In this issue
§ Aphids in wheat
§ Alfalfa weevil
§ Soybean aphid update
§ Start clean: Protect yields now in no-till soybean
§ Delayed preemergence and early postemergence herbicide applications in corn
§ Update on Roundup Ready Alfalfa Legal Issues
§ Low cost high tech crop scouting with handheld gps
§ Powdery mildew beginning to appear on wheat
§ Regional reports
§ Weather
Christina DiFonzo, Entomology
This week there are reports of sprays going on for aphid
infestations in wheat. Commercial companies are promoting intensive wheat
management in
It is typical to first see aphids in late April or early May
in wheat. The oat bird-cherry aphid is the first aphid we find in April or
early May. It is olive green, and has an orange (rusty) patch on its behind.
You can actually see this orange patch with your naked eye. In late May and
early June, English grain aphid appears. This is a large green aphid with long
black cornicles (“tail-pipes”) and long legs with “black knees.” You may also
see corn leaf aphids (blue-green, short black cornicles, short black legs) and
the greenbug (light green with a dark stripe on its back). Oat bird-cherry
aphid may overwinter in
Direct feeding damage. Aphids feed by sucking plant juices. A few aphids per plant do not cause a problem, but if populations are very high, enough water and nutrients can be removed to effect yield.
Salivary toxin. A
few aphids inject a toxin into plants as they feed. I already mentioned Russian
wheat aphid, which is not found in
Virus transmission. All of the aphids mentioned above can transmit barley yellow dwarf virus (BYDV) to wheat, barley and oats. For fall-planted winter wheat, the source of the virus is most likely grasses outside the field. Transmission in the fall is more important than transmission in late spring, since the virus infects the plant for a longer period of time.
In my ten years in
Unlike scouting and thresholds for some insects, scouting methods and thresholds for aphids on wheat are well-researched and reliable. Thresholds are based on examining tillers for aphids. Examine the upper and lower leaf surface, as well as rolled-up portions of the leaves and stem. Don’t just walk the edge of the field (aphid infestations often start at the edge.) Walk 30 to 50 paces into the field, sample a tiller, then walk another 30 to 50 paces, and so forth. Finding the aphids on each tiller is more important than distinguishing species. Depending on your sample scheme (see Table 1), you can count aphids or simply note the presence or absence, on 100 stems per field.
The threshold is 12 to 15 aphids per tiller up to the boot stage. The aphid species does not matter, only the number of total aphids per stem. If you don’t want to count aphids, you can use a presence or absence sampling method, determining the number of infested tillers. Species does not matter. Total number of aphids per tiller does not matter. You only want to know if the tiller is infested with at least one aphid (presence) or not (absence). Once you know the proportion of tillers with aphids, you can use a decision table to determine the need for treatment.
Pick 25 tillers in the field and examine them for aphids. According to the table, if 25 (100 percent) of the tillers are infested, you stop sampling because you are over the threshold and should treat. If zero to 18 of the tillers have aphids, you also should stop sampling because you are below threshold. You should not treat. However, if 19 to 24 of the tillers have aphids, you can’t make a decision yet. You must keep sampling. Pick another 5 tillers, examine them for aphids, and add the result to the total. Now your decision is based on the second line of the table (30 tillers examined). Continue until you make a decision or you sample 100 tillers. Usually, you will make a decision very quickly within the first 25 or 30 tillers examined.
Table 1. Decision
table for presence/ absence sampling of cereal aphids
|
|
Number
of infested tillers |
||
|
Total number of tillers examined |
Stop sampling… Do Not Treat |
Keep sampling (pick 5 more tillers) |
Stop sampling… Treat |
|
25 |
0-18 |
19-24 |
25 |
|
30 |
0-22 |
23-29 |
30 |
|
35 |
0-27 |
28-34 |
35 |
|
40 |
0-31 |
32-39 |
40 |
|
45 |
0-35 |
36-43 |
44- 45 |
|
50 |
0-40 |
41-48 |
49-50 |
|
55 |
0-44 |
45-53 |
54-55 |
|
60 |
0-48 |
49-58 |
59-60 |
|
65 |
0-53 |
54-62 |
63-65 |
|
70 |
0-57 |
58-67 |
68-70 |
|
75 |
0-61 |
62-72 |
73-75 |
|
80 |
0-66 |
67-77 |
78-80 |
|
85 |
0-70 |
71-81 |
82-85 |
|
90 |
0-75 |
76-86 |
87-90 |
|
95 |
0-79 |
80-91 |
92-95 |
|
100 |
0-84 |
If 84-100 tillers infested, then treat |
|
1. You examine 20 tillers and find that four tillers have aphids. Your decision? Stop sampling! Don’t treat.
2. You examine 25 tillers and find that 20 tillers have aphids. Your decision? Keep sampling! Pick five more tillers.
The five new tillers all have aphids. Your decision? Keep sampling, pick five more tillers. Twenty infested tillers plus five infested tillers equals 25 infested tillers out of 30 total. According to the table, you keep going (between 23 to 29 out of 30).
