Ada Szczepaniec
Despite low numbers and slow emergence, corn rootworms need to remain on our radars. In addition to the familiar corn rootworm issue, we also have a potential pest to scout for in southern SD – stink bugs.
We have noted corn rootworm adults emerging slowly in our test plots in northern and southern parts of South Dakota, but apparently adult rootworms are emerging rapidly in Minnesota. Bruce Potter, the IPM Coordinator with University of Minnesota Extension reported both northern and western corn rootworms, and noted evidence of extended diapause northern rootworms in fields in western MN.
Because we have had a cooler than normal summer and crop growth is delayed, so may be the beetles. Larval feeding may be ending especially in the southernmost areas of South Dakota and digging roots soon in those areas is recommended to assess larval damage and make management decisions for next year. As I wrote last week, it will be difficult to predict timing this year because of the wide range of crop progress along I-29. Scouting is recommended, and if you see adult emergence root digging should follow soon. If you wait too long, regrowth of the roots will hinder accurate assessment of the damage. Also don’t forget to pay very close attention to the late pollinating corn – it usually is the favorite hangout spot for corn rootworm females to get a good source of carbohydrates and lay eggs. Late corn consistently suffers greater corn rootworm damage the following year. Even a potentially ‘light’ corn rootworm summer may prove to be tricky!
One other report from Nebraska may be relevant to corn producers in southeast SD. Stink bugs have been reported in corn south of us. Brown stink bugs are more common in corn (Figure 1), but you can easily spot other stink bugs, such as the green sink bug, in corn too. Stink bugs are sometimes known as shield bugs. They have straw-like mouthparts and can pierce the husks and damage developing kernels. Immature stink bugs (nymphs) look similar to adults, but lack fully developed wings
Figure 1. (Above) Brown stink bug. Photo: A. Szczepaniec
Thresholds for stink bugs in corn have not been ironed out, but preliminary research out of University of Nebraska, Lincoln indicates that treatments are advised if you find one stink bug ¼ inch or larger per four plants prior to pollination; or one stink bug ¼ inch or larger per two plants after pollination and up to early dough stage. These thresholds correspond to roughly 25% of plants infested before pollination, and 50% of plants infested after pollination and prior to early dough.
Source : SDSU