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STINK BUGS FOUND DAMAGING CORN IN EASTERN NEBRASKA

This article appeared in CropWatch, a UNL on-line publication. We have seen stink bugs in northeast Nebraska area fields, so if you see damage similar to this, it may be stink bug related.

A crop consultant reported finding stink bugs feeding on the base of seedling corn plants in Saunders County and sent the following pictures.

We have been receiving more frequent reports the last few years of stink bug damage to corn. Stink bugs insert their needle-like mouthparts into the base of seedling corn plants and insert salivary enzymes into the plant which assist in their feeding on the plant tissue. Depending on the plant stage attacked, injury symptoms may include death of the growing point, leaf distortion and twisting of the plant, or yellow streaks or holes in the leaves as they emerge from the whorl. Previous observations indicate that fields where the seed furrow was not fully closed due to planting during wet field conditions may favor injury by stink bugs by allowing access to the plant's growing point below ground.

We cannot identify the stink bug species based on these photos, but they are likely one of the Euchistus species, which include the brown stink bug and one-spotted stink bug. These may overwinter in Nebraska and begin feeding in fields of alfalfa or small grains, and then migrate to corn as it emerges. Often injury appears first on the field border as the stink bugs move into the field. If damage is observed soon enough it may be possible to treat the field border only. With time the stink bugs can move throughout the field.

There is no published research to establish an economic injury level for these insects, but some states suggest that black cutworm thresholds should be used. (TH & Bob Wright)

Stink bug at the base of the plant feeding.

Typical damage from stink bugs on seedling corn.

Twisting of the plant or other growth distortion is also typical of stink bug feeding injury.

CONTROL OF PROBLEM WEEDS IN ROUNDUP-READY SOYBEAN WITH GLYPHOSATE TANK MIXES

Widespread and repeated use of glyphosate-based herbicides in Roundup-Ready crops raised several concerns from the practical standpoint such as potential for weed resistance and shifts in weed species. Our fields are experiencing a slow shift in weed species. In the last few years, university weed extension specialists have been receiving phone calls and complaints on glyphosate failing to control certain weed species, including some “new weeds”, which includes: marestail (horseweed), morning-glory (common and ivyleaf), wild buckwheat, Pennsylvania smartweed, lady's thumb, venice mallow, yellow sweetclover, field bindweed, waterhemp, kochia, Russian thistle, primrose species and volunteer Roundup-Ready corn.

The purpose of this article is to summarize data from our studies conducted at Concord and North Platte in 2004, with the objective to test glyphosate tank-mixed with other herbicides to control the above mentioned weed species.

We used a labeled rate of glyphosate (Roundup WeatherMax @ 22 oz/a) tank-mixed with “half rate” of the 7 most common broadleaf POST herbicides such as: Classic 25DF (0.3 oz/a), Cobra/Phoenix 2EC (5 oz/a), Raptor 1SC (3 oz/a), Pursuit (Extreme) (3pt/a), Reflex/Flaxstar 2EC (8 oz/a) , Scepter 70DG (1.44 oz/a), and Ultra Blazer 2 SC (12 oz/a). Each tank-mix contained appropriate amounts of additives such as AMS (2.5 lbs/a), NIS (0.125% v/v) and/or COC (1% v/v) as indicated on the product label. Each tank mix was applied at 3 growth stages of the weed, targeting (1) 2 - 5" tall weeds (early POST), (2) 6-12" weeds (mid POST) and (3) 12-20" weeds (late POST).

The level of weed control at 21 days after herbicide treatment, varied from 10% to 100% depending on the weed species and a tank-mix used, while the weed size was still an important factor that determined the overall level of weed control (see Table 1). Most species that were 2-5" tall (early POST applications) were controlled relatively well with a tank-mix of the labeled rate of Roundup WeatherMax with appropriate herbicides. For example, a tank-mix of Roundup and Classic proved 90% control of sweet clover 4" tall compared to a much lower control levels of 40% and 10% for 8" and 14" tall plants, respectively, indicating the importance of the plant size. Few species were controlled well regardless of their size. For example, a tank-mix of Roundup and Classic provided excellent control (> 90%) of Russian thistle and kochia regardless of the plant size. For weed specific control levels and tank-mixes, see Table 1.

This data indicates potential to effectively control these species with various tank mixes if applied early POST (for weeds up to 5" tall). Taller weeds will require higher rates of broadleaf herbicides, perhaps full recommended rates. A study is needed to confirm such hypothesis.

Tank mixing glyphosate with various herbicides would also provide additional mode of action for weed control, thus reducing a chance for weed resistance. Furthermore, products like Extreme and Scepter could also provide additional soil residual activity for prolonged weed control, which is one of the goals of an integrated weed management program (eg. integrating several tools for weed control). (SK)

Table 1. Weed species and their heights at the time of herbicide application, and level of weed control (%) at 21 days after application with 22 oz rate of Roundup WeatherMax tank mixed with various herbicides at Concord in 2004 (preliminary data).

David P. Shelton
Extension Agricultural Engineer

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