when micronutrients (such as iron or zinc) are locked into the soil, or when the soil is too cold for the plants to use the fertilizer applied to the soil. Foliar-applied nutrients are absorbed and used by the plant quite rapidly. Absorption begins within minutes after application and, with most nutrients, it is completed within 1 to 2 days. Foliar nutrition can be a supplement to soil nutrition at a critical time for the plant, but not a substitute since greater amounts of plant material are needed than what can be absorbed through the plant leaf at any given time. At transplanting time, an application of phosphorus spray will help in the establishment of the young plant in cold soils. For perennial plants, early spring growth is usually limited by cold soil, even when the air is warm. Under such conditions, soil microorganisms are not active enough to convert nutrients into forms available for roots to absorb; yet, if the nutrients were available, the plants could utilize them. A nutrient spray to the foliage will provide the needed nutrients immediately, allowing the plants to begin growth.

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A1 Mist Sprayer Resources your Pasture
and Insect/Vector Control Specialists!

Continental Wholesale LLC
15 5th Ave S.E.
Hampton IA 50441

Phone 641-456-3165 · Fax 641-456-2406
US Toll Free 800-869-7203

E-Mail: info@continentalwholesale.com