June 22, 2006
In this issue
§ Insect update
§ Is it spider mite? NO!
§ Is it ice or insects?
§ New pocket-sized bulletin on beneficial insects
§ Tips to avoid weed control antagonism when applying Mn fertilizer with glyphosate
§ Fomesafen carryover to corn
§ Avoid herbicide spray tank contamination
§ Wheat disease update
§ Soybean rust update
§ Regional reports
§ Weather news
With the exception of a few predictable issues – potato leafhopper in alfalfa, armyworm in weedy corn – things are quiet on the insect front. Populations of soybean aphid remain low. European corn borer moths are flying and laying eggs, but numbers are low. Japanese beetle and European chafer adults are emerging, so grub damage is ending in many fields. Corn rootworm larvae are beginning to feed but damage isn’t apparent yet. Otherwise, few insect problems are being reported.
This season, Extension entomologists from the Midwest are exchanging information via conference calls every few weeks. This week, soybean aphid, bean leaf beetle and European corn borer populations are reported as low across the region. Items of interest were:
§ Corn rootworm adults are emerging in Illinois, the earliest emergence noted by entomologists in that state.
§ Corn blotch leafminer numbers are high in Nebraska. We had this problem a couple summers ago in late July/early August. Dr. Bob Wright, University of Nebraska, provided a picture of CBL on whorl-stage corn.
Earlier this week I received reports of people treating yellow soybeans for spider mite. Although it is possible to have spider mites this early, it isn’t typical. Mites are usually a problem in late July into August during the hot, dry periods. The descriptions of the alleged mite damage (The leaves are a bright shade of yellow, the whole field is yellow, it’s the same for all fields in the area.) didn’t jive with symptoms of early-season mite infestation, which include stippling damage to individual plant cells and often starts on the edges of field. Examining samples from these mite-infested fields revealed that no mites were present, and the symptoms were not that of mite injury (See photos and explanation from Steve Gower in MSU Diagnostic Services.). To make matters worse, individuals who treated used pyrethroids, many of which are notorious for flaring (increasing) mite populations by removing beneficial insects. The recommended mite products are OPs, for example dimethoate, Lorsban and generic chlorpyrifos products. Actually my primary recommendation is to find the real cause for the yellowing; it is highly unlikely to be spider mite. Yellow soybean fields are very common at this point. Even if mites were a problem in a few locations, recent rains reduced the likelihood of a spider mite outbreak.
Good pictures of leaf damage from spider mite and shots of typical field infestations (edge effects) can be found on the Iowa State Entomology Department image page at:
http://www.ent.iastate.edu/imagegal/plantpath/soybean/spidermite/
In past years, I’ve visited fields with tattered and ripped leaves attributed to insect feeding, only to find hail damage. With the recent thunderstorm activity, I am reprinting this list of tips that point towards hail rather than insects.
Distribution of damage in space. Is the damage found at a constant level across the entire field? If so, this points to an environmental cause such as hail. In contrast, insect damage is often patchy, worse in some areas than others, or concentrated along edges or in areas of poor crop growth.
Distribution of damage in time. Leaves with damage are of a similar age (hit at same time with hail), while new growth is not affected. In contrast, with a recent or on-going insect infestation, you expect at least some new growth to be affected.
Damage to neighboring crops, weeds. The same type of damage is found on larger weeds in the field, on plants along the edge of the field, and in neighboring, especially different, crops. This indicates a widespread event affecting many plants, i.e., hail.
Lack of consumption. Leaves may be tattered, torn and ripped, but leaf tissue itself is not necessarily missing. The tattered leaf can often be "reconstructed" by aligning the tears. In contrast, feeding by defoliating insects removes leaf tissue.
Lack of insects or signs of insects. No insects are found, or at least consistently found, associated with the damage. There is also a lack of cast skins, frass (bug droppings), slime trails or other signs that insects were present.
Coffee talk. The talk in the coffee shop is about recent thunderstorms, not about armyworms and beetles.
