Vol. 20, No. 14, July 28, 2005

Jan Byrne, MSU Diagnostic Services
Sandy Perry, SBR Sentinel Plot Coordinator

Fourteen reports were filed from the 20 plots during the reporting week.

No soybean rust has been found in Michigan or anywhere else in the region, including Ontario, Canada.

Plant height: Ranged from 20 inches to 40 inches, 4 plots = 20 in., 1 plot = 22 in., 2 plots = 24 in., 3 plots = 30 in., and one plot each at 35, 36, 38 and 40 inches.

Degree of canopy closure: Ranged between 90 and 100 percent.

Soybean diseases present: Eleven plots = low brown spot, 2 plots = low bacterial blight, 7 plots = low downy mildew, 2 plots = low Phytophthora stem canker.

Insects present: Four plots = a few soybean aphids per plant, 8 plots = 0-50 per leaf, 2 plots = 0-10 spider mites per leaf, and 2 plots = low levels of Japanese beetles. One plot had been recently sprayed for soybean aphids and 3 plots reported that soybean aphid numbers were increasing.

No soybean samples were submitted to MSU Diagnostic Services to be assayed for soybean rust during the reporting period.

MSU Diagnostic Services reports the following pests and problems found on field crop samples submitted in the last 2 weeks:

Christina DiFonzo, Entomology

Fields range from a few soybean aphids to “dripping” with aphids, even on the same farm.

Hundreds of tiny, white newborn babies are being deposited by winged aphids (See related article on the aphid suction trap in this issue) on calm mornings and afternoons. This is our first experience with such heavy deposition of babies over such a long period – now stretching into several weeks. In a single morning, a field can essentially go over the 250 threshold if 50 to 100 winged aphids land and deposit four to five babies each! The key to dealing with the babies is to remember the second half of the current aphid recommendation: 250 aphids per plant with increasing aphid populations. Interestingly, in many fields colonized by babies, the tiny babies are not growing into adult aphids, which would only take a matter of days. Instead, it appears that predators are cleaning up babies and that new babies are simply deposited each day (predation is balancing deposition). Thus the plants continue to have small baby aphids, but no or few adults. My best guess is that fields that are exhibiting this type of situation do not have an “increasing” aphid population – they simply have a static, recycling population of babies. However, watch these fields carefully to see if the situation changes and babies begin to survive to adulthood. In that case, a treatment decision may have to be made on short notice.

Armyworm is reported in corn from Mt. Pleasant north into the UP and over across the Thumb. Fields are described as “totally stripped of leaves” to “significant feeding.” Armyworm problems indeed can appear fast. Small larvae are present, but go unnoticed until they become large enough to eat a lot of leaf material. Then, defoliation can occur in a matter of days. In the majority of cases, the impacted fields had a grassy weed problem earlier in the season – perfect egg laying situation for armyworm females.

In some cases, no ground equipment or aircraft is available to spray – these fields cannot be treated, and the hope is that the defoliation will end soon. The reported armyworms appear to be at least one inch in length, so they will pupate soon and stop feeding. Also, when outbreaks occur, we often see beneficial organisms such as diseases and parasitic flies reducing populations (See photos). In cases where equipment is available, pyrethroids such as Ambush, Asana, Baythroid, Capture, Mustang, Pounce and Warrior should do a good job of killing larvae. Sprays do not need to penetrate down to the ground, as larvae will climb up the plant to feed in the evening. Corn can partially recover from armyworm defoliation if the growing point is unaffected, but the amount of recovery will depend on the stage of the corn, as well as how much leaf material is left.

Corn rootworm beetle emergence is tremendous this year. There are numerous reports of downed corn as storm fronts move across the state. Now is the time to dig and evaluate roots to determine:

1)   The cause of downed corn

2)   The efficacy of insecticides and transgenic corn

3)   The presence of variant feeding on first-year, rotated corn.

Beetles are also heavy in soybean in southern Michigan and surprisingly in central Michigan as well. This is a sign of variant behavior, and these beetles may be laying eggs in soybean, so that larvae will feed on and damage corn rotated into the field next year. Variant may be sampled by using yellow sticky traps in soybean fields. Place four to six yellow traps on T-posts across the field, adjusting the height of the traps so they are just above the canopy. Change the traps on a routine basis, counting the number of rootworm beetles stuck on the trap. If possible, count the traps in the field to avoid getting sticky goop all over the place. Also, once traps are folded back together, then unfolded, insects have a tendency to break apart and identification is more difficult. Once you get the total number of rootworms on a trap, divide that number by the number of days that the trap was exposed. This gives you the number of beetles per trap per day. Finding less than one to two per trap per day is not of concern. Finding three to four beetles per trap per day suggests variant is in your area. Five to seven beetles per trap per day predicts that you will have root pruning on corn next year, and the damage may be economic. Finding 10 or more beetles per trap suggests that damage next year will be severe with entire nodes of roots gone.

