Southwest Michigan field crop regional report – June 13, 2014

Crop growth in Southwest Michigan has been favorable. Plan to join us June 24 at our next IPM Breakfast Meeting.


Warm and moist conditions have been generally favorable for crop growth. The average growing degree days (GDD) base 50 accumulated since May 1 is 523. We normally accumulate 17.4 GDDs each day over the next 10 days. NOAA’s 6-10 and 8-14 day outlooks for Southwest Michigan is for above normal temperatures and way above normal precipitation for the near term forecast, and a return to more normal temperatures while remaining above normal precipitation for the 8-14 day period.

Crop reports

Advanced corn is V5-V7 and rapidly moving beyond the typical post-emergence herbicide window. Growth rate is excellent so far. Seed corn and commercial corn sidedress nitrogen operations are on-going, and the race is on to get nitrogen on before the crop gets too tall on early planted corn. Insects have not been much of a factor so far. By the GDD numbers, European corn borer peak flight could have been expected around 630-650 GDDs base 50, which was around 100 heat units ago in St. Joseph County.

In seed corn, scout for fish scale-like, off-white egg masses on the underside of corn leaves. Early instar larval feeding appears as windowpane damage followed by shot holes in the leaves. If you are finding egg masses or damage in seed corn, contact your seed company agronomist for guidance on thresholds. Also, consider the herbicide organophosphate (OP) insecticide discussion below before spraying an op insecticide, if necessary. Treatment window is often between 800 and 1,000 GDDs base 50. Commercial corn with Bt for corn borers should not need treatment.

Western corn rootworm hatch should be happening about now. Iowa State University uses a base 52 heat accumulation model from Jan. 1 to predict 50 percent larval hatch. Their research shows that about 50 percent hatch occurs from 684-767 GDDs base 52. While the Michigan State University Enviro-weather stations do not report base 52 heat accumulations, we can use the base 50 heat accumulations as a relative guide to western corn rootworm development. The Mendon Enviro-weather station has accumulated 780 GDDs base 50 since Jan. 1, and the Constantine Enviro-weather station has accumulated 782 GDDs. If you take away two GDDs from each warm day over the last two months, you can see that we should be pretty close to their midpoint benchmark for 50 percent hatch. We are also beginning to see lightning bugs, which have been the long time "old timer" indicator that rootworm hatch is underway in Southwest Michigan.

Also, white grub damage often begins to show up as pockets in fields that become very uneven in growth. If Asiatic garden beetles are the culprit, damage often appears on sandy knolls.

A recent seed corn discussion focused mainly on weed control issues. Some post-emergence sprays have minimal crop size restrictions, which can be hard to reach when you have multiple planting delays between the male and female inbreds. There can easily be three different growth stages of corn in a seed corn field, creating either issues of potential damage or ineffective weed control while waiting for the latest planted potions of the field to grow to the minimum plant height.

Early planted soybeans are in the three to four trifoliate stage and growing rapidly. Most of the beans have been emerged for four weeks now and some fields are beginning to show significant weed infestations and should be sprayed as soon as possible. Most fields are looking in good shape. No reports of soybean aphids.

Potatoes have excellent early crop growth. Nitrogen applications are important, and some fields have been receiving aerial applications to keep the plant growth moving. The early planted potatoes are at row closure. We are approximately 45 days from the early harvest, and are now about to enter the late blight infection window. A few Colorado potato beetles have been found.

Pickle cucumber planting is just starting in earnest in South Central Michigan.

Early cutting of alfalfa forages is on-going. Pockets of alfalfa weevil really impacted some first cutting quality. Compression of field operations due to short weather windows without a doubt had significant impact. Continue to watch regrowth for alfalfa weevil, although later cuttings should be just about beyond the window now. Potato leafhopper numbers have been low, but can move up quickly. Scout and be prepared to protect early regrowth if they become an issue.

Wheat is at flowering to early grain fill. Many fields were treated with fungicides. Most fields do not have much leaf disease issue on the upper canopy that we have walked.