Now available from the MSU Extension Bulletin office: Identifying Natural Enemies in Field Crops, MSU Bulletin inventory number E2949. The cost is $10 per copy, $7 per copy for bulk orders (10 or more copies). (view image) Contact the MSU Bulletin office to order:
117 Central Services
Michigan State University
East Lansing, MI 48824-1001
Phone: 517-353-6740
Fax: 517-353-7168
Office Hours: M-F 8:00am - 5:00pm
http://www.emdc.msue.msu.edu/
Additional information and sample pages from the flip book
are at: http://www.ipm.msu.edu/pubs-natural.htm
During last year’s soybean aphid outbreak, I received numerous questions about beneficial insects. Beneficial insects play a critical role in managing soybean aphid populations (I’ve already seen ladybeetles cleaning-up aphid colonies on buckthorn this spring). And populations of many other field crop and vegetable pests are kept in check or reduced by natural enemies. This timely pocket guide (developed by Mary Gardiner, a graduate student in the MSU Biological Control Lab) has color pictures of common beneficial insects – both predators and parasitoids – and spiders. It provides information on identification, lifecycle and diet. The pocket guide has glossy pages and a spiral binding, so you can use it in the field. Although it is geared for field crops, it is appropriate for use in other crops and by homeowners. If you plan to attend the MSU Diagnostic Day on July 21, you will receive a copy of this guide, as we will use it as part of a session on soybean aphid biological control.
Manganese (Mn) deficiency is the most common crop micronutrient problem in Michigan, particularly in soybeans and wheat. The availability of manganese to the plant generally decreases as soil pH levels increase. Consequently, soybeans grown in the calcareous soils of Michigan’s Thumb area and in the lake-bed soils in Michigan’s Southeast Lower Peninsula historically have been found to be deficient in Mn. When possible, producers in these areas prefer to tank-mix Mn micronutrient solutions with foliar applied herbicides to eliminate an extra trip across the field. As glyphosate is estimated to be used on approximately 80 percent of Michigan soybean acreage, reported reductions in weed control on some of these acres caused by tank-mixed Mn applications is an important issue. The cold, wet weather experienced in May could have exacerbated Mn deficiency problems due to poor soybean root growth. In a project funded by the Michigan Soybean Promotion Committee, MSU researchers have shown that weed control can be antagonized when some Mn fertilizers are tank-mixed with glyphosate.
Field experiments showed a significant antagonism in common lambsquarters and velvetleaf when glyphosate was tank-mixed with ethylaminoacetate-Mn, and slight antagonisms in tank-mixes with lignin sulfate-Mn and MnSO4-powder. Greenhouse studies have shown that an EDTA-Mn formulation enhanced glyphosate efficacy (by 25% in giant foxtail and 40% in velvetleaf). However, tank-mixes of each of the other Mn products caused significant antagonisms, reducing weed control by 10 to 30% when compared to glyphosate alone.
One possible method for avoiding the antagonism is to apply the Mn fertilizer at a different time than glyphosate. In a greenhouse study the ethylaminoacetate-Mn fertilizer was applied 6, 4, and two days before, two days after and at the same time as glyphosate. There were no differences in herbicide efficacy in giant foxtail for any of the two-pass timings. In velvetleaf, Mn sprayed two days before the glyphosate application reduced weed control by 15%. But this was not as severe as the 30% reduction when glyphosate and ethylaminoacetate-Mn were tank-mixed.
A second method for avoiding the antagonism is to add an adjuvant to the spray tank that will prevent the antagonism, either by chelating the Mn tightly (with chelates such as EDTA or citric acid) or by preventing the Mn from binding to the glyphosate molecule (by adding ammonium sulfate [AMS]). In greenhouse experiments, AMS and EDTA improved herbicide efficacy in all glyphosate-Mn tank mixes except for EDTA-Mn, where efficacy remained the same. Citric acid antagonized the Mn-EDTA-glyphosate tank-mix, but improved the efficacy of all other Mn formulations. The degree that each adjuvant improved the different Mn-glyphosate tank-mixes varied, and will be the subject of future studies.
In summary, if conditions are optimal for glyphosate control of weeds, i.e. weed pressure is low and weed size is small, you may get adequate weed control with glyphosate tankmixes with commercially available manganese formulations. However, even under these optimal conditions it is still advisable to add AMS (17 lbs per 100 gallons of water) to minimize the antagonism imposed by the Mn. If weed control conditions are marginal, i.e. moderate weed pressure and/or moderate weed size, a chelated form of Mn such as an EDTA-Mn formulation, plus AMS is recommended with glyphosate tankmixes. Finally, if weed control conditions are poor, i.e. heavy weed pressure (especially lambsquarters and velvetleaf) and/or large weed size, Mn should not be tankmixed with glyphosate. Rather, in these tough weed control conditions, Mn should be applied in a separate application following the glyphosate application.
