Welcome to Sangamon-Menard Extension’s April 21st edition of “Crop Update.” This publication is updated weekly during the growing season.

In this Issue:

• PLANTING UPDATE – Corn planters are “on the move” making progress.
• IN BRIEF – Feed value, armyworm news, cutworm reports, aphids, etc.
• POD AND STEM BLIGHT REVIEW – Fingers are pointing but what is it?
• WHEAT CURL MITE – A tiny little vector of a really rough virus.

NOTE: Sangamon-Menard Extension lost access to its ever popular “Ag Photos Page” late last year. A new and revised “Ag Photos Page”:http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1 is now available at our website.

PLANTING UPDATE

As of April 19, a windshield survey showed the following progress in planted corn acreage for the mentioned regions:

• Oakford to Petersburg – 70-75% of the corn planted
• Petersburg to Springfield – 65-70% of the corn planted
• Springfield to Auburn – 75-80% of the corn planted

Corn is beginning to “spike through” with roughly 10-15% of planted corn in the Sangamon-Menard unit now emerged (southern Sangamon county shows the greatest progress in this arena). While some beans fields have been planted, progress “on the bean front” is still less than significant. Wheat in the two counties (on average), now shows the second joint and has thus passed the stage we term “Feekes 7.” In some areas, it has accelerated well into “Feekes 8” (flag leaf emergence).

IN BRIEF

• RELATIVE FEED VALUE – Average alfalfa stem heights in the area range from 14-18 inches (depending upon the field surveyed) and thus correspond to Relative Feed Values (RFVs) of 275-240 respectively. RFV is an estimate of nutritional value/digestibility made in comparison to full bloom alfalfa. Most producers pressing for high quality alfalfa hay hope for a final RFV of 150. One can measure the height of alfalfa with a yard stick, identify the stage of alfalfa growth, and access a simple chart termed PEAQ (Predictive Equations for Alfalfa Quality) for a fairly reliable estimate of alfalfa RFV. (Visit http://peaq.traill.uiuc.edu/ for further details).

• TRUE ARMYWORM MOTHS – The most recent edition of “The Pest Management and Crop Development Bulletin” noted impressive Kentucky true armyworm moth flights. Those same moths fly into Illinois from the southern U.S. each year, and we historically encounter armyworm larvae toward the mid part of May. We humbly ask that producers pay attention to moths flitting about porch lights, letting us now what they see. Armyworm moths, inch-long, tan colored moths have two small white dots on their wings surrounded by a hallo of black. (“Ag Photos Page”: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1 :type in “armyworm moth”). Please report any such moth observations to our office by calling 782-4617 or e-mail mpmontgo@uiuc.edu.

• BLACK CUTWORM MOTHS – Black cutworm moths are in the area. Sangamon-Menard Extension traps (monitored by Pioneer and Lincoln Land FS) have noted moths near Chatham, Ashland, Pleasant Plains, Berry, Illiopolis, and just across the Sangamon County line near Ashland. None of our traps have detected noteworthy/threatening moth flights (Note: Pleasant Plains max capture: 6 moths/two day period – Berry max capture: 3-5 moths/two day periods – 9 moth/two day period is deemed critical). Pressure does continue to build in the state. We’ll keep you posted.

• PEA APHIDS – Kevin Black, Growmark, has reported exceptional pea aphid populations in southern Illinois alfalfa during recent e-mails. In that correspondence, Kevin noted that “aphids coated the stems of nearly every plant” in some fields and that “accurate sweep counts were impossible.” In some cases, Kevin could “measure aphids by the pint.” Sangamon-Menard Extension has visited alfalfa during the last week. While we can find pea aphids, area sampled fields (thankfully) appear devoid of such intense pressure. However, we have also received a few “intense lady beetle” reports in alfalfa which could indicate “more intense” aphid populations “on the radar screen” (lady beetles feed on aphids). Producers should scout for this pest just in case. Thresholds are 100 aphids/sweep (conducted via 15 inch sweep net). (“Ag Photos Page”:http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1 :type in “pea aphid”).

• BIRD CHERRY OAT APHIDS – One of three aphids typically noted in wheat (English grain aphids and greenbugs are the other two and tend to be more significant pests), these aphids have a dark gray color with a slight smudge of red or pink on the tail end and can occasionally be found in wheat as of press time. (“Ag Photos Page”: http://web.extension.uiuc.edu/PhotoLibPublic/?libID=1 :type in “bird cherry oat aphid”).

