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ISSUE 1  May 7, 1998

WHEAT MIDGE DEGREE DAYS . . . ALREADY

    With the warm spring temperatures, degree days (DD) are accumulating at a rapid rate, especially compared to the past four years. The result is development of our insects earlier than we have become accustomed. We have already reached the point where our wheat is being planted into the window of time where synchrony between wheat midge emergence and heading occurs.

These DD accumulations correspond with the following events in the midge population.

DD                        EVENT

  450

the midge breaks the larval cocoon and moves close to soil surface to form the pupal cocoon.

1300

10% of the females will have emerged

1475

about 50% of the females will have emerged

1600

about 90% of the females will have emerged.

 

Identifying Wheat at Risk to Midge

Heading for HRSW should occur at around 1000 -1100 DD. When 150 -200 DD accumulate prior to seeding wheat, the peak midge emergence and wheat heading will be synchronized. Soil conditions will also have an impact on midge. Soil moisture must be adequate to allow adult emergence from the soil, and warm temperatures, calm conditions, and adequate moisture during heading are also required by midge for economic injury to occur. Flooded soils will also impact emergence. This may delay expected emergence times based on DD, since soils are kept cooler.

 

Wheat Midge Degree Days
Used as a Guideline for HRSW Risk Assessment

HRSW planted PRIOR to accumulating 200 DD will head before wheat midge emerge.

HRSW planted FROM 200 to 600 DD will be heading at the time wheat midge are emerging

HRSW planted AFTER 600 DD will head after peak emergence and should be at low risk to midge infestation (higher risk of frost, however)

 

Dates When First 200 Degree Days Were
                       Accumulated
   Towards Wheat Midge Development

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North Dakota Agricultural Weather Network (NDAWN)
                Weather records can be accessed at:

http://www.ext.nodak.edu/weather/

Phillip Glogoza
Extension Entomologist

 

BE ALERT . . .CUTWORMS, FLEA BEETLES & WIREWORMS IN SUGAR BEETS

    Cutworms, flea beetles and wireworms are three insects that may cause early season stand losses in sugar beets. Now is the time to start scouting for these insects.

    Lets examine the problems from a symptomatic stand point rather than describe the life-cycle and biology of each insect. If you find areas in the field (one or two sugar beets all the way up to larger irregular spots) where sugar beets have been neatly cut-off near the soil surface, cutworms are feeding on the young beets. Cutworms are the larval form of moths. The larvae are greenish_brown to greenish_grey. The head is pale brown with darker brown freckles. Mature worms are 1 inches long. The eggs were laid last summer or fall in the soil where sugar beets are now planted. The eggs have hatched and the growing larvae are hungry! When suspected cutworm damage is found, check for live cutworms around the damaged plants by digging in the soil at the base of damaged plants. Count and record the number of damaged plants. Note the size of the cutworms being found. The treatment threshold has been reached if 5 percent (five or more of the 100 plants) show cutworm feeding and small larvae are still present. For insecticides used to control cutworms consult your "1998 Field Crop Insect Management Guide". A pyrethroid insecticide (Asana XL) has just received a label for control of cutworms on sugar beets and is not listed in the guide. More on this insecticide following the next two insect pests.

    There are several species of flea beetles that will defoliate sugar beets. The most common are small (1/8"), black, and shiny. They are somewhat oval-shaped with the hind legs being enlarged. They jump when disturbed and hide under the leaves of sugar beet seedlings. Flea beetles generally move into fields from the edge or headland. The younger the plants being attacked, the more significant the injury. If significant stand loss (plant stand counts of < 35,000 plants /A) occurs, treatment for flea beetles can be justified. For control of flea beetles in sugar beets, consult the "1998 Field Crop Insect Management Guide".

    Wireworms are one of the most difficult insects to detect and one of the hardest to control. They will completely consume the inside of a germinating beet seed. It will also consume any fresh tissue of seedlings and can significantly reduce plant stands. If you have seedling emergence that is somewhat irregular, start digging for wireworms in the soil around the seed or seedling. Wireworms are elongate, heavily segmented, pale yellow to brown wire-like worms that vary in length from to 1 inches. They tend to prefer lighter textured soils. In the spring, after overwintering in the soil, wireworms migrate closer to the soil surface and seek germinating seeds as a food source. For control of wireworms consult the "1998 Field Crop Insect Management Guide".

