July 12, 2007
In this issue
§ Aphids slow, but mites may show
§ Corn rootworm adults emerge
§ Western bean cutworm moths captured for a second season
§ Fungicide applications of strobilurins to corn and soybeans when there is little disease
§ Regional reports
§ Weather
Next issue July 26
Christina DiFonzo, Entomology
After a big debut in June in some locations, soybean aphids
are for the most part sitting quietly. Aphids are still present in all fields
we sample, and the percentage of infested plants is slowly increasing. However,
the number of aphids per plant remains low. Contrast this to 2005 the last
outbreak year in
The slow aphid growth mirrors the condition of the soybean crop. It has been hot and dry in many locations, so small beans flowered early. Aphids do better on actively growing parts of plants. Also, aphids reproduce best at moderate temperatures in the mid 80’s. I’ve noticed in many of my research fields the plants are short and the rows have not filled in, and on hot days it is very hot in the canopy. This could also contribute to slow growth. If temperatures were moderate and rains were more frequent to increase plant growth, the aphid populations might also increase. For now, check fields with no or few aphids every 7-10 days until infestation increases to 50-70 percent of plants, then scout more frequently.
Meanwhile, hot dry weather brings up the potential for spider mites in soybeans. I haven’t heard of any symptomatic fields just yet, but mites are present at low numbers in beans by this time of the year waiting for their big break. Spider mites feed on numerous crops and under certain conditions increase to the point where they affect yield. This is especially true under dry conditions (recall the 2001 field season) 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. Stippling 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 yellow and die from mite damage, the photosynthetic ability of the plant is reduced. With additional water loss, leaf drop, and reduced photosynthesis, yield and quality is reduced by severe mite feeding.
Note that yellowing of leaves may not be due to spider mite – yellowing may be caused by herbicide injury, nutrient deficiency, poor root growth or other mysterious causes. Do not let someone convince you to spray yellow beans for spider mite unless you have actually seen the spider mites yourself. Mite populations will be heavy on beans that are yellowing, easy to see by tapping a leaf over white paper, and stippled plant cells will be obvious using a hand lens.
Note that even if you do have spider mites, control is difficult. Multiple insecticide applications can lead to resistance and make the problems worse. It is thus very important to avoid unnecessary sprays, including insurance applications for soybean aphid. “I’m going across the field anyway, so I’ll just throw something in the tank” may actually increase mites under the right conditions. Mite predators are not obvious to you, but by killing them you may notice the increase in mites.
It is also important to avoid unnecessary insurance
applications of fungicides. Mite entomopathogens (beneficial mite-killing
fungi) are not obvious to you either, but if you remove or inhibit their growth
you may again notice mites. In other words, the pest management choices you
make now can create or exacerbate a mite problem later in the season. Certainly
some situations (if you are over threshold for soybean aphid or if soybean rust
spores are carried into
§ Start with a pinch of spider mites.
§ Add very little water.
§ Stir in a reduced rate of an insecticide, poorly applied, to kill mobile predators, but avoiding most of the mites.
§ Fold in a fungicide, thoroughly, to cover all surfaces.
§ Repeat.
Bake at 95 degrees daytime temperatures for several weeks. The Surprise is done when leaves turn yellow. Note - To obtain a crispier texture, bake for an additional week.
Christina DiFonzo, Entomology
Corn rootworm adults are emerging in southern and central
For a light read to put you in the mood for root digging, check out a good article by rootworm gurus Mike Gray and Kevin Steffey from the University of Illinois: “Comparing Soil Insecticides and Bt Corn Rootworm Hybrids: Do Root Ratings Make Sense Anymore?” This article discusses the problems with rating larval damage in conventional versus Bt hybrids. It is available at: http://www.ipm.uiuc.edu/bulletin/article.php?id=796.
Christina DiFonzo, Entomology
Last season I reported that western bean cutworm, an
emerging pest of corn in the Midwest, was trapped for the first time in
Diane Brown-Rytlewski
Plant Pathology
Some growers may be contemplating the use of foliar fungicides on hybrid corn this season, due to higher market prices for corn, marketing of fungicide products, or concern over increased disease risk from planting corn-on-corn. Growers may have similar thoughts of applying foliar fungicides to soybeans due to higher market prices.
Conditions are not favorable for the development of most
foliar diseases in corn. In many parts of the state, rolled leaves can be seen
during the middle of the day, clear evidence that corn is experiencing moisture
stress. Conditions for foliar diseases of soybean are similarly unfavorable. Substantial
areas of
In
However, the issue of applying foliar fungicides to hybrid
corn or soybeans [primarily Headline and Quilt (corn) and Headline (soybeans),
which contain an active ingredient in the family of fungicides known as
strobilurins] when there is little disease continues to come up. In many parts
of
So far, there has been little university-conducted research
in
In the article “Can
foliar fungicide raise corn yield when there's little disease?”(The Bulletin,
Resistance
is an inherited change in a plant pathogen’s susceptibility to a fungicide. Intensive
use, overuse or misuse of certain fungicides can result in the development of
resistance. Using fungicides containing strobilurins as a product for
yield enhancement when disease activity is below levels that threaten yield,
contributes to the risk of development of fungicide resistance. Spores can be transported over long
distances and millions of spores are produced. Remember, these products
are fungicides. Strobilurins are in the “high risk” category for resistance.
