Marshall County s Agriculture and Natural Resources Update. By Carl A. Bradley, Extension Plant Pathologist

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1 The end of July 2016 Row Crop Edition of Nikki s News Marshall County s Agriculture and Natural Resources Update Update on Southern Rust of Corn 7/19/16 By Carl A. Bradley, Extension Plant Pathologist Southern rust was observed in the University of Kentucky Hybrid Corn Performance Test in Webster County, KY on July 18, The disease was observed by the keen eyes of UK Plant Pathology interns, Andrew Gennett and Conner Raymond, and confirmed by Brenda Kennedy at the UK Plant Disease Diagnostic Laboratory in Princeton. To my knowledge, this is the first confirmed observation of southern rust in Kentucky for the 2016 season. Information about foliar fungicides, southern rust, and other foliar corn diseases is available in an article appearing in last week s issue of Kentucky Pest News. You can find this at: Cooperative Extension Service Marshall County 1933 Mayfield Hwy. Benton, KY (270) Fax: (270) Soybean Disease Considerations p. 2 Caterpillars May Affect Late Corn Planting In Different Areas of ky 2016 p. 3 Take Aim at Tobacco Target Spot & Frogeye Now p. 4 Southern rust may be difficult to differentiate from common rust, but identification of this disease is crucial since most corn hybrids are susceptible to southern rust. It is important to work with your local county Extension agent in submitting any suspect samples to the UK Plant Disease Diagnostic Laboratory. In addition, a free online webcast is available that shows ways to differentiate southern rust vs. common rust of corn. Soybean Yield Expectations when Planting in July/Aug. p. 5

2 Soybean Disease Considerations 7/19/16 Carl A. Bradley, Extension Plant Pathologist The continued frequent rainfalls and high relative humidity we have been experiencing have led to conditions favorable for the development of foliar diseases of soybean. Some diseases to look for are listed below. Septoria Brown Spot Probably the most commonly observed foliar soybean disease is Septoria brown spot (caused by Septoria glycines) (Figure 1, Photo by Carl Bradley). Figure 1 shows brown lesions and yellowing on the leaf edges caused by the Septoria brown spot pathogen of soybean. Although Septoria brown spot can commonly be observed, its potential to economically reduce soybean yields is not great. This disease tends to spread vertically (from bottom to top) in the soybean canopy. Only in very wet years, does this disease make it to the upper canopy, where it has the potential to reduce yields. This disease has the ability to cause premature defoliation, and when this occurs in the upper third of the soybean canopy, then yield reductions can occur. Frogeye Leaf Spot Frogeye leaf spot (caused by Cercospora sojina) is another foliar disease of soybean that can be observed in warm, humid, and wet growing seasons (Figure 2, photo by Carl Bradley.) Of all the commonly observed foliar soybean diseases that occur in this area of the U.S., frogeye leaf spot has the most potential to cause yield reductions. However, some soybean varieties are highly resistant to this disease, and yield reductions due to frogeye leaf spot will not occur on these resistant varieties. Cercospora Leaf Blight Cercospora leaf blight (Figure 3, photo by Carl Bradley) (disease caused by Cercospora kikuchii) Symptoms are purpling of soybean leaf. This is another disease that can be observed, but usually begins to appear later in the year. Because this disease generally is observed later in the year in Kentucky, yield reductions from this disease likely do not commonly occur. Foliar Fungicide Considerations Foliar fungicides can be useful tools in managing some of these foliar soybean diseases; however, a blanket application across all acres is not the best approach to take. From my program s soybean foliar fungicide research in Illinois, we did not always observe a profitable yield return with the use of foliar fungicides on soybean; however, when a significant level of foliar diseases were present and were being managed with the foliar fungicides, profitable yield returns were more likely. Of the three diseases listed above, management of frogeye leaf spot with foliar fungicides generally provided the greatest impact on yield. This was also observed in a research trial I conducted in Princeton, KY last year, where effective foliar fungicides applied to a soybean variety very susceptible to frogeye leaf spot resulted into approximately a 15 bu/a yield response compared to the non-treated check, which had severe frogeye leaf spot. It is important to know how susceptible your soybean varieties are to frogeye leaf spot, and to scout for this disease in susceptible varieties. Continued on page 6. Figure 1 Figure 2 Figure 3

