Christmas trees
Field crops
Fruit
Home and yard
Nursery and landscape
Turfgrass
Vegetable
Diagnostic Services
Soil/Plant Nutrient Lab
Enviro-weather
Regional IPM Center
Pesticide safety
Organic: New Ag Network
Invasive species
Sustainable ag & food systems
MSU ANR departments
MSU Extension
Site index
Contacts/permissions
| Field Crop Advisory Team Alert newsletter | ||||
|
||||
 |
||||
| Vol. 21, No. 17, September 7, 2006 |
||||
In this issue Nematodes attacking soybeans Stewart’s disease reported in field corn in Michigan Regional reports Weather news
|
|
|||
|
||||
| Nematodes attacking soybeans Fred Warner MSU Diagnostic Services Soybean is host to many types of plant-parasitic nematodes. Obviously, the nematode that demands the most attention is the soybean cyst (SCN). SCN is a major limiting factor in the production of soybeans worldwide and is estimated to cost U.S. soybean producers over 1 billion dollars annually. However, because of its importance, other nematodes are often ignored. Northern root-knot, lesion, lance, dagger, stunt, pin and spiral nematodes are found in soil samples collected from soybean fields in Michigan. Of these, only root-knot nematodes are regarded as serious pathogens of soybean worldwide, ranking in the top 10 of most important soybean pathogens. In our state, however, the northern root-knot nematode is infrequently (less than 25% of samples) detected in soil and root samples. This is probably due to the fact that soybean is often rotated with field corn or small grains and these plants are non-hosts for the northern root-knot nematode. Virtually all other types of plants will host this nematode, and it is a serious problem in vegetable, fruit and landscape plant production. The damage threshold for the northern root-knot nematode is unknown for Michigan but is estimated at 500 second-stage juveniles (J2s) per root and soil sample. |
||||
| Lesion nematodes are common (25 to 75% of samples) in samples collected from soybean fields. These nematodes are not regarded as serious pathogens of soybean, but anecdotal evidence suggests their feeding will result in the production of symptoms including yield loss in Michigan. They are typically found in high population densities on soybean when soybean cyst nematode is absent. As SCN numbers increase, lesion nematode population densities often decrease. Lesion nematodes are a concern because they feed on virtually all species of cultivated plants. In addition, they can predispose plants to invasion by other soil plant pathogens that inhabit the soil. The damage threshold for lesion nematode in Michigan is estimated at 300 per root and soil sample although lower numbers have been reported to damage soybeans in the southern United States. As mentioned, lesion nematodes can reduce yields of other field (row) crops, so they should be closely monitored and managed. Lance nematodes are infrequently (less than 25% of samples) found in soybean samples collected from Michigan. They are rather large nematodes and are considered fairly serious pathogens of soybeans in the southern United States where the damage threshold is reported to be 4-100 per 100 cm3 soil. In Michigan, we estimate this threshold at 125 per root and soil sample. Lance nematode is also an important pathogen of corn. Dagger nematodes are not considered important pathogens of soybean in Michigan. They are often found in high numbers on corn, and damage has been observed at population densities above 250 per 100 cm3 soil. Many grass species appear to host dagger nematodes. These nematodes are important in fruit production because they vector some very important plant viruses. Stunt nematodes are similar to daggers in that they are largely insignificant on soybean but can reduce corn yields. They all do very well on many grass hosts. They do not vector plant viruses. Pin and spiral nematodes are common in soil samples collected from fields in Michigan where field crops have been grown. Neither is regarded as a pathogen of soybean. Anecdotal evidence suggests that pin nematodes can retard growth of sugar beet in our state. High population densities of spiral nematodes are, on occasion, associated with stunt corn plants. When root and soil samples are collected from fields and submitted for nematode analyses to Diagnostic Services at MSU, all genera (cyst, root-knot, lesion, etc. are common names of nematode genera) of plant-parasitic nematodes are identified and counted. For samples submitted using the MSPC-sponsored SCN program or sentinel plots, risk ratings will be assigned for all nematodes on soybean. Nematode risk ratings are as follows: 0 = none; 1 = low; 2 = moderate and 3 = high. Management recommendations will also be included. Additional information regarding nematodes on field crops can be found in MSU Extension Publication E-1582, Insect, Nematode and Disease Control in Michigan Field Crops or any of the MSU publications on field crops ecology. For questions, please call me at 517-432-1333, Dr. George Bird at 517-353-3890 or Angela Tenney at 517-353-8563. