To Scout For Armyworm Damage

On June 19, 2020

To Scout For Armyworm Damage

Every few years, we seem to get the right conditions for armyworm to do well in Pennsylvania and this is one of those years. Last week some folks had found armyworm damage, and the number of reports increased in the intervening week. Extension Entomologist John Tooker encourages growers to scout their corn, wheat, and hay fields for armyworm damage. For corn growers, armyworm is more common following grass cover crops, but they can show up in other situations, including in alfalfa.

True armyworm damage to corn begins from the edge of the leaves, and often looks ragged with large pieces of tissue removed, but armyworms rarely eat or cross the midrib In heavy damage, little more than the midrib of corn leaves can be left.  Armyworms feed at night and during the day in corn hide in the whorl, where their brown, wet, mushy feces accumulate. The great majority of feeding damage occurs when the larvae are nearly mature, which accounts for much of the damage seemingly appearing overnight.  In wheat, armyworms will first feed on leaves and then progress upward to the head, which they can clip off as they try to get enough food.  During the day, they hide at the base of plants.  Clipped heads on the plant or the ground are good signs of their presence.

Some Bt corn hybrids can provide protection against armyworm, but only hybrids expressing the Vip3A protein, so growers should review their trait information to know whether to expect any control. Insecticidal seed coatings do not provide significant control of armyworm, so the best control option is to scout fields and apply rescue treatments.  When scouting corn fields, look for leaf feeding and presence of caterpillars in the whorl. Control efforts are usually not economical unless 10 percent or more of the plants are infested. A variety of insecticides, including common pyrethroids, are available and effective for controlling true armyworm, but keep in mind that control gets to be more challenging as caterpillars grow and get to be one-inch long or greater. For growers wanting to conserve natural enemies in their fields, a few products provide good control of armyworm and have little activity against predators and parasitoids; these active ingredients include methoxyfenozide (Intrepid 2F, Troubadour 2F) and spinosad (Tracer and Entrust, the latter is organically approved). Growers should use higher rates the heavier the infestation and the larger the caterpillars. For details on insecticide options, see the Agronomy Guide ( and be sure to consult labels for specifics for each product.  For more details on true armyworm, see our fact sheet:


To Get Free Personal Protective Equipment (PPE) To Use In Running Your Small  Business Safely

Free personal protective equipment (PPE) is now available to Lancaster County-based businesses with 100 or fewer employees through Face masks, thermometers and hand sanitizer are included in PPE kits, which help to ensure the safe operation of businesses. The supply is significant and intended to serve most of the county’s small businesses.The EDC and the Lancaster Chamber are working with Penn State Extension, the Lancaster County Agriculture Council and the Lancaster Farmland Trust to provide information on key programs to the county’s agriculture community.

Representatives from these organizations will assist in answering questions and distributing PPE. Individuals who have questions or would like PPE should call Penn State Extension at 717-394-6851.The Lancaster County Economic Recovery Plan is funded by the $95 million in Coronavirus Aid, Relief, and Economic Security Act money that Lancaster County received from the federal government.

To Determine Appropriate Sidedress Nitrogen Rates

Many farmers have learned from the last two years of heavy rainfall during the growing season that keeping the majority of nitrogen (N) for corn in the bag, bin, or tank until sidedressing is one of the best ways to prevent N losses from occurring early in the season.  If you decided to split your N applications this spring, now is the time to determine an appropriate sidedress N rate.  

Extension Soil Fertility Specialist Charlie White explains there are several in-season N availability assessments that can be used in the coming weeks to help make this decision.  The pre-sidedress soil nitrate test (PSNT) and the chlorophyll meter test, are designed to assess the amount of N that is becoming available from mineralization of soil organic matter.  In fields with a frequent manure history or that are rotating out of a legume hay crop, significant N mineralization from organic matter can substantially offset the amount of N fertilizer that is required.  These tests are not designed to detect how much N fertilizer that was applied at planting is still available in the soil profile, however.  For those who applied their entire projected N fertilizer requirement at planting, assessing N availability and determining whether there is a need to sidedress additional N becomes more complicated. 

The PSNT test involves taking a soil sample to 12” deep and sending the sample to a lab for analysis of the soil nitrate concentration.  The test should be taken when the corn crop is 12” tall, or about the V5 stage.  For normal planting dates, the sampling window usually occurs in mid-June.  When relatively little N has been applied at planting (<50 to 60 lbs N/ac), the soil nitrate level at this growth stage is an indicator of the rate of N mineralization thus far in the growing season and this value has been calibrated to predict future N mineralization throughout the growing season.  The level of N mineralization predicted by the test is then used to adjust the sidedress N requirement.  Soil samples collected for the PSNT should be dried immediately after collection (preferably before sending to the lab) by spreading the soil in a thin layer on a paper bag, paper plate, or newspaper with an electric fan blowing air over it to speed drying. 


Alternatively, moist soil samples can be kept refrigerated and you can drop them off in person at the soil testing lab.  The point here is to prevent microbes in the soil from continuing to mineralize and nitrify N in the soil sample between when it is collected from the field and when it is analyzed in the lab.  It is also important not to collect a soil sample immediately after a heavy rainstorm, since the rain can leach nitrate into the subsoil below the 12” sampling depth.  Rather, wait several days after a heavy rainstorm so nitrate levels in the top 12” of soil can recover.  The PSNT fact sheet (Agronomy Facts 17)  has more information about the test and a formula for calculating a recommended sidedress N application rate based on the field history, yield goal, and the PSNT result.

Another option for assessing N mineralization in the soil and determining how much N to sidedress is the chlorophyll meter test. This will be discussed in next weeks column.

Quote Of The Week: “Every sunset brings the promise of a new dawn.” Ralph Waldo Emerson