Posts Tagged ‘true armyworm’

Agronomic Crop Insects – April 22, 2011

Friday, April 22nd, 2011

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Continue to scout fields for both alfalfa weevil and pea aphids. Economic levels of both can be found in alfalfa fields at this time. As a general guideline, you should consider a treatment in alfalfa less than 10 inches tall if you find 40-50 aphids per stem. The treatment threshold for alfalfa 10 inches or taller in height is 75- 100 per stem. Although beneficial insects can help to crash aphid populations, cooler temperatures will slow their activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. As soon as temperatures increase, we will start to see a significant increase in feeding damage from alfalfa weevil. As alfalfa approaches harvest, the decision to cut instead of treat may be considered. However, this option should only be used if you plan to cut shortly after you find an economic threshold level since damage can occur quickly. Cutting should only be considered as a management option if you can cut within 3- 5 days of finding an economic level. Also, the effectiveness of using cutting as a management strategy is affected by temperatures after cutting. If the temperature remain cool, it has not always been effective. Since you need “stubble heat” to get control. As you get close to harvest, be sure to check labels carefully for time between application and harvest.

Field Corn
As soon plants emerge, be sure to check for cutworm feeding, even if an at-planting insecticide or a Bt corn was used for cutworm control. The wet soil conditions this spring have resulted in a higher level of grey garden slugs being found under residue in no-till fields. Although we see more problems in seedling corn when temperatures remain cooler and soil remains wet, it is generally during the warmer days of April when we start to see egg hatch. You will need to sift through previous crop residue and look at the soil surface for slugs. We are generally finding eggs and adults at this time; however we have started to see the first juveniles as well. The eggs, which are clear and about half the size of a BB, are often found in clusters within crop residue or at the soil surface. Although no thresholds are available, past experience in the Mid-Atlantic has indicated that pre-plant levels of five or more grey garden slugs per square foot can indicate the potential for a problem. In 2010, DuPont issued a 2ee recommendation for Lannate LV for slug management (http://www.cdms.net/LDat/ld183004.pdf); however, we have limited experience with the use of Lannate for slug management. Most of our experience has been with the use of a broadcast application of Deadline M-Ps at the low end of the labeled rate (http://www.cdms.net/LDat/ld7CL003.pdf). For more information on slug biology, sampling and management, please refer to the following fact sheet from Ohio State University: http://ohioline.osu.edu/ent-fact/pdf/0020.pdf.

SmartStax Approved for Refuge-In-Bag
Here is a summary of information on recent federal labeling of refuge-in-the-bag (RIB) from the Ohio State C.O.R.N newsletter (Ron Hammond, Extension Entomologist). Commercialization is pending individual state authorizations and notifications, as required.

“Two SmartStax corn products having the refuge-in-the-bag (RIB) concept have received registration from the U.S. Environmental Protection Agency, Genuity SmartStax RIB Complete by Monsanto Company and REFUGE ADVANCEDpowered by SmartStax by Dow AgroSciences. Both of these products are a blend of 95 percent SmartStax corn seed and 5 percent refuge (non-Bt) seed that farmers can plant across their entire field. This means farmers who plant these products no longer need to plant a separate, structured refuge for above-or below-ground pests in the Corn Belt. These new products are the outcome of collaboration between Monsanto and Dow AgroSciences, with both expecting a full commercial launch with broad lineups of hybrids for sale for 2012 planting.”

Small Grains
Although aphid population remain low, weather conditions favoring quick increases in populations include a combination of cool temperatures followed by a quick increase in temperatures. Although beneficial insects can help to crash aphid populations, cooler temperatures will slow their activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. Since barley heads are starting to emerge in some locations, be sure to watch for the movement of aphids into grain heads. In many cases, beneficial activity is still not high enough to take care of populations that can move from the lower canopy of the plants into the grain heads. http://ag.udel.edu/extension/IPM/ExtensionFactSheets/AphidControlinSmallGrainIPM-4.pdf

Cereal leaf populations still remain relatively low but we can now find the first larvae in fields. Refer to our factsheet (http://ag.udel.edu/extension/IPM/ExtensionFactSheets/CerealLeafBeetleFactSheetIPM-5.pdf) as well as the Agronomic Crop Insects article in WCU 19:2 for sampling and treatment guidelines.