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| back to top |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Stewart’s disease reported in field corn in Michigan Willie Kirk, Diane Brown-Rytlewski and Jan Byrne; Plant Pathology Beth Bishop, and Chris DiFonzo; Entomology Stewart’s disease of corn has been reported in several field corn fields in Saginaw and Allegan counties so far this summer. The disease has also been confirmed in Clinton and Gratiot. So far we do not how extensive this disease is in Michigan. Stewart’s disease is a disease of corn, caused by the bacterium Pantoea (Erwinia) stewartii and is sometimes referred to as bacterial wilt or bacterial leaf blight. The disease is common in North America, but is economically important only during periodic outbreaks (In a literature survey we found the disease appeared about every 30 years in Michigan in sweet corn.). Stewart’s disease is generally associated with sweet corn, but some hybrids and inbred lines of field corn are very susceptible. It is transmitted to corn seedlings during feeding by the corn flea beetle (CFB), Chaetocnema pulicaria (Photo 1). Bacteria invade the vascular tissue of the plant (Photo 2); disrupt nutrient and water flow, and cause leaf lesions (Photo 3), leaf wilting, barren stalks, or plant death. Stewart’s disease has two phases; the wilt phase and the leaf blight phase. The symptoms initially appear as leaf lesions originating from corn flea beetle feeding scars (Figure 1 and 4). Disease severity depends on the variety and on plant age at the time of infection. Early plantings of highly susceptible seed corn inbreds and sweet corn hybrids are likely to have the most severe symptoms. The bacterium is carried in the digestive tract of the corn flea beetle. Stewart’s disease severity is thought to be dependent on the overwintering survival of infected corn flea beetles, which in turn is dependent on winter temperatures. Earlier last century, a risk index was developed, defined as the sum of the monthly average temperatures (°F) during December, January and February. Indices less than 90 predict no risk for Stewart’s wilt, and greater than 100 predict severe risk. The overwintering habitat of the vector is not well understood, but is thought to be in the upper soil profile and in the root zone of grasses; however, the predictive index was based on ambient air temperature. The temperature profiles of the upper soil, as well as the duration of temperature below a critical threshold, may result in a more accurate prediction of corn flea beetle survival. High risk indices were recorded in winters of 1997-1998 (greater than 100), and low risk indices in 1998-99 (less than 90) the latter forecasting poor survival of corn flea beetle, yet sweet corn growers experienced an average of 44% crop loss (susceptible varieties) from the disease in both 1998 and 1999. A survey of Michigan sweet corn growers indicated that growers aware of the index did not use it as they considered it unreliable. Previous monitoring. (Discontinued in 2003 after Stewart’s disease no longer reported in Michigan) The temperature of soil (6-inch depth), soil surface and air (36 inches above the soil) was monitored at various locations within fields (tree or ditch line, margin of grass beyond the headland, at the edge of the field and 30 feet into the field) in different Michigan counties from 1997-2003. In all years, corn flea beetle have survived the winter and emerged during the spring to early summer from 1998 to 2003. However, since 1999, the incidence of Stewart’s Disease has declined markedly. The results for 2002 through 2003 are shown in Table 1. The soil temperature at each location within the fields remained on average close to 32°F at both Clinton and Macomb sites. The soil temperature average predicts possible to high survival potential especially at the ditch margin (where corn flea beetle are thought to hibernate). Soil surface and air temperatures were generally more variable than soil temperature (see standard errors in Table 1). The least variable location within both fields was at the margin of the ditch. However, it is not yet known how many hours of exposure below a fatal temperature are required to kill corn flea beetle. As in previous years, traps will be set to evaluate the survival of the beetles over the winter, and from these numbers, it may be possible to determine which of the temperature recording sites within the fields best predicts survival. In additional studies conducted in Monroe and Macomb, overwintering survival of corn flea beetles in different sites was monitored by yellow sticky traps. Traps were placed in these sites in the fall of 2001. Traps were collected and replaced weekly. Corn flea beetles captured on these traps were counted. Traps were also placed in these same sites in the spring of 2002. Flea beetles overwintering in different sites clearly had different survival rates (as determined by comparing the number caught on traps in fall 2001 vs. spring 2002). As expected, beetles overwintering in the protected ditch bank survived in higher proportions than beetles overwintering next to the relatively unprotected farm road. From late August through late October 2002, corn flea beetle were captured in Macomb and Monroe counties. The percentage of corn flea beetle carrying the Stewart’s disease bacterium (E. stewartii) was calculated using a technique developed at MSU. Each corn flea beetle was crushed and plated on Erwinia-selective culture medium. The yellow colonies were further subcultured and their DNA extracted. The bacterium Erwinia stewartii has a unique pattern of DNA in a specific area of its DNA plastid which can be identified using a molecular technique called PCR. If the DNA plastid contains one or both of two unique bands, it shows up on an agarose gel as a bright band. The percentage of corn flea beetle carrying E. stewartii was then calculated (see Table 2). The percentage (and number of captured corn flea beetle) declined through late 2002, but it was clear that a very small proportion of corn flea beetle were carrying the bacterium. Although it is not possible yet to determine how temperature survival prediction potential will interact with the bacterium carrying potential of corn flea beetle, it is clear that both factors play a crucial role in determining Stewart’s disease risk potential. Many growers