ISSUE 3 May 28, 2009
INSECT DEVELOPMENT IS DELAYED - WHEAT MIDGE
With the cool spring temperatures, crop development is not the only thing that is behind normal, insect development has also been slowed. Letís use wheat midge as an example.
The 2009 risk forecast for wheat midge infestation was low throughout most of the state based on the previous seasonís cocoon counts in the soil (Fig. 1).
Although the risk is low, isolated pockets of economic populations of wheat midge can still occur if wheat midge is emerging at the same time as wheat is in the susceptible stage (heading to early flowering), and environmental conditions are favorable. A degree day (DD) model can help identify the high risk planting windows for wheat midge infestation of hard red spring wheat (HRSW). The high risk window for HRSW planting is 200-600 DD (using a base of 40 F) where wheat will head at the same time wheat midge is emerging. The current DD accumulations for wheat midge are mapped in Fig. 2.
Currently, most of North Dakota is in that high risk window for planting HRSW (between 200 and 600 DD). Based on the 5-year average for wheat midge DD accumulations, departures from the 5-year average range from -100 DD in the southern tier to -200 DD in the northern tier (Fig. 3). Any wheat that was planted prior to 200 DD accumulations will be at low risk for wheat midge infestation, because wheat will head before wheat midge emerge. For North Dakota, the southern region was at 200 DD on May 7, central region on May 14, and northern region on May 21. Likewise, any HRSW planted after 600 DD will also to at low risk to wheat midge infestation; however, the risk for frost injury is higher.
To track wheat midge growing degree days, go to NDAWN, Applications, Wheat and Midge Degree Days. Then, select the ĎMidge Degree Daysí under ĎTo get a mapí and enter 2009-03-01 as your start date (or plant date) and current date to see accumulated DD for wheat midge.
Funding for the wheat midge soil survey was provided by the North Dakota Wheat Commission.
WATCH FOR TICKS!
While I was out hiking and bird watching in the Sheyenne National Grasslands this beautiful Memorial Day weekend, it was difficult to go far without finding another tick crawling up my leg! Hereís some handy facts about ticks to keep you safe this summer.
In North Dakota, there are about 14 species of ticks. The most common ticks in our area are ticks in the genus Dermacentor. Three species are found in ND: American dog tick (D. variabilis), Rocky Mountain wood tick (D. andersoni), and winter tick (D. albipictus). Of these, American dog tick is the most common species (Fig. 4).
Lyme disease is vectored by the black-legged tick (Ixodes scapularis), also known as deer ticks. Fortunately, the black-legged tick does not occur naturally in North Dakota, but may be brought in from neighboring states (Fig. 5 & 6). Some symptoms of Lyme disease include fever, headache, fatigue, muscle and joint aches, and swollen lymph nodes. About 70-80 percent of infected people develop a circular or bullís-eye skin rash at the bite site. If you suspect that you are bitten by a Lyme disease tick, it is very important to always get the tick properly identified by an expert in the Department of Entomology at NDSU and seek Medical attention.
Ticks are blood-feeding external parasites of several mammal species, including humans, dogs, cattle, and horses. They have piercing-sucking mouthparts that are inserted through the skin of their host and into vascular tissue. Once engorged with a blood meal, a tick will drop off its host to mate, lay eggs, or continue development. The life cycle of ticks is comprised of four distinct developmental stages: one inactive stage - egg, and three active blood-feeding stages - larva, then nymph, and finally adult. Adult males and females require several days of feeding, after which the male copulates with one or several females and then dies. Adult females drop to the ground after mating and begin laying eggs. Females die after laying eggs. Eggs are laid on the ground in masses of over 1,000 eggs and require several days to develop depending on environmental conditions. Emerging larvae have six legs and may crawl up on vegetation and wait for a suitable host to pass by. Larvae attach to a host, and after a blood meal drop to the ground to molt into eight-legged nymphs. Again, nymphs crawl up on vegetation and wait for a host. Engorged nymphs may rest for long periods of time before molting into the adult stage. There is probably one generation per year for American dog tick and winter tick in North Dakota. Rocky Mountain tick has a two to three year life cycle. These ticks probably overwinter as larvae or nymphs. Black-legged ticks take about 1 to 2 years to complete development and the tick must take a blood meal at each active stage. Pathogens, including the bacterium that causes Lyme disease, may be present in their saliva and are transmitted as they feed on the person or animal.
The best way to prevent tick infestations around the home is by keeping lawns mowed (height of 3 inches or less) and removing high grass, weeds, leaf litter, and undergrowth near the home. Property that borders woodlots typically present the most risk, with tick numbers generally declining as you move farther from the woods. Ticks require high humidity to survive and do not do well on lawns or fields that are routinely exposed to direct sunlight. Wild animals (deer, birds, mice) and pets can transport ticks long distances and into your yard or home. Chemicals (pesticides) that kill ticks can be applied to your yard as a last resort if large numbers of ticks are present. The critical point is the timing of application to target early life stages (nymphal/larval ticks), usually early June. This can help reduce the number of ticks later in the season. Some of the pesticides that are effective for controlling ticks by homeowners are listed below:
(Sevin): A commonly used garden inseciticde. Available as a spray or granule for ticks on turf and recreational areas.
Cyfluthrin (Tempo, other brands): Labeled for tick control on turf and ornamentals.
Deltamethrin (Suspend, DeltaGard G): Available as a spray or granule. Labeled for tick control in residential areas where ticks may be found.
S-fenvalerate (Zema Lawn Spray): Labeled for tick control on turf and ornamentals.
Permethrin (PermaKill 4Week Tick Killer): Labeled for use against ticks on the lawn.
Liquid formulations of pesticides will kill nymphs in spring, larvae in summer, and adults in the fall; whereas granular formulations of pesticides are more effective on nymphs that are overwintering in the fall or larvae that are hatching in the early summer.
Remember to practice personal protective measures as well. Wearing long sleeves and long pants to prevent ticks from reaching your skin. Tuck your shirt into your pants and your pant cuffs into your socks or boots. Use an insect repellent containing DEET on any exposed skin and clothing to repel ticks. Permethrin can be spray onto clothing. Finally, be sure to check your clothing and body carefully for ticks when youíve been outdoors.
To remove an imbedded tick properly, use a fine forceps and grasp the capitulum (head) as close to the wounds as possible, and then apply a steady upward force until the tick is free (Fig. 7). If part or all of the mouthparts (hypostome) remain in wound, it can be treated as a sliver. DO NOT use petroleum products to remove a tick, squeeze the body, or heat tick with a match.