Resistance has been already documented in several crops for several different
pathogens.
If you still plan to “experiment” with the plant health
aspect of strobilurins,
1) Know what the variety or hybrid is. For both corn and soybeans only the moderately susceptible and highly susceptible hybrids and varieties have demonstrated yield impacts in fungicide applications
2) Have more than one check strip, wider than your combine, and space them across the field. Three should be plenty, but two is not enough
3) In your comparisons, do not include the parts of the field where you have weed escapes or along tree lines. These areas are going to yield less, so this is false data whether it was treated or not. Make sure other variables such as soil types, soil fertility variations and pest issues are not biasing your field experiment
4) Approximately three weeks after applications, walk some of the strips. For corn, look at the ear leaf; what percent leaf area has got lesions in the treated vs nontreated? Is gray leaf spot, anthracnose, or northern leaf blight present? For soybeans, look at the upper canopy for frogeye or downy mildew and on the lower canopy look at how much brown spot is present.
5) Take averages. When you do harvest your fields, take several strips, both untreated and treated. Then take the average of the untreated strips and compare that average to the treated. Fields are not uniform and with our stand issues and unevenness across many fields this year, there is going to be even more variability.
Ned Birkey
It has been
unusually hot and dry with rains seeming to skip parts or the entire area. Everyone
can use a good soaking rain.
Crop reports
Alfalfa growth is “stalled” somewhat with the dry conditions. Potato leafhoppers are out in force. Some second cutting has occurred and more probably should, as harvest weather has been great.
Corn is suffering in the 90-degree heat and without precipitation. Many fields are at the VT growth stage and many fields have uneven plant development. European corn borer numbers are very low.
Oats are turning quickly in this heat. Yields and test weights may be off.
Soybeans do not seem to be growing much at all, as I
do not have to move up the yellow, sticky traps in some counties. Most fields
are at the R2 flowering growth stage. One western bean cutworm moth was in a
trap in
Wheat harvest started on July 2 with balers and
drills following some combines in western
It has been hot and dry since the Memorial Day holiday. We’ve had only a few days of cooler temperatures and some scattered rain.
Bruce MacKellar
The drought continues throughout southwest
The earliest planted commercial corn is at or just past pollination. Irrigated commercial corn looks fairly good. Even under irrigation, we seem to have more variability of crop height than we have seen in recent years. Dryland corn has really been hurt by the drought. The stress has been severe enough to see actual plant stand loss in many portions of fields. Plants have been under severe moisture stress for more than 10 days in many locations. Some fields have probably suffered more than 50-60 percent loss of yield potential. Other areas are approaching this level of stress very quickly. If we do not see significant rainfall within a week, much of the area’s dryland corn production will be lost.
We have seen significant Asiatic garden beetle mating activity in the Centreville area this week. Actually, there were thousands of the beetles swarming around the halogen lights outside the St. Joseph County MSU Extension building on Monday evening. They appear to like to gather in areas at night where there are shrubs or trees adjacent to bright lights. We have seen significant pockets of damage caused by Asiatic garden beetle larval feeding on corn where soybeans were planted in the field the previous year. The larval stage of this new insect pest is a white grub, similar in size and appearance to a Japanese beetle grub. Look for Asiatic garden beetle mating activity around brightly lit trees and shrubs to determine if the new pest is active in your area. We have seen beetles active in areas as far north as Paw Paw.
We have seen some western bean cutworm activity in southwest
We are in the process of de-tasseling seed corn. Producers are struggling to keep up with the water demand through irrigation. Fields are being treated with fungicides to help protect against leaf diseases. Cooler temperatures should be favorable for pollination. The activity of silk clipping insects such as western corn rootworm adults and Japanese beetle adults should be monitored to make sure they do not impact pollination. Late splits on nitrogen are also being applied.
Irrigated soybeans
continue to grow well. The best beans are approaching 26-28 inches in height,
and are setting pods. Dryland beans are also suffering from the drought with
stand loss in some fields, especially those planted later in the season that
did not get a chance to develop significant root systems. Plants are very
short. Soybeans have better potential to recover from drought stress conditions
than corn at Vt, but impact on yield potential will still be significant.
Alfalfa and pasture growth has really slowed down to a crawl for fields that are not irrigated. Many livestock producers will have to start (or already have been) feeding hay. On alfalfa, potato leafhoppers continue to be found in high numbers.