have determined they will use an insecticidal seed treatment as an insurance against Stewart’s disease for two reasons; the temperature predictor is unreliable, and seed is usually treated during the winter months prior to the end of February (the end of the prediction period). The use of the molecular prediction system may help growers determine potential risk in the future once we have determined the critical inoculum potential that may initiate and epidemic the following year. The thermal indicators for both Allegan and Saginaw (Table 3) for 2005-06 indicated that the survival potential for corn flea beetle was very high (using soil temperature as an indicator), but that if air temperature was used as an indicator, survival potential was low. Having symptoms and signs (bacterial streaming) of Stewart’s disease at this stage of the season should not cause concern for this year’s crop. However, the presence of corn flea beetle plus Stewart’s disease affected plants indicates a potential for carryover to 2007. For a problem to occur in 2007, the thermal survival potential for corn flea beetle has also to be taken into account. As noted in the previous paragraph, growers may have to decide early whether or not to use an insecticidal seed treatment such as Gaucho in 2007; alternatively growers could rely on a foliar insecticide (if corn flea beetle survive and are reported in the spring of 2007) to avoid the cost of a seed treatment. Additional information about varietal susceptibility to Stewart’s disease (if known) should be requested when selecting varieties for 2007. A video is available at http://www.greeen.msu.edu/newspage.htm on Stewart’s disease management in sweet corn with a brief footage of corn flea beetle (live). Table 1. Average temperature from December 1, 2002, to February 28, 2003, at four locations (field ditch base, margin of field ditch, edge of field and 50 ft into the field) within two fields at Manchester (Clinton County) and Romeo (Macomb County) at 6" soil depth, soil surface and 36" above the soil surface.
Table 2. Number of corn flea beetles trapped during late August, mid-September and mid-October in 2002 at five sites in Macomb and Monroe counties and the percentage testing positive for presence of Erwinia stewartii. The absence of data in September and October means that no beetles were trapped.
Table 3. Average temperature from December 1, 2005, to February 28, 2006, at 2 and 4" soil depth, soil surface and 48" above the soil surface.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| back to top |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Regional reports Weather has been unsettled with scattered and locally heavy rain and even hail. Temperatures are moderate and rains are generally welcome, though rains are past the point of helping most crops. Commodity reports Alfalfa has potato leafhoppers over threshold. The third cutting is continuing, though unsettled weather is not helping with a timely harvest. Corn is mostly dented and some is mature. Silage harvest began about two weeks ago. Some corn will be harvested in September. Some on-farm grain storage is being constructed. European corn borer and corn earworm traps are still catching moths. Soybeans are turning in some fields with a few fields losing leaves. Late August rains will help the yield of some green soybean fields. Japanese beetles are still prevalent. Bean leaf beetles and corn rootworm beetles can be found, though very few soybean aphids. The MSU Soybean Variety Trial location in Lenawee County will be signed today so farmers can observe the varieties. It is located on Holloway Road, west of Bucholtz Highway and north of Deerfield. It will be interesting to learn if tropical storm Ernesto has brought any soybean rust spores to Michigan. At a field day yesterday, a Conklin sales rep asked if any farmers had Asian rust and a Washtenaw County farmer and a Monroe County farmer raised their hands. I seriously doubt that any of them knew what they were talking about. Wheat acreage will remain high this fall, depending upon the fall soybean harvest and timely wheat seeding weather and despite high stocks on hand. Some farmers contracted 2007 and 2008 wheat last winter for over $4 per bushel. Miscellaneous I anticipate increased corn acreage next year and as much wheat seeding as time allows this fall, at the expense of soybean acres. Our last fall field day will be Wednesday, September 13, 5:00 PM to 7:00 PM at the Herb Smith farm, Morocco Road, Temperance. This is a conventional herbicide soybean variety demonstration plot. All area farmers are welcome and invited to participate. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| back to top |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
3 -- West Central Dry weather has continued for the past two weeks as the rains have been light and scattered. Many crops in Montcalm and Newago counties are showing signs of being moisture stressed. High temperatures over the past two weeks have been in the lower mid-70s to lower 80s. Low temperatures have been in the 50s Commodity reports Nearly all of the corn crop is in the dent stage or beyond. A significant portion has reached black layer and is drying down. Corn silage harvest is in full swing. At the corn silage moisture clinic held in Fremont, most samples brought in were ready to chop for high quality ensiling at 60 to 70% moisture content. Above average yields are common. Harvest of high moisture corn will begin soon weather permitting. Dry bean harvest is in full swing with 10 to 20% of the crop harvested. Yields have been very good so far with reports of dryland light red kidney bean yields of 18-19 cwt. per acre. Soybeans are starting to turn with most of the crop looking as though it will yield well despite the recent dry weather. Hay harvest is winding down with some very good quality third and fourth cutting alfalfa hay being harvested. All in all this has been a very good year for hay production. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| back to top |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