A seed corn sample submitted to the lab this week from St. Joseph County, Michigan, had symptoms indicative of fomesafen (Flexstar/Reflex) carryover. We are in the process of testing for fomesafen residue in the soil.
Fomesafen injury to corn is very distinct and will result in midrib and subvein clearing, which appears as a “stripping” of the leaves (view photos). The tissue between the veins will not yellow; this is symptomatic of nutritional deficiencies. Improper unfurling to a “buggy whipping” of the leaves may result from more severe fomesafen injury. The midrib can also be weakened and collapsed.
Fomesafen is often used for postemergence control of late emerging broadleaf weeds in soybean, dry bean and snap been. Fomesafen carries a 10-month rotation restriction to both seed and field corn. Late applications of fomesafen followed by fairly early corn planting the next season can result in nearing this restriction. Studies have shown that fomesafen is broken down in the soil more quickly under anaerobic (oxygen deficient) conditions. Anaerobic conditions result after a rainfall event in which water infiltration forces out oxygen in the pore spaces of the soil. In a season of drought or low precipitation, fomesafen may not be fully degraded and has the potential to carryover in sandy or even very well-drained soils. Corn injury may be first noticed on sandy hills and knolls because these areas can only hold moisture for a short period of time.
Later planted and replanted crops have put us in the situation where postemergence herbicide applications will be made to several different crops during the same time period. Because of the vast number of acres that need to be sprayed with different types of products, caution needs to be taken to avoid spray tank contamination. In the past, it was particularly important to make sure the spray tank was clean when switching between corn and soybeans or other sensitive crops; however with herbicide-resistant crops, it is important now more than ever to not only make sure the spray equipment is clean when switching between crops, but when switching from herbicide-resistant crops, like Roundup Ready to conventional crops.
To avoid spray tank contamination, it is important to take the extra time and care to thoroughly clean out spray equipment: tank, lines, filters, sumps, pumps and nozzles. All of these areas can be a potential source of contamination. Even though the spray tank has been thoroughly rinsed, small amounts of herbicide residue can linger in the spray lines and filters. This can cause considerable damage to the next crop that is sprayed. For example, imagine spraying glyphosate on a Roundup Ready soybean field and then switching to spraying a postemergence corn herbicide on a conventional corn hybrid. How much damage do you think you would observe in the corn? I could imagine the first few hundred feet with dead corn plants, which could lead to substantial yield reductions at the end of the season. Or what if you sprayed dicamba postemergence on your corn and then switched to spraying soybeans or dry beans without properly cleaning out your sprayer. How many acres would you expect to see with cupped or twisted beans? Because these issues happen every year, it is important to thoroughly clean out your spray equipment when switching from one herbicide to the next. Below are a few tips to avoid spray tank contamination.
§ Always clean spray equipment thoroughly when switching from one crop to another or switching from an herbicide-resistant to a conventional crop hybrid or variety.
§ Just spraying until the sprayer is empty does not mean the sprayer is clean. There are herbicide residues that can be on the side of the spray tank in the spray lines, sump, pump, filters and nozzles. It is important to thoroughly clean all of these areas.
§ Clean spray equipment immediately or as soon as possible after spraying. Dried herbicide residues are more difficult to remove from the sprayer.
§ Always follow the herbicide label for directions and recommendations for the best method and cleaning agent to use when cleaning out the spray equipment. Several labels specify agents that work best at removing that particular herbicide’s residue from the spray equipment.
There have been reports across the state of scattered occurrences of white heads in wheat fields, but so far, serious outbreaks of head scab have not been reported. Likewise, there have been reports of leaf rust throughout the state. Stagnospora leaf and glume blotch (Stagnospora nodorum, formerly known as Septoria leaf and glume blotch) is appearing in a few fields in the central areas of the state. Glume infections appear as purplish brown to gray lesions containing tiny dark spots (fruiting bodies) starting at the top of the glume. Affected kernels may appear shriveled. The temperature range favorable for infection is from 59 to about 80°F. Cool, wet weather during flag leaf emergence favors the development of the leaf blight. Wet, windy weather favors the spread of this disease from infected leaves to the glumes.
