Seventeen-Year Cicada Among Insects in Sights of DATCP Pest-Watchers Agri-View: Crop News

Wisconsin's Pest Survey began its 52nd year of service to the state's crop producers last week when the state ag department pest-watchers made their first reports on the tail of an untimely spring snowstorm.

After record-highs in the low 80s in various portions of the state late last month, April temperatures plummeted into the low 30s by day and the 20s by night, damaging a lot of alfalfa around the state.

While last week's blowing snow put a number of insects on hold, along with the start of fieldwork, the ag department's pest experts are giving growers early-season heads-up for a number of crops.

While technically not a crop pest, the insect deserving top billing this year is the 17-year cicada, just because it last showed up in Wisconsin in 1990 - the year East and West Germany were reunited, the Hubble space telescope was launched, Nelson Mandela was released after 27 years in prison, smoking was banned on all domestic airplane flights, and the Record of the Year was Bette Midler's "Wind Beneath My Wings."

"More importantly, in 1990, periodical cicadas... mated and laid a brood of eggs that has... lived two feet underground as nymphs feeding on the sap of tree roots. Seventeen years have passed since Bette sang her way to the top and the eggs of Magicicada Brood XIII were laid. In a matter of weeks, the plump, subterranean nymphs will claw their way to the soil surface and transform into clear-winged crooners whose sole purpose is to mate, reproduce, and die," reports Krista Hamilton, plant pest and disease specialist with the Wisconsin Department of Agriculture, Trade and Consumer Protection.

"In addition to southern Wisconsin, cicadas of Brood XIII are expected to emerge in parts of Iowa, Illinois, Indiana and Michigan. During the 2007 event, densities of thousands of cicadas per acre could emerge and cause physical damage to small trees or shrubs, from feeding and egg laying," she warns. "Periodical cicada densities exceeding one million per acre have been documented."

Hamilton says orchard and nursery owners in the southern portion of the state with young trees or shrubs should take measures to prevent damage. The simplest way to protect small trees and shrubs is to cover them with screening or cheesecloth when the cicadas begin to emerge. Plants should be kept covered for at least four weeks or until most of the cicadas have died off.

Pesticide applications are impractical given the sheer number of emerging cicadas, she says. "Besides, this once-every-17-years event aerates the soil, provides food to thousands of predators, and acts as a natural pruning mechanism," she says, noting that the DATCP will be tracking the "cicada extravaganza" in late May and June.

Now onto the more usual lineup of crop-pest "suspects."

Overwintered black cutworm moths from source populations as far away as southern Texas and eastern Mexico embarked on their annual northward migration into Wisconsin last month. Strong southerly winds on March 25 and 26 are credited with the delivery of black cutworm moths from reservoirs in the Gulf States.

The first moths of 2007 arrived on March 29, slightly more than a week earlier than last year. Captures of moths between March 29 and April 2 mark the earliest arrival of this migratory corn pest into southwestern Wisconsin in the last seven years of monitoring.

DATCP survey specialists are now watching for a concentrated pheromone trap catch of 8 to 9 moths in a 1- or 2-night period. This event is used to predict when the progeny of the migratory cutworm moths have reached the fourth instar, the developmental stage at which they become capable of cutting corn seedlings. Captures at 48 trapping sites ranged from zero to two moths between March 29 and April 2, but no activity has been registered since then, says Hamilton.

Flight activity of black cutworm is being tracked using a network of traps established along major roadways in southwestern Wisconsin. The 2007 monitoring effort is larger than ever before and should help DATCP pest-watchers to provide an accurate forecast when corn is most susceptible to cutting by black cutworm larvae.

Stewart's wilt back

The trend toward milder winters has led to increased winter survival of corn flea beetles and an increased incidence of Stewart's wilt in Wisconsin. After a 56-year absence from the state, an isolated case of Stewart's wilt was detected in a Walworth County cornfield in 1999. Seed field inspections in 2000 found Stewart's wilt in 10 counties of the state, and in 2001 no disease was detected. In the years 2002-2004, only one or two infected fields were recorded each year. Stewart's wilt was detected in three Grant County seed production fields in 2006.

The return of this disease to Wisconsin after more than a half a century indicates the geographic range of overwintering corn flea beetles and Stewart's wilt has expanded northward, according to DATCP.

The risk of Stewart's wilt in Wisconsin for the 2007 growing season has been assessed using two models that integrate average monthly temperatures for December, January and February to predict corn flea beetle survival and the probable occurrence of Stewarts wilt during the seedling and late leaf stages of corn development.

Based on the Iowa State Model, the risk of the occurrence of Stewart's wilt is high in one location in the southeast (Kenosha), moderate to high in the other southeastern locations (Milwaukee and Racine), moderate to high in three of four south central locations (Afton, Brodhead and Watertown), moderate to high in one southwestern location (Dodgeville), and moderate to high in one east central location (Manitowoc). A low to moderate risk is predicted for all other locations.

Handle treated seed with care

Greg Helmbrecht, the department's seed specialist, advises growers to use caution when handling pesticide-treated seed this spring, to prevent contamination of grain destined for animal or human food.

