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Stink Bugs in Corn
We have corn that was planted in early April through mid-May in our area so this information should cover the spread. Although, stink bugs aren't a pest of wheat, they will feed on wheat up to the time of harvest. Wheat harvest can push stink bugs into nearby corn, but this isn't a guarantee. Stink bugs can show up anywhere and at any time.
Scout corn for stink bugs from V1 through R2. Check all edges first (especially sources like woods, weeds and other crops), since they concentrate toward edges and not field middles. The number of sampling stops will depend on the number of stink bugs present and field size. At each sampling stop, check at least 10 corn plants. Sampling the entire plant is not necessary. From V1 to V6, scout the base of the plant on the stalk below the lowest green leaf. From V14 to VT, find where the primary ear is located or peel back leaves to find where it is forming. Scout the stalk from the first leaf above and below the primary ear. From R1 to R2, scout the stalk at one leaf above and two leaves below the primary ear. Thresholds vary depending on growth stage and are based on a 100 plant sample as described below (see table). These thresholds are not percentages, but numbers. If a single plant has multiple stink bugs, this must be counted into the total. If the number of stink bugs exceeds the number in the "treat" category, treat the field even if 100 plants have not been sampled. If the number of stink bugs per plant falls between the "treat" and "do not treat" category, take more samples until a confident decision can be made.
Insect Control: Many insecticides in the pyrethroid class are effective for brown stink bug in corn. However, bifenthrin is the most effective both because it can be applied at a rate that contains more active ingredient than other pyrethroids and because it is more toxic to brown stink bugs. Expect only a week residual.
Two critical factors to achieve control are:
Coverage- deliver insecticide where the stink bugs are located (photo below). Ensure canopy penetration with proper nozzle, pressure and volume selection.
Timing- the most critical time to treat from V14 to VT is just before the primary ear is exposed. Aim to control stink bugs when the primary ear is between these stages, but preferably on the early side to avoid banana ear.
Adding a fungicide to an insecticide when controlling stink bug in V14-R2 corn is a question we receive every year.
During this time of the year, we can have times of wet and humid weather conditions with high temperatures. With two of the three parts of the disease triangle in place, the pathogen is all that is needed to connect the lines.
Corn growers should be prepared to be proactive instead of reactive when it comes to making fungicide applications to prevent our most costly disease, southern corn rust. Southern Corn Rust can spread at a very rapid pace, and be potentially devastating to corn yields. A lot goes into deciding to spray a fungicide. This decision can be made easier when having to control stink bugs. However, each year is different, and pulling the trigger for preventive fungicide application is not automatic.
When the disease has been identified in your area and is moving throughout the environment, spraying to control southern corn rust may be vital to protecting yield.
Thus, initial efforts should include scouting and identifying the fields that are most at risk to protect.
Scout fields based on planting date and maturity. If the disease is detected, applying a triazole or a combination of triazoles, strobilurins, and pyrazole dicaboximides can help alleviate the disease pressure and provide protection from future infection. Please see the table below for efficacy ratings.
Another primary point to consider is that a fungicide treatment will add additional cost to production. Avoiding treatment places emphasis on a lack of potential yield loss based upon the assumption that this disease will not spread. Producers need to weigh potential yield, price of corn, production cost, and other factors against pesticide application cost to make a decision that fits personal risk management. Having thus said, assuming a $12/acre aerial application cost + $12 per acre fungicide cost, the breakeven cost at $4/bu of corn means only saving 6 bushels per acre. Assume a yield of 100 bu/ac and a minimum yield loss of 10%, and the cost of protective fungicide treatment is a much cheaper option. Assume the same yield with 30% yield loss from Southern Corn Rust, and the favorable decision to treat becomes very obvious!
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