The five new tillers all have aphids. Your decision? Keep sampling. 25 + 5 = 30 infested tiller out of 30 total tillers. You are still within the “keep sampling” column.
The five new tillers are not infested. Your decision? STOP SAMPLING. 30 + 0 = 30 infested out of 40 total tillers. You do not have to treat.
Christina DiFonzo, Entomology
Reports of heavy alfalfa weevil feeding are coming in from
southern
Another scouting method is the “stem and bucket” action
threshold from
If a field is over threshold, cutting is the preferred control method because it preserves natural enemies and pollinators, and saves the cost of application. Also, most insecticides cannot be used within seven to 21 days of cutting, depending on the product. Most fields this year are too early to cut, so they may need to sprayed. When a decision is made to spray, remember to note the pre-harvest intervals (PHI) of insecticides labeled for alfalfa. The PHIs range from zero to 28 days, depending on the product and rate per acre. Also remember, that there are many beneficial insects in alfalfa killed by sprays with longer residuals. Most labels include honeybee warning statements. Bee populations are taking a beating this season. Many of you may have heard of a new, unidentified disease, colony collapse disorder, which has devastated bee hives this spring. Since honey bees pollinate many of our food crops, it is extremely important to preserve the bees that are left. It is a good policy to notify beekeepers in the neighborhood when you do spray, because they may be able to move hives or restrict bee movement for a few hours. Fields in bloom should never be sprayed because all of the insecticides registered for alfalfa are toxic to bees. (These fields should be cut)
After cutting, remember to check for weevil larvae on the regrowth,
which can delay or prevent green-up. The threshold after cutting is six to
eight larvae per square foot of regrowth.
Christina DiFonzo, Entomology
There is good news and bad news related to soybean aphids.
Entomologists from Illinois, Indiana, Ontario, Ohio and Michigan all report having a surprisingly difficult time finding soybean aphids on buckthorn, given the number of eggs this winter. It appears that the cold weather did reduce populations on exposed trees. Bob O’Neil from Purdue and Dave Voegtlin from Illinois conducted their annual spring survey of buckthorn last week, traveling from Indiana east into Ohio, west back across Michigan, to the Quad Cities. Here is a portion of Bob’s report:
“ We surveyed R.
cathartica in 9 sites…We found aphids in all but one site. Aphid numbers in
all sites except those in the
Bob’s survey results
confirm that there has been a reduction in aphid numbers this spring.
Does that mean no
soybean aphids in 2007? Here is the rest of Bob’s report: “But relative to
other years, the numbers were relatively ‘high.’ In 2006 your intrepid
explorers sampled the north east
In other words, the
April cold snap appears to have reduced aphid numbers, but likely not enough to
avoid an outbreak in
Christy Sprague
Crop & Soil Sciences
Timely burndown herbicide applications in no-till fields are extremely important in protecting soybean yield. As no-till drills start planting soybeans, remember the importance of a timely burndown application. The tendency for a number of growers, particularly those planting Roundup Ready soybean, will be to plant into a weedy mess and not worry about applying their burndown herbicide until later, or to wait until most of the summer annual weeds have emerged before making their first post-emergence glyphosate application.
These delayed burndown applications can reduce soybean yield, by inhibiting soybean emergence and growth. By delaying these applications, weeds become larger and can often be tougher to control. Many times dense weed populations (or mats) can even interfere with planting. Competition from these early-season weeds can reduce soybean yield by as much as 16 percent (8.3 bu) (Figure 1). This could lead to as much as a $56.44/A loss in revenue at the end of the season with current soybean prices ($6.80).
Additionally, these carpets of weeds can harbor soybean insects and diseases causing additional problems for the soybean crop. Remember early control of these weeds is important. If a burndown herbicide application cannot be made prior to planting, it should be made shortly thereafter. Any delays in these applications can reduce soybean yield. A complete listing of burndown herbicides and their effectiveness ratings can be found in Table 2C of the 2007 Weed Control Guide for Field Crops (E-434). Remember, treatments that contain 1 pt/A of 2,4-D ester need to be applied a minimum of seven days before soybean planting.