Defoliation is present in many fields, caused by a complex of insects: Japanese beetles skeletonize leaves, creating a lacy appearance. Bean leaf beetle and corn rootworm beetle chew round holes in leaves. Grasshoppers often chew from the leaf margin. The threshold for defoliation during pod fill is 25 percent. The human eye often overestimates defoliation. It is common to find pockets of worse defoliation on upper leaves, particularly where Japanese beetles cluster to mate in a small area and feed heavily. When assessing defoliation, examine more than the top leaves. Plants can compensate for feeding, and light can also filter down to leaves in the mid-canopy. One thing to watch for is pod feeding by bean leaf beetle, rather than simply defoliation. Pod feeding can directly impact yield and quality, and the threshold is only 10 percent of pods damaged. This type of feeding usually occurs later into August.

Christina DiFonzo, Entomology

As promised in the July 14 Field Crop CAT Alert, below are the counts from one of the three suction traps running in Michigan. The traps are located at the Kellogg Biological Station in Hickory Corners, on the MSU campus and at the Saginaw Valley Bean and Beet Research Farm south of Saginaw. The table below gives the counts only for the MSU campus trap, because it has been running for the longest period of time. From the last week of June, catches of winged soybean aphids have been steadily increasing.

The table also lists some of the other aphid species captured in the trap. I provide notes about the host range (Where are these aphids coming from?) as well as some of the important viruses that are transmitted by each.

How do the counts from Michigan compare with other states in the regional trapping network? In the accompanying map is a summary of the soybean aphid catch from traps in five states, all from the week of July 15.

Here is a quote from Dr. Dave Voegtlin, who is sorting the catches from the regional trapping network, “I am sure that you don't have to tell Chris that Michigan has lots of soybean aphids… The remnants of hurricane Dennis provided central Illinois with mild north west winds for two or three days in a row at the end of that week. A perfect situation for Michigan to export its aphid resource and I believe that is what we saw in the number of alates in the field. If this heat does not slow the aphids down, August is going to be lively.”

Christina DiFonzo, Entomology

Reports of spider mite damage are coming in from across Michigan, but particularly in drier areas such as the southern part of the Thumb. Soybeans and dry beans are obviously at risk, but even sugar beets can experience mite problems. Garden plants, flowers and shrubs around fields may also harbor heavy mite populations. The following is an article I wrote in 2001, the last big mite season. It gives information on mite life cycle, damage and scouting, as well as updated control information.

Eggs hatch in a few days and small mites begin to feed. Immature mites resemble the adults, except that they are smaller in size. They grow by molting, and if you look closely at a mite-infested leaf, you sometimes see the shed skins of immature mites. A leaf heavily colonized by mites will have eggs, immatures, adults, shed skins and webbing.

Damage
Spider mites feed on numerous crops, and under certain conditions, will increase to the point where they affect yield. This is especially true under dry conditions or on sandy soils where water stress is an issue. Mites pierce individual plant cells and suck out the contents, initially causing tiny yellow spots (called stippling) on leaves. This feeding also increases water loss from the plant. As populations increase, symptoms include yellowing of leaves and in more severe cases browning, bronzing or death of foliage. As leaves become yellow and die from mite damage, the photosynthetic ability of the plant is reduced. With the additional water loss, leaf drop and reduced photosynthesis, yield and quality of crops is reduced by severe mite feeding.

** Dry bean: dimethoate (0.5 – 1 pint/ acre). Will also control potato leafhopper.

** Sugarbeets: Lorsban (1-2 pints/ acre)

** Soybeans: Lorsban (0.5 – 1 pint/ acre) or dimethoate (1 pint/ acre)

Another consideration when both mites and aphids are present is choice of products for control.

§      If aphids are your target, both organophosphate [OP] insecticides (Lorsban, dimethoate, Orthene) and pyrethroids (Asana, Baythroid, Mustang, Pounce, Warrior, etc) can be used.

§      If mites are the target, then an OP is preferred. OPs tend to work better against mites than pyrethroids, which tend to flare mite populations.

§      If both pests are present, OPs again are the preferred option to reduce risk of flaring mites. However, Lorsban is the preferred option within the OPs. Although dimethoate is a low cost, effective mite control, it is less effective for aphid control compared to Lorsban.

Christina DiFonzo, Entomology

Orthene 90s from Valent now has a 2ee label for soybean aphid control in soybeans. The label rate is 0.56 to 1.1 lb per acre. The reentry interval is 14 days, and the preharvest interval is 14 days. The label also allows for tank mixing with certain herbicides and soybean fungicides.

