Source: CropWatch
News service from University of Nebraska Institute of Agriculture and Natural Resources Cooperative Extension

There are now many more planting time options available to growers to choose from to manage seedling attacking insects and corn rootworms in corn. In soybeans, recent registration of seed treatments has given growers another alternative to control early season pests.

In the last few years, a couple changes have occurred in the fight against seedling- attacking insects. Several liquid insecticides were labeled for use in corn and advances in seed coating technology have allowed insecticides and fungicides to be applied to the seed on both corn and soybean, enabling farmers to buy pre-treated seed that is ready to plant.

Seed-applied insecticides

While seed coating advancements have led to increased protection from more pests, the costs of these pre-treated products are higher than the traditional hopper-box treatments. There are some advantages to using seed-applied insecticides, including:

• uniform seed treatment;
• ease of use; no mixing or measuring is required, and there is no special equipment to use;
• less exposure to insecticide residues and dusts;
• rates of active ingredients are low compared to soil insecticides; and
• some seed treatments are systemic and will provide some control of foliage feeding insects such as flea beetles.

As with many products, there also are disadvantages or misconceptions that should be considered, including the following for seed treatments:

• do not increase plant stands; they only help protect what you have;
• do not protect against poor germination due to mechanical damage to seed, poor storage, genetic differences, or poor farming practices;
• no season long protection; and
• do not protect against all insects; and
• may affect planting uniformity when planted at high rates.

CORN SEED TREATMENT

The newer seed-applied insecticides attempt to go beyond the traditional early season protection role. Not only do they protect against early season insects such as wireworms and seedcorn maggots, some are labeled for use against flea beetles, black cutworms and corn rootworms. Some are combinations of insecticides and fungicides and so also protect against disease.

Two newer products, Cruiser and Poncho, have combined to gather a large portion of the market for seed treatments in corn. They are both neonicotinoids and are applied directly to the seed by commercial seed treaters. These products work on the insects’ central nervous system by binding nicotinic acetylcholine receptors. They are effective as contact insecticides and are systemically active. The rates of each product will vary depending on the target insects.

Product costs range from $3 to $5 an acre for seedling insect control and from $15 to $18 an acre for corn rootworm control. Costs could be lower if purchased as a “package” with seed and herbicide products. This compares with the cost of a planter box treatment in the range of $1.50 to $2.00 per acre, or a one-half rate of soil insecticide at $5 to $8 per acre.

Cruiser (thiamethoxam), a Syngenta product, is registered for field, pop, seed, and sweet corn, and soybeans, along with wheat, barley, sorghum, sugar beets, cotton, oilseed rape, and canola. The seedling insect rate on corn is 0.125 mg active ingredient per kernel. The corn rootworm (the label says light to moderate infestation) is 1.125 mg ai/kernel. Cruiser is often sold as “Cruiser Extreme Pak” which is a combination of Cruiser and fungicides Dynasty, Maxim XL, and Apron XL.

Poncho (clothianidin) is a Gustafson/Bayer product. It was first labeled in June 2003 and was widely used in 2004 and 2005. It replaced Gaucho and Prescribe (both imidacloprid products) in corn. Gustafson considers it more active systemically and more toxic to insects than imidacloprid. The two common use rates for Poncho are 0.25 mg ai/kernel (Poncho 250) for seedling insects and 1.25 mg ai/kernel (Poncho 1250) for corn rootworms.

Planter concerns

Seeds treated at high rates with Cruiser and Poncho are visibly thicker due to the amount of active ingredient applied to the seed. While few growers using these seeds have reported any planter problems, it is important for growers to calibrate planters to ensure the proper seeding rate. Also, it is a good idea to use talc or another seed flow enhancer as recommended by the planter equipment manufacturers.

Alternatives to seed-applied treatments

Corn planted in April, when soil temperatures are below 60 degrees, should be protected from seedling attacking insects. For seedling insects, planter box treatments with imidacloprid and bifenthrin as active ingredients work well and are cheaper than seed- applied products, however, they require more labor and there are exposure concerns because of the fine dust associated with application. These products are available at almost all farm chemical dealers.

Many growers apply liquid insecticides in-furrow with or without starter fertilizer. These products include: Warrior, Pounce, Regent, Baythroid and Capture. Generic Warrior (lambda-cyhalothrin), Pounce (permethrin), and Capture (bifenthrin) are now available. Granular insecticides at one-half rates also are an option. Product prices will be comparable to seed-applied treatments, depending on the rate used.

For corn rootworms in Nebraska, crop rotation is still the best overall alternative. In continuous corn, granular insecticides still provide the best root protection, along with liquids such as Capture and Regent. Adult control to prevent egg laying is still feasible in some areas of Nebraska. Transgenic corn provides excellent control of corn rootworms in most instances.

Recommendations

Cruiser and Poncho both give excellent control of seedling attacking insects such as wireworms and seed corn maggots. Although black cutworms are suppressed or controlled, either product (along with others) may be overwhelmed by large numbers of cutworms. Dingy, darksided, or other cutworms that overwinter as partially grown larvae cause most cutworm problems in Nebraska. This may affect control, and there is little data about controlling these species. Fields treated with Cruiser and Poncho should still be scouted for cutworm problems and rescued if necessary.