"Seed treated with an insecticide or fungicide pesticide protects seedlings from insects and disease threats, but can be harmful to animals or farmers' bank accounts if mishandled," he warns, noting that "even one pesticide-treated seed can be enough to contaminate an entire truckload or storage bin and cause the load to be rejected."

Clean-up efforts after hauling treated seed are critical to preventing contamination at harvest. Check gravity boxes, truck beds, wagons and all equipment that handled treated seed, particularly if that piece of equipment will be used to haul harvested grain, animal feed or forage. A simple visual inspection of the wagons or other farm equipment is not enough, Helmbrecht warns.

"Any piece of equipment that contacts treated seed must be thoroughly cleaned by pressure washing and then thoroughly inspected. If pressure washing is not an option, avoid using that piece of equipment to handle untreated seed or grain later on," he says.

Farmers should also take these steps to keep pesticide-treated seed separate from untreated seed and grain and to prevent exposure to animals and animal feed:

Avoid leaving treated seed out in the open where it can be eaten by birds or other animals

Store any unused seed securely and separately away from grain storage areas

Return unused seed to your seed supplier or deliver it to a sanitary landfill.

Apple growers: get ready

Pheromone traps used to monitor the orchard pest, spotted tentiform leafminer (STLM), should now be in place in the southern two-thirds of the state. Emergence of the first flight of moths was expected to begin this week once temperatures get into the 50s and 60s. Egg laying is projected to occur around 75 to 127 growing degree days (base 50 degrees). Once moths start to appear in traps, the earliest event to watch for is the first peak capture. This event comes quickly, once 150 GDD have been reached. A peak capture of moths suggests a majority of the population has emerged, thus mating and egg laying is most concentrated. To determine the need for early-season control, plan to scout for sapfeeder mines on the undersides of apple leaves about one week after the first peak flight has occurred.

Insects that overwinter in the pupal stage, such as the redbanded leafroller and STLM, emerge from winter ready to transform into adults once spring temperatures exceed a certain threshold. That threshold was surpassed late last month and a few early adults took flight in southwestern Wisconsin orchards. Captures of 0 to 4 moths were reported from April 5 to 12. Like STLM, activity of the redbanded leafroller is expected to accelerate this week.

Cabbage looper is a key pest of concern to the Wisconsin cabbage industry. Cabbage growers interested in monitoring the arrival and flight activity of cabbage looper moths are encouraged to sign up for the DATCP cabbage looper trapping network. The ag department will supply all trapping supplies including pheromone lures and Scentry mesh traps at no cost to volunteers. In return, cooperators will be required to send in moth counts once a week. If you would like to participate, contact Clarissa Hammond at 608-224-4544 or clarissa.Hammond@wisconsin.gov.

Weeds also on way

As early as late March, green dandelion rosettes were observed in thawing fields. Among the earliest emerging weed species found in row crops are horseweed, white cockle, field pennycress and shepherd's purse.

"Most early-season weed management programs emphasize control of emerging plants as opposed to preventing new seed entries into the seedbank. Although seed shed is not a hot topic at this time of year, weed seeds can easily be disseminated during early season farming activities," says Hammond. In fact, weed seeds are readily scattered by farm equipment (i.e. the planter, tillage equipment) and when manure is spread."

Prevent movement of seeds between fields by cleaning equipment between fields or at least when moving from a previously weedy field to a non-weedy field, she says.

"Many seeds are adapted to withstand the digestive system of cattle and are spread onto fields in manure applications. Seeds deposited in fields with manure have a built-in nutrient supply. If the application is made early enough and temperatures remain warm, as is often the case, these weeds will get a significant head start on development relative to the field crops which emerge weeks later," Hammond reports.

Growers can get a rough idea of weed seeds in manure by keeping tabs on what goes into their animals. If growers observe intermittent or evenly spaced patches of weeds that appear to follow equipment routes through a field, manure may be the culprit, notes Hammond.

Emerald ash borer threat

Last but not least is the threat of emerald ash borer to Wisconsin farmers' ash trees. DATCP has been on the hunt for the emerald ash borer since December. After peeling nearly 1,000 trees in 30 counties, no sign of the deadly ash pest has been found. But many more trees have been girdled and left standing in a continuing effort to monitor a number of high-risk areas of the state for signs of EAB. Those trees will be felled next fall and winter and examined for signs of EAB infestation.

The known locations of EAB continue to grow in the infested Midwest states. Lower Michigan, Illinois, Indiana and Ohio are all under a federal quarantine that forbids the movement of hardwood firewood and ash products out of those states. In Maryland, officials are working to control an infestation that officials believed was under control a couple years ago, after an accidental shipment of infested ash nursery stock from Michigan, says Mick Skwarok, EAB outreach specialist with the department.

If EAB is discovered in Wisconsin this year, steps will be taken to quarantine the infested county and begin investigating the size and "age" of the infestation. A management plan will be developed, with the removal of ash trees in the infested area "as only one optional response," Skwarok concludes.

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