Based on my past experiences working in potato, Orthene should work well on soybean aphid. In the plant, Orthene is systemic and breaks down into a compound that is even more toxic to sucking insects than the original active ingredient. It is an OP (like Lorsban and dimethoate), however, I do not know if it has the “fuming” action under hot conditions that we see with Lorsban. Like the other OPs, Orthene breaks down in days (rather than weeks) which allows beneficial insects to recolonize a field, OR allows recolonizing aphids to survive (However you want to look at it!). Orthene is listed as a moderate miticide and would be preferred over a pyrethroid if mite populations are heavy in a field along with aphids. Orthene is one of the products in our spray trials this summer, so we will have efficacy data available at winter Extension meetings.

Jim Kells and Kathrin Schirmacher,
Crop & Soil Sciences

Annual weed densities are very high in wheat stubble this year. These weeds must be managed soon in order to prevent seed production. Several effective options are available for management of annual weeds in wheat stubble. However, these practices must be implemented before seed production to avoid significant additions of seeds to the weed seed bank.

After wheat harvest, weeds take advantage of available resources, especially newfound sunlight, and will grow rapidly, especially in years with adequate soil moisture in July and August. These weeds are capable of producing large amounts of seed prior to a killing frost.

Common ragweed, velvetleaf, common lambsquarters, redroot pigweed and foxtail species are examples of common summer annual weeds in wheat stubble. At this time of the year these weeds are completing their life cycles by flowering and producing seed. The main goal following wheat harvest is to prevent or reduce weed seed production. Post-harvest weed control options include tillage, mowing, and herbicides. In general, management of annual weeds in wheat stubble is not difficult, however timeliness is critical.

Tillage is a viable option for control of both broadleaf and grass weeds. Mowing will reduce seed production of most grass and broadleaf weeds. However, mowing is often less effective on grasses since seeds can be produced on tillers low on the plant. Glyphosate and 2,4-D are common herbicides used for post-harvest weed management in wheat stubble. Refer to the herbicide labels for appropriate rates, adjuvants and tank mixes.

Ned Birkey

Farmers are now optimistic that corn and soybean yields will be “decent” with the recent rains. It is hard to imagine that August weather can be worse on crops or temperaments than has been June and early July weather.

Corn has tasseled and is pollinating, regardless of plant height. European corn borer trap counts are increasing and corn rootworms and Japanese beetles are actively feeding. We have already had more corn borer damage than in recent years. Farmers should carefully evaluate fields to see which fields to harvest early to avoid lodging losses.

Oat harvest has just finished with average yields. Oats are still in demand for feed and some people like the oat straw.

Soybeans have grown a foot or more in some fields over the past two weeks. Since fields were planted perhaps 30 days earlier than last year, farmers are pleased with the recent growth. Many fields are now waist high with new growth and are at the R2 to R3 growth stage. Aphid populations are skyrocketing – 1,000 per plant in one case. No variant Western corn rootworms have been found in one set of yellow, unbaited, sticky traps, but walking in the same field you can find an occasional Western corn rootworm. How do you get good spray coverage for aphids in 36-inch tall soybeans? Where is the target height for the sprayer boom? One farmer is using 100 psi, another 70 psi. With aphids and, in the future rust, farmers will have to do more thinking about boom height, spray pressure, nozzle selection, etc. Japanese beetle populations seem highest since the late 90s. Bean leaf beetles and grasshoppers are also evident.

Wheat harvest is finished with yields down 10 to 35 percent.

 Grain prices have had some good, if temporary, rallies. The August 12 USDA crop report will be very important as a substantial area of the Corn Belt has been under drought stress.

Fred Springborn

Corn growth has progressed. Much of the crop is about to put out the last leaf before tassel emergence. Leaf rolling is prevalent in dryland corn in the northern and western areas of the region and on the very sandy soils elsewhere. European corn borer moth numbers in pheromone traps are very low as second generation has not yet emerged.

Dry beans are growing rapidly under irrigation. Most of this crop is experiencing overall good growing conditions.

In soybeans, soybean aphid has been observed generally below threshold.

Second cutting alfalfa is complete. Potato leafhoppers are present in alfalfa fields and should continue to be monitored.

Paul Gross

Soybeans look very good and the yield potential is giving farmers reasons to be optimistic. Soybean aphids are in nearly every field at various populations. It is very important that you get out and scout your fields and know what the numbers are and what the thresholds are. We are also seeing fields over threshold for spider mites and are being treated. Continue to scout for aphids because the population can grow rapidly.

Wheat harvest is nearly complete. Most of the white wheat has been harvested and the red will be finished when the weather conditions allow. Quality has been very good but the yields have been disappointing with most fields in the 50 to 60 bushel range. Little or no scab has been reported.

Harvest of third cutting alfalfa will begin this week. There are still some farmers making second cutting. After a light first cutting most yields of second cutting has been very good. There should be surplus supplies in the region this year because we have had timely rains throughout the growing season. Leafhoppers are a problem in many fields. Scout for this pest.

Sugar beet fields look good where there are good stands. The recent rains will really benefit fields that were replanted and are a little behind.

Harvest of oats and barley is just getting underway.