3 Caterpillars May Affect Late Corn Planting In Different Areas of ky 2016 Raul T. Villanueva, Patricia Lucas, and Ric Bessin, Extension Entomologist Insect Description & Damage In Clinton and Todd counties, damage to corn and sweet sorghum has been reported to Drs. Lee Townsend and Ric Bessin since mid-june; and I have noticed injuries on corn foliage in Princeton during the last 2 weeks. This damage might be caused by the European corn borer (ECB), Ostrinia nubilalis, or the fall armyworm (FAW), Spodotera frugiperda. Caterpillars of these two species consume leaves during their larval development. This feeding results in plants with ragged appearance and the presence of abundant frass or feces near the whorl. Figure 1. Shows caterpillar damage on corn by European corn borer (ECB). Notice the abundant frass on the whorl from ECB or fall armyworm caterpillars. (Photo: Raul Villanueva, UK) Figure 1 Larvae of these species sometimes are hard to see. It is necessary to look deep into a whorl to find a larva. Once inside the whorl, larvae are well protected, and insecticides applications won t be effective. Trap Counts The presence of this damage coincides with the captures of male specimens of ECB and FAW in pheromone baited traps in Princeton and Lexington, respectively. Trap catches of ECB reached their peak by June 5 (greater than 110 ECB/trap), whereas FAW captures in Lexington peaked by June 10 (greater than 60 FAW/trap). In both cases, their numbers were much higher than the 5-year average captures for the two species at the corresponding dates (Figure 2). Data on pheromone baited traps of these two species, as well as cutworms, armyworms, Southwestern corn borer, and corn earworm/ can be found on the UK IPM webpage. Figure 2. Numbers of male European corn borer, and fall armyworm captured in pheromone baited traps in Princeton and Lexington, respectively in 2016 and a 5-year average. Life Cycles ECB overwinters as larvae in Kentucky and the high numbers of male captures might be associated with the mild winter in FAW migrates every year from their overwintering states along the Gulf Coast, and its population usually reaches its peak in August and September in Kentucky during late pre-tassel. Figure 2 FAW has 5 generations in southern states; in Kentucky it can have 3 generations per year. Plants can recover from earlier damage; however, late damage can affect the ears and cause economic losses. Scouting & Management Scouting for ECB and FAW is somewhat similar. To scout for these species, consultants/growers should check 20 consecutive plants (selecting the first randomly) from at least 5 locations in the field. However, for management decisions regarding insecticides applications, the time of scouting and threshold are somewhat different. For the first generation ECB, control should be done if 50% of the plants show fresh windowpane damage. Also, ECB can cause different yields losses depending on the number of borers in the plant and the plant stage (Table 1). Continued on page 6.

4 Take Aim at Tobacco Target Spot & Frogeye Now By Emily Pfeufer, Extension Plant Pathologist In our research plots and in grower fields, we are beginning to see target spot and frogeye pressure. Target spot is caused by Thanatephorus cucumeris (more commonly known as Rhizoctonia solani) and frogeye is caused by Cercospora nicotianae. These are both true fungi, not oomycetes (water molds) like the black shank and blue mold pathogens. Foliar fungicide applications may be necessary for effective management of these diseases. Figure 1: Frogeye lesions on a lower leaf, with white centers bordered by a tan ring and surrounded by a yellow halo (Photo: Kenneth Seebold, UK). Figure 2: Target spot lesions on lower leaf, with fallen-out centers and concentric rings (Photo: Kenneth Seebold, UK). Symptoms Both target spot and frogeye start in the oldest, lowest leaves on the plant. Early lesions look very similar between the two diseases, however, target spots tend to expand in rainy conditions, while frogeye lesions will stay smaller than a dime. Frogeye will have white centers, surrounded by a thin tan ring with yellow on the outside (Figure 1); target spots will be primarily brown. Larger target spot lesions develop rings within the spot, and sometimes the centers will fall out (Figure 2). Target spot near the stem end of the leaf can lead to total leaf loss. Environmental Conditions Rainy environmental conditions will speed up development of both diseases. Raindrops splash spores from the pathogens into the upper leaves, allowing these diseases to progress higher on the plant. Chemical Management If tobacco growers have not already done so, consider making a Quadris application. Going through available data from multiple states, in most years spraying Quadris 4 to 6 weeks after setting tobacco reduces target spot. This is most effective if drop nozzles are used, so the chemical is applied where the disease begins. Growers may consider increasing the Quadris rate to oz / A for additional protection against blue mold, if there is local concern about this disease. Quadris burn may result if plants are sprayed at high rates under stressful environmental conditions, so growers are encouraged to take precautions. Always follow the product label for safety information and allowable uses. Additional Resources 2016 Fungicide Guide for Burley and Dark Tobacco (PPFS-AG-T-08) Burley and Dark Tobacco Multi-state Production Guide (ID-160)