Look for tolerant varieties to plant for next year. Use certified seed. Seed treatments may also help. This fungus survives on seed, in crop residue and can overwinter on winter wheat. Foliar fungicides are effective at controlling leaf and glume blotch, but applications need to be made by heading, or earlier, depending on the fungicide used.
Soybean rust has been found on soybeans in southern Florida. The impacts of tropical storm Alberto on the spread of rust haven’t shown up yet, but sentinel plots are being watched closely.
I just returned Tuesday (June 20) from a trip to Florida to visit the North Florida Research and Education Center at Quincy. There is a tremendous amount of soybean rust research going on there. I was taken out to several locations to scout for rust in kudzu. My genial southern hosts didn’t need to caution me twice not to venture into the kudzu too far due to snakes – cottonmouths, rattlers and coral snakes. I spent time looking at soybean rust lesions, spores and symptoms. The workshop offered in July would be a worthwhile educational experience for any professional looking for some hands-on experience with soybean rust. I’ve included their announcement below.
The University of Florida and the Southern Plant Diagnostic Network would like to invite interested soybean professionals to participate in a hands-on short course on July 13, 2006. The North Florida Research and Education Center at Quincy, Florida, will host up to 100 agricultural professionals, consultants and specialists for an intensive identification course. More information including registration, schedule, transportation and lodging details may be found at: http://spdn.ifas.ufl.edu/soybean_rust_identification_short_course.htm.
This short course will be modeled after last year's – hopefully without the occurrence of a hurricane this time around. The program includes hand lens and microscope observation of infected soybeans, field observation of infected kudzu and, we hope, soybeans and tours of current soybean rust field research.
This workshop will be offered without a registration fee, thanks to the generosity of the North Central Soybean Research Program. We do have a space limitation of 100 people, so we plan to offer the spaces on a first-come, first-served basis.
For a registration form, visit:
http://www.ipm.msu.edu/cat06field/pdf/sbrreg.pdf
Our weather has been unsettled to put it mildly. Severe thunderstorms, hail, a tornado and high winds have occurred several times this past week. Tecumseh had 3 inches of rain at one time, while neighboring Deerfield had 0.5 inch in the same storm. In storms Wednesday evening (June 21), southern Lenawee County received over 7 inches of rain and southern Monroe County had over 6 inches. Ten miles away, the rain was only 2.5 inches.
Alfalfa is finished with the first cutting and the rains have really helped the regrowth. Potato leafhoppers have not been a problem because of the severe weather. First cutting sales have been good despite there being plenty of hay available.
Corn fields either look very uniform or not. Advanced fields are at the V9 growth stage, are nice and dark green and well past everything except for some high boy post sprays of giant ragweed, hemp dogbane, thistles or other troublesome weeds. European corn borer moths are still active with 50 being the highest trap count this week. Armyworms are here also. Some fields have torn leaves from hail. Many fields today have water in them.
Soybeans never seem to grow fast enough in the early season. Fields range from VE to V5. Weeds have the upper hand, but post sprays are continuing. Many fields are now too wet for tractors. Leaf feeding from bean leaf beetles is evident, though not at threshold levels.
Wheat looks very good except for some wind damage. Wheat is turning color and there is little Fusarium head scab evident. The MSU Wheat Variety Trial in Lenawee County is signed. It is located on Piotter Road, just south of Holloway Road, north of Deerfield or south of Britton. I still think wheat harvest will be in early July this year.
ADM’s river facility in Toledo has already loaded more boats with corn than all of last year. Much of it is going to the Middle East. They are currently paying a premium for corn with prices earlier this week at 7 cents under Chicago. They are shipping wheat by rail to Oklahoma where there is a small hard red wheat crop to make room for our soft red wheat crop. Nabisco in Toledo is booked up with wheat into 2007.
Improved corn growing weather this week. Highs have been in the 80’s with lows in the upper 50’s and mid 60’s. We received 0.8 of an inch of rain on Wednesday (June 21) this week and only a tenth or two on Sunday (June 18).
Corn growth has improved this week: growth stages range from V1 to V8. Color has improved in most fields with the improved growing conditions.
Dry bean planting is winding down. Many fields have emerged.
Wheat is just starting to turn in advanced fields. Septoria glumb blotch is apparent in several fields. Head scab symptoms can be found in many wheat fields at very low levels. No reports of armyworm injury at this time. Oat growth is progressing. Nearly all fields have headed. Low levels of cereal leaf beetle have been observed.