• GRAIN MARKETING BOOT CAMP – Curious about various marketing tools or just have general questions pertaining to marketing? If so, check out a new U of I Extension website termed the “Grain Marketing Boot Camp” at: http://web.extension.uiuc.edu/grainmarketing/basics_broker.html.

POD AND STEM BLIGHT REVIEW

Many a rumor has floated around about “poor germ bean seed.” Likewise, many have also speculated that “pod and stem blight” was the culprit of this problem (this point is in dispute). The exact scope of “poor germ problems” remains to be seen as does the exact “culprit” responsible for any such problems (remember – the rumor mill tends to run full speed at this time of year). That said, a review of the disease termed “pod and stem blight” is probably warranted.

A complex of fungi are likely responsible for the symptoms agronomists and plant pathologists term “pod and stem blight” with most noting those fungi belonging to the genus Diaporthe or Phomopsis. The fungi responsible typically overwinter as mycelium (fungal hairs) on debris and seeds. During the early summer, either of two structures may be produced. Flask shaped fruiting structures, filled with spores, are often produced on stem debris. The flask shaped structures are termed “perithecia” and the resulting spores spread the disease to the immediate proximity of these perithecia. The other structures produced are termed pycnidia. These fruiting structures produce spore masses that “ooze” from the fruiting body. The resulting spores from either pathway germinate and enter the plant progressing within and between plant cells. Warm, wet weather favors this disease which tends to appear after the middle part of the season.

Since the progression of the disease is relatively slow, the disease tends to best infect seed if it infects pods as the plant begins to yellow. Infected seed may crack and shrivel and may even be covered with white fungal hair. Should even a couple percentage points worth of the lot be infected, germination may be significantly impacted. Pycnidia, fruiting bodies, are produced on the plant and are often noted in rows that may cover the entire surface of the bean stem but are more typically observed near the nodes. Such symptoms often do not develop until the plant begins to senesce. The fungus does not fair well in dry conditions.

Options for managing this disease typically consist of rotation, planting high quality seed, utilizing a fungicide seed treatment where seed quality is questionable, planting later (earlier planting tends to increase the likelihood of well progressed Pod and Stem Blight), and reducing damage and stress to the plant (insects are often noted). Avoiding a delay in harvest tends to deter this problem by decreasing the period of time that this disease can “get at” the seed.

WHEAT CURL MITE

Viral diseases in wheat have been a popular subject recently with the latest edition of the U of I “Pest Management and Crop Development Bulletin” addressing the topic. Barley Yellow Dwarf and Soil-borne Wheat Mosaic have been noted during typical in-field “wheat virus discussions” as has the disease termed “Wheat Streak Mosaic Virus – WSMV.” The latter has led to some interesting questions about the principle WSMV vector, namely an insect-relative termed the “wheat curl mite.” Where WSMV is suspect, this pest is typically present as well.

Wheat curl mites are exceptionally small, measuring only about 1/100th of an inch in length, and are thus not typically noted via the naked eye. (1 – “Handbook of Corn Insects”) Possessing only two pair of legs (four legs total found near the head), both the adult and nymph stage of the wheat curl mite are gray-white in color, “cigar shaped,” and narrower than “the space between the veins on a wheat leaf.” (2 – “Wheat Curl Mite” by Slodenbeck, KSU Cooperative Extension) Adult mites lay eggs in rows along the leaf surface, and the typical wheat curl mite takes approximately 8-10 days to progress from an egg to an adult. Maximum reproduction rates are encountered when temperatures hover near 80 degrees and taper to zero as temperatures near freezing (2). Actively growing plants (i.e. adequate moisture) also will aide mite reproductive rates. Multiple generations occur each year, and the mites tend to feed on the upper portion of a host plant, often clustering along the margins of an infested leaf (sometimes causing it to “curl”). This WSMV vector can be found throughout the U.S.

The exceptionally small size of the wheat curl mite necessitates that it be “aided” in movement. Significant movement of the mite (extra-field movement) thus typically occurs via wind currents. Wheat curl mites typically can not survive more than a day or two removed from green host tissue (the exact period varies and is dependent upon environmental conditions) and tend to move in a cyclical fashion from drying wheat to green tissues (volunteer wheat, pasture grasses, corn, etc.) during the mid-summer and from dying alternate hosts back into newly emerged/green wheat during the fall. Young nymphs acquire Wheat Streak Mosaic Virus via feeding on infected plants. The virus is drawn in with sap during feeding and persists (one to several weeks) within the gut of the nymph (1). Adult wheat curl mite vectors of WSMV do not pass the virus on to the egg stage.

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