By John Tooker
As the growing season progresses steadily, I wanted to bring a few potential pests to your attention. Reminding folks of these pest species will help you stay alert should you encounter them in your fields.
First, Kelly Patches (Penn State Extension, Franklin County) has been the first in the state to report soybean aphids. Populations are small with isolated individuals on scattered plants, but it is good to recognize that they have begun to arrive. At this early stage in their establishment and population growth, natural enemies are key for limiting populations. Do all you can to maintain populations of lady beetles, harvestmen, minute pirate bugs and other species; in other words, limit unnecessary insecticide applications, which are particularly hard on beneficial species. As the season progresses, I encourage folks to scout soybean fields regularly to monitor aphids populations and use Integrated Pest Management to manage them should populations approach the economic threshold of 250 aphids per plant. For more information see our fact sheet.
Second, potato leafhoppers are clearly here and hopperburn is evident in some alfalfa fields. This pest species is best managed with Integrated Pest Management to avoid causing other problems with regular insecticide applications. In 2014, we had many reports of aphid outbreaks in alfalfa fields. These outbreaks resulted from routine application of pyrethroids during each cutting. Applications targeting potato leafhopper most likely knocked out beneficial insects and spiders that usually control aphid populations in alfalfa. When these predators were excluded with insecticide applications, aphid populations were free to grow. To avoid this problem, scout for potato leafhopper and, if populations are above the economic threshold, cut the alfalfa if possible, otherwise spray only when necessary. In our experience, managing leafhoppers can often be managed with just one spray during the whole growing season, if one is able to use cutting as a control option. From more information and economic thresholds, see our fact sheet
, which accounts for higher values of hay.
Third, while scouting corn this week, I encountered isolated plants with true armyworm damage. Seeing this damage reminds me of really bad years recently when armyworms decimated hay and corn fields. So, stay vigilant and scout fields to detect the damage, particularly if wheat fields are nearby. Armyworm can occasionally cause problems feeding on wheat in wheat or other small grains sowed for harvest, but tend to be problematic more often in corn when small grains are harvested because armyworms move between fields. Armyworms tend to feed at night along the margins of corn leaves, avoiding midribs. During the day, larvae hide in leaf sheaths or in the soil or leaf litter. Rescue treatments are usually the most efficient and economical tactic for managing true armyworm because populations are very spotty and preventative applications may not have sufficient residual activity to kill caterpillars that hatch later. Armyworms can warrant treatment should infestations reach 25% of plants in a field. A recently revised fact sheet
provides more information on armyworm.
Lastly, colleagues in the Midwest are reporting emergence of western corn rootworm adults, and I have found that feeding damage on roots from rootworm larvae is evident in some corn fields in Pennsylvania. Recall that western corn rootworm is a pest of continuous corn in Pennsylvania, and it most easily controlled with crop rotation with soybeans or alfalfa. If you are seeing lodged plants in continuous corn, it is worth investigating to determine the cause. Also recall that some populations of western corn rootworm in the Midwest have developed resistance to some of the Bt hybrids, and last summer in Pennsylvania we found some similarly suspicious fields in three counties. The tests are about to begin to determine whether those rootworm populations were actually resistant to Bt varieties. We collected beetles from some of those sites, and in the lab these beetles laid eggs, and we overwintered those eggs. The eggs are about to hatch and we will assess the survival of the larvae on Bt and non-Bt plants. We will share results of these studies when we have them.