5 -- Thumb Soil moisture is pretty good in most areas. Rainfall in the last week of August supplied adequate moisture for crop maturity. Of course, there are exceptions where some crops are drying down prematurely from lack of moisture. Commodity reports The sugar beets are using this late season moisture well with added root growth. Cercospera leafspot spread has been slowed by cool night temperatures, but must be kept under control, especially for those beets that won’t be harvested until mid- to late October. That is 6 to 8 weeks that plants should be kept clean of leafspot. Continue to watch www.beetcast.com for accumulation of DSV’s in your area. The corn crop looks very good. Silage chopping is well under way with good yields. Some fields are showing natural dry down while others are losing leaf area from disease or dry soil. Most of the foliar disease in this area on corn plants is Stewart’s wilt, which was spread by the flea beetle feeding on corn leaves. The timing of this disease should minimize the yield loss from the loss of leaf area. Physiological maturity (black layer) has been reached in many fields. This should lead to lower grain moisture at harvest and minimize drying expenses Visual appearance shows maturity in many soybean fields with maturity less than 2.5 and early planting. Some pods near the top of plants have aborted and/or aborted beans within pods. Lower pods look good. The effect of the dry August and very high temperatures may be found in reduced seed size, but all fields will differ. Some early harvest of dry beans has shown variable yields. This follows the season long variability in this crop. Longer season or later maturing beans may be able get some benefit from late season rainfall. Some fields injured by excess rainfall early in the year will need a late frost to make a crop. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| back to top |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Weather news Jeff Andresen Agricultural Meteorology Geography An upper air troughing feature will build into the Great Lakes region by Saturday, September 9, bringing cooler temperatures and a chance for showers and a few thunderstorms to Michigan. A cool front will move from northwest to southeast across the state during the next 24 to 48 hours, leading to scattered showers and thunderstorms beginning early Friday morning in Upper Michigan and over the Lower Peninsula Friday and Saturday. Precipitation totals through Sunday will generally range from a quarter to a half inch where rain falls with some areas remaining dry. Canadian high pressure is expected to move into the state and region Sunday behind the frontal system, bringing noticeably cooler and drier weather for the latter half of the upcoming weekend into early next week. Mean temperatures during the next several days will average near the normals with highs Friday generally in the 70s to low 80s and lows in the 50s. By Saturday, and behind the cold front, look for highs to fall back into the low or mid-60s north to the low 70s south with lows reaching the upper 30s to the mid-50s. Some scattered frost is a possibility in low-lying, interior sections of Upper Michigan overnight Saturday and Sunday. Early next week, forecast guidance is offering contrasting solutions with some guidance suggesting the formation and passage of an area of low pressure and widespread precipitation through at least southern sections of Michigan while other guidance keeps all of the state cool and dry under the influence of high pressure to our north. My guess is that the latter scenario is more probable at this point, with cool, windy and dry weather likely Monday through Wednesday. Highs during that time frame will range from the 60s north to the low 70s south with lows in the 40s to low 50s. Medium range forecast guidance calls for the upper air troughing pattern mentioned above to gradually give way to a more west to east zonal pattern over the continental United States. The official NOAA Climate Prediction Center 6-10 and 8-14 day outlooks (covering September 12-16) calls for temperatures to range from near normal over Lower Michigan to above normal over the Upper Peninsula and for near normal precipitation totals. During the 8-14 day time frame (covering September 14-20) temperatures are expected to range from below normal levels over Upper Michigan to near normal levels across the Lower Peninsula. Precipitation totals are forecast to increase to above normal levels statewide. Given recent discontinuity and disparity among some of the forecast guidance tools, forecaster confidence in both of these outlooks is rated as below normal. Further ahead, the latest version of NOAA’s long lead outlook for the month of September calls for increased odds of above normal temperatures over northern sections of the state and for the equal chances/climatology scenario of near equal odds of above-, near-, and below-normal temperatures over southern sections of the state. The outlook also calls for the climatology scenario for precipitation statewide. Finally, the three-month seasonal outlook for the September-November period calls for increased chances of milder and drier than normal weather statewide. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Back to top | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Email the web developer.