Over the last 10 days I have had several calls about stink bugs in small corn. There have been some fields treated, however, at this time it has not been widespread. Stink bugs damage small corn by feeding through the whorl or side of the stem hitting the growing point which either causes â€œdead heartâ€ or severely stunts the plant. Severely stunted plants may not die but essentially become a weed. In many cases, corn that has been fed on without hitting the growing point will recover. Even if the growing point is not hit, in some situations where stink bugs feed through the stem you will see irregular growth. One thing that has always bothered consultants is that fields can be scouted thoroughly and still you will find damaged plants. This will always be the case since it is impossible to scout every plant in a field. Often damage appears to be much higher than it actually is since you can walk small corn fields quickly and the damaged plants stand out. Often times you will see several plants in a row with stink bug damage. It is important to scout early because when symptomology shows up the stink bugs are usually long gone. â€œAfter the factâ€ symptomology is fairly easy to diagnose because you see a row of elongated holes in the leaves as they unroll that often become stretched out and irregular around the margins turning yellow or white. Stink bug damage can be anywhere in a field but often times is more concentrated around field borders. Yield loss from stink bugs in seedling corn is essentially the same as you would expect with stand loss from any other factor.
The primary stink bug species we deal with in seedling corn is brown stink bugs but we occasionally see green stink bugs mixed in with them. I have had several calls this year about high numbers of rice stink bugs in corn. I would ignore rice stink bugs in your counts. Rice stink bugs are small seed feeders which generally do not feed in corn. There are unusually high numbers of rice stink bugs in wheat this year and as they move out of wheat it would not be unusual to find them in crops such as corn although they are not hurting the corn. Rice stink bugs will often move out of corn fields as quickly as they move into them as they are searching out suitable host (small seeded grasses primarily).
When scouting corn for stink bugs you must search the whole plant. Look in whorls, sides of stems, and at the base of the plants. Brown stink bugs are difficult to see at the ground level because they blend in well with the soil surface. The threshold for stink bugs in seedling corn is 10% infested plants on corn less than 24 inches tall. Pyrethroids are generally used to treat stink bugs in seedling corn. Although pyrethroids have only been marginally effective on brown stink bugs in other crops such as soybeans, in corn they generally do a much better job since coverage is very good on small corn.