Twospotted spider mite.
Twospotted spider mite.

With most of the attention on the central and eastern Corn Belt, very little attention has been focused on the western Corn Belt or High Plains this year—a region that is experiencing better than average corn growth from most reports. But that doesn’t mean the area isn’t having its annual July and August problem with mites.

You would think that because Banks grass mites and two-spotted spider mites have shown up annually for decades, mite control would be top of mind for those corn growers, but apparently not. Some companies are still reminding growers to scout and be on the “front edge of a developing mite infestation.”

Two companies have recently been promoting their miticide products—Arysta LifeScience with Comite II and Valent with its Zeal.

As Lowell Sandell, regional field market development specialist, Valent, said, “The most important times to protect the corn plant are tasseling up to the dough stage of ear maturity—basically when the ear is forming and starting to fill out.”

This means a product such as Zeal SC miticide could be appropriate to use close to its 21-day preharest interval.

Application Options

There has been a lot of research over the years related to timing of a miticide application to protect the plant and also the method of application in the High Plains where mites at some level are always a concern, particularly the panhandle of Texas, panhandle of Oklahoma, western Kansas, eastern Colorado and southwest Nebraska.

Sandell notes the rest of Nebraska and some other areas have intermittent problems with mite populations dependent on the weather. He said, “It has not been a tremendously good year for mites in some of the High Plains including Nebraska up to this point. … But there is still quite a bit of growing season left.” If mite populations increase late in the season, he added, protecting the ear up through the dough stage is important.

There is a lot of talk about using aerial application, such as a recent Arysta LifeScience mailing that promoted aerial application of Comite II miticide and Fortix fungicide, but ground application of a miticide can also be effective, according to the regional senior technical sales manager for Arysta LifeScience, Brian Battles.

“Ground application works early, because mites start on the lower leaves, and they are on the underside of the leaves where they start to colonize. When a consultant walks into a corn field and finds colonies the size of a thumbnail, that is when a control spray is needed,” Battles said.

He said, “Ground application with drop nozzles down between the rows and spraying the miticide volume back up vertically under the canopy and spraying the bottom of the leaves is an option but the majority of Comite II is applied by air.”

Protecting Yield

Battles and Texas A&M AgriLife Extension agree that a 20 percent yield loss from not treating mite infestations is common. Having worked in the High Plains market in various positions for the past 30 years, Battles knows first-hand that there are portions of the region, such as southwest Kansas, where mites will show up every year.

Battle noted Comite’s history of being marketed for 35 years and how it has maintained a good share of the market with no known mite resistance to the product because Comite II has three different sites of activity.  He adds that it is effective on all motile stages of mites.

Sandell said Valent has heavily promoted Zeal in its liquid formulation. It gives corn growers the potential for consecutive year use and in rotation with other miticides to limit resistance. It is a completely different mode of action than Comite II and other miticides labeled for corn.

Zeal is “very targeted to mites” with a slower kill than some products. It inhibits the mite molting process or keeps it from moving to its next stage of life, but the miticide also keeps eggs laid by treated adults from hatching.

Good coverage is always necessary for miticides because the mites are sucking and piercing pests; therefore, Zeal’s formulation that causes the spray to spread across and under the leaf, “translaminar” activity, instead of sitting on the leaf in a droplet, is something that Sandell touts.

Limited miticide use by some farmers in certain situations is because products have been deadly to beneficial insects. Here again, Sandell is quick to note that Zeal is “softer on beneficials than most currently labeled miticides on corn.”

With corn planting somewhat extended and some lower than average temperatures earlier in the year, a lot of corn is in various stages of susceptibility to mites. Products are available and have a history of good performance.

The return on investment for mite control still pencils out according to both Battles and Sandell.