Corn rootworm control with these seed treatments has been erratic in various university trials. Often these seed treatments will not prevent root damage to the same extent that soil insecticides do; however, yield results appear to be favorable, indicating that the corn plants may be recovering better than expected considering the root damage sustained. More yield trials are needed to establish a definite relationship between seed treatments and other corn rootworm control options. Caution should be used when choosing these products as a primary rootworm control. Ideally, they should be used in fields with low to moderate pressure, although it is difficult to determine which continuous corn fields would fall into those categories, unless the field was scouted for rootworm adults on a regular basis the previous summer.

Economics

Soil insecticides at full rates will cost $11-15 an acre (based on prices found on the Internet as of 2/20/2006). Reduced rates for seedling insect control depend on the rate selected by the grower. Generic permethrin costs approximately $0.50 an ounce. Warrior and Capture cost about $1.75 an ounce. Baythroid costs about $2.00 an ounce. Check with your local dealers or Internet vendors for the latest prices.

Growers should carefully assess the risk and reward of using any insecticide treatment. Seed attacking insects such as wireworms are very sporadic and normally do not affect a large number of acres. Does it pay to treat every acre with an insecticide when only a few acres will be affected? Do your replant costs over the years justify this annual expense? Or do you believe that the increased stand and potentially higher yield shown in some experiments justify the added cost of seed treatments or liquid insecticides for seedling attacking insects?

Research results

One seedling insect complex that has had little research data available is white grubs. In 2005, we were fortunate to discover a field that had a significant infestation in corn. The field was located just west of Randolph in Cedar County. The white grub was identified as Phyllophaga implicita, a three-year grub often associated with damage to crops in the Midwest. In this experiment several seed treatments, granular and liquid insecticides were applied at planting to try to protect the seedlings from damage. The data summarized in Table 1 is the final stand count taken on June 9. Live plants were counted per 30 foot of row. Stand counts followed by the same letter are not statistically different.

SOYBEAN SEED TREATMENT

Two insecticidal seed treatments are now available for soybean producers in Nebraska: Gaucho (Bayer CropSciences) and Cruiser (Syngenta). Both are neonicitinoid insecticides used to control early season insect pests of soybean. The active ingredient in Gaucho is imidacloprid and in Cruiser, thiamethoxam. Cruiser will be sold as Cruiser Maxx Pak, which includes the fungicide Apron Maxx RFC.

Both products show excellent early season control of leaf feeding and sap feeding insects because of systemic activity that distributes the insecticide through the plant; however, producers should consider how these products fit into Nebraska soybean production.

Our major early season soybean insect pest is the bean leaf beetle. In the early spring the overwintered beetles become active and often enter soybean fields as soon as plants emerge. Although the defoliation the beetles cause can appear quite severe, research in Nebraska and elsewhere has shown that it usually does not result in economic damage. Soybean plants can compensate for a large amount of early tissue loss, so it takes a considerable amount of beetle feeding (generally over 50% defoliation) to impact yield. A possible exception to this may be in early-planted fields, particularly when the plants emerge well before surrounding fields. Because the beetles move to soybean fields so soon after seedling emergence, early-planted fields will usually have more beetles and suffer the most injury. For those who regularly plant before most of their neighbors and have a history of high beetle numbers and/or bean pod mottle virus, insecticidal seed treatments may be an option. Both Cruiser and Gaucho have proved efficacious against early season bean leaf beetle in our insecticide trials.

The other soybean insect pest that some have suggested can be controlled with insecticidal seed treatments is the soybean aphid. Although early season aphid mortality and sublethal effects have been observed with insecticidal seed treatments, we do not recommend seed treatments for controlling soybean aphids in Nebraska.

To date in Nebraska, the soybean aphid has not been an early season pest; it has been a late season pest. Most of our soybeans are planted in May, and we generally don’t begin to see aphids until mid to late July, well past the early vegetative stages, and in most fields soybean aphid populations peak in August. This is too long to expect currently available seed treatments to have a significant effect. In addition, not all Nebraska soybean fields will have economic populations of soybean aphids, including northeast Nebraska where we have seen the most soybean aphid injury. In Nebraska, one well-timed foliar insecticide application, based on two or more field visits, will adequately control soybean aphids and protect yield.

SORGHUM SEED TREATMENT

Early season soil insect injury in sorghum is less common than in corn, but damage may occur from wireworms, seed corn beetles and cutworms. Planting time insecticide treatments are advisable in fields with a history of injury.

Seed treatments also are an option for sorghum producers. Gaucho (imidacloprid) and Cruiser (thiamethoxam) insecticides are labeled for use on sorghum. These products provide early season protection from soil insect pests and because of their systemic activity also provide protection against above ground pests.

Previous UNL research and company literature suggest that imidacloprid and thiamethoxam provide control of above ground insects for 30-40 days after planting. In Nebraska, we typically do not see early season infestations of greenbugs, so these treatments are not recommended for greenbug control. In parts of southeastern Nebraska where chinch bugs have been a problem, these seed treatments can help protect seedling sorghum. However, high populations of chinch bugs migrating from nearby wheat fields can overwhelm the protection of seed treatments, so rescue treatments may be needed even in fields using a seed treatment.

Other planting time options in sorghum include planter box seed treatments containing lindane, Furadan 4F applied in-furrow, or Counter 15G. Counter 15G should only be applied as a 7-inch band placed directly behind the planter shoe in front of the press wheel, and lightly incorporated with drag chains or tines. In-furrow applications are not labeled because of phytotoxicity concerns.

Keith Jarvi
IPM Extension Assistant
Tom Hunt
Extension Entomologist
Both at the Northeast REC
Bob Wright
Extension Entomologist
UNL-Lincoln