David Hillger and Jim Kells
Crop & Soil Sciences
There can be many challenges for herbicide application following planting, such as high winds and rainfall. Therefore, it is likely there will be situations where corn has emerged before preemergence herbicides have been applied. In fields with emerged corn and no herbicide applied, growers have two primary options: to use an herbicide program typically applied before emergence; or switch to a total postemergence strategy. There are several possible herbicide programs with each strategy.
Table 1K
(pg. 53) in the 2007 Weed Control
Guide for Field Crops lists herbicides typically applied preemergence.
Many of these herbicides are also labelled for application after corn
emergence. Axiom and Princep7 should only be applied before corn emergence. To
avoid confusion, tank mix combinations are not included this table. Details on
the specific restrictions for tank mixtures can be found on the herbicide
labels. Although some herbicide labels allow application to emerged corn using
28 percent liquid nitrogen fertilizer as the herbicide carrier, we advise that
all herbicide treatments to emerged corn be applied with water as the carrier.
Applying herbicides to emerged corn with 28 percent liquid nitrogen as the
carrier, poses a risk of severe crop injury. This risk is increased under cool,
cloudy conditions prior to application, a common occurrence in
Preemergence herbicides should be applied as soon after planting as possible. Delayed application increases the risk of poor herbicide performance, especially for grass control. When herbicide application is delayed until after crop emergence, rotary hoeing is recommended. The rotary hoeing may be done before or after the herbicide application, but must be done when the weeds are very small. If the delayed application includes Banvel/Clarity, Distinct, Marksman (or other herbicides containing dicamba) or Prowl/Prowl H2O/Pendimax, crop safety will be greater if the rotary hoeing is done before herbicide application.
For several years, MSU has demonstrated the importance of
timely herbicide applications to prevent the loss of yield in corn. We have
shown that it is necessary to control weeds before they reach four inches of
growth to prevent measurable yield reduction. Two-pass herbicide applications (preemergence
followed by postemergence or two postemergence) or timely single postemergence
applications with residual control are most effective at preserving yield and
maximizing gross margin. Information about the effectiveness and economics of
preemergence and post emergence herbicide programs can be found in the
three-year summary of Commercial Herbicide Program Comparisons found on the MSU
Weed Science website at http://www.msuweeds.com/publications/.
Herbicide options for total postemergence weed control are dependent on the hybrid
planted in the field. Many postemergence herbicides can be used on any corn
hybrid, while others such as
David Hillger
Crop & Soil Sciences
The United States District Court in
For now, all glyphosate-resistant alfalfa that was seeded prior to March 30, 2007 is exempt from this ruling and can be harvested, sold and fed to animals. The new production guidelines are to be in place in the next 30 days and as these become available, we will pass them along to you.
More information about this can be found at Monsanto’s website, monsanto.com. The most recent court filings on glyphosate-resistant alfalfa can be found on the MSU Weed Science website, www.msuweeds.com.
Kurt Thelen
Crop & Soil Sciences
Advances in handheld global positioning system (GPS) receivers provide growers with a low cost tool for crop scouting. A satellite based augmentation system has been developed by the government for the aviation industry to improve the accuracy and integrity of information signals broadcast by GPS satellites. This technology is driving down the price and increasing the accuracy of handheld GPS receivers. The primary commercial market for these low cost handheld units is for travel and recreational navigation. However, the technology has many practical applications in crop scouting.
Global positioning systems are not new to agriculture. In fact, they are custom equipment on most combines and large tractors. To achieve the level of precision needed for most agricultural applications, these units typically relied on land-based differential correction signals in addition to the GPS satellite signals. These land-based correction signals are available from several sources including the U.S. Coast Guard beacons, and pay-to-use subscription services. The correction signal, antennae requirements, and correction factor software contributed to the relatively high price of these GPS units.
The U.S. Federal Aviation Administration and Department of
Transportation developed a satellite-based correction system called WAAS for
“wide area augmentation system.” WAAS uses a system of approximately 25
ground-based reference stations, which monitor GPS satellite data. Two primary
stations located on each coast, receive data from the reference stations and
calculate a GPS correction signal, which accounts for GPS satellite signal
errors from ionospheric disturbances, timing and satellite orbit errors. The
correction signal is then broadcast through one of two satellites with a fixed
orbit over the equator. The correction signal is compatible with the basic GPS
signal structure and is able to be picked up free of charge by any WAAS enabled
receiver. Initial WAAS testing, confirmed performance accuracy of three to six
feet horizontal and six to nine feet vertical throughout the majority of the
continental
How can these handheld GPS units be used in crop scouting? Many applications are possible, and given farmer ingenuity, many new uses will likely evolve over the next few years. The devices can be used to accurately identify the location of insect, disease, weed, nutrient, pH, tile blow-outs and other soil problems in the field observed while scouting. Once the problem areas are marked and electronically stored in the device’s memory, the unit can be used to navigate back to them later on for corrective action. The ability to navigate back to identified trouble spots makes this technology ideal for monitoring the effectiveness of applied treatments, whether they be pesticides, fertilizers or pH adjustments. In addition to marking and navigating, many of these handheld units have the capability to measure distances and even calculate acreage. Since the units measure elevation in addition to lateral position, they can also be used to determine surface drainage patterns. Most units also have a limited memory, which can be used to store shape-files of fields. The possibilities are endless, but perhaps best of all, once the field work is done, you can use the same unit to mark and navigate to your favorite fishing and hunting hotspots.