 

ASANA XL RECEIVES SUGARBEET LABEL

    Asana XL has just received a label for grasshopper, leafhopper, cutworm, and beet webworm control in sugar beets. Asana XL is the first pyrethroid labeled for beets. It has different insecticide chemistry and mode of action compared with currently labeled insecticides used for sugar beet insect control. Caution should be used when tank mixing Asana XL with herbicides and fungicides. Do not mix Asana XL with "Super Tin" (fentin hydroxide). Micro-rates of sugar beet herbicides Betamix and Betanex should not result in significant injury to sugarbeets. Full rates of these herbicides used in combination with Asana XL have the potential to cause significant injury to sugar beets. For questions on tank mixes of Asana XL with fungicides and herbicides, call Alan Dexter, Art Lamey, Allen Cattanach, Phil Glogoza or Scott Armstrong.

Scott Armstrong
NDSU Entomologist


CRUCIFER FLEA BEETLES ARE HOPPING WITH THE WARM SPRING

    Crucifer flea beetles (Phyllotreta cruciferae (Goeze)) were first captured on sticky yellow cards in canola plantings at the North Central Research Extension Center in Minot on April 23, 1998. Traps were located in two fields: one cultivated canola field and one no-till dormant seeded canola field. As expected, the trap catch was higher in the cultivated canola field than the no-till dormant seeded field. We believe that crucifer flea beetles prefer plants grown in conventional tillage compared to no-till, because of the warmer soil temperatures. After several warm days last week, the numbers increased 10-fold based on average sticky yellow card counts. Trap counts were the highest for traps located in the overwintering sites compared to traps located in the field or field edges. The hungry flea beetles are moving into fields to find suitable host plants (canola) to feed on. Pitting and leaf feeding can be easily seen on volunteer canola.

What Does This Mean for Recently or Soon to be Planted Canola Fields?

    First, crucifer flea beetles are emerging and will continue to increase in numbers as we have more warm spring days. So, continue to push for early plantings to avoid the period of peak activities! In the next few weeks, populations will emerge at a slow pace with cool temperatures or at a fast pace with warm temperatures. Unfortunately, a degree day model is not available for forecasting the initial and peak activity of the crucifer flea beetle. Part of this trapping study is to address this question.

    If growers used treated (e.g., gaucho) canola seed, the seedlings should be protected for at least part of the seedling stage. Gaucho usually provides about 3 weeks of protection, or 2 weeks after canola emergence in the field. In contrast, lindane treated seed will protect for only 11 days after seeding, or 5-6 days after emergence.

    Remember that adult flea beetles are active and continually emerging for a three-week period in the spring. As a result, field monitoring is critical for untreated or partially protected fields, or fields with a history of high flea beetle populations. Growers should watch seedling fields for flea beetle attack on a daily basis following germination. Check several locations in the field (e.g., edges and center). Hot, sunny weather produces high feeding activity, while cool, damp weather slows feeding and favors crop growth. In some instances, crucifer flea beetles can move quickly and infest large fields by flying; in other instances beetles invade slowly and creep moving from plant to plant in a field.

    If the seed treatment did not provide adequate protection or was not used, a foliar insecticidal application may be necessary. Foliar applications are only recommended when an economic threshold of 25% damaged plants is reached. When flea beetle populations are high, more than one application may be required due to the short residual of insecticides labeled for crucifer flea beetle control in ND, and the threat of reinfestation from surrounding areas. Foliar applications must be applied quickly for effective control. One of the difficulties growers' face is being able to cover large numbers of acres quickly when feeding pressure is high. Registered products in ND for foliar applications include: endosulfan (0.75 lb/acre), ethyl-methyl parathion (0.5 lb/acre), and methyl parathion (0.5 lb/acre). All of these insecticides are highly toxic insecticides and EPA restricted use product.

Janet Knodel
Area Crop Protection Specialist
and Mike Weiss
Entomologist


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