5 Soybean Yield Expectations when Planting in July/Aug. Carrie Knott, Extension Agronomist-Princeton, University of Kentucky The 2016 soybean season has quickly become a challenge for much of the state. For soybean fields planted in June, stands were reduced because of the extremely dry conditions across much of the state. Some regions received less than 2 for the entire month of June. These struggling soybean stands were then inundated with significant rain starting over the Fourth of July weekend and not ending until last week. The official precipitation recorded by University of Kentucky Agricultural Weather Center was as much as 10 for parts of the state. However, localized reports of more than 16 occurred. This led to considerable flooding in the state or at a minimum extended periods of saturated soil conditions. As such, many producers are considering replanting soybean fields. The first question on most minds is How much yield should I expect from late-planted soybeans? Based upon a 6-year (2006 to 2011) study that examined two relative maturity groups (late group II and mid group IV) the most recent estimate of Kentucky s soybean yield loss per day is: 0.50% yield loss per day for mid group IV soybean beginning May 9 (Figure 1) and 0.42% yield loss per day for late group II soybean beginning April 20 (Figure 2) To calculate expected soybean yield, based upon planting date: 1. Calculate the # of days after the optimal planting date a. Optimal Planting Date i. May 9 for mid group IV ii. April 20 for late group II 2. Calculate expected yield loss a. Multiply the number of days past the optimal planting date by yield loss per day b. Yield Loss per Day i. 0.50% for mid group IV ii. 0.42% for late group II 3. Multiply average soybean yield by expected yield loss EXAMPLE 1: Plant a mid group IV maturity group on July 19 Days past May 9, the optimal planting date, is 71 days 22 days in May + 30 days in June + 19 days in JUly = 71 days Expected yield loss, 0.50% per day x 71 days = 35.5% loss for a July 19 soybean planting Soybean yields average 80 bu/a for your farm 80 bu/a x 35.5% = 28.4 bu/a expected for a Mid Group IV soybean planted July 19 EXAMPLE 2: Plant a late group II maturity group on July 19 Days past April 20, the optimal planting date, is 90 days 10 days in April + 31 days in May + 30 days in June + 19 days in July = 90 days Expected yield loss, 0.42% per day x 90 days = 37.8% loss for a July 19 soybean planting Expected soybean yield, Your typical soybean average for late group II soybeans is 65 bu/a 65 bu/a x 37.8% = 24.6 bu/a expected for a Late Group II soybean planted July 19 Continued on page 6.

6 Soybean Disease Considerations 7/19/16 Continued: Resistance to the strobilurin class of fungicides exists in all three of the pathogens listed above. Therefore, if the decision to apply a fungicide is made, be sure that the fungicide product contains a mixture of active ingredients from different chemistry classes. Strobilurin fungicide resistance in the frogeye leaf spot pathogen has been documented in several counties in Kentucky. Strobilurin fungicide resistance in the Septoria brown spot pathogen was observed in northern Illinois in 2013 for the first time, but extensive surveys in other states have not been conducted. Strobilurin fungicide resistance in the Cercospora leaf blight pathogen commonly occurs in Louisiana, but no information is currently available for other states. For more information about fungicide resistance in soybean pathogens, please check out the Soybean Fungicide Resistance Hub online at the Plant Management Network. Caterpillars May Affect Late Corn Planting In Different Areas of ky 2016 COntinued: For FAW activity, begin checking corn by mid-june. Small FAW larvae cause window pane damage to leaves similar to ECB. For FAW, check plants a few days before tasseling, search deep into the whorls for large larvae. These larvae may attack young ears. Continue to check for this insect until silks begin to dry. Thresholds for FAW are presented on Table 2. In both cases (ECB and FAW), check thoroughly for the presence of live larvae. Soybean Yield Expectations when Planting in July (and possibly August) in Kentucky CONTINUED: Additional Considerations: When choosing a cultivar for July or August plantings consider one that is 0.5 to 1.0 relative maturity less than a full season cultivar. This may help reduce the risk of frost damage in the fall, due to an early frost event. Full-season soybean cultivars range from 3.5 to 5.0 relative maturities in Kentucky. Relative maturities between 4.0 to 5.0 are typically considered a full-season soybean in far Western Kentucky (Purchase Area) and southern Kentucky (south of the Western Kentucky Parkway). Relative maturities of 3.5 to 4.5 are more typical full-season soybean cultivars for the rest of Kentucky. Be aware that reducing the relative maturity of the soybean cultivar by more than about 1.0 relative maturity may increase the risk that the pods will be near or at the soil level. This is because the internode distances are typically reduced as planting date is delayed, which can have a much more dramatic effect on shorter relative maturities. The calculations above for expected soybean yield assume normal weather conditions occur after planting. That means adequate precipitation occurs, maximum temperatures are not excessive during flowering and seed pod development, and frost does not occur before soybean maturation. If any of these, or other stress events occur, soybean yield may be markedly lower than estimated above. Marshall County Agriculture and Natural Resources Agent