Discussion with weed control specialist Christy Sprague

Palmer Amaranth research continues. Some populations of Palmer amaranth in Southwest Michigan have exhibited potential resistance to atrazine, which leaves the HPPD inhibitor (bleacher) herbicides very important in controlling this pest in corn and seed corn. Palmer amaranth in the MSU plots is about 3 inches in size now, which is about the upper size limit for effective control with post-emergence herbicides. Hopefully, most soybean fields that have challenges with Palmer amaranth were planted with Liberty Link soybeans, which is one of the most effective treatment options for later season control.

Michigan State University Extension weed control specialist Christy Sprague says that one of the best ways to identify small Palmer amaranth from the other pigweed species is look for a lack of hair on the leaves and especially stems, which is found on redroot and smooth pigweed. The other key indicator is the long petioles, or leaflet stems attached to the plants main stem. Waterhemp leaflets are extremely long and narrow, which can help to differentiate between these two species.

Other herbicide-resistant weeds growers here might expect to see are glyphosate-resistant marestail and multiple herbicide-resistant waterhemp, discussed in previous paragraph. Sprague is concerned that glyphosate-resistant giant ragweed could also be moving up from Northern Indiana. The Michigan Soybean Promotion Committee is still offering to have any weed suspected of being resistant to a herbicide in Michigan be submitted for a grow out analysis to MSU. Growers should collect weed seed from the suspect plants later in the season and contact the St. Joseph County MSU Extension office for more details on testing.

Another challenge that we discussed was the potential for interaction between some corn herbicides and OP insecticides. With the advent of Bt-rootworm corn for rootworm control, many growers stopped using soil insecticides in their fields. This was not true in many seed corn fields as we had sporadic issues with Asiatic garden beetle white grubs, and growers did not want to take the chance of an infestation on this high value crop. As Asiatic garden beetles spread across the region, and with the threat of Bt-resistant rootworms, some folks have stepped up the use of soil insecticides on commercial corn recently. Several of the newer corn herbicides and pre-mixes have restrictions on their use if OP soil insecticides were used. The main classes of herbicides with the restrictions are ALS inhibitors and HPPD inhibitors.

In the simplest of terms, the injury is caused when the plant tries to metabolize both the OP insecticide and these classes of herbicides at the same time, which can overwhelm the metabolic pathways used and cause injury. An article written in April 2013 by Aaron Hager, weed control specialist at University of Illinois, provides a good explanation of why the injury occurs and a list of herbicides and insecticides that have restrictions.  Remember that OP insecticide sprays used to control early season insects like cutworms and armyworms can also be restricted if these herbicides were used. If you are unsure of the classes of herbicides you applied on your fields, the corn and soybean herbicide classification chart is an excellent resource in helping you determine which herbicide families you used.

Upcoming meetings

MSU's Weed Control Field Day is scheduled for July 2 at the MSU Plant Pathology farm, located on the west side of College Road north of Jolly Road. Pre-registration is $25 per person by June 25 and includes lunch. On-site registration is $35. Refreshments begin at 8:30-9:30 a.m. with the field crop tour running until 11:30 a.m., the non-GMO soybean weed control tour runs from 1-3 p.m., and the vegetable tour with MSU’s Bernie Zandstra starts at 1 p.m. at the Horticulture farm south of Jolly Road on College Road. This excellent event is a great way to evaluate herbicide options and their performance in these important crops. Registration information is available at

Our next IPM Breakfast Meeting will be held June 24 at the Royal Cafe in Centreville, Michigan. Our invited guest speaker is Martin Chilvers, MSU field crops plant pathologist. The IPM Breakfast Meeting is a discussion of current crop conditions, pest infestations and agronomic practices used in the production of field and specialty crops grown in Southwest Michigan. The collective discussion between growers, agri-business professionals and crop consultants in attendance is summarized in this report. The group meets every other Tuesday at 7- 8:30 a.m. during the early growing season.

Other Michigan State University Extension field crop regional reports from this week:

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