Wheat harvest is nearing completion. Yields have been steady, but are lower than perhaps what we expected. Yields of 55-65 bu per acre are common, even on irrigated fields.
Fred Springborn
A few scattered showers came through the area over the past two
weeks, giving a lucky few some temporary relief from the dry weather we have
experienced this season. Most growers are experiencing near drought conditions.
Irrigation systems are running across
Wheat harvest is well under way with average to poor yields reported. Oats are turning with harvest two weeks away for many fields.
Corn growth ranges from V5 and tightly rolled to pollinating with the majority in the range of V10 to tassel emergence. Irrigated corn is progressing well. European corn borer trap catches are very low with most traps catching zero moths. One corn earworm trap caught 32 moths this week at our Trufant location
Dry bean stands are very good where there was adequate moisture, where soil was allowed to dry out before planting emergence is spotty.
Most soybeans fields are V5-V6. Soybean stands appear fairly uniform, but need moisture badly. Insects present are Japanese beetle and potato leafhopper. There are very low numbers of soybean aphid.
Alfalfa second cutting is underway. Leaf hopper feeding is above threshold in many fields. Re-growth is slow and spotty due to dry weather is generally seen.
Sugar beets are doing well by and large. Even irrigated beets have shown moisture stress on several days where temperatures were high and humidity was low.
Paul Gross
It has been a mixed bag of weather the last two weeks across
the region. The needed rain that was predicted has been disappointing for the
most part. Parts of the region have received over two inches, while other areas
measured only 0.2 of an inch. There was an area in
The corn crop ranges from knee high to tasseling. The cooler temperatures will provide some relief as the crop enters the pollination stage. Corn on light soils will have yield loss due to lack of rain fall. Corn on heavier soils is showing signs of drought stress. These fields will need rain soon to prevent yield loss.
Soybeans are growing very slow and are shorter than normal for this time of year. Stands are okay, and we are not seeing any disease problems. Scout fields for soybean aphids. Aphid populations are still very low.
Wheat harvest is well under way. The southern part of the region will complete harvest in a few days and the northern part of the region is just getting going. Most are reporting just average yields and good quality. The fields on light ground are yielding very poor. There are no reports of head scab, so most farmers are pleased with little to no docking even though yields are less than expected.
Harvest of second cutting alfalfa is underway with most reporting poor yield due to lack of rain and leafhopper damage. Scout fields after green up for this pest. There are reports of hay being in high demand and bringing a premium price. Pastures are burning up and farmers are feeding hay.
Oats are turning, and an average to below average yield is expected due to lack of rain.
Dry beans stands are good. Leafhopper populations are high and need to be controlled.
Mark Seamon
On and off breaks from the high temperatures have been welcomed by people, as well as the crops where rainfall has been slim. Rainfall has been good in some areas and very short in others. The source of rainfall in the past six weeks has been small intense thunderstorms, which makes each rain event variable from field to field. The amount of rainfall has been mostly less than 0.5 inch per event, which is welcomed and appreciated, but will not get the large crops through for very long. The next couple of weeks will be critical, especially in pollinating corn.
Alfalfa re-growth is slow and fighting against potato leafhopper feeding.
Sugar beets continue to add growth and are filling the rows in most fields. Weeds are now breaking through the crop canopy. Some fields are showing some dying beets, likely from rhizoctonia, which is shown as tip rot. Watch for DSV accumulations for cercospera leafspot prevention.
The wheat harvest has nicely begun across the Thumb. Late planted fields are slower to mature and have delayed harvest. Grain quality is reported to be good with high test weight and low or no vomitoxin. The test weight will likely decrease as some fields get rained on just before harvest. Grain yields have been reported in the 60-90 bushel range. This yield is pretty impressive with the late season moisture stress that this crop suffered.
Corn is moving quickly through growth stages with the accumulation of heat units. Crop height has become uneven through the past dry period. Tassel emergence has begun in early planted fields. The recent rainfall and lower temperatures will be good for pollination. Other areas with less or no rainfall may struggle through this period.
In soybeans, most fields have good stands with steady but slow growth. Soybean aphids are widespread, but mostly low in populations. Some fields are being sprayed with the second application of glyphosate.
Dry beans, similar to soybeans, have had good emergence, but are progressing somewhat slowly. Some fields that received some rainfall are quickly adding size. Potato leafhoppers continue to pressure new growth.
Peter Kurtz
Geography
The heat wave that began last weekend and continued through
Tuesday in the southern half of the
Highs will range today from the low 60’s in sections of the
Upper Peninsula to the upper 70’s in the southeast. Highs on Friday will range
from the mid 60’s in the north to the low 70’s south. Tomorrow appears to be
the coolest day for the
The 6-10 day outlook covering
the period July 17-21, which was issued yesterday, is now dramatically
different from the outlook issued a couple of days ago. Above normal
temperatures are now likely statewide with normal precipitation in the Lower
Peninsula and slightly above normal precipitation in the