Diane Brown-Rytlewski
Plant Pathology
Powdery mildew is beginning to show up on wheat in
In the April 26 Field Crop CAT Alert, Management of foliar wheat disease, Part 2, is a rating table of fungicides evaluated for effectiveness against powdery mildew, and the growth stage limitations for applying certain fungicides. You can check the MSU variety trials ratings (http://www.css.msu.edu/varietytrials/) to get an idea of how your variety performed in statewide university trials, and use your own field experience with a variety to determine how susceptible it is to mildew. The variety trial ratings for powdery mildew are scored from 0-9, with (0 the lowest amount of mildew, to 9 the highest) There is a yearly, two year, and three year average score. Looking at the average rating over several years will give you a better idea of performance than looking at a single year.
Ned Birkey
Our weather was great for fieldwork and planting until a thunderstorm came up Wednesday, May 9 with about one inch of rain. Now it is great for ducks. Let’s just hope the weather is not good for the Mighty Ducks as they play the Red Wings tomorrow night. This was the first measurable precipitation in the month of May, and was not needed (or wanted) just yet. The low soil temperature dipped below 50 degrees this past week, but has zoomed up to 60 degrees overnight. No one is stopping planting or cares what the soil temperature is now that May is here with mild temperatures.
Alfalfa weevil is over threshold and fields should be
scouted, as harvest is still about two weeks away. Fields are about 12 to 15
inches tall, with mixed hay grasses even taller. Some alfalfa stands did not
come through the winter real well and are thinner than normal.
Corn is emerging with good soil moisture and nice,
“normal” spring temperatures. Advanced fields are at the V2 stage, though most
fields are still emerging. European corn borer traps and lures will be picked
up on May 21 and go into sweet corn fields in Monroe,
Soybean planting is progressing though I have not seen any emerged plants. Soybean aphid and rust sentinel plots will be located in Monroe, Washtenaw and Lenawee counties this summer.
Wheat is at Feekes’ growth stage 6 and 7. Powdery mildew is present and at high levels, partly due to good growth and dense foliage. Aphids are a hot topic as one chemical company is recommending spraying. I have not seen any fields that are over threshold, but I am not discounting the other reports.
I will have a summer intern, Mark Mathe, starting the week of May 14. He (and I) will be running the trap and plot circuit for Monroe, Wayne, Washtenaw and Lenawee counties this summer. So far high fertilizer prices have not changed application rates very much and supplies appear to be adequate.
Bruce MacKellar
Soils dried out and planting began in earnest last week. Rainfall totals ranged from 0.1 - 1.2 inches from the storms on Tuesday evening, May 8. Heavy rains were very localized from this event. The rainfall will be appreciated on the newly planted fields. Soil moisture conditions at depth and in surface waters remain favorable in the region.
Commercial corn
planting really caught up this last week.
In
Seed corn planting is progressing well. The companies have put on the breaks in planting in some instances to ensure that there is enough capacity in equipment and man hours to complete de-tasseling in a timely manner. Very little if any of the seed corn has emerged at this point.
Soybeans: Soybean planting has also progressed well over the weekend. The areas that raise seed corn tend to get an early jump on bean planting acreage. Soybean planting progress should improve rapidly with the forecast and as corn planting wraps up around the region.
Alfalfa growth
has moved into high gear with the warmer temperatures. Alfalfa
weevil damage is prevalent and well above threshold in many counties across
Wheat is looking pretty good in the southwest region this year. This may be due in part to the destruction of thin stands to plant corn. The wheat is primarily in Feeke’s Growth Stages 6 and 7. Mike Staton, the Berrien County ANR Educator, reports that he has seen advanced fields as far along as Feeke’s Stage 9 (beginning flag leaf emergence). There continues to be evidence of powdery mildew on the plants. It would be worthwhile for folks to keep an eye on their wheat fields as the season progresses to watch for the leaf disease movement towards the upper leaves of the plant, especially the flag leaf. Wetter and cooler conditions can be favorable for the development of leaf diseases in wheat. Click here for more information on Powdery Mildew and other wheat foliar diseases.