Harvest of first cutting of alfalfa is generally complete. Many producers have taken advantage of the extended period of dry weather last week to get good quality dry hay put up. Potato leafhopper is present in many fields and warrants monitoring.
The region received anywhere from 1.5 to 2.5 inches of rain Tuesday and Wednesday (June 20-21). For the most part, the rain was very welcomed as some areas of the region were in need of rain. With crops growing rapidly and with the warmer weather, we could use this amount every week. The warmer weather has really improved crop growth and many fields that were looking poorly are starting get rolling. I think it is safe to say that planting was wrapped up last week.
The corn is doing very well with the warmer weather and some timely rain. Many of the stands are variable with knee-high corn down to just emerging. The fields that were patched in or replanted will be really creating some challenges come harvest. Field activities include nitrogen applications and weed control. There are reports of armyworm in Gratiot County, so continue scouting fields for this pest. There were also reports of cutworm in corn planted into sod.
Soybeans are progressing nicely with the solid seeded fields canopying. There is lots of variability in stands, and weeds are an issue. Field activities include herbicide applications.
The wheat crop is beginning to turn. We had some wheat go down with the rains over the last few days, but nothing serious. We are seeing lots of septoria and some glume blotch. Most growers are holding their breath as the crop matures.
Harvest of first cutting alfalfa is winding down. The early cut fields are about 12 to 16 inches tall and second cutting will begin next week in some areas. Potato leafhoppers are present in most fields. Scout fields for this pest.
Dry beans are all planted and most have emerged. Stands are generally good. Field activities include cultivating and spraying for leafhoppers. Scout fields for this pest.
Normal temperatures and good soil moisture have combined to help crops put on a lot of vegetative growth this past week. Rainfall has been variable with a range of 0.3 to more than 2 inches across the area.
The alfalfa crop looks good in most cases. Second cutting should be good where first cutting was made early.
Top growth of sugar beets is adding to the crop canopy quickly. DSV’s are adding up pretty quickly for prediction of Cercospera leafspot infection. Watch the BEETCAST web site for timely updates on this.
Many wheat fields have experienced some lodging with rain and wind in the past week. Color change is evident with some of the change being advanced from dry soil conditions. Leaf rust can be found in most fields. Yield potential looks good with large heads and good weather conditions during grain fill.
Plant growth in corn has been rapid in the past week. Most corn is picking up nitrogen from preplant or sidedress applications and appears healthy. Replanted areas have emerged quickly and are growing well.
Slow growth and development is keeping soybeans from looking as good as most of us would like at this time. A few fields have good growth, but these are the exception. Most are less than 6 inches tall with only a few trifoliates emerged. Control of wild carrot has been difficult in no-till fields.
Dry bean planting has pretty much wrapped up. Early planted beans emerged quickly and consistently while later planted beans were planted into dryer soil conditions and experienced uneven emergence.
Following severe weather across parts of Michigan on Wednesday (June 21), the jet stream is expected to gradually transition into a northwesterly configuration across the Great Lakes region during the next couple of days, bringing fair, cooler and drier weather.
In the short term, two separate cool fronts are forecast to move through the state Thursday. However, given very little low-level moisture to work with, only isolated or scattered showers are expected during the day Thursday and Thursday evening with most areas remaining dry, especially across northern and central sections of the state. Fair and dry weather is expected to develop statewide by Friday and continue through the majority of the upcoming weekend as high pressure moves into the region. Temperatures will fall from high temperatures Thursday ranging from the 70s north to the low and mid-80s south back to the upper 60s to upper 70s by Friday continuing through the weekend. Low temperatures will fall back to the mid-40s to mid-50s during the next several days. Overall temperatures during the next five days are forecast to generally average 2 to 4 degrees below the normals. Following a dry weekend, rainfall will be possible once again by next Tuesday as a weather system approaches from the west.
Medium range forecast guidance suggests the establishment of a large upper air ridge across the southwestern United States with a troughing feature across the east, which would keep Michigan under the general influence of northwesterly flow aloft in a somewhat benign weather pattern.
The 6-10 day outlook (covering June 27 of June through July 1) calls for mean temperatures to range from near normal temperatures across the southern one-half of the state to above normal levels elsewhere and for below normal precipitation totals statewide. During the 8-14 day timeframe (covering June 29 through July 5), the outlook calls for mean temperatures and precipitation totals to moderate to near normal levels statewide.