Once grain heads have emerged, you should also begin sampling small grains for grass sawfly and armyworm larvae. Although we can see economic damage from local overwintering armyworm populations, we often see significant outbreaks in years when moths coming from the South migrate to our area. Reports from trapping programs in Kentucky are indicating that trap catches for 2011 appear to be following their 2006 & 2008 outbreak levels – so be sure to begin checking for small larvae. http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN1264.pdf

Remember, armyworm larvae are nocturnal so look for larvae at the base of the plants during the day. As a general guideline, a treatment should be considered if you find one armyworm per foot of row for barley and 1-2 per foot of row for wheat. The first small sawflies have been found by consultants in wheat and barley in Kent and Sussex counties. Since sawflies feed on the plants during the day, small sawfly larvae can often be detected early using a sweep net. However, there is no threshold for sweep net samples. Once sawfly larvae are detected, sample for larvae in 5 foot of row innerspace in 5-10 locations in a field to make a treatment decision. You will need to shake the plants to dislodge sawfly larvae that feed on the plants during the day. As a guideline, a treatment should be applied when you find 2 larvae per 5 foot of row innerspace or 0.4 larvae per foot of row. If armyworms and sawflies are present in the same field, the threshold for each should be reduced by one-half. The higher rates of insecticides are needed for grass sawfly control. http://ag.udel.edu/extension/IPM/ExtensionFactSheets/SawflyandArmywormIPM-6.pdf

 

Agronomic Crop Insects – April 30, 2010

Thursday, April 29th, 2010

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
If economic levels of alfalfa weevil were present before harvest and you decide to cut instead of spray, be sure to check fields within one week of cutting for damage to the regrowth. If temperatures remain cool after cutting, there is often not enough “stubble heat” to control populations with early cutting. In some cases, damage to re-growth can be significant. A stubble treatment will be needed if you find 2 or more weevils per stem and the population levels remain steady.

Small Grains
During the past week, there has been a significant increase in populations of cereal leaf beetle larvae, especially in areas where adult egg laying has been abundant over the last few weeks. In many cases, larvae were very small (about the size of a pin-head) early in the week; however, they will quickly increase in size with the predicted warm temperatures. In addition, they can be found throughout the plant canopy so you need to look at the entire plant when sampling. Damage can occur quickly under these conditions so be sure to scout carefully for cereal leaf beetle larvae. The treatment threshold is 25 eggs and/or small larvae total per 100 tillers.

With the predicted warmer temperatures, we will also see an increase in true armyworm catches. Although true armyworms overwinter in our area, we can also get migrant moths from the South. Therefore, be sure to scout all small grains for armyworms at this time. Remember, on barley, head clipping can occur in a relatively short time. As a general guideline, the threshold for armyworms in barley is one per foot of row and for wheat one-two per foot of row.

In addition to armyworms, do not forget to watch for sawflies since larvae can be found in fields throughout the state. As a review, adult sawflies generally emerge in early April and begin to lay eggs in the leaf margins of small grains. Most egg laying is complete by early May but can be delayed by cooler temperatures. The first small larvae generally feed on the lower leaf blades and larval development takes approximately 21-30 days. Barley and wheat are both damaged by sawflies; however, during years of high population pressure, barley may experience more damage. Sawfly larvae prefer to feed on the stems and can be more damaging than armyworms. Stem clipping often occurs before leaf feeding is complete and/or the grain reaches physiological maturity. Since sawflies can clip heads quickly, be sure to scout carefully for larvae and watch closely for clipped heads. As a guideline, a treatment should be applied for sawflies when you find 2 larvae per 5 foot of row innerspace or 0.4 larvae per foot of row. However, remember if the number of clipped heads is twice the worm count for sawflies then it may be too late to treat for them.

Since aphids feeding in the heads of small grains can result in a loss in test weight, be sure to watch for movement of aphids into the grain heads. As a general guideline, a treatment should be considered if you find 20 aphids per head and beneficial insect activity is low. You need at least one beneficial insect per every 50-100 aphids to help crash populations.

Lastly, before treating for any insect be sure to check the days between last application and harvest when selecting a spray material.

True Armyworms and Grass Sawfly

Wednesday, March 26th, 2008

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Each year economic levels of true armyworm and grass sawfly can be found in fields throughout the state. Field scouting is the only way to determine if economic levels are present in your fields. The following information is a review of the biology and life history of grass sawfly and true armyworm in wheat.

Grass sawfly adults emerge in early April and begin to lay eggs in the leaf margins of small grains. Most egg-laying is complete by early May. The first larvae can be found by late April feeding on the lower leaf blades. Mature larvae can be distinguished by their solid green color, amber head with a brown band and many legs. Larval development takes approximately 21-30 days. By mid-June, larvae burrow into the ground and begin a period of summer diapause (hibernation). Sawfly larvae prefer to feed on the stems and are potentially more damaging than armyworms. Larvae begin to climb and feed on stems when the larvae are half grown and the grain is in the tiller to head stage. Stem clipping often occurs before leaf feeding is complete and/or the grain reaches physiological maturity. Head clipping often peaks before peak armyworm damage. (more…)