Fred Springborn
Minimum soil temperatures as recorded at the MSU Experiment Farm in Entrican are now in the upper 40s and often above 50. Rain showers were light to moderate on Tuesday, May 8 with much of the area receiving 0.33 to 0.75 of an inch of rain.
Wheat is in Feekes growth stage 6 in most fields and 7 in others. Where herbicides have not yet been applied, growers now need to use herbicides other then the growth regulators, such as 2,4-D to avoid injury. Few disease problems have been reported or observed at this time
Oat planting is essentially complete. Most fields have emerged with good stands.
Sugar beet planting is wrapping up. There is still a portion of the crop yet to be planted on the heavier more poorly drained soils.
Corn planting has made rapid progress with 50 percent of the crop planted. A few fields have emerged and many more will likely emerge in the next few days, as we have very good conditions for germination and emergence in many fields.
Soybean planting has begun in earnest with 10 percent in the ground.
Paul Gross
There were five very good days for planting over the past week. Rain on Wednesday, May 9, will keep farmers out of the fields for a day or two depending on the amounts of rain. The amount varied widely from a quarter inch to well over an inch. One farmer indicated he will be out of the field until next week while others may be planting by the end of the day Thursday. Soil temperatures are in the low sixties so germination of the newly planted crops will be timely. There was frost in the northern part of the region Sunday and Monday mornings. With the warmer weather, we expect insect populations to begin to increase so scouting growing crops is advised.
Corn planting has progressed to about 50 percent across the region. Some of the early planted fields have begun to emerge and you are able to row the corn. Planting conditions have been just average and with the rain planting will resume as fields dry out. Several fields that will be no-tilled have weeds growing rapidly and herbicide applications are advised as soon as possible.
Soybeans are about 20 percent planted across the region. No report of emergence at this time. Planting progress will continue as field conditions allow. No reported problems at this time.
The wheat crop is in Feeke’s 5-6 and doing very well. Nitrogen and herbicide applications are nearly complete. We have seen some light pressure from powdery mildew, but it remains low in the plant. Aphids have been reported in fields, but very low numbers. Scout fields for pest problems.
Alfalfa is 10-12
inches tall and doing well. We have observed some light frost injury from frost
over the weekend, but do not expect any yield loss. Fields that have been
scouted have had little to no alfalfa weevil feeding at this point. Based on
reports from southern
Oats are planted and the early planted fields are emerging. The rain on Wednesday will speed the emergence and make for some very good stands.
Mark Seamon
Most of the thumb area received about a half inch to one inch of rain on Wednesday. This rain was welcome to some farmers but most would like to see more planting progress before another break in field work.
Sugar beet emergence in most fields has been good due to good soil moisture after planting. Some fields planted in late April are struggling to emerge due to soil crusting. The fields planted in March are showing two true leaves, while most others are in the cotyledon stage. Some seedling diseases and flee beetle feeding has been found.
The wheat crop looks good in most areas. Weed control applications are pretty well finished. Average growth stage is around the Feekes 6. Foliar diseases are minimal but that may be changing with increased air temperatures, denser crop canopy and rainfall.
Corn planting has made great progress in the past week, which gets this area to about 80 percent planted. Planting conditions were mostly good with good moisture at the 2-inch depth. Weed control from PPI and preplant herbicides should work well with rainfall soon after application. A few early planted fields in lighter soil have emerged with consistent stands. Many more are near the surface and will emerge with this moisture and warm temperatures.
Soybean planting is started nicely with about 20 percent of the crop planted. A few growers have finished corn plating and switched to soybeans, but most progress has been from growers who can plant both crops at the same time.
Jeff
Andresen
Agricultural Meteorology
Geography
On the morning of Thursday, May 10, the weak frontal
boundary that brought showers and thunderstorms to much of
Fair and dry weather is expected once again for the latter half of next week. Temperatures will fall back from daytime readings in the upper 70's and low 80's Thursday, to the mid 50's far north to the upper 60's to low 70's south by Saturday. Low temperatures will generally range from the low to mid 50's south Thursday morning, falling back to a range from the mid 30's north to the upper 40s south by Sunday. Some scattered light frost is possible Saturday and Sunday mornings across far northern sections of the state. Daytime temperatures will rebound once again Monday ahead of the next weather system, with highs in most areas back into the 70's.
Medium range forecast
guidance is suggesting the formation of a ridging feature across the western