• Western bean cutworm flight still impressive.
• Scouting for eggs should continue for fields not yet treated.
• Most Bt hybrids will not give control, scouting + insecticide treatment is only option.
• If possible wait until 90-95% tassel emergence before insecticide treatment.

According to our moth captures from the last week (see trap report) we are just past peak moth flight, that means more to come. The large flight this season, in northern Indiana and adjoining areas of Ohio and Michigan, are the result of the many fields found infested with larvae late last year. So high numbers of caterpillars entered the winter, which proved to be a mild one. In short, the high pressure is no surprise. This pest is potentially damaging to almost all corn in the region, because the Bt trait commonly found in the vast majority of corn hybrids (Cry1F) offer no control of this pest; resistance is a reality now <http://msuent.com/assets/pdf/BtTraitTable15March2017.pdf>.

Scouting and treatment are essential to prevent ear feeding and infection by the potentially even more damaging ear rot fungi that can readily develop in damaged ears later in the season.

Many pest managers are finding fields over the 5% (plants with one egg mass) threshold although the tassel/silks have not yet emerged. In cases like this, the best bet is to wait until 90-95% silking, even though eggs will continue to be laid and hatch. The young caterpillars will feed in leaf axils until the plant enters the reproductive stages and can be contacted with insecticides during their “final walk” from axils to the developing ear. Most producers will not want to spray twice, so the best way to maximize efficacy is to wait and get as many of the larvae as possible when the lure of the silk is present. Of course, once caterpillars are in the ear all hope of insecticidal control is lost. On a positive note, we have seen, first-hand, that even fields that with over 25% of plants with egg masses can be treated with insecticides and obtain excellent results. There are many compounds available, see the list here <http://extension.entm.purdue.edu/publications/E-219.pdf>.

It is very important to select the correct soybean leaves when tissue sampling to determine nutritional needs during the growing season. The most recent, mature trifoliate leaf will provide the truest assessment of the plant’s nutrition. This is usually the leaves from the third or fourth nodes from the top of the plant, depending on the development of the upper most trifoliate. If the upper most leaf is less than, or equal to, the size a quarter then pull the trifoliate leaf from the fourth node for your sample. However, if the upper most leaf is equal to, or greater than, the size of a half dollar, then chose the trifoliate leaf from the third node. For each sample submitted to a laboratory for analysis, pull 20-25 trifoliate leaves in the desired area, placed loosely in a paper bag marked with identifiers such as name, field, location, date, and growth stage of the soybean. Do not allow the leaves to remain moist, as they will mold quickly and ruin the sample.

If you are tissue sampling multiple times during the season, you should wait at least 10-14 days between samples. This will allow any past foliar fertilizer(s) applied to be incorporated into the plant and assessed. It will also test a new set of nodal leaves that have developed since the last sampling.

Reprinted with permission from the Kentucky Pest News, July 18, 2017.

Southern rust of corn, caused by the fungus Puccinia polysora, was confirmed by the University of Kentucky Plant Disease Diagnostic Laboratory (PDDL) this week on samples from Caldwell County and Graves County. This is the first confirmation of southern rust in Kentucky in 2017, and the impact of this finding for Kentucky corn farmers will depend on current crop growth stage.

Fields that are between tasseling (VT) and milk (R3) growth stages may benefit from a fungicide application if southern rust is present. If fields have already received a fungicide application, they should be scouted to determine disease severity prior to a second application. More details on symptoms and signs of southern rust and recommendations for fungicide use can be found in a previous Kentucky Pest News (KPN) article that can be accessed here.

If you suspect you have southern rust in your field, work with local county Extension agents to submit samples to the PDDL for proper identification. Confirmations will be posted on the Integrated Pest Information Platform for Extension and Education (iPiPE) as discussed in a previous KPN article that can be accessed here. On the map, red counties/parishes indicate that southern rust has been confirmed by university/Extension personnel.

On July 20, 2017, the Purdue Plant and Pest Diagnostic Laboratory (PPDL) microscopically confirmed Southern Rust (Puccinia polysora) on a corn leaf sample submitted from Parke county. 

Orange spore pustules of Southern rust on corn develop predominantly on the top of the leaf—as opposed to the brownish - red spore pustules of common rust that develop on both upper and lower surfaces of the corn leaf.

For more information and images please refer to Purdue publication BP-82 : Common and Southern Corn Rusts 
https://www.extension.purdue.edu/extmedia/BP/BP-82-W.pdf.

 Although the location, color, and shape of the pustules can assist in the identification of the type of rust infection on corn leaves, if you suspect you have Southern rust in your field, submit samples to the Purdue Plant and Pest Diagnostic Lab (PPDL) for proper identification.  We provide definitive, accurate, confirmation of Southern Rust by microscopic examination of the shape and size of the rust spores.  The sample handling fee for a sample is $11.00.  Sample submission forms are available at: www.ppdl.purdue.edu.

Please feel free to contact us if you have questions.

Gail Ruhl 
Senior Plant Disease Diagnostician
ruhlg@purdue.edu

Tom Creswell
Director, PPDL
creswell@purdue.edu
765-494-8081