Fruit & Vegetable Magazine

Features Production Research
Tools to wage war on sweet corn pests


May 4, 2012
By Ronda Payne

Topics
An example of a bird cherry oat aphid (left) and English grain aphids (right). Joe A. MacGown, Mississippi State University

Aphids, beetles and weeds are not new annoyances to sweet corn growers, but those who have successfully fought the battle with these trouble-makers may find it’s time to go to war again. Let the battle-leader in you take comfort that there are a few new weapons to launch into the field.

In a joint presentation at the Pacific Agriculture Show held in Abbotsford, B.C. in late January, Tracy Hueppelsheuser of the B.C. Ministry of Agriculture and Grant McMillan of ICMS, spoke about pest management and treatment tools for sweet corn. Because both experts are based in B.C., their observations took place in the region, but treatment options apply to crops across the nation.

Aphids are not a friend to sweet corn – they are the enemy. They are persistent, sap-sucking, destructive and prolific.

Advertisment

Because they ride wind currents easily, even a cornfield previously free of the pests may become a feeding ground with the aid of an ill wind.

The bird cherry oat aphid is a species that particularly enjoys B.C. corn. While it is incapable of over-wintering in Canada, every year it hitches a ride on the winds coming up from the warmer regions of the United States. Farmers obviously are challenged in their war with the aphid as prevention is difficult, if not impossible, for a pest that comes when it pleases.

The bird cherry oat aphid can be dark green or black in colour, winged or un-winged (youth are always un-winged) and range in size from 1/32 of an inch up to 1/8 of an inch. Not only can they impede pollination, fertilization and impact cob quality, but their presence and the black, sooty mold their honeydew leads to, is unattractive to retail buyers.

Although the aphids have natural predators – like lady bird beetles, green lacewings, syrphid fly larvae and parasitic wasps – these biocontrols are unlikely to be successful in adequate aphid control because their populations do not build up quickly enough to prevent crop damage. “Larger artillery” is generally required if aphids take hold during crop pollination and fertilization stages, which, if left unchecked will cause incomplete kernel development.

“They (the bird cherry oat aphid) are attracted to flowering corn, the tassels and silks, from June to September,” noted Hueppelsheuser. “They create tonnes of honeydew, which contaminates the tassles and husks.”

According to Hueppelsheuser, control of the pests at the tasselling stage will help prevent aphid damage based crop losses and will enable proper cob development. Two common, registered insecticides mentioned in her portion of the presentations are either ineffective or are no longer being manufactured. However, she noted the Group 4 insecticide, Assail (acetamiprid), delivers adequate control for one to two weeks.

“Assail is registered now that Pirimor is no longer available,” she stated. “It is best used early on (in the infestation).”

Assail is also registered on a variety of fruit and vegetable crops for other pests. It works through contact and ingestion. Thorough application of the product, ensuring good coverage of plant foliage, is the best way to ensure effectiveness.

One drawback of Assail is that it is toxic if sprayed directly onto bees, so growers must take care when applying it. It is also toxic to aquatic organisms. Hueppelsheuser recommends visiting the searchable pesticide label site of Health Canada at http://pr-rp.hc-sc.gc.ca/ls-re/index-eng.php to read the label and determine if the spray is right for your field. She encourages producers to keep watching the website for new products.

An occasionally returning soldier in the battle of the cornfield is the dusky sap beetle, which has a preference for cobs that may have been damaged by birds or other insects. About six millimetres in length, a “standard” cylindrical beetle body appearance and generally brown to black in colour, they are easy to spot on the surface of corn. The trouble is, because these pests are drawn to decaying plant material, like browning silks, the adults and larvae burrow their way into the cobs to dine on the kernels within where adults lay their eggs.

“The sap beetle shows up once in a while,” Hueppelsheuser said. “Keep and eye out for it.”

There are no registered pesticides for the dusky sap beetle, in Canada; however there are non-chemical practices to make use of to aid in beetle management. Unlike the aphid, the beetle does over winter in cornfields, so ploughing crop debris under to eliminate that home is effective. Choosing varieties of corn that have tightly packed kernels and long husks can also be effective in deterring the pests.

A new herbicide has been registered for use on sweet corn to assist with weeds. BASF agreed to apply the product Integrity to sweet corn, in addition to their testing of the product on field corn, McMillan noted as he took the stage.

As a result of the testing, this newly registered tool is labeled as a safe herbicide for sweet corn. Integrity is a mixture of Kixor and Frontier and was tested on six cultivars in fields in Abbotsford and Yarrow, B.C., resulting in 80 per cent or greater control of weeds.

In his presentation, McMillan detailed that 1/4 to 1/2 inches of moisture is required within seven to 10 days of product application to ensure efficacy in control of grasses and broad leaf weeds. Even though it is a broad spectrum weed control product, Integrity was tested at a double spray rate and was found safe.

This is good news for producers as it ensures no crop injury will occur in the case of overspray or an accidental second pass of the product on corn.

As is the case with any good weed management practice, McMillan concluded his presentation with the note, “You must rotate products through the (herbicide) groups to prevent weed resistance and mutation.”

Certainly going to the battlefield can be daunting, but with the right weapons in hand, you